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Paper des Monats
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Nickel-based alloys have been widely used for gas turbine blades owing to their excellent mechanical properties and corrosion resistance at high temperatures. The operating temperatures of modern gas turbines have been increased in pursuit of increased thermal efficiency. Turbine blades are exposed to these high temperatures combined with mechanical stresses, resulting in material damage through creep, fatigue, and other mechanisms. These turbine blades must be regularly inspected and replaced as needed, to prevent the loss of efficiency, breakdown, and catastrophic failure. Repair of the damaged turbine blades is often a more practical and cost-effective option than replacement, as replacement is associated with high costs and loss of material resources. To this end, state-of-the-art repair technologies including different additive manufacturing and brazing processes are considered to ensure efficient repair and optimum properties of repaired components.
In any repaired part, materials property-mismatches and/or inner defects may facilitate the crack initiation and propagation and thus reduce the number of load cycles to failure. Therefore, a fundamental understanding of the fatigue crack growth and fracture mechanisms in joining zones is required to enable the prediction of the remaining life of repaired components and to further improve and adapt the repair technologies.
Fatigue crack growth experiments have been conducted on SEN (Single Edge Notch) specimens joined via brazing, and pre-sintered Preform (PSP) and multi-materials (casted/printed) specimens layered via additive manufacturing (AM). The experiments were performed at 950 °C and various stress ratios. The crack growth was measured using DCPD (Direct Current Potential Drop) method. The stress intensity factors for joined SEN specimens were calculated using the finite element method and then used to derive the fatigue crack growth curves. Metallographic and fractographic analyses were conducted to get insight into the fracture mechanism.
Results show that the experimental technique for fatigue crack growth was successfully adapted and applied for testing joined specimens. Furthermore, the initial tests indicate that the investigated braze filler material provides a lower resistance to crack growth, and bonding defects cause a crack to deviate to the interface of the base material and joining zone. In AM-sandwich specimens, the crack growth rates are significantly reduced when the crack reaches the interface of printed material and casted material. The obtained crack growth data can be used to calibrate a crack growth model, which will further be utilized to predict the remaining life of repaired components.
High Temperature Fatigue Crack Growth in Nickel-Based Alloys Refurbished by Additive Manufacturing
(2024)
Hybrid additive manufacturing plays a crucial role in the restoration of gas turbine blades, where, e.g., the damaged blade tip is reconstructed by the additive manufacturing process on the existing blade made of a parent nickel-based alloy. However, inherent process-related defects in additively manufactured material, along with the interface created between the additively manufactured and the cast base material, impact the fatigue crack growth behavior in bi-material components. This study investigates the fatigue crack growth behavior in bi-material specimens of nickel-based alloys, specifically, additively manufactured STAL15 and cast alloy 247DS. The tests were conducted at 950 °C with stress ratios of 0.1 and −1. Metallographic and fractographic investigations were carried out to understand crack growth mechanisms. The results revealed significant retardation in crack growth at the interface. This study highlights the potential contributions of residual stresses and microstructural differences to the observed crack growth retardation phenomenon, along with the conclusion from an earlier study on the effect of yield strength mismatch on crack growth behavior at a perpendicular interface in bi-material specimens.
Nickelbasierte Superlegierungen werden in großem Umfang für Gasturbinenschaufeln verwendet, da sie einer Kombination aus hoher Belastung und hohen Temperaturen widerstehen können. Um die Effizienz moderner Gasturbinen zu verbessern, werden hohe Betriebstemperaturen angestrebt. Diese hohen Temperaturen verbunden mit mechanischen Belastungen führen zu Materialschäden aufgrund von Kriechen, Ermüdung und anderen Schadensmechanismen. Aus diesem Grund werden Turbinenschaufeln regelmäßig im Rahmen von Wartungs- und Instandsetzungsmaßnahmen geprüft und falls erforderlich ausgetauscht, um ein katastrophales Versagen im Betrieb zu vermeiden. Ein kompletter Austausch ist mit sehr hohen Kosten verbunden, weshalb geeignete Reparaturverfahren entwickelt wurden und werden. Neue Reparaturtechnologien wie die Additive Fertigung, Lötverfahren und der Einsatz von vorgesinterten Vorformen (Presintered Preform PSP) sollen eine effiziente Reparatur und optimale Eigenschaften der reparierten Bauteile sichterstellen.
Im Allgemeinen stellen die Fügezonen typische Schwachstellen dar, da sie die Anrissbildung und Rissausbreitung erleichtern und die Anzahl der Lastzyklen bis zum Bruch reduzieren können. Aus diesem Grund ist eine umfassende Untersuchung des Rissfortschrittsverhaltens in diesen, durch neue Reparaturtechnologien entstandenen Bereichen erforderlich, um die Restlebensdauer der Turbinenschaufeln vorherzusagen.
Als ein erster Beitrag zu dieser Fragestellung werden Ergebnisse von Rissfortschrittsversuchen (Fig. 1) an SENT-Proben vorgestellt, die durch Engspaltlöten gefügt wurden. Die Versuche wurden bei einer Temperatur von 950 °C und einem Spannungsverhältnis R = 0,1 durchgeführt. Die Erfassung des Rissfortschritts erfolgte mit dem Gleichstrom-Potentialsonden-Verfahren. Mit der Finite-Element-Methode konnte der Spannungsintensitätsfaktor für gefügte SENT-Proben berechnet werden, der dann zur Berechnung der Risswachstumskurven verwendet wurde. Eine abschließende licht- und rasterelektronenmikroskopische Untersuchung der Bruchflächen soll einen Beitrag zum Verständnis der Bruchmechanismen liefern und klären, ob der Riss sich im Lotwerkstoff, im Grundwerkstoff oder in der Grenzfläche ausbreitet. Die Ergebnisse werden zur Kalibrierung des Rissfortschrittsmodells und der Auslegung zukünftiger Komponenten verwendet.
Photon-based additive manufacturing technologies such as SLA, DLP, LCM, moreover volumetric two-photon-polymerization, Xolography and holographic technologies promise the highest accuracy and dimensional freedom. But to transfer the light through the feedstock it needs sufficient transparency at the used light wavelength. Ceramic particles used for powder processing routes act as scattering sites and therefore hinder the light transmission, unless…
The particle size and particle size distribution are chosen small and narrow enough. Particles which are smaller than roughly 1/10th of the light wavelength, mostly nanoparticles around 5nm size, decrease scattering vastly. This turns resins even with homogeneously distributed ceramic weight fraction of up to 80% transparent again. Feedstocks could be prepared for the highly accurate two-photon-polymerization gaining the smallest yttria stabilized zirconia structures with a resolution of 500nm and unique mechanical properties. The same feedstocks could be applied to DLP and LCM as layer-by-layer AM-technologies for bigger parts. Hybridizing both technologies lead to ceramic parts with microscopic accuracy at macroscopic dimensions. The feedstock was even applied to the volumetric Xolography with the highest transparency requirement so far and to versatile and flexible holographic AM.
Highly filled nano-particle containing transparent ceramic feedstocks open the way for technical ceramics in high precision manufacturing where the performance and durability and accessibility are increased and created by the unique ceramic properties such as mechanical strength, chemical and thermal resistance and biocompatibility
In order to be able to manipulate ceramic powder compacts and ceramic suspensions (slurries) in their volume with light, a minimum transparency of the materials is required. Compared to polymers and metals, ceramic materials are characterized by the fact that they have a wide electronic band gap and therefore a wide optical window of transparency. The optical window generally ranges from less than 0.3 µm to 5 µm wavelength. Therefore, to focus light into the volume of a ceramic powder compact, its light scattering properties need to be tailored. In this study, we present the physical background and material development strategies for the application of two-photon polymerization (2PP), Xolography and selective volumetric sintering for the additive manufacturing of structures in the volume of ceramic slips and green compacts.
Nickel-based alloys have been widely used for gas turbine blades owing to their excellent mechanical properties and corrosion resistance at high temperatures. The operating temperatures of modern gas turbines have been increased in pursuit of increased thermal efficiency. Turbine blades are exposed to these high temperatures combined with mechanical stresses, resulting in material damage through creep, fatigue, and other mechanisms. These turbine blades must be regularly inspected and replaced as needed, to prevent the loss of efficiency, breakdown, and catastrophic failure. Repair of the damaged turbine blades is often a more practical and cost-effective option than replacement, as replacement is associated with high costs and loss of material resources. To this end, state-of-the-art repair technologies including different additive manufacturing and brazing processes are considered to ensure efficient repair and optimum properties of repaired components.
In any repaired part, materials property-mismatches and/or inner defects may facilitate the crack initiation and propagation and thus reduce the number of load cycles to failure. Therefore, a fundamental understanding of the fatigue crack growth and fracture mechanisms in joining zones is required to enable the prediction of the remaining life of repaired components and to further improve and adapt the repair technologies.
Fatigue crack growth experiments have been conducted on SEN (Single Edge Notch) specimens joined via brazing, and pre-sintered Preform (PSP) and multi-materials (casted/printed) specimens layered via additive manufacturing (AM). The experiments were performed at 950 °C and various stress ratios. The crack growth was measured using DCPD (Direct Current Potential Drop) method. The stress intensity factors for joined SEN specimens were calculated using the finite element method and then used to derive the fatigue crack growth curves. Metallographic and fractographic analyses were conducted to get insight into the fracture mechanism.
Results show that the experimental technique for fatigue crack growth was successfully adapted and applied for testing joined specimens. Furthermore, the initial tests indicate that the investigated braze filler material provides a lower resistance to crack growth, and bonding defects cause a crack to deviate to the interface of the base material and joining zone. In AM-sandwich specimens, the crack growth rates are significantly reduced when the crack reaches the interface of printed material and casted material. The obtained crack growth data can be used to calibrate a crack growth model, which will further be utilized to predict the remaining life of repaired components.
Photoresponsive molecular crystals have sparked interest owing to their potential application prospects. In this study, we achieved dual mechanical responses of a cyanostilbene-based crystal BN. The crystal exhibited both stress-induced mechanical flexibility and light-induced photomechanical bending. Two distinct mechanical responses are related to different underlying phenomena and were not interlinked. While elasticity is attributed to criss-cross packing arrangement in the isotropic structure, photomechanical bending is attributed to the formation of heterogeneous phase distribution due to monomer to dimer cycloaddition product formation. The crystal did not demonstrate photoswitching activity. However, it exhibited thermal reversibility, highlighting reversible dimer to monomer conversion.
This talk presents the EU funded project PlasticTrace. It shows the challenges in micro- and nanoplastic reference materials and gives some solutions regarding spectroscipc methods such as Raman or IR microscopy to determine the particle numbers. Materials are prepared by cryo milling to get some powder that is later pressed into tablets. The polymer type used is PET, because that is highly important for drinking water directive of EU commission.
Protection against terrorist or accidental scenarios in industrial settings requires suitable designs of structures to resist blast loads. Field testing as well as finite element simulations are among the techniques available to engineers in the understanding of the structural behavior against blast loading. As blast testing of complex scenarios can be very resource intensive, tests are generally performed for simplified scenarios. Numerical tools can be used to model these scenarios in order to get a better insight into blast loading, structural response and the resulting damage to the structure. In the next steps, the simplified scenario is successively modified in numerical simulations to incorporate complexities that cannot be covered in blast testing experiments. One of the conditions for this approach to work is that the original simplified numerical simulation is valid. The scopes and challenges encountered in such a validation are the focus of this presentation. A relatively ‘simple’ field test of a horizontal reinforced concrete (RC) slab subjected to blast loading is taken as an example for validation of the performance of numerical tools. The blast test incorporated various measurement techniques to quantify the blast load as well as the behavior of the RC slab. Blast load was measured using flush-mounted piezoelectric pressure gauges, whereas acceleration sensors and fiber-optic sensor cables were used to characterize the dynamic behavior of the slab under blast loading. Additionally, damage characteristics were ascertained also using fiber-optic sensing. The application of such measurement techniques, along with different numerical software available for the analysis of the scenario in question,
demonstrate the scope of our contribution.
Traceable morphological and chemical characterization of nanomaterials with respect to the various possible sizes, size distributions, shapes, and concentrations of real-world nanoparticles (NPs) is a challenging task. Particularly for the nonspherical, non-monodisperse nanoparticles – as typically for most of the commercial particles, including their strong tendency to agglomerate, there is a lack of standard operation procedures providing accurate nanoparticle characterisation.
In the framework of the pre-standardisation framework of VAMAS (Versailles Project on Advanced Materials and Standards, www.vamas.org) two interlaboratory comparison (ILC) studies are being carried out under the Technical Working Area (TWA) 34 “Nanoparticle Populations”:i) Project #15 addresses the analysis of the size and shape distribution of TiO2 bipyramidal NPs by traceable imaging methods such as TEM, SEM, STEM-in-SEM, AFM as well as with SAXS as an ensemble method. This ILC is thought as the next level development of the case studies exemplified in the published ISO standards ISO 21363 and ISO 19749. It was agreed to complete the first ILC with the NPs already prepared according to the same procedure on a TEM grid, and, at a later stage, to carry out second ILCs with the same NPs distributed to the participants as liquid suspensions together with protocols for the uniform NP deposition on suited substrates - as developed and optimized within the European project nPSize. Once having good deposition protocols available, the door for automated image analysis gets opened. Corresponding image analysis protocols and reporting templates have been distributed to the ILC participants, too.
ii) Project #16: two spherical SiO2 NP samples with bi-modal size distributions in two nominal relative number concentrations were prepared and distributed also as liquid suspensions accompanied by sample preparation, measurement, and image analysis protocols and reporting templates. Here, the NP concentration is the primary parameter to be measured. For the imaging methods it is targeted to
measure the relative nanoparticle concentrations (relative populations of the two modes).
The results of all the participating laboratories, in both ILCs, compiled in comparative representations will be shown and discussed for the first time. The reduction of the measurement uncertainties associated to the size, shape and number-concentration results induced by the significant improvement of the sample preparation on substrates (as single particles with a high-density coverage), combined with well-defined image analysis procedures will be highlighted.
Finally, a very recent 3rd ILC an the determination of lateral size of Graphene Oxide flakes by SEM is presented as project P13 under VAMAS TWA41 Graphene and Related 2D.
