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Remote gas sensors mounted on mobile robots enable the mapping of gas distributions in large or poorly accessible areas. A challenging task however, is the generation of three-dimensional distribution maps from these spatially sparse gas measurements. To obtain high-quality reconstructions, the choice of optimal measuring poses is of great importance. Remote gas sensors, that are commonly used in Robot Assisted Gas Tomography (RAGT), require reflecting surfaces within the sensor’s range, limiting the possible sensing geometries, regardless of whether the robots are ground-based or airborne. By combining ground and aerial robots into a heterogeneous swarm whose agents are equipped with reflectors and remote gas sensors, remote inter-robot gas measurements become available, taking RAGT to the next dimension – releasing those constraints. In this paper, we demonstrate the feasibility of drone-to-drone measurements under realistic conditions and highlight the resulting opportunities.
Sediments and soils can act as sinks of species of inorganic mercury (Hg2+), while they are simultaneously sources of organic species, such as monomethylmercury (MMHg). Although the fraction of MMHg in total Hg of sediments is suggested to be only 0.1–1%, MMHg poses a threat for humans and wildlife due to its toxic properties, high bioaccumulation potential and the ability to pass the blood-brain barrier. One example of a highly Hg contaminated waterbody is the Finow Canal, the oldest artificial waterway still in operation in Germany. Here, Hg mass fractions of up to 100 µg/g were found in the sediment in previous studies. These are suggested to be associated with a chemical plant producing mercury-based seed dressings. Despite this high mass fraction of Hg, no Hg speciation studies have been conducted there up to now.
In this study, Hg speciation in sediments of Finow Canal at locations before and after the known polluted site was conducted using species-specific isotope dilution (SSID) GC-ICP-ToF-MS. Mass fractions of up to 0.41 µg/g MMHg were determined. In addition, waterbodies around the initially polluted site were investigated and elevated concentrations were also determined around 14 km downstream. For MMHg analysis, the performance of ICP-ToF-MS for SSID GC/ICP-MS was compared with ICP-Q-MS and ICP-SF-MS. Here, isotope ratio precision was similar between the tested instruments. However, the (quasi-) simultaneous detection of the whole mass spectrum will probably offer a much higher precision of ICP-ToF-MS, when more than one isotope system is used.
These results are the first evidence of the occurrence of MMHg in this region and show the need for further investigations of the whole regional ecosystem, as well as the consideration of possible measures of remediation. SSID GC-ICP-(ToF)-MS is a suitable tool for investigating species-specific (multi) isotope systems for environmental monitoring.
The combination of high corrosion resistance and good mechanical properties of duplex steels (DSS) is due to their chemical composition and the balanced phase ratio of ferrite (α) and austenite (γ).
Many industrial applications require a material joint of DSS. Tungsten inert gas (TIG) welding is relatively easy to use, requires little space and allows automated welding, with very high reproducibility and is therefore excellent for welding DSS.
During solidification of these steels, critical phase ratios of α and γ can occur, leading to solidification cracking, susceptibility to corrosion, lower ductility, and critical strength values. Therefore, to obtain the desired material properties, the α/γ distribution must be reliably predicted. This is usually done using the WRC1992 diagram. However, the prediction accuracy of the ferrite content in this diagram is usually not accurate enough and must therefore be optimized. It is therefore necessary to monitor even the smallest changes in the chemical composition of the weld metal, ideally during welding. This is done in these experiments using Laser-induced Breakdown Spectroscopy (LIBS). A major advantage of this technique is the highly accurate time- and spatially-resolved measurement of chemical composition during welding. Previous work has quantified the chemical composition in the weld metal and heat affected zone. In the presented study, the influence of individual elements, such as Nb and Cu, on the resulting weld microstructure is investigated.
Large scale hydrogen assisted cracking test for thick walled SAW joints for offshore applications
(2023)
Offshore wind turbines continuously increase in size and weight and demand adequate offshore foundations concepts like monopiles, tripods or jackets. These components are typically submerged arc welded (SAW) high-strength thick steel plates like the S420ML. During welding, the