Bonds and local atomic environments are crucial descriptors of material properties. They have been used to create design rules and heuristics and as features in machine learning of materials properties. Implementations and algorithms (e.g., ChemEnv and LobsterEnv) for identifying local atomic environments based on geometrical characteristics and quantum-chemical bonding analysis are nowadays available. Fully automatic workflows and analysis tools have been developed to use quantum-chemical bonding analysis on a large scale. The lecture will demonstrate how our tools, that assess local atomic environments and perform automatic bonding analysis, help to develop new machine learning models and a new intuitive understanding of materials. Furthermore, the general trend toward automation in computational materials science and some of our recent contributions will be discussed.
Many organisations are being driven towards employing sustainable practices to counteract the growing concerns of environmental and social issues. With various stakeholders including governments, suppliers and customers putting on pressure the process industry is no exception. However, many industrial firms struggle to implement sustainability measures. One of the usual first steps when conducting implementation is to analyse the current situation. For this analysis, indicators are commonly used to measure, monitor, and report a company’s sustainable development performance. However, the selection of appropriate indicators is often challenging due to the current lack of relevant methodologies, guidelines, and insights into a practitioner perspective.
To address this challenge, this work focuses on the creation of a user-orientated method, which helps practitioners in the process industry to select relevant indicators for their plant and assist in the deduction of sustainability measures. This includes addressing the difficulties of implementation and regarding the current needs like the inclusion of indicators for reporting or the quantification of gathered metrics.
The presentation is divided into two parts. The first part is about the influence of the oxygen content to results testing the oxygen compatibility. BAM performed tests with several nonmetallic sealing materials such as PTFE, PA 6.6, and EPDM with different oxygen contents between 21 Vol% and pure oxygen. Using the standardized oxygen pressure surge tester, the results have shown, that even a small increase in the oxygen content above 21% in air is associated with a significant reduction on the maximum test pressure at which no reaction of the material occurs. Using the standardized tester to determine the autogenous ignition temperature of the materials in oxygen, the results have shown, that even a small increase in the oxygen content above 21% in air is associated with a significant reduction on the autogenous ignition temperature at which the material shows self-ignition without an additional ignition source. The second part of the presentation is about the oxygen endurance test according to DIN EN ISO 10297, which is generally performed with air or with nitrogen. However, BAM performed this test with oxygen. In some cases, different test results were found: Valves failed the endurance test with oxygen but passed the endurance test with air. Based on the results with different oxygen content and with the oxygen endurance tester, it is unclear, why materials and valves for oxygen are still not consistently tested with oxygen.
Motivation: A precise diagnosis of atherosclerosis is of clinical importance, since cardiovascular disease remain one of the leading causes of death worldwide.
Goal(s): The goal of this study was to evaluate the feasibility of characterizing a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS4) using molecular magnetic resonance imaging in a preclnical model of atherosclerosis.
Approach: Molecular magnetic resonance imaging using a novel probe targeted against ADAMTS4 was used in a high-fat murine model.
Results: It was possible to image atherosclerotic lesions in a mouse model using an ADAMTS4- specific probe for magnetic resonance imaging.
Impact: Using molecular MRI targeting ADAMTS4 is a promising method for characterization of plaque composition and could possibly impact plaque vulnerability assessment in the diagnosis and treatment of atherosclerosis in patients.
In this paper we present a new hydrogen-based test rig for an ongoing feasibility study of using hydrogen as an energy source for the thermal testing of transport packages containing radioactive materials. The test rig will be capable of combusting hydrogen for a wide range of different burner geometries, mass flows and if necessary hydrogen blends. As this type of fire test according to the IAEA boundary conditions does not yet exist, a large number of preliminary investigations, safety assessments and calculations must be carried out in order to develop a viable concept for hydrogen fires. In the first step of the feasibility study, the temperature, structure, and radiation of various hydrogen flames are surveyed. In future works, the results will make it possible to design burner frames that are suitable for fire reference tests in order to make comparisons with pool and propane fires used in assessment procedures today. In parallel comparative numerical simulations are conducted to model the thermal behaviour of hydrogen flames using the software package Ansys®. On the one hand, the numerical simulations support the experiments by providing an overview of numerous parameters and the measuring range; on the other hand, they will help with the design of the burner frame in future work. This paper gives an overview in the design and capabilities of the test rig. Furthermore, the results of the parameter studies show that burner geometry and mass flow provide a significant design margin for the thermal shape of the hydrogen flames. In addition, the results of the initial numerical calculations will be used to determine the necessary sensors, the positions, and their operating range. Only the optimal interaction allows a controlled system that permits user-defined hydrogen fires.
In Germany, the search for a final repository for highly radioactive material is currently based on the assumption that interim storage will take considerably longer than was anticipated. At that time, authorization procedures assumed that interim storage would be brief, until the containment systems could be placed in a final repository. For today's new approvals and extensions, the IAEA (International Atomic Energy Agency) regulations for the transport of radioactive material require an assessment of all components and component groups with regard to ageing. To assess the safety requirements not only over the previously envisaged periods but also over long durations, numerous individual parts and component groups must be examined and evaluated for ageing and interactions between materials. The metal seals of a double lid sealing system, for example, are critical components that must be studied with respect to ageing. In a containment system for radioactive material, metal seals must not only undergo classic ageing, but also withstand mechanical influences and radiation over extended periods. In addition to assessments by the applicants, BAM must also independently analyze and evaluate these ageing mechanisms as part of its sovereign mandate.
Another challenge in both new approvals and extensions is the assessment of transport regarding changes in the state of the art, which are not synchronously assessed in the regulations. In transporting radioactive material, a classic oil fire has been assumed in a hypothetical accident scenario from the development of the regulations to the present day. Due to the rapid development of propulsion technologies in recent years, such as battery or hydrogen-powered vehicles, investigations must be conducted in the revision process of the IAEA regulations to assess the impact of these new technologies on safety assessments. It is important for the member states of the IAEA to know whether new technologies are covered by the regulations or if changes are necessary to continue issuing international licenses. By focusing on batteries from the material to the cell to the module and the application, BAM contributes to the evaluation of batteries at every step of the chain. In addition to the safety of current and new battery technologies, BAM also endeavors to address issues of compositional trace and sustainable energy materials.
The integration of advanced simulation models into industrial applications, especially in civil engineering, is a challenge that requires to develop new concepts. In particular, this is related to the validation of models using open access and FAIR data as well as objective methods for identifying model parameters and model comparison with the integration of both the models and their calibration into reproducible workflow systems.
The challenges are illustratively discussed for a variety of applications ranging from bridge monitoring over the structural behavior under blast loading up to the additive manufacturing of concrete. An important basis for model validation is the existence of machine-readable data structures for experimental data, e.g. based on semantic representations. In addition, platforms to share this structured data in a searchable format in addition with reproducible scientific workflows must be established.
Based on these tools, objective methods for model parameter estimation and validation of the models are a critical step in ensuring their accuracy and usefulness in industrial applications. Bayesian inference is one approach that can be used to optimize simulation parameters, improving the accuracy of the model while being able to estimate the uncertainty. Integrating these procedures in a real-time application with a bidirectional information exchange between the physical systems and the virtual simulation model leads to the concept of digital twins.
For complex simulation models, the computational efficiency is a significant barrier both for real-time applications and in the context of model calibration with potentially millions of required forward-model evaluations. As a consequence, reduced order modeling approaches such as the proper generalized decomposition method can be used to build an efficient to evaluate model - speeding up the online computation but requiring a precomputation in an offline phase.
Finally, a perspective for integrating material and structural design into a joint design optimization is given. The integration of advanced simulation models into industrial applications is a rapidly evolving field with significant potential for innovation and progress. From additive manufacturing of concrete to digital twins and reduced order modeling, there are many tools and approaches that can be used to improve industrial processes and drive progress in a variety of industries.
Experimental And Numerical Analyses For The Evaluation Of Heat Fluxes Of A Fire Reference Test
(2024)
Packages for the transport of high-level radioactive material are designed to endure severe accidents. To obtain approval, these transport packages must adhere to the specification-based criteria of the IAEA SSR-6 [1]. To ensure compliance with these requirements, specific mechanical and thermal tests need to be appointed with respect to the package type. Typically, IAEA SSR-6 [1] prescribes mechanical tests followed by a thermal fire test as part of a cumulative test sequence. To approve the fire test, BAM uses a reference package representing the original package in its outer geometry for characterizing the actual fire and its impact on the package. This serves a dual purpose: it allows the precise adjustment of experimental parameters for the package design to be approved, and it provides input parameters for thermomechanical simulations, cf. [2]. With the help of this methodology for characterizing boundary conditions of the package, temperature evolutions within the reference package can be studied in a Finite-Element Analyses (FEA). This helps to compare the experiments with the numerical simulations on the case of the reference package, but also serves at the same time for preliminary simulations with the package design to be approved.
The thermal test consists of a 30-minute fully engulfing 800°C pool fire or an equally severe fire, e.g. a propane gas fire. The fire reference test is performed prior to the regulatory fire test with the package design to be approved. The fire reference package in the described case is a closed sheet 316L steel cylinder with a wall thickness of 10 mm, a length of 182 mm, and a diameter of 102 mm. The package was instrumented with thermocouples and filled with heat resistant insulating material.
Metal additive manufacturing (Metal AM) continues to gain momentum. Many companies explore the manufacturing of innovative products, including components for safety critical applications. Despite the intensive research of recent years, a fundamental understanding of the process‑structure‑property relationships remains challenging due to, i.a., the inherently complex and highly hierarchical microstructures arising from the wide range of build process parameter variability. This contribution presents the resu lts of an experimental study on the creep behavior of an austenitic 316L stainless steel produced by laser powder bed fusion (PBF LB/M/316L) with an emphasis on understanding the effects of microstructure on creep mechanisms. Hot tensile tests and constant force creep tests at 600 °C and 650 °C, X ray computed tomography, as well as optical and electron microscopy were performed. The produced PBF LB/M/316L exhibits a low void population 0.01 %) resulting from the manufacturing parameters used and which a llowed us to understand the effects of other microstructural aspects on creep behavior, e.g., grain morphology and dislocation substructure. A hot‑rolled variant of 316L hwas also tested as a reference. The produced PBF LB/M/316L possesses shorter primary and secondary creep stages and times to rupture and smaller creep stress exponents than the hot‑rolled variant. Overall, the creep damage is more extensive in the PBF LB/M/316L and is characterized as predominantly intergranular. It is considered that the damage behavior is mainly impacted by the formation of precipitates at the grain boundaries combined with their unfavorable orientation. The dislocation substructure and local elemental segregation appear to have a decisive impact on the overall creep behavior.
We simulate a homologous series of guanidinium-based columnar ionic liquid crystals (ILCs) using coarse-grained molecular dynamics (MD) simulations with the Martini force field. We systematically vary the length of alkyl side chains, ILC-n (n = 8, 12, 16), and compare our results with previous experimental findings. Experimentally, ILC-8 exhibits a narrow mesophase window and weak columnar order, while ILC-12 and ILC-16 display a broad mesophase window and high columnar order. The MD simulations show that ILC-8 forms a percolated structure, whereas the longer chain analogues self-assemble into columns, with columnar assembly becoming more prominent as the side chain length increases, in qualitative agreement with the experiments. Furthermore, the intercolumnar distance increases monotonically with increasing side chain length and decreases with increasing temperature. Finally, we find that the diffusion coefficient and ionic conductivity decrease substantially with increasing chain length, consistent with experimental observations. We attribute this decrease in mobility to the formation of hexagonally ordered columns, which restrict transport more than percolated networks.
Black fungi belong to different classes of Ascomycota but evolved similar morpho-physiological adaptations such as yeast-like growth and constitutive melanin formation to colonize extreme competition-free environments. They are ubiquitously found on air-exposed surfaces, from ancient marble monuments to modern solar panels. The rock inhabitant Knufia petricola was chosen to become a model for these extremotolerant black fungi. Plasmid-based and ribonucleoprotein-based CRISPR/Cas9 techniques were introduced to precisely introduce one to multiple double strand breaks into the DNA to modify, replace or add sequences to the genome either using the available selection marker systems (hygR, natR, genR, baR, suR) or by marker-free approaches. Multiplexing is very efficient, allowing for four or more simultaneous genome editing events. The newly generated cloning vectors containing the Tet on construct for doxycycline-controlled gene expression, and the validated sites in the K. petricola genome for color-selectable (pks1, phs1, ade2) or neutral insertion (igr1 to 5) of expression constructs complete the reverse genetics toolbox. One or multiple endogenous or heterologous genes can be expressed on demand from different genomic loci or from a single construct by using 2A self-cleaving peptides. We thus can express genes from synthetic clusters in a non-pigmented background (Δpks1/Δphs1). The fact that K. petricola only produces few secondary metabolites (DHN melanin, carotenoids, mycosporines and a siderophore) and plant cell-wall degrading enzymes but is capable to take the burden of acetyl-CoA-consuming metabolism and protein secretion renders K. petricola a promising host for the expression of heterologous genes encoding high-end secondary metabolites and enzymes.
In times of digital data processing and sharing, a central challenge for the Materials Science and Engineering (MSE) community is the complete digital representation of materials, including their relevant processing and microstructure details and the resulting properties. This digital representation, supported by digital infrastructures, enables entirely new qualities of collaborative work and is central to how we will conduct MSE research and develop products in the future. The main challenges are the composition, shaping, and description of the data so that it can be easily interpreted, trusted, and re-used. This presentation introduces our current effort to develop a best practice framework for generating and distributing creep reference datasets for Ni-based superalloys, which builds on previous approaches. Researchers can use such datasets to compare their own experimental or simulation results, used, for instance, to perform simulation-based alloy design and optimization or in the verification of the own testing equipment. The concept includes building an easily accessible digital infrastructure to annotate and discover the datasets and the integration of an ontology that aligns with the necessary metadata schema. With the help of an ontology, the reference dataset for creep can be semantically described, thus enabling the digital representation and reusage of shared concepts from domain experts and the community. To achieve this, it is necessary to establish a defined vocabulary with corresponding relations and annotations. The interplay between a digital infrastructure, the agreement on the necessary metadata and related metadata schema, and an underlying ontology will ensure that data and results can be easily shared, taken up, and re-used, thus fulfilling the FAIR principles (Findable, Accessible, Interoperable, Reusable). Furthermore, we aim to develop a widely accepted definition of reference data and data quality levels and to reach a self-supported community process. We intend to motivate the discussion about reference material datasets, necessary metadata, and future collaborations within the creep community.
In this paper we present a new hydrogen-based test rig for an ongoing feasibility study of using hydrogen as an energy source for the thermal testing of transport packages containing radioactive materials. The test rig will be capable of combusting hydrogen for a wide range of different burner geometries, mass flows and if necessary hydrogen blends. As this type of fire test according to the IAEA boundary conditions does not yet exist, a large number of preliminary investigations, safety assessments and calculations must be carried out in order to develop a viable concept for hydrogen fires. In the first step of the feasibility study, the temperature, structure, and radiation of various hydrogen flames are surveyed. In future works, the results will make it possible to design burner frames that are suitable for fire reference tests in order to make comparisons with pool and propane fires used in assessment procedures today. In parallel comparative numerical simulations are conducted to model the thermal behaviour of hydrogen flames using the software package Ansys®. On the one hand, the numerical simulations support the experiments by providing an overview of numerous parameters and the measuring range; on the other hand, they will help with the design of the burner frame in future work. This paper gives an overview in the design and capabilities of the test rig. Furthermore, the results of the parameter studies show that burner geometry and mass flow provide a significant design margin for the thermal shape of the hydrogen flames. In addition, the results of the initial numerical calculations will be used to determine the necessary sensors, the positions, and their operating range. Only the optimal interaction allows a controlled system that permits user-defined hydrogen fires.
Monitoring hydrogen composite pressure vessels using surface applied distributed fiber optic sensors
(2024)
We report on surface-applied distributed fibre optic sensors for monitoring composite pressure vessels designed for hydrogen storage. Previous reports have revealed that integrating optical fibres within vessel composite structures effectively enables the monitoring of structural behavior throughout their lifetime.
However, integrating optical fibres during the manufacturing process is complex and time-consuming. Therefore, we aim to simplify this process by attaching the optical fibres to the vessel’s surface. This method is significantly more timeefficient than the integration process and can be applied to any vessel. Our results demonstrate that surface-applied fibre optic sensors can detect and precisely localise damage.
Additionally, signs of damage can be recognised even before the damage occurs. Predictive maintenance using fibre optic sensors could reduce premature maintenance costs and periodic inspections while increasing safety and extending the vessel’s useful service life. The role of machine learning in predictive maintenance is also discussed.
Innovation and scientific progress are often located in the synthesis of new flame retardants or in the compounding of new composites. Thus, although nearly everyone applies fire tests to ascertain the flame retardancy achieved, regular, cost-efficient fire testing is preferred, sometimes its reliability and meaningfulness are questioned. The goal of this revised chapter is to inspire the exploitation of the potential of fire testing beyond a soulless pass-and-fail or isolated number rating. Recommendations are given as to how fire behaviour can be investigated and how data can be evaluated faithfully and meaningfully. Backgrounds and benchmarks are discussed as thought-provoking impulses which could allow bench-scale fire testing to be exploited as a vital basis and powerful tool for science-based development.
Experimental and Numerical Analyses for the Evaluation of Heat Fluxes of a Fire Reference Test
(2024)
Packages for the transport of high-level radioactive material are designed to endure severe accidents. To obtain approval, these transport packages must adhere to the specification-based criteria of the IAEA SSR-6. To ensure compliance with these requirements, specific mechanical and thermal tests need to be appointed with respect to the package type. Typically, IAEA SSR-6 prescribes mechanical tests followed by a thermal fire test as part of a cumulative test sequence. To approve the fire test, BAM uses a reference package representing the original package in its outer geometry for characterizing the actual fire and its impact on the package. This serves a dual purpose: it allows the precise adjustment of experimental parameters for the package design to be approved, and it provides input parameters for thermomechanical simulations, cf. With the help of this methodology for characterizing boundary conditions of the package, temperature evolutions within the reference package can be studied in a Finite-Element Analyses (FEA). This helps to compare the experiments with the numerical simulations on the case of the reference package, but also serves at the same time for preliminary simulations with the package design to be approved.
The thermal test consists of a 30-minute fully engulfing 800°C pool fire or an equally severe fire, e.g. a propane gas fire. The fire reference test is performed prior to the regulatory fire test with the package design to be approved. The fire reference package in the described case is a closed sheet 316L steel cylinder with a wall thickness of 10 mm, a length of 182 mm, and a diameter of 102 mm. The package was instrumented with thermocouples and filled with heat resistant insulating material.
Applying synergistic multicomponent systems is often key to efficient flame retardancy. Different flame retardants are combined or used together with fillers, adjuvants, or synergists to enhance their efficiency, reduce the worsening of other properties, or reduce the costs. Further, fibres and other reinforcing fillers contribute to fire properties crucially. Although the main flame-retardant modes of action are known, the scientific understanding usually falls short, when it comes to complex multicomponent systems, the crucial tiny optimizations, or quantifying in terms of specific fire properties. This book chapter illuminates the need for the multicomponent approach, the concept of synergistic flame retardants, and the main phenomena. Multicomponent systems are discussed in their capacity as general powerful strategy for achieving and optimizing future flame retardant polymeric materials.
This research group has been demonstrating the significant advantages of using Nb2O5 coatings for functionalizing titanium, aluminium, and stainless steels. Regarding the biomedical sector and considering Ti-6Al-4V alloy, the reactive sputtering technique improved the cell viability, the osteogenic performance of cells involved in the osseointegration process as well as the ability to delay bacterial proliferation. The characteristics of the Nb2O5 coatings were assessed before by using standard methods, which provide information only a few tens of nanometers depth. Given that the Nb2O5 coating fabricated in this work exhibits a thickness of approximately 300 nm, the GE-XANES technique emerges as the most suitable method for this analysis. Additional information was provided with the aid of nanoindentation load-depth (P-h) curves. GE-XANES results indicated the formation of a homogeneous layer of Nb2O5 coating on the Ti-6Al-4V surfaces. The deposition process improved the surface hardness of the Ti-6Al-4V alloy (4.38 GPa versus 5.62 GPa) considering the 2 mN load.
The decommissioning or refurbishment of nuclear facilities necessitates either the storage or disposal of large radioactive components such as steam generators, pressurizers, reactor pressure vessels and heads, and coolant pumps, to list the major contributors. These components or objects are large in size and mass, measuring up to approximately 6 meters in diameter, up to 20 meters in length, and weighing over 400 000 kg. In many situations, the components are transported off-site to a storage, disposal or recycling/treatment facility. Previously, many large objects had to be transported under special arrangement.
The latest 2018 edition of the International Atomic Energy Agency (IAEA) Regulations for the Safe Transport of Radioactive Material, No. SSR-6, incorporates regulations for the shipment of contaminated, but not activated large objects as a new category of surface contaminated object, SCO-III, based on the IAEA “performance package” concept.
This paper provides background and practical guidance on these regulations. Additionally, first experiences with SCO-III in the approval process are presented.
For SCO-III components a mechanical assessment regarding the tests specified in the transport regulations SSR-6 for demonstrating ability to withstand normal conditions of transport is required - a free drop of the package onto an unyielding target and a penetration test have to be investigated. Large components are unique objects; therefore, it is not possible to choose experimental testing as assessment method. The application of a complex numerical analysis for mechanical proof is necessary.
The assessment of the loads takes place based on local stress distributions.
The large nuclear components have typically been transported in an unpackaged manner, so that the external shell of the component provides the containment wall.
The paper will represent the methods, which are used for the evaluation of the mechanical integrity of the object for transport approval.
Low Transformation Temperature (LTT) welding consumables represent an innovative approach to realize compressive residual stress in weld and HAZ. LTT welding consumables use the volume-expanding martensitic phase transformation near room temperature to generate compressive residual stress during cooling. This article focusses on the weld geometry of LTT welding consumables and their influence on residual stress reduction. For this purpose, LTT layers were additionally applied to the front sides of conventionally welded longitudinal stiffeners. By varying parameters such as offset and welding speed, different weld geometries could be realized. These were analyzed for geometric parameters, chemical composition and residual stress using X-ray diffraction and fatigue testing. While the chemical composition was only slightly influenced by parameters changes, a clear influence was observed regarding to weld geometry and residual stress. The conventionally weld was characterized by tensile residual stress of ≈350 MPa at the weld toe, the additional LTT weld bead exhibits compressive and tensile residual stress of ≈-150MPa to ≈+150MPa depending to the parameter variation.
Chitin/Chitosan Biocomposite Foams with Chitins from Different Organisms for Sound Absorption
(2024)
Foams are widely used for applications in construction, energy absorption, and building insulation. We developed sustainable chitin/chitosan-based foams derived from snow crab and Aspergillus niger (α-chitin) and from squid (β-chitin), which were obtained via a “shake and bake” process. The foam structure, mechanical, thermophysical, sound absorption, and flammability properties were studied. Stable foams were obtained from snow crab and squid chitin, whereas A.niger-based foams were inhomogeneous. Foams derived from the former biomass sources displayed densities of 0.07−0.30 g/cm3 and bulk porosities of 78−94% with only a minimal number of closed pores. According to mercury porosimetry (MP) and X-ray computed microtomography (μXRCT), pore sizes ranged from 3 μm to 1.5 mm, with the majority of pores being larger than 400 μm. In mechanical compression tests, β-chitin-based foams showed higher specific compressive strength and modulus (up to 0.1 * = 9.00 MPa/E* = 107.37 MPa) compared to the α-chitin-based series. Dynamic vapor sorption (DVS) measurements revealed that the β-chitin (from squid) series overall took up more water vapor (≤40 wt %) than the α-chitin (from snow crab) series (≤33 wt %). Flammability tests showed that the developed foams were suitable for fire protection class E, superior to common polyurethane (PU) foams, and sound absorption tests showed promising results for applications only little influenced by humidity.
Colloids provide manifold opportunities for targeted product design due to their tunable properties with respect to size, shape, composition, surface, and spectral characteristics. However, the determination of structure-property relationships is quite challenging as most particulate samples exhibit polydispersity of their disperse properties. Analytical ultracentrifugation (AUC) is a fractionating technique and highly accurate method for the multidimensional analysis of nanoparticles as it permits the differentiation of spectral information linked to hydro- and thermodynamic properties of the particles.
So far, characterization capabilities for fluorescent nanoparticles by AUC were limited, as the formerly commercially available fluorescence detector could not provide any spectral information. Using a multiwavelength emission detector developed in our group, it is possible to extract spectra of fluorescent particles and biomolecules alongside their sedimentation and diffusion coefficients within a single centrifugation experiment.
In our contribution, we will highlight that even narrowly distributed core/shell CdSe/CdS quantum dots still show size- and structure-dependent shifts of their fluorescence spectra, which can be resolved with our AUC system in an ensemble measurement. Thereby, we can link spectral changes of only a few nanometers to particle sizes retrieved with Angstrom size resolution. Single-particle measurements not only supported the results obtained with the AUC system but also provided deeper insights into the photophysical processes of individual QDs, clearly demonstrating the complementary nature of the techniques used. With our novel multiwavelength emission detector and the established extinction-based detector for AUC, a comprehensive platform for the holistic characterization of fluorescent colloids is now available.
This book presents the proceedings of the Thirteenth International Conference Structures in Fire. The conference took place at the Department of Civil Engineering, University of Coimbra, Portugal, from 19 to 21 June 2024, under the auspices of the SIF movement. Structural fire safety is a crucial aspect of the design of buildings and infrastructures. Significant advances in research have increased the knowledge on this topic. However, until the 1990s, there were few forums for structural fire engineers to exchange ideas and share research findings. SIF (Structures in Fire) specialised workshop series was conceived in the late 1990s and the “First International SIF Workshop” was held in Copenhagen, Denmark in 2000, followed by workshops in Christchurch, New Zealand (2002), Ottawa, Canada (2004) and Aveiro, Portugal (2006). The series of workshops evolved into conferences and the 2008 event in Singapore was the fifth International Conference on Structures in Fire. This was followed by events in East Lansing, USA (2010), Zurich, Switzerland (2012), Shanghai, China (2014), New Jersey, USA (2016), Belfast, UK (2018), Brisbane, Australia (2020) and Hong Kong, China (2022). Information about previous conferences, including complete proceedings, can be found at www.structuresinfire.com. The main mission of SIF conferences is to provide an opportunity for researchers and engineers from the global structural fire engineering community to participate, share and discuss the recent findings, innovations and developments with their peers in an open and international forum. Following the great success of the previous International Conferences, the University of Coimbra was selected to host the 13th International Conference on Structures in Fire. As with most of the recent conferences, the number of papers submitted far exceeds the number of papers that can be accommodated in the three-day programme, even with two parallel sessions. SIF 2024 received 249 abstracts before the deadline and accepted 172 abstracts after the review process by at least three reviewers from the scientific committee. These proceedings represent 132 full papers, collectively representing the state of the art in fundamental knowledge and practical application of structures in fire. Forty-two countries from around the globe have contributed to them. The papers are grouped into the following research topics: Applications of Structural Fire Engineering, Composite Structures in Fire, Concrete Structures in Fire, Timber Structures in Fire, Masonry Structures in Fire, Steel Structures in Fire, Experimental Research of Structures in Fire, Numerical Modelling of Structures in Fire, Other Topics Related to Structures in Fire. Finally, the Organizing Committee would like to thank the continuous support from the SIF Steering Committee chaired by Prof Jean-Marc Franssen. We also would like to thank to the Scientific Committee chaired by Prof Paulo Vila Real, the authors and all the supporting staff (and volunteer team) from the Institute for Sustainability and Innovation in Structural Engineering (ISISE) in Coimbra, for making SIF 2024 a successful conference.
Fire-induced spalling of normal strength concrete with different types of blended Portland cement
(2024)
The cement industry is looking to reduce its overall CO2 footprint. Greener manufacturing can be achieved by the introduction of more clinker-reduced cements. Concrete exposed to fire tends to show explosive spalling caused by thermomechanical and thermohydraulic processes. It is therefore essential to determine how concretes with clinker-reduced cements behave under fire exposure, especially for concretes containing calcined clays, as these are expected to be the supplementary cementitious material of the future.
In this paper, normal strength concretes with four different cements (CEM I, CEM II/A-LL, CEM III/A and CEM II/B-Q) were examined for their fire-induced spalling behaviour. In addition, a mix with PP fibres was investigated for each concrete. The experiments were conducted on ring-restrained cylindrical specimens exposed to the hydrocarbon fire curve. The results showed that the cement type influences spalling behaviour. Samples with CEM I spalled the least, followed by CEM II/A-LL and CEM III/A.
Finally, samples with CEM II/B-Q showed the most severe damage. It was found that the spalling behaviour of different concretes correlates with the moisture content before exposure to fire, meaning that higher moisture content leads to higher spalling susceptibility. The use of 2 kg/m³ PP fibres completely inhibited spalling regardless of the cement type used and therefore remains a successful avoidance strategy.
The recently certified reference material (CRM) BAM-N012 as cubical iron oxide FeOx nanoparticles (NPs) of 8 nm area equivalent square edge length (ESL) and the RM candidate BAM-N013 as nearly spherical NPs of 22 nm size were analyzed in detail by electron microscopy (EM).
For the metrological characterization with SEM, STEM in SEM and TEM, the understanding of the imaging contrasts and sensitivities, and the correct interpretation of the (art)effects which are inherent to each detection mode is necessary.
The same sample areas with NPs deposited on a TEM grid were analyzed by two SEM acquisition modes, i. e. SE InLens and STEM in SEM using a dedicated transmission sample holder, and further, correlatively, analyzed with TEM.
With increasing kV, SE InLens shows increasing particle size (unless overcharging at the particle boundaries is filtered), as a known effect. For STEM-in-SEM the particle size decreases significantly and individual particles are identified easier (at 2 kV only a few single particles can be detected automatically).
❑ Documentation of the sample preparation and measurement conditions (including optimization process) is important for reproducibility.
❑ Plasma cleaning, analysis in the transmission mode at SEM is recommended for FeOx NPs.
❑ Selection of the threshold algorithm can significantly alter the reported ECD.
Porous films play an important role particularly in energy applications like photovoltaics, electrolysis or batteries. Thin film properties such as thickness, chemical composition, crystallinity of the framework, and porosity define the activity of the porous films. The accurate morpho-chemical characterisation of mesoporous thin films is a challenging analytical task which requires the consideration of new analytical approaches based on the combination of data of different methods able to address the structure and chemical composition at the nanoscale. In this contribution we characterise thin mesoporous iridium-titanium mixed oxide film properties by Electron Probe Microanalysis (EPMA) with Energy-Dispersive X-ray Spectroscopy (EDS) at an SEM applied in a dedicated “thin film analysis” approach (1). Thus, the film mass deposition, film thickness and the film density can be determined. Further, by dividing the measured film density to an assumed (theoretical) metal oxide framework (skeletal) density, the thin film porosity can be extracted, too.
In order to assess the homogeneity of the thin film properties like the chemical composition, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Auger Electron Spectrometry are applied in the depth profiling mode, so that possible in-depth gradients are detected. Lateral inhomogeneities in the chemical composition and structure of the thin mesoporous films are also identified by applying the same methods in the line-scan or mapping mode, which can be further combined with in-depth sputtering for 3D information. The role of the spatial resolution of the analytical methods considered, which can go down well below 100 nm, will be highlighted.
This paper presents an experimental study on the hydraulic failure of a submerged layer of cemented soil stressed by a localized upward water flow. Different mixtures of glass beads bonded with solid paraffin bridges were used as artificial material for the cemented granular soil. Variations in the cementation strength of the material were carefully introduced with different particle sizes and binder contents. The hydraulic fracture tests were then carried out with an upward flow injected at a controlled rate through a small section at the bottom of the samples. From a phenomenological perspective, the results reveal the existence of at least three modes of failure for a cemented soil layer: (1) overall block uplift, (2) block rupture by median crack at the inflow zone, and (3) progressive excavation of a fluidized path along the walls. The critical flow rate and pressure drop conditions at failure have been carefully quantified for the different mixtures and layer thicknesses, leading to a fair estimation of the hydraulic resistance of the samples, which here is found to be virtually independent of the grain size. However, the test results also showed inconsistent failure modes precluding so far the derivation of a simple phase diagram. Nevertheless, it was possible to rationalize all the measured data by employing appropriate modifications of the classical dimensionless numbers that describe the fluidization of purely frictional materials, whereby the cementation strength of the soil is quantified at the microscale through the yield tensile force of the intergranular bonds. Irrespective of its subsequent development, during which boundary conditions obviously play a major role, the initiation of the instability appears to take place very locally at the inlet when the drag force induced by the flow overcomes the cementation strength of the paraffin bonds. The results of this study thus appear to endorse the extension of the dimensional relationships of particulate systems in interaction with fluid flows to the case of cemented granular materials, in a similar vein as in recent previous studies.
In this lecture, following points are addressed:
– Advantages of correlative analysis in electron microscopy
– Measurement principle of the different electron microscopy modes used
– Presentation of the nanomaterials used for this study
– Role of sample preparation
– Sequence kV variation with InLens & transmission detection of the same field-of-view
– Conclusive remarks including Monte Carlo simulations
In the area of plant engineering, steel components are provided with a wear protection coating for efficient use to protect them against corrosive, tribological, thermal and mechanical stresses. The use of innovative ultrasound-assisted milling processes and plasma-welded nickel- and cobalt-based wear protection coatings are being investigated to determine how more favourable machinability can be achieved while retaining the same wear protection potential. The focus is on the NiCrSiFeB alloy, which is intended to replace CoCr alloys in the area of screw machines. The utilization of ultrasonic-assisted milling for the machining of coating materials is a novel approach. The modification of hard facing layers in terms of microstructure and precipitation morphology as well as suitability for machining is investigated and compared with the CoCr alloy. The alloy modifications are generated by a PTA process by systematically adjusting the preheating and interpass temperatures, a crack-free wear-resistant layer can be generated, which is subsequently machined by a milling process. In addition to the crack-free properties, the microstructure, the bonding as well as the mixing between the NiCrSiFeB alloy and a 1.8550 as well as between the CoCr alloy and a 1.4828 are analysed and compared in the joining areas. In addition, heating and cooling rates are determined and a chemical analysis of the weld metals is performed. Furthermore, it was found that the build-up layers of NiCrSiFeB alloy are more difficult to machine using the milling process than the CoCr alloy, as higher milling forces are required.
Die Beschaffung und Verarbeitung von Werkstoffen für hochbelastete Komponenten sind meist kostenintensiv. Bestrebungen zur Kosten- und Ressourceneffizienz führen zu komplexeren Strukturen bzw. Konturen, sodass additive Fertigungsschritte zur Bauteilreparatur und -fertigung deutliche ökonomische Vorteile bieten. Hierfür sind additive und abtragende Fertigungsschritte komplementär und gezielt aufeinander abzustimmen, um beanspruchungsgerechte Funktionsflächen herzustellen. Hinsichtlich Inhomogenität und Anisotropie der Gefüge und Eigenschaften sowie fertigungsbedingter Beanspruchungen sind für den wirtschaftlichen Einsatz bei KMU, gerade für drahtbasierte Fertigungsverfahren und Wechselwirkungen nachfolgender Zerspanung dieser schwer spanbaren Werkstoffe noch viele Kenntnisse notwendig. Deshalb sind Untersuchungen zu diesen Einflüssen und Wechselwirkungen unter Nutzung innovativer Ansätze durchgeführt worden. Mit typischen kostenintensiven Ni- und Co-Cr-Legierungen wurden additive Bauteile, Auftrag- und Reparaturschweißungen hergestellt und Schweißzusätze für das PTA-Verfahren modifiziert, um die Erstarrungsmorphologie und das Eigenschaftsprofil zu optimieren. Die Übertragung auf MSG-Verfahren sicherte einen breiten industriellen Einsatz für hohe Auftragraten ab. Dies geschah mithilfe von modifizierten Fülldrähten sowie beschichteten Massivdrähten. Die wirtschaftliche spanende Bearbeitbarkeit wurde mit Zerspanbarkeitsanalysen für Schlichtfräsen und vergleichend für ultraschallunterstütze Fräsprozesse sichergestellt. Instrumentierte Experimente und Werkstoffanalytik hinsichtlich der Einflüsse auf Schmelzbad, Gefüge und Ausscheidungen sowie auf Randzoneneigenschaften und Eigenspannungen ermöglichten umfassende Erkenntnisse zur kombinierten additiven und abtragenden Fertigung. Dabei hat sich herausgestellt, dass eine Modifikation der Schweißzusatzwerkstoffe eine Homogenisierung der Mikrostruktur bedingt, welche wiederum den Zerspanprozess stabilisiert und letztendlich zu reduzierten Zerspankräften führt. Ferner wurde festgestellt, dass der ultraschallunterstützte Fräsprozess im Vergleich zum konventionellen Fräsprozess eine signifikante Reduzierung der Zerspankraft sowie eine höhere Oberflächenintegrität bedingt. Insbesondere die Induzierung oberflächennaher Druckeigenspannungen ist dabei hervorzuheben. Durch Bauteilversuche und -prüfungen, erfolgreiche Übertragbarkeitsstudien weiterer innovativer Werkstoffe verbunden mit Handlungsempfehlungen und der Zusammenarbeit mit den jeweiligen Normungsgremien, profitieren KMU von einer hochwirtschaftlichen Herstellung und Reparatur kostenintensiver Komponenten.
Considering the existing challenges involved in the transfer of flame retardant (FR) formulations from epoxy (EP) resins to glass fiber reinforced composites (GFRCs), obtaining data on the post-fire flexural properties of such composites is even more challenging as this involves balancing test parameters with potential composite delamination. In this study, solvent-free FR additives: ammonium polyphosphate (APP), and inorganic silicate (InSi) were added at 10, 30% and 50% w/w loading to a Bisphenol A diglycidyl ether (DGEBA)-dicyandiamide (DICY)-Urone resin matrix. These resin formulations were transferred to bidirectional (BD) glass fiber composites via prepregs. A novel, but facile approach was developed to prepare the composite samples for furnace tests at 400 oC. The composites were also subjected to fire exposure at different heat fluxes and times via a bench-scale test and subsequently tested via three-point bending. At approximately 3.5% P content, the FRs significantly improve the fire performance of both the resins and composites. However, they also degrade the systems’ pre- and postfire flexural modulus and strength. Therefore, improving the flame-retardant mode of action of the FRs in the composites, contrastingly reduces their structural integrity post-fire leading to a trade-off effect.
Microalloying elements such as Nb and Ti play a decisive function in achieving the desired mechanical strength of quenched and tempered, high-strength fine-grain structural steels with a nominal yield strength ≥ 690 MPa. The current specifications for the chemical composition only provide manufacturers with upper limits. However, even minor deviations in the alloy concept can have a significant impact on the mechanical properties. Consequently, accurate prediction of weldability and the integrity of welded joints becomes difficult or even impossible due to differences in composition and the resulting microstructures. Undesirable consequences include a possible softening of the heat-affected zone (HAZ) or, conversely, hardening effects. In view of these challenges, various microalloying strategies with different Ti and Nb contents are being systematically investigated for the first time using specially developed laboratory casting alloys. Each alloying route is based on the common S690QL, maintaining both the chemical composition and the heat treatment parameters.
To analyse the weldability, three-layer welds were performed using gas metal arc welding (GMAW) and critical microstructures, such as areas of the heat-affected zone (HAZ) that exhibit significant softening or hardening, were identified. The effect of the softened HAZ region on failure was evaluated using transverse tensile specimens. Digital image correlation (DIC) is used to image changes in local strains in different HAZ regions in situ. Using a specially developed mirror system, the local strains of the microstructure zones on the top and bottom of the weld are recorded simultaneously. This makes it possible to analyse how the weld seam geometry (e.g., V-seam) influences the strain gradients. In addition, the analysis of the local deformation helps to understand the effects of the softened HAZ on the global strain, the fracture constriction, the fracture position, and the overall fracture behavior
Considering the existing challenges involved in the transfer of flame retardant (FR) formulations from epoxy (EP) resins to glass fiber reinforced composites (GFRCs), obtaining data on the post-fire flexural properties of such composites is even more challenging as this involves balancing test parameters with potential composite delamination. In this study, solvent-free FR additives: ammonium polyphosphate (APP), and inorganic silicate (InSi) were added at 10, 30% and 50% w/w loading to a Bisphenol A diglycidyl ether (DGEBA)-dicyandiamide (DICY)-Urone resin matrix. These resin formulations were transferred to bidirectional (BD) glass fiber composites via prepregs. A novel, but facile approach was developed to prepare the composite samples for furnace tests at 400 oC. The composites were also subjected to fire exposure at different heat fluxes and times via a bench-scale test and subsequently tested via three-point bending. At approximately 3.5% P content, the FRs significantly improve the fire performance of both the resins and composites. However, they also degrade the systems’ pre- and postfire flexural modulus and strength. Therefore, improving the flame-retardant mode of action of the FRs in the composites, contrastingly reduces their structural integrity post-fire leading to a trade-off effect.
Advanced optical materials inspired by natural minerals and non-toxic light elements, such as the Hackmanites (Na8Al6Si6O24(Cl,S)2), find vast possibilities of applications as they can simultaneously perform photochromism and persistent luminescence (PersL). In this work, we have explored a rapid and energy-efficient microwaveassisted (MASS) methodology for the synthesis of PersL and photochromic hackmanites. In addition, we have prepared hackmanite materials using a zeolite-free precursor to control the Na–Al–Si ratio and study its influence on the materials photoluminescent properties. The PersL hackmanites showed a white-bluish emission color, with up to 2 h of emission time. Zeolite-free photochromic materials were able to change the color from white to purple/blue efficiently with a few seconds of 254 nm excitation, but the usage of zeolite precursors enhanced the overall optical performance. Microwave synthesis times of 10–40 min were demonstrated to be optimal, as longer times boosted the formation of nepheline spurious phase, which decreases luminescence efficiency. In this way, the MASS method led to a reduction of reaction time up to 98 %, yielding hackmanite materials with similar photoluminescent or photochromic properties compared to those obtained by a 24 h conventional solid-state synthesis. This work represents a significant improvement toward coupling eco-friendly synthetic processes to
eco-friendly solid-state materials for PersL illumination and PersL/photochromism optical marking.
AbstractGallium fluoride phosphate glasses feature low refractive index, high energy radiation resistance, wide transmission range, and favorable emission characteristics of rare‐earth dopants. For the development of optimized glass compositions, a fundamental understanding of these properties in terms of glass structure is sought. We report nuclear magnetic resonance (NMR) structural studies of glasses in the system xGa(PO3)3–(40 − x)GaF3–20BaF2–20ZnF2–20SrF2 (x = 5, 10, 15, 20, and 25 mol%). 31P NMR results with 71Ga recoupling show that the network structure is dominated by P–O–Ga linkages, and no P–O–P linkages exist. 71Ga NMR results show that Ga is mainly six‐coordinated featuring a mixed fluoride/phosphate coordination. Quantitative estimates of this ligand distribution around gallium were obtained by 71Ga{31P} spin echo double resonance (REDOR) measurements. Photophysical properties suggest changes in the Eu(III) ligand distribution toward a fluoride‐dominated environment at low P/F ratio while the glass network is largely sustained by bridging oxygen atoms via P–O–Ga linkages.
The magnetohydrodynamic (MHD) technology is recognized as a promising approach for improving the quality of deep penetration laser beam welding. This study employs experimental and numerical methods to investigate the effects of an auxiliary oscillating magnetic field on reducing porosity in the laser beam welding of 5754
aluminum alloy. The experimental results clearly demonstrate a significant reduction of 97% in the porosity ratio of the welded joints applied with an oscillating magnetic field compared to those without magnetic field, thereby validating the efficiency of applying MHD technology in mitigating porosity during the laser beam welding process. In addition, a transient 3D multi-physical model has been developed, integrating the MHD model and metal vapor plume, to gain a more comprehensive understanding of the porosity suppression mechanism. The weld pool shape is significantly widened and enlarged because of the Lorentz force, which facilitates the escape of gas bubbles. Meanwhile, the introduction of an oscillating magnetic field generates a time-averaged downward Lorentz force. This averaged downward Lorentz force, in turn, enhances and stables the downward fluid flow, which hinders the bubble backward movement. Meanwhile, this averaged downward Lorentz force induces an upward electromagnetic expulsive force on the bubble, which effectively increases the upward escape velocity of bubbles in the weld pool. The simulation results agree well with the experimental results.
Der Absorptionsgrad metallischer Werkstoffe spielt bei Fügeprozessen mit einer Strahlungsquelle wie dem Hochleistungslaserstrahltiefschweißen eine bedeutende Rolle. Dieser beeinflusst die Menge der absorbierten Laserenergie, welche zum Aufschmelzen sowie zur lokalen Verdampfung des zu verbindenden Materials führt. Die Laserstrahlabsorption wird von vielen physikalischen Faktoren, z.B. Laserprofil, Laserwellenlänge, Materialeigenschaft sowie Temperatur, entschieden. Dennoch wird die Temperaturabhängigkeit in vielen Simulationsarbeiten häufig ignoriert und stattdessen ein empirisch angepasster Parameter zur Kalibrierung der Ergebnisse implementiert. Diese Vorgehensweise wirkt sich negativ auf die Zuverlässigkeit des numerischen Modells sowie auf die Vorhersagbarkeit der Simulationsergebnisse aus. In der vorliegenden Arbeit wird die Temperaturabhängigkeit des Laserabsorptionsgrades in ein selbstkonsistentes zweiphasiges Modell unter Berücksichtigung der gekoppelten 3D-Fluidströmung und Wärmeübertragung einbezogen. Die berechnete Laserstrahlabsorption wird durch die temperaturabhängigen Materialeigenschaften, die Lasercharakteristik und den Einfallswinkel des Laserstrahls bestimmt. Die freie Oberfläche jeder Phase wird mithilfe der Volume-of-Fluid Methode (VOF), berechnet und die Laser-Material-Wechselwirkung wird durch ein implementiertes Ray-Tracing-Verfahren modelliert, welches auf einem lokalisierten Level-Set-Algorithmus basiert. Anschließend wird die transiente Wärmeeinbringung und die Geometrie der Schweißnaht analysiert und mit dem temperaturunabhängigen Absorptionsmodell verglichen. Es wurde festgestellt, dass die Temperaturabhängigkeit der Laserabsorption entscheidend für die genaue Bestimmung der Wärmeeinbringung und der Schmelzbadgeometrie ist. Das entwickelte Modell wurde anhand der experimentellen Untersuchungen validiert und die Bedeutung der Temperaturabhängigkeit bei der Laserstrahlabsorption wurde für die Simulation des Laserstrahltiefschweißens quantifiziert.
The residual post-fire mechanical properties of fiber-reinforced epoxy (EP) composites are influenced by their fire residues after burning. This study uses intumescent/low-melting glass flame retardants (FRs) to tailor fire residues in epoxy resin. Processibility of prepregs, and their quality are analysed for transfer of the flame-retardant epoxy resins to layered glass-fiber reinforced composites (GFRCs). Minimal effects were found on the pre-fire flexural strengths of the composites due to low loading of the FRs. However, when transferred to GFRCS, the fire residues diminish significantly. Process, testing, and material adaptations are required to improve theoretical and experimental estimations of the post-fire mechanics of the composites.
Bei der Versorgung von Zähnen mit dentalen Kronenrestaurationen entsteht ein Kronen-Zement-Zahn-Komplex (KZZK). Dentale Werkstoffe überzeugen mit besten Materialeigenschaften, aber wie funktionieren sie im Verbund? Unsere zentrale Annahme lautet, dass die Alterung des KZZK eine zentrale Rolle bei Misserfolgen spielt. Präsentiert werden die Methodik und Bilder der ersten Arbeitsphase.
Structural Health Monitoring (SHM) wird zunehmend zur kontinuierlichen Zustandsbewertung von Ingenieurbauwerken eingesetzt. Wichtige Bewertungsparameter sind globale Systemeigenschaften, wie z. B. Eigenfrequenzen, zu deren Bestimmung Beschleunigungssensoren eingesetzt werden. Häufig werden sog. MEMS-Sensoren (Micro Electro Mechanical Systems) verwendet, die jedoch ein hohes Rauschniveau aufweisen. Alternativ können rauschärmere IEPE-Sensoren (Integrated Electronics Piezo Electric) eingesetzt werden, die auch bei geringster Strukturanregung Schwingungen zuverlässig erfassen. Ferner besteht das Problem, dass Änderungen der Eigenfrequenzen infolge Bauwerksschädigung schwer von Änderungen der Eigenfrequenzen infolge Umwelteinflüssen zu unterscheiden sind. Letztere verändern die Eigenschaften der Struktur und die des Messsystems. Um Umwelteinflüsse auf das Messsystem im Anwendungsgebiet Ingenieurbau zu untersuchen, wurden IEPE-Beschleunigungsaufnehmer hinsichtlich ihres Übertragungsverhaltens im niederfrequenten Beschleunigungsbereich analysiert. Es zeigt sich, dass das Verhalten nicht nur frequenz-, sondern auch temperaturabhängig ist, während die Luftfeuchte keinen Einfluss hat. Diese für das Bauwerk unbedenklichen Einflüsse müssen für eine robuste Zustandsüberwachung kompensiert werden. Für die Anwendung im Ingenieurbau werden IEPE-Sensoren empfohlen, da sie ein hohes Signal-zu-Rausch-Verhältnis aufweisen und niederfrequente Bauwerksschwingungen zuverlässig erfassen.
The weldability of stainless steels is largely controlled by the chemical composition, and alloys with ferritic or ferritic-austenitic solidification show the highest resistance to hot cracking. As the resulting phase balance also affects the final properties, it may be beneficial to both foresee and measure the weld metal ferrite content. The WRC ’92 constitution diagram is currently the most accurate prediction tool available, but it does not take the cooling rate into consideration and the precision may be less accurate for stainless steels with high ferrite numbers (FN). This study aims to assess the reliability of the WRC ’92 diagram for weld metals with FN > 50. The chemical composition was altered through gas tungsten arc welding (GTAW) of UNS S32205 with ER347 filler wire that had been PVD-coated with either niobium (Nb), copper (Cu), nickel (Ni), manganese (Mn), carbon (C), or silicon (Si). The actual ferrite content was evaluated using image analysis, FERITSCOPE® and X-ray diffraction (XRD). While predictions from the WRC ’92 diagram were deemed acceptable for Ni, Si, and Mn, notable deviations were observed for Nb, Cu, and C. The FeriteScope exhibited a consistent trend with image analysis, albeit with slightly higher FN values, wider scatter, and the conversion factor from FN to vol.-% is open for discussion. The lowest accuracy and largest spread were obtained using non-contact XRD, rendering it unsuitable for ferrite measurements of welds. These findings underscore the need for improved prediction tools and appropriate measurement methods for assessing ferrite content in duplex weld metals.
As the first commercial sodium-ion-batteries (SIBs) are available for purchase, it is possible to investigate material composition. Gaining an insight into the material composition of these SIBs is of interest not only for the classification of possible safety risks and hazards, but also in regards to recycling. Herein we report the preliminary investigations of the chemical and structural composition of first commercial SIB-cells. Two different SIB-cells with different specification were compared regarding electrode size, thickness and further parameters. Furthermore, the composition of the active materials and electrolyte was investigated and compared.
One remaining handicap for spatially resolved elemental quantification in biological samples is the lack of a suitable internal standard (IS) that can be reliably measured across both calibration standards and samples. In this work, multielement quantitative intracellular imaging of cells tagged with lanthanide nanoparticles containing key lanthanides, e.g., Eu and Ho, is described using a novel strategy that uses the ratio of IS elements and LA-ICP-TOFMS analysis. To achieve this, an internal standard layer is deposited onto microscope slides containing either gelatin calibration standards or Euand Ho-tagged cell samples. This IS layer contains both gallium (Ga) and indium (In).
Monitoring either element as an IS individually showed significant variability in intensity signal between sample or standards prepared across multiple microscope slides, which is indicative of the difficulties in producing a homogeneous film at intracellular resolution.
However, normalization of the lanthanide signal to the ratio of the IS elements improved the calibration correlation coefficients from 0.9885 to 0.9971 and 0.9805 to 0.9980 for Eu and Ho, respectively, while providing a consistent signal to monitor the ablation behavior between standards and samples. By analyzing an independent quality control (QC) gelatin sample spiked with Eu and Ho, it was observed that without normalization to the IS ratio the concentrations of Eu and Ho were highly biased by approximately 20% in comparison to the expected values.
Similarly, this overestimation was also observed in the lanthanide concentration distribution of the cell samples in comparison with
the normalized data.
An understanding of Hydrogen-Oxygen/Air-Diluents gas mixtures combustion characteristics and their accurate prediction is crucial for ensuring the safety of hydrogen-related applications, reducing accidents risk, and protecting lives and property. Hydrogen detonation propagations are characterized by the detonation cell size, used to quantitatively predict for a mixture to detonate including, among others, the initiation energy, critical and minimum tube diameters. For the prediction of explosion limits, detonation run-up-distances and cell sizes, various empirical, semi-empirical and numerical models can be found in literature. These models are usually limited to a narrow range of explosion process or geometrical experimental parameters. Moreover, based on the limited availability of the detonation cell widths measurements, current estimation models are seemingly inaccurate. Machine learning models can be utilized to make justifiable prediction on the detonation cell sizes of hydrogen-air mixtures and other gaseous explosive mixtures cell sizes, explosion limits or run-up distance to detonation based on the mixture type, temperature, pressure, equivalence ratios as well as on geometrical parameters with consideration of highly diverse experimental data measurements uncertainties. Therefore, an up-to date database for explosion characteristics will be established and machine learning models will be developed, trained, tested, and validated using experimental data to predict explosion characteristics of hydrogen mixtures. The models predicted results will be validated against existing models. It will be tested whether machine learning models are able to predict the explosion characteristics of hydrogen mixtures with better accuracy and more comprehensively than conventional empirical and numerical models to be found in literature.
Im Forschungsprojekt DiMoWind-Inspect wurde untersucht, welche Grundvoraussetzungen geschaffen werden müssen, um digitale Methoden für die Instandhaltung von Offshore-Windenergieanlagen einsetzen zu können. Daten aus allen Lebensphasen der Anlagen werden derzeit nur selten effizient dafür genutzt, um die sinnvollsten Instandhaltungsmaßnahmen am richtigen Ort, zum richtigen Zeitpunkt und mit den geringsten Kosten durchzuführen. Eine im Vorhaben entwickelte einheitliche Strukturierung der bisher häufig unstrukturierten Bau- und Instandhaltungsdaten ermöglicht ihre übergreifende, anwenderspezifische Verfügbarkeit. Hierfür werden Prinzipien des Referenzkennzeichnungssystems RDS-PP adaptiert. Es wird aufgezeigt, wie neben Bauteilen auch zusätzliche Informationen wie Instandhaltungsmaßnahmen oder Mängel strukturiert werden können. Dem Ansatz des Building Information Modeling folgend werden die Bauwerkskomponenten direkt mit den Informationen aus Inspektionen und weiteren Instandhaltungsmaßnahmen verknüpft. So können Informationen aus dem Betrieb über den Zustand der Struktur verarbeitet und für die maßgebenden Berechnungen und Nachweise zur Verfügung gestellt werden. Als Anwendungsfall wird ein zweistufiges Konzept vorgestellt, das zur Bewertung der Ermüdungslebensdauer eines korrosionsgeschädigten Konstruktionsdetails der Gründungsstruktur einer Offshore-Windenergieanlage mit Informationen aus der Instandhaltung eingesetzt wird.
Many modern ultrasonic methods in the fields of Non-Destructive Testing (NDT) and Structural Health Monitoring (SHM) require simulations in research. Researchers either use simulation data initially during development to investigate certain aspects, or the simulation process is directly part of the research task. Examples of the second case are inverse methods for parameter estimation, model-assisted probability of detection analysis or the generation of training data for AI algorithms. All these applications require algorithms that are as efficient as possible. For methods based on explicit time-step methods, a significant increase in efficiency can be achieved if a so-called lumped mass matrix can be used, which approximates the consistent mass matrix but is easier to invert.
The finite element method has been the subject of many studies on approximations of the mass matrix. In contrast, the lumped mass matrix in the context of the Scaled Boundary Finite Element Method (SBFEM) is a current field of research [1,2]. In the time domain, the semi-analytical SBFEM is notable for its flexibility to be applied to polygonal meshes. In particular, image-based mesh generation using a quadtree algorithm is possible. In general, polygonal meshes have the same flexibility as triangular meshes, but polygonal meshes can have additional advantages such as greater tolerance to distortion.
In this contribution, the SBFEM formulation based on bubble functions [3] for the time domain is presented for two-dimensional elastic waves. The adjustments necessary for a good approximating lumped mass matrix are emphasized. Several grid generation methods for polygonal elements are shown. Figure 1 depicts the difference between the consistent mass matrix and the lumped mass matrix for a normal polygonal mesh. Finally, the accuracy of mass lumping for linear, quadratic and cubic shape functions is presented and the computational efficiency is demonstrated using exemplary waveguide geometries.
Additive manufacturing (AM, also known as 3D printing) of metals is becoming increasingly important in industrial applications. Reasons for this include the ability to realize complex component designs and the use of novel materials. This distinguishes AM from conventional manufacturing methods such as subtractive manufacturing (turning, milling, etc.). The most widely used AM process for metals is laser powder bed fusion (PBF-LB/M, also known as selective laser melting SLM). Currently, it has the highest degree of industrialization and the largest number of machines in use. In PBF-LB/M, the feedstock is present as metal powder in an inert gas atmosphere inside a process chamber where a laser melts it locally. By repeatedly lowering the build platform, applying a new layer of powder, and then selectively melting it with the laser, a component is built up layer by layer. The local temperature distributions that occur during this process determine not only the properties of the finished component, but also the possible formation of defects such as pores and cracks. Due to the high relevance of the thermal history for precise geometries and defect formation, a temporally and spatially resolved measurement of quantitative (or real/actual) temperatures would be optimal. Quantitative values would ensure comparability and repeatability of the AM process which would also positively affect the quality and safety of the manufactured component. Furthermore, it would also contribute to the validation of simulations and to a deeper understanding of the manufacturing process itself.
At present, however, only qualitative monitoring of the thermal radiation is performed (e.g., by monitoring the melt pool using a photodiode), and safety-relevant components must be inspected ex situ afterwards which is time-consuming and costly. A reason for the lack of quantitative temperature data from the process are the challenging conditions of the PBF-LB/M process with high scanning speeds and a small laser spot diameter. Furthermore, the emissivity of the surface changes at high dynamics (temporally/spatially) as well as with temperature and wavelength. This specifically makes contactless temperature determination based on emitted infrared radiation challenging for PBF-LB/M. Although classical thermography offers very good qualitative insights, it is not sufficient for a reliable quantitative temperature determination without a complex temperature calibration including image segmentation and assignment of previously determined emissivities.
For this reason, this publication presents the hyperspectral thermography approach for the PBF-LB/M process: The emitted infrared radiation is measured simultaneously at many adjacent wavelengths. In this study, this is realized via a fast hyperspectral line camera that operates in the short-wave infrared range. The thermal radiation of a line on the target is spectrally dispersed and detected to measure the radiant exitance along that line. If the melt pool of the PBF-LB/M process moves through this line at a sufficient frame rate, a spatial reconstruction of an effective melt pool is possible.
One approach to determine the desired emissivities and the quantitative temperature from this hyperspectral data are temperature-emissivity separation (TES) methods. A major problem is that n spectral measurements are available, but n+1 parameters are required for each image pixel (n emissivity values + one temperature value). TES methods offer the possibility to approximate this mathematically underconstrained problem in a reliable and traceable way by analytically parameterizing the spectral emissivity with a few degrees of freedom. Using this approach, setup and method are applied to a research machine for PBF-LB/M, called SAMMIE (Sensor-based Additive Manufacturing Machine). First results under AM process conditions are shown which form the basis for the determination of quantitative temperatures in the PBFLB/M process. This marks an important contribution to improving the comparability and repeatability of production, validating simulations, and understanding the process itself. When fully developed and validated, the presented method can also provide reference measurements to evaluate and optimize other, more practical monitoring methods, such as melt pool monitoring or optical tomography. In the long run, this will help to increase confidence in the safety of AM products.
As energy carrier of the future, green hydrogen can make a decisive contribution to a sustainable energy supply. Particularly important is the decarbonization of heavy industry. Therefore, a reliable supply of hydrogen must be guaranteed. A hydrogen pipeline grid can achieve this purpose. In Europe concrete plans for a hydrogen pipeline grid already exist, as the so called “European Hydrogen backbone”. As building a completely new pipeline grid is economically not justifiable, a dual-way strategy of repurposing natural gas (NG) pipelines and newly built pipelines is intended.
Long distance pipeline grids require regular maintenance and repairs. For NG pipelines in-service welding is state of the art. Concepts such as hot-tapping (drilling into pressurized pipelines) and “stoppling” (sealing off pipeline sections after installing bypasses or pressure relieves) allow the repair of damaged pipeline sections or the installation of new branches without shutting the pipeline down, which in most cases isn’t possible from an economic standpoint.
The EIGA 121/14 guideline already pointed out in 2014 that “A hydrogen hot-tap shall not be considered a rou-tine procedure, […]”. This shows that the determination of the transferability of these repair concepts to hydrogen pipelines is of utmost importance. Due to the degrading effects of hydrogen on mechanical properties, commonly referred to as “hydrogen embrittlement” it is necessary to understand and investigate the occurring effects. In the special case of repair welding on in-service hydrogen pipelines an increased hydrogen uptake due to a large heat input and microstructural changes in the material needs to be considered. Therefore, material degradation must be investigated to determine whether modifications of repair procedures are necessary to ensure a reliable and safe hydrogen transportation via pipelines.
For this reason, this paper gives an overview on existing weld repair concepts and its risks and limitations in terms of hydrogen absorption and possible embrittlement effects when transferred to hydrogen pipelines. The complexity lies in a large variety of materials (low alloyed steels), pipeline diameters and corresponding weld-ed joints. The material compatibility of materials in used (repurposed NG-pipelines) and new condition must be investigated. Particularly for repurposed/used pipelines the effect of a pre-matured/corroded inner surface and sometimes insufficient documentation of the material “history” needs to be considered.
An overview on ongoing and completed R&D-projects with respect to repair concepts for hydrogen pipelines and hydrogen effects on pipeline materials is given.
Monocercomonoides exilis is the first known amitochondriate eukaryote. Loss of mitochondria in M. exilis ocurred after the replacement of the essential mitochondrial iron-sulfur cluster (ISC) assembly machinery by a unique, bacteria-derived, cytosolic SUF system. It has been hypothesized that the MeSuf pathway, in cooperation with proteins of the cytosolic iron-sulfur protein assembly (CIA) system, is responsible for the biogenesis of FeS clusters in M. exilis, yet biochemical evidence is pending. Here, we address the M. exilis MeSuf system and show that SUF genes, individually or in tandem, support the loading of iron-sulfur (FeS) clusters into the reporter protein IscR in Escherichia coli. The Suf proteins MeSufB, MeSufC, and MeSufDSU interact in vivo with one another and with Suf proteins of E. coli. In vitro, the M. exilis Suf proteins form large complexes of varying composition and hence may function as a dynamic biosynthetic system in the protist. The putative FeS cluster scaffold MeSufB-MeSufC (MeSufBC) forms multiple oligomeric complexes, some of which bind FeS clusters and form selectively only in the presence of adenosine nucleotides.
The multi-domain fusion protein MeSufDSU binds a PLP cofactor and can form higher-order complexes with MeSufB and MeSufC. Our work demonstrates the biochemical property of M. exilis Suf proteins to act as a functional FeS cluster assembly system and provides insights into the molecular mechanism of this unique eukaryotic SUF system.
We correlated nontarget screening (NTS) features and extractable organic fluorine (EOF) data for PFAS analysis in environmental samples. Soils, sediments, and ashes from different locations (Germany, France, and Lithuania) (n = 34) were analyzed via liquid chromatography-high-resolution mass spectrometry and high-resolution continuum source-graphite furnace molecular absorption spectrometry. NTS feature prioritization based on mass to carbon (m/C) and mass defect to carbon (MD/C) ratios was applied to discriminate potential PFAS features from common co-extracted organic matrix. Our results show a high correlation between quantitative EOF and the prioritized feature number (R2 = 0.87; rPearson = 0.93) and the total peak area of
prioritized features (R2 = 0.97; rPearson = 0.98), while commonly applied MD ranges for filtering showed much weaker correlation with EOF. The observed correlations in PFAS-contaminated samples highlight that MD/C−m/C prioritization is associated with a good indication of the overall PFAS burden as evidenced by EOF. Also, semiquantitative data can be extracted as shown by EOF versus prioritized peak areas. The correlations indicate that weakly fluorinated compounds were negligible and that the EOF was mostly composed of highly fluorinated substances. Our method features the potential to automatically screen large NTS data sets for potential PFAS, determine the contribution of PFAS to EOF, and provide preliminary estimates of the overall PFAS burden.
Die additive Fertigung (Additive Manufacturing AM, auch als 3D Druck bekannt) von Metallen nimmt einen stetig wachsenden Stellenwert in industriellen Anwendungen ein. Gründe dafür sind u.a. die Möglichkeit der Umsetzung komplexer Bauteildesigns und die Nutzung neuartiger Werkstoffe. Damit hebt sich AM von konventionellen Fertigungsmethoden wie der subtraktiven Fertigung (Drehen, Fräsen, etc.) ab. Das für Metalle am weitesten verbreitete AM-Verfahren ist das Laser-Pulverbettschweißen (Laser Powder Bed Fusion PBF-LB/M, auch als Selective Laser Melting SLM bekannt). Es besitzt aktuell den höchsten Industrialisierungsgrad und die größte Anzahl an eingesetzten Maschinen. Bei PBF-LB/M liegt der metallische Ausgangswerkstoff unter Inertgasatmosphäre innerhalb einer Prozesskammer in einem Bett als Pulver vor und ein Laser schmilzt dieses lokal auf. Durch wiederholtes Auftragen einer neuen Pulverschicht und anschließendes selektives Schmelzen mit Hilfe des Lasers findet der lagenweise Aufbau eines Bauteils statt. Die dabei auftretenden lokalen Temperaturverteilungen bestimmen sowohl die Eigenschaften des gefertigten Bauteils als auch das mögliche Auftreten von Defekten wie Poren oder Risse. Durch diese Relevanz der thermischen Historie wäre die Aufzeichnung der auftretenden Realtemperaturen in zeitlicher und räumlicher Abhängigkeit optimal. Mit quantitativen Werten wären Vergleichbarkeit und Wiederholbarkeit des AM-Prozesses gegeben, was sich auch positiv auf Qualität und Sicherheit des gefertigten Bauteils auswirkt. Außerdem wäre ein Beitrag zur Validierung von Simulationen sowie zur Gewinnung eines tieferen Verständnisses des Fertigungsprozesses gegeben.
Jedoch findet aktuell lediglich ein qualitatives Monitoring statt (bspw. mittels Überwachung des Schweißbades durch eine Photodiode) und sicherheitsrelevante Bauteile müssen zeit- und kostenaufwändig im Nachgang ex-situ geprüft werden. Grund dafür sind auch die herausfordernden Bedingungen des PBF-LB/M-Prozesses mit hohen Scangeschwindigkeiten bei geringem Durchmesser des Laserspots. Des Weiteren erschweren die auftretenden Emissionsgradänderungen mit hoher Dynamik (zeitlich, räumlich) und den gegebenen Abhängigkeiten (temperatur-/wellenlängenabhängig) eine berührungslose Temperaturbestimmung basierend auf emittierter Infrarotstrahlung deutlich. Klassische Thermografie bietet zwar sehr gute qualitative Einblicke, ist dabei jedoch ohne eine aufwändige Temperaturkalibrierung inklusive Bildsegmentierung und Zuweisung von vorher ermittelten Emissionsgraden für eine verlässliche Bestimmung der Realtemperatur nicht ausreichend. Aus diesem Grund wird in dieser Veröffentlichung der Ansatz der hyperspektralen Thermografie für den PBF-LB/M Prozess vorgestellt: Die emittierte Infrarotstrahlung wird gleichzeitig bei einer Vielzahl von benachbarten Wellenlängenbereichen gemessen. Dies wird in dieser Untersuchung mittels einer selbst zusammengestellten hyperspektralen Linienkamera, die im kurzwelligen Infrarotbereich arbeitet, realisiert. Hierbei wird die thermische Strahlung einer Linie auf dem Messobjekt spektral aufgespalten und detektiert, sodass die spektrale spezifische Ausstrahlung entlang dieser Linie vermessen werden kann. Bewegt sich das Schmelzbad des PBF-LB/M Prozesses bei ausreichender Bildfrequenz durch diese Linie, ist eine räumliche Rekonstruktion eines effektiven Schmelzbades möglich.
Ein Ansatz, um aus diesen hyperspektralen Daten die gesuchten Emissionsgrade sowie die Realtemperatur zu ermitteln, sind Methoden der Temperatur-Emissionsgrad-Separation (TES). Ein Hauptproblem besteht darin, dass n spektrale Messungen verfügbar sind, jedoch n+1 Kenngrößen für jeden Bildpixel gesucht werden (n Emissionsgrade + eine Temperatur). TES-Methoden liefern die Möglichkeit, dieses mathematisch unterbestimmte Problem verlässlich und nachvollziehbar zu approximieren, indem der spektrale Emissionsgrad mit wenigen Freiheitsgraden analytisch parametriert wird. Mit Hilfe dieses Ansatzes werden Setup und Methoden an SAMMIE (Sensor-based Additive Manufacturing Machine), einer Forschungsmaschine für PBF-LB/M, angewendet. Erste Ergebnisse unter AM-Prozessbedingungen werden gezeigt, welche die Grundlage für die Bestimmung von Realtemperaturen im PBF-LB/M-Prozess bilden. Dies leistet einen wichtigen Beitrag zur verbesserten Vergleichbarkeit und Wiederholbarkeit der Fertigung, zur Validierung von Simulationen sowie zum Verständnis des Prozesses selbst. Das unterstützt langfristig dabei das Vertrauen in die Sicherheit von AM-Produkten zu stärken.
Neutron imaging can provide unique contrast mechanisms. In order to yield reliable and reproducible attenuation coefficients for quantification, one needs to fully understand and characterize the experimental set-up. One effect that has been largely overlooked in scintillator-camera based neutron imaging systems is the backlight scattering or back illumination in the detection system which can significantly affect the quantification of attenuation coefficients and lead to severe errors and image artifacts. Herein, backlighting is investigated by varying the illuminated detector area and the magnitude of the attenuation. The attenuation coefficient of multiple metal plates was determined by polychromatic neutrons bu the CONRAD V7 instrument. The strength of the back illumination strongly depends upon the sample absorption. While it is relatively moderate (a few percent) for weak absorbing samples, it can be severe when the sample is a strong absorber or thick.
Der Band 5 der N.i.Ke.-Schriftenreihe präsentiert den aktuellen Stand materialwissenschaftlicher und bildgebender Verfahren, die bei der Untersuchung von Zeichnungen Anwendung finden. Im ersten Teil der Publikation werden die klassischen Zeichnungsträger und Zeichnungsmaterialien vorgestellt. Der mittlere Teil der Publikation beschreibt die relevanten materialwissenschaftlichen und bildgebenden Verfahren. Der letzte Teil diskutiert anhand einiger Fallbeispiele die Möglichkeiten und Grenzen der Methoden.
Non-equilibrium microstructure evolution in additive manufacturing (AM) is a major barrier for establishing a safe and sustainable application of AM in industrial processes. The constant heat source in the AM continuously affects the just-solidified grains beneath the melting pool, leading to directional grain growth (DGG). While real-time measurements of the non-equilibrium microstructure evolution is challenging, here developing a computational framework to systematically explore DGG becomes imperative.
We have advanced a comprehensive approach, integrating mean-field modeling and phase-field simulations, to elucidate the dynamics of DGG under an external driving force. Our simulations unveil a steady-state power-law grain growth kinetics during DGG, characterized by the interplay between curvature-driven dynamics at grain boundary junctions and directional driving forces.
Inorganic and organic functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are relevant for many key technologies of the 21st century. Decisive for most applications of NM are their specific surface properties, which are largely controlled by the chemical nature and number of ligands and functional groups (FG on the NM surface. The surface chemistry can strongly affect the physicochemical properties of NM, their charge, hydrophilicity/hydrophobicity, reactivity, stability, and processability and thereby their impact on the environment and biological species as well as their possible risk for human health. Thus, reliable, validated, and eventually standardized analytical methods for the characterization of NM surface chemistry, i.e., the chemical identification, quantification, and accessibility of FG and surface ligands 1,2] flanked by interlaboratory comparisons, control samples, and reference materials, 2 ,3 are of considerable importance for process and quality control of NM production and function. This is also important for the safe use of NM the design of novel NM, and sustainable concepts for NM fabrication. Here, we provide an overview of analytical methods for FG analysis and quantification and highlight method and material related challenges for selected NM. Analytical techniques address ed include electrochemical titration methods, optical assays, nuclear magnetic resonance (NMR) and vibrational (IR) spectroscopy, and X ray based and thermal analysis methods. Criteria for method classification and evaluation include the need for a signal generating label, provision of either the total or derivatizable number of FG, and suitability for process and production control.
The use of proton-transfer-reaction mass spectrometry (PTR-MS) for the determination of formaldehyde, ammonia and volatile sulfur organic compounds is described and suggestions are made for the application of stationary PTR-MS in a test laboratory. One advantage of PTR-MS compared to TD-GC-MS (thermal desorption gas chromatography mass spectrome-try) is the faster online measurement. Another advantage is the simultaneous determination of formaldehyde, ammonia, very volatile organic compounds (VVOC) and volatile organic com-pounds (VOC) which normally needs four different kinds of sampling. Coupling the PTR-MS with (multiple) air sample canisters or (multiple) emission test chambers would enable a quick analysis of indoor air and material emissions.
Structural health monitoring (SHM) using ultrasonic-guided waves (UGWs) enables continuous monitoring of components with complex geometries and provides extensive information about their structural integrity and their overall condition. Composite overwrapped pressure vessels (COPVs) used for storing hydrogen gases at very high pressures are an example of a critical infrastructure that could benefit significantly from SHM. This can be used to increase the periodic inspection intervals, ensure safe operating conditions by early detection of anomalies, and ultimately estimate the remaining lifetime of COPVs. Therefore, in the digital quality infrastructure initiative (QI-Digital) in Germany, an SHM system is being developed for COPVs used in a hydrogen refueling station. In this study, the results of a lifetime fatigue test on a Type IV COPV subjected to many thousands of load cycles under different temperatures and pressures are presented to demonstrate the strengths and challenges associated with such an SHM system. During the cyclic testing up to the final material failure of the COPV, a sensor network of fifteen surface-mounted piezoelectric (PZT) wafers was used to collect the UGW data. However, the pressure variations, the aging process of the COPV, the environmental parameters, and possible damages simultaneously have an impact on the recorded signals. This issue and the lack of labeled data make signal processing and analysis even more demanding. Thus, in this study, semi-supervised, and unsupervised deep learning approaches are utilized to separate the influence of different variables on the UGW data with the final aim of detecting and localizing the damage before critical failure.
Low-Temperature High Stress (LTHS) creep plays a crucial role in Ni-base Superalloys, particularly affecting components like blades near the root. Below 850°C, the precipitate microstructure remains stable, characterized by periodically arranged ’ cubic precipitates surrounded by the -matrix. In these conditions, macroscopic traces of cubic slip have been observed in <111> oriented tensile specimens, whereas their microscopic origin has been a topic of debate. Furthermore, in LTHS conditions, Superlattice Intrinsic, Extrinsic Stacking Faults (SISF/SESF), or micro-twins are also frequently reported in crept specimens. Usually, these mechanisms are investigated separately, so that a unified picture and a detailed understanding of these mechanisms and their activation conditions have only recently emerged in the literature, despite the intensive investigations of the last decades.
The objective of this work is to develop a dislocation-based constitutive law that includes these recent developments. In particular, the pseudo-cubic slip mechanism is considered as resulting from the lack of hardening in <111> oriented tensile specimens and is represented by a novel estimate of the back-stresses based on the spectral decomposition of a tensorial representation of the back-stress. An additional novelty is that SISF- and SESF-related slip systems are accounted for as distinct slip systems with corresponding dislocation densities. The model has been implemented as a user-defined constitutive law for commercial Finite Element codes and identified as well as validated with data from the literature obtained with <001>, <011> and <111> oriented crystals tested in tension and compression creep.
Grain boundary embrittlement in medium-Mn steels and liquid metal embrittlement (LME) in Zn-coated high strength steels are among key challenges on the way of safe application of sustainable steels for automotive industry. Using a novel density-based model for grain boundaries, we reveal that the affinity of a grain boundary to attract Mn and Zn atoms result in a segregation transition accompanied by interfacial structural changes. In case of the Zn, the simulations show that the amount of segregation abruptly increases with decreasing temperature, while the Zn content in the alloy, required for triggering the segregation transition, decreases. The results are discussed in the context of CALPHAD-integrated density-based grain boundary phase diagrams.
Die Fourier-Transformations-Infrarotspektroskopie (FTIR-Spektroskopie) bietet eine herausragende Charakterisierungsmöglichkeit für Bitumen und bitumenhaltige Bindemittel. In Kombination mit multivariaten Analysemethoden und somit einem chemometrischen Ansatz erlaubt die FTIR-Charakterisierung Aussagen über verschiedene übergeordnete Eigenschaften, wie die Raffinerie, den Alterungszustand oder die Alterungsempfindlichkeit, eine Abschätzung verschiedener chemischer und physikalischer Kennwerte, wie z.B. den Asphaltengehalt, den Erweichungspunkt Ring und Kugel, die Nadelpenetration sowie den komplexen Schermodul und den Phasenwinkel sowie die Identifizierung verschiedener Additive wie Polymere oder Wachse.
We introduce a novel adaptive Gaussian Process Regression (GPR) methodology for efficient construction of surrogate models for Bayesian inverse problems with expensive forward model evaluations. An adaptive design strategy focuses on optimizing both the positioning and simulation accuracy of training data in order to reduce the computational cost of simulating training data without compromising the fidelity of the posterior distributions of parameters. The method interleaves a goal-oriented active learning algorithm selecting evaluation points and tolerances based on the expected impact on the Kullback-Leibler divergence of surrogated and true posterior with a Markov Chain Monte Carlo sampling of the posterior. The performance benefit of the adaptive approach is demonstrated for two simple test problems.
The Jack Rabbit II (JR II) chlorine field trials in 2015 and 2016 involved nine 5–20 ton releases of pressurized liquefied chlorine from a tank mounted 1 m above a broad flat desert sand surface. A model comparison study was initiated, where 17 widely-used dense-gas dispersion models were run by scientists in seven countries. Predictions were submitted following specified formats, using specified emissions and meteorology inputs. To compare with the model predictions, sets of observations were defined for the arc-maximum 1–3 s averaged concentrations (arc max C) and for cloud widths and heights (to 20 ppm and 200 ppm contours) at distances from 0.2 to 11.0 km from the release. The initial focus is on the three field trials (1, 6, and 7) that have the highest observed concentrations and that have detailed emissions information. It is found that these models are able to satisfactorily simulate (generally within a factor of two) the observed arc max C's and their variation with downwind distance at this flat desert site. At each downwind distance, the scatter in the arc max C predictions covers about 1 ½ orders of magnitude, but the observed arc max C is within the range of the predictions. The median of the cloud width predictions is about 50% larger than the observed value for the three trials. The median of the cloud height predictions is within about 10% of the observed value. For both cloud width and/or height, there are a few models with large (factor of 3 or higher) overpredictions. Of the 17 models, when compared to observations, there is a core group of 5 or 6 with consistently (across all three trials and all distances) less mean error and scatter in their predictions of arc max C and cloud width and height. However, as a group, the 17 models are performing adequately (using the “factor of two” rule of thumb). An important caveat is that, at the JR II desert site, chlorine deposition is minimal. At a site with vegetation and/or organic-rich soil, the effects of removal of chlorine by deposition are expected to be significant.
In this work, we continue to develop and investigate the Thermal Shock Response Spectrum (TSRS) method as an alternative data processing method for infrared thermography (IRT). We focus on improving the current TSRS algorithm and present an optimization methodology for finding the optimal thermal Q-factor and characteristic frequency pair, which is based on the widely applied random sampling method. We show the qualitative relationship between the determined optimal characteristic frequency and the corresponding maximum difference in diffusion length between reference and defective models, as calculated by selecting a specific one-dimensional thermal N-layer model. The investigations were performed on an inhomogeneous plate made of carbon fiber reinforced polymer (CFRP) with artificial square defects at different depths. Furthermore, two different heat sources were used: a xenon flash lamp and a laser. These sources are not only distinct by their underlying physics but also generate inherently different pulse shapes. To quantitatively estimate the contrast between defect and non-defect areas, and to compare these results with commonly used infrared thermography (IRT) data post-processing methods such as Pulse Phase Thermography (PPT) and Thermographic Signal Reconstruction (TSR), the Tanimoto criterion (TC) and signal-tonoise ratio (SNR) were used.
The main advantage of air-coupled ultrasonic testing is the absence of a liquid couplant, which can damage some materials. However, most air-coupled testing scenarios have the challenge of low signals and a signal-to-noise ratio (SNR) several orders of magnitude lower than with couplant-assisted techniques. Since this challenge of small SNR also exists in radar technology, the pulse compression used there was adapted and applied to the physical conditions of air-coupled ultrasonic testing. This paper presents ultrasonic transmission measurements on a carbon-fibre-reinforced polymer plate using two experimental setups: 1) a thermoacoustic transmitter and an optical microphone and 2) a pair of ferroelectret transducers as transmitter and receiver. Thermoacoustic transmitters convert electrical energy to heat, which causes the air to expand thus producing acoustic waves. The optical microphone is based on a Fabry-Perot interferometer. Ferroelectrets are charged cellular polymers, having piezoelectric properties and excellent acoustic matching to air. Both thermoacoustic transmitters and ferroelectrets are non-linear regarding the relationship between the excited sound pressure and the excitation voltage. Due to these physical boundary conditions, unipolar coding was used to modulate the excitation signals. Various codes were tested, and parameters of the excitation pulses were varied to find the optimal combination for each experimental setup. The application of pulse compression to the combination of thermoacoustic transmitter and optical microphone increased the signal-to-noise ratio by up to 16 dB and for the ferroelectret transducers by up to 23 dB.
A journey in science from a graduate student in physical chemistry to head of division biophotonics
(2024)
I will provide a personal overview of the most important steps of my career in science, a journey from a graduate student in physical chemistry in an environment dominated by male-scientists over a postdoc with a female professor in the US to the leader of a research group, head of division Biophotonics at BAM. This will include my choices of research topics, how I learnt to write well cited publications, even on topics such as reference materials and quality assurance,1-4 and eventually started to give lectures at Free University Berlin granting me the right to act as first supervisor of undergraduate and graduate students.
The main advantage of air-coupled ultrasonic testing is the absence of a liquid couplant, which can damage some materials. However, most air-coupled testing scenarios have the challenge of low signals and a signal-to-noise ratio (SNR) several orders of magnitude lower than with couplant-assisted tech-niques. Since this challenge of small SNR also exists in radar technology, the pulse compression used there was adapted and applied to the physical conditions of air-coupled ultrasonic testing. This paper presents ultrasonic transmission measurements on a carbon-fibre-reinforced polymer plate using two experimental setups: 1) a thermoacoustic transmitter and an optical microphone and 2) a pair of ferroe-lectret transducers as transmitter and receiver. Thermoacoustic transmitters convert electrical energy to heat, which causes the air to expand thus producing acoustic waves. The optical microphone is based on a Fabry-Perot interferometer. Ferroelectrets are charged cellular polymers, having piezoelectric proper-ties and excellent acoustic matching to air. Both thermoacoustic transmitters and ferroelectrets are non-linear regarding the relationship between the excited sound pressure and the excitation voltage. Due to these physical boundary conditions, unipolar coding was used to modulate the excitation signals. Vari-ous codes were tested, and parameters of the excitation pulses were varied to find the optimal combina-tion for each experimental setup. The application of pulse compression to the combination of thermo-acoustic transmitter and optical microphone increased the signal-to-noise ratio by up to 16 dB and for the ferroelectret transducers by up to 23 dB.
This talk addresses aging induced property changes of metallic glasses. Priority is given thermally and mechanically induced structural changes, of which the time-dependent dynamics is tracked using coherent scattering. Strong intermittency is observed and accelerated transport is seen at the smallest applied stresses. These findings have significant implications for how metallic glass components respond in realistic service conditions.
Following the new paradigm of materials development, design and optimization, digitalization is the main goal in materials sciences (MS) which imposes a huge challenge. In this respect, the quality assurance of processes and output data as well as the interoperability between applications following FAIR (findability, accessibility, interoperability, reusability) principles are to be ensured. For storage, processing, and querying of data in contextualized form, Semantic Web Technologies (SWT) are used since they allow for machine-actionable and human-readable knowledge representations needed for data management, retrieval, and (re)use.
In this respect, the motivation for digital transformation in materials sciences stemming from the need to handle the ever-increasing volume and complexity of data will be elaborated on. By embracing digital tools and methodologies, researchers can enhance the efficiency, accuracy, and reproducibility of their work. The benefits of digital transformation in materials sciences are manifold, including improved data management, enhanced collaboration, and accelerated innovation. Being a core component of this transformation, ensuring data reliability and reproducibility is critical for the advancement of the field, enabling researchers to build on each other's work with confidence. Implementing FAIR data principles facilitates this by making data more accessible and usable across different platforms and studies. Furthermore, Semantic Web technologies (SWT) and ontologies play a crucial role in achieving these goals. Ontologies, typically consisting of the T-Box (terminological component) and A-Box (assertional component), provide a structured framework for representing knowledge. This presentation will outline the path of ontology creation and the formal transformation procedure, highlighting the various ontology levels that organize data into meaningful hierarchies.
Real-world use cases presented, such as the Tensile Test Ontology (TTO) and the Orowan Demonstrator, illustrate the practical applications of these technologies. These examples will demonstrate how ontologies can be leveraged to standardize data and facilitate interoperability between different systems and research groups. Finally, in this presentation, Ontopanel is introduced, a tool designed to aid in the creation and management of ontologies. Ontopanel simplifies the process of developing and maintaining ontologies, making it accessible to researchers and practitioners in the field. By integrating these technologies and principles, the materials science community can move towards a more digital, interconnected, and efficient future making the knowledge and education on these topics very valuable.
Nichtrostende Stähle sind in Tunnelbauwerken weitverbreitete Werkstoffe, die für Konstruktionsteile verschiedenster Art häufig verwendet werden. Von einfachen Hilfsbauteilen wie Kabelkanälen bis hin zu komplexen Konstruktionen von Schilderbrücken. Tunnel sind aus Sicht des Korrosionsschutzes sehr speziell und zählen in Mitteleuropa zu den korrosivsten atmosphärischen Umgebungsbedingungen. Grund hierfür ist die Kombination aus hoher Feuchtigkeit, Abgasen der Fahrzeuge (SO2, NOx) und dem winterlichen Streusalzeinsatz (Cl-). Die daraus entstehen-den feuchten Oberflächenfilme sind hochchloridhaltig und weisen durch Reaktionen mit Schwefeldioxid sehr niedrige pH-Werte auf. Durch die in Tunnelbauwerken gleichzeitige fehlende Abwaschung der Oberflächenfilme durch Regenereignisse können sich die Verunreinigungen an vielen Ausstattungsteilen über die Einsatzzeit aufkonzentrieren. Für metallene Bauteile und insbesondere auch für nichtrostende Stähle ist dadurch eine hohe Korrosionsbeanspruchung vorhanden, die bei der Werkstoffauswahl bzw. beim Korrosionsschutz zu berücksichtigen ist. Aufgrund der Gefahr für das Auftreten Spannungsrisskorrosion bei einigen nichtrostenden Stahlsorten in Tunnelatmosphären, sind Regeln für die Werkstoffauswahl in Tunneln aufgestellt worden, die seit vielen Jahrzehnten gültig sind. Diese Regeln waren bis 2015 national in der allgemeinen bauaufsichtlichen Zulassung Z-30.3-6 für nichtrostende Stähle festgehalten und werden seit 2015 im europäische Regelwerk DIN EN 1993 1 4 (Eurocode 3) verbindlich genormt. In den ZTV-ING für den Straßenbau wird in Abschnitt 4 auf diese Regelwerke Bezug genommen.
Die Entwicklungen des nichtrostenden Stahlmarktes in den letzten Jahren, insbesondere für den Bausektor, gehen hin zu den Duplexstählen, da diese aufgrund ihres legierungsspezifisch abgesenkten Nickelgehaltes häufig kostengünstiger als die vergleichbaren Austenite sind. Neben vorteilhaften mechanisch-technologischen Eigenschaften, wie zum Beispiel höhere Festigkeiten, weisen sie zudem auch ausgezeichnete Korrosionsbeständigkeiten auf. Hierzu wurden zahlreiche Studien und Forschungsarbeiten durchgeführt, die diese Vorteile bekräftigen konnten. In Tunnelanwendungen sind Duplexstähle bislang wenig untersucht und deren Korrosionsverhalten kann in dieser speziellen Atmosphäre daher nur bedingt eingeschätzt werden.
Das Forschungsprojekt soll diese Erkenntnislücke schließen und durch eine breit angelegte Parameterstudie Duplexstähle für Tunnelanwendungen qualifizieren. Dafür wurden die Korrosionsbedingungen in den Tunneln umfassend untersucht, die Korrosivität der Tunnelatmosphäre anhand normativer Regelwerke beschrieben und dem Korrosionszustand der Prüfkörper aus nichtrostenden Stählen gegenübergestellt.
BAM Inside #5/2024
(2024)
BAM Inside #4/2024
(2024)
Die Fließfähigkeit von Metallpulvern gilt als wichtige Pulvereigenschaft für den additiven Aufbau mittels Laser, wobei bisher wenige Arbeiten die Auswirkungen im Laserpulverauftragschweißen (Engl.: Directed Energy Deposition DED-LB) untersuchen. Arbeiten, die sich mit den Pulvereigenschaften für Pulverbettverfahren beschäftigen, zeigen Korrelationen zwischen Partikelgrößenverteilung und Fließeigenschaften mit der Bauteildichte und den mechanischen Eigenschaften. Sie bewerten insbesondere Pulverbettdichte und -stabilität. In der vorliegenden Arbeit werden daher die Eigenschaften zweier Pulverfraktionen (20 µm – 63 µm und 63 µm – 150 µm) des austenitischen Stahls AISI 316L und deren freien Ausfluss im Vergleich zur Pulverdichte untersucht. Die Untersuchungen zeigen, dass die feinere Pulverfraktion eine um 14,5 % höhere Durchflussrate erzielt als die gröbere Fraktion. korreliert die Ergebnisse zur inneren Porosität und Partikelgrößenverteilung.
Die Analyse der Bauteilqualität zeigt einen geringen Einfluss der Korngrößenverteilung auf die Porosiät der DED-LB aufgebauten Quader.
Hochbelastete Stahlbauteile lassen sich durch Auftragen von Kobalt-Chrom Legierungen vor Verschleiß schützen. Die plötzliche Änderung der Materialeigenschaften führt jedoch zu Spannungen und Rissen im Anbindungsbereich. Daraus resultierende Abplatzungen stellen eine Gefahr für die Funktionsfähigkeit der Maschine und damit für Mensch und Umwelt dar. Um die Belastbarkeit der Schutzschicht zu verbessern, kann die Anbindung durch einen gradierten Materialübergang optimiert werden. Diese funktional gradierten Materialien können mittels pulverbasiertem Directed Energy Deposition aufgetragen werden. Die Methodik zum Aufbau und zur Qualitätssicherung solcher Materialien wurde in vorangegangenen Arbeiten für dickwandige Geometrien gezeigt. Für dünnwandige Geometrien ist die Anwendbarkeit bisher unzureichend untersucht worden. Diese Arbeit zeigt am Beispiel einer dünnwandigen gradierten Schneckengeometrie die Einsatzfähigkeit der Methodik. Dafür wird die Gefügestruktur der Gradierung auf Fehler untersucht und der Härteverlauf gemessen. Außerdem wird die relative Dichte anhand eines bereits trainierten neuronalen Netzes vorhergesagt und mit einer Porositätsuntersuchung verglichen.
This presentation is part of the Engineering Risk Analysis group open seminars. It aims to showcase the results of an ongoing study centered on developing a novel probabilistic methodology for 3D geotechnical site characterization. This methodology integrates data from Cone Penetration Tests (CPTs) and categorical borehole data. The presentation covers the mathematical details of the proposed Multivariate Gaussian Process model and demonstrates its application to a real geotechnical site in New Zealand.
Quantifying uncertainties in subsurface properties and stratigraphy can lead to better understanding of the ground conditions and enhance the design and assessment of geotechnical structures. Several studies have utilized Cone Penetration Test (CPT) data and employed Bayesian and Machine Learning methods to quantify the geological uncertainty, based on the Robertson’s soil classification charts and the Soil Behaviour Type Index (Ic). The incorporation of borehole data can reduce the stratigraphic uncertainty. Significant challenges can arise, however, mainly due to the intrinsic differences between field and laboratory-based soil classification systems, which can potentially lead to inconsistent soil classification. To this end, this study proposes a multivariate Gaussian Process model that utilizes site-specific data and: i) jointly models multiple categorical (USCS labels) and continuous (Ic) variables, ii) learns a (shared) spatial correlation structure and the betweenoutputs covariance, and iii) produces two types of dependent classification outputs. The results indicate that the integration of geotechnical and geological information into a unified model can provide more reliable predictions of the subsurface stratification, by allowing simultaneous interpretation of USCS and Ic profiles. Importantly, the model demonstrates the potential to integrate multiple variables of different types, aiming to contribute to the development of a methodology for joint modeling of geotechnical, geological and geophysical data.
The development of a robust hydrogen infrastructure poses challenges to materials exposed to high pressurized hydrogen environments. Polymeric materials, which are expected to perform as seals, gaskets, O-rings, hoses among other applications face high risk of damage due to rapid gas decompression (RGD) which might cause operational safety issues. In this study, we intend to assess the effects of a high pressurized hydrogen environment on carbon black filled (CB) elastomers. The materials were exposed to 100 MPa hydrogen atmosphere at room temperature and at 85°C. Ex-situ characterization was performed during the first 30 minutes after decompression and repeated two days after the exposure when total gas desorption has taken place. The physical and mechanical characteristics of the materials were determined by means of density and volume change, hardness and tensile tests, and dynamic mechanical analysis.
Intermittent microplasticity via dislocation avalanches indicates scale-invariance, which is a paradigm shift away from traditional bulk deformation. Recently, we have developed an experimental method to trace the spatiotemporal dynamics of correlated dislocation activity (dislocation avalanches) in microcrystals (Phys. Rev. Mat. 2 (2018) 120601; Phys. Rev. Mat. 3 (2019) 080601). Here we exploit the temperature sensitive deformation of bcc metals. A marked change of the slip-size distribution is observed in the studied microcrystals, with increasingly small event-sizes dominating with decreasing temperature. This shows how a reduction in thermal energy increasingly suppresses the length-scale of dislocation avalanches, indicating how long-range correlations become gradually limited to the scale of the lattice. Our results further show that the stress-strain response is composed of strain-increments that are either thermally activated or essentially athermal. Temperature-dependent small-scale testing in combination with state-of-the-art discrete dislocation dynamics (DDD) simulations of Nb microcrystals are used to reveal these insights.
Quenching a metallic liquid sufficiently fast can give rise to an amorphous solid, typically referred to as a metallic glass. This out-of-equilibrium material has a long suite of remarkable mechanical and physical properties but suffers from property deterioration via structural relaxation. As a function of time, relaxation may indeed constitute significant threads to safe applications. Consequently, relaxation of glasses has a long history across different amorphous materials and typical characterization methods promote a picture of gradually evolving and smooth relaxation, as for example obtained from mechanical spectroscopy. However, the true structural dynamics and underlying mechanisms remain far from understood and have hampered a physically informed atomic-scale picture of transport and physical aging of glasses.
Here we exploit the ability to track atomic-scale dynamics with x-ray photon correlation spectroscopy (XPCS) and resolve an unprecedented spectrum of short- and long-term relaxation time scales in metallic glasses. Conducted across temperatures and under the application of stress, the results reveal anything else than smooth aging and gradual energy minimization. In fact, temporal fluctuations persist throughout isothermal conditions over several hundred thousand of seconds, demonstrating heterogeneous dynamics at the atomic scale. In concert with microsecond molecular dynamic simulations, we identify possible mechanisms of correlated atomic-scale dynamics that can underly the temporal fluctuations and structural decorrelations. Despite temporally heterogeneous, the Kohlrausch-Williams-Watts functions is well suited to capture the average intermediate relaxation time regime, but at very long time scales an asymptotic power-law emerges. This indicates anomalous diffusion and gives overall strong evidence for temporal fractional diffusion in metallic glasses. We discuss these results in terms of the structural fast and slow relaxation modes as well as a true microstructure in metallic glasses.
Inspired by the ability to track atomic-scale dynamics with x-ray photon correlation spectroscopy (XPCS)1 and recent results of long-term atomistic simulations on material transport2, we reveal here an unprecedented spectrum of short- and long-term relaxation dynamics. Tracked along a 300 000 s long isotherm at 0.98Tg, a Zr-based bulk metallic glass exhibits temporal fluctuations that persist throughout the entire isotherm, demonstrating a continuous heterogeneous dynamics at the probed length scale. In concert with microsecond molecular dynamic simulations, we identify intermittent cluster dynamics as the origin for temporal signatures in the corresponding intensity cross-correlations. Despite temporally heterogeneous aging, the Kohlrausch-Williams-Watts functions is well suited to capture the average intermediate relaxation time regime, but at very long time scales an asymptotic power-law better describes the data. This indicates anomalous diffusion and gives overall strong evidence for temporal fractional diffusion in metallic glasses. We discuss these results in terms of the underlying structural fast and slow relaxation modes and their manifestation in the temporal form of the structural decorrelations.
Metallic glasses (MGs) are disordered solids that exhibit a range of outstanding mechanical, thermomechanical, and functional properties. Whilst being a promising class of structural materials, well-defined and exploitable structure-property relationships are still lacking. This offsets them strongly from the crystalline counterparts, for which length-scale based property determination has been key for decades.
In recent years, both atomistic simulations and experiments have nurtured the view of heterogeneities that manifest themselves either as a structural partitioning into well-relaxed percolated network components and more frustrated domains in atomistic simulations, or as spatially-resolved property fluctuations revealed with atomic force microscopy. These signatures depend sensitively on the processing history and likely reflect emerging medium-range order fluctuations at the scale of 1-10 nanometers.
Here we demonstrate and discuss the emergence of spatially resolved property fluctuations at length scales that are one to two orders of magnitude larger. Such long-range decorrelation length scales are hard to reconcile in a monolithic glass but may offer the perspective of experimentally easy-to-access length-scale based structure-property relationships. Whilst long-range property fluctuations can be seen in both the plastic and elastic response, we focus here on high-throughput elastic nanoindentation mapping across the surface of a Zr-based model glass. After a deconvolution of surface topography and curvature effects, the spatially-resolved elastic response reveals an elastic microstructure with a correlation length of ca. 150-170 nm. Analytical scanning-transmission electron microscopy (STEM) is used to link the elastic property fluctuations to the chemistry and structure of the MG. In concert, nano-elastic mapping and STEM suggests that structural variations in the glass are responsible for the unexpectedly large length scales. We discuss these findings in terms of the materials processing history and the perspective of exploiting nanoindentation-based spatial mapping to uncover structural length scales in atomically disordered solids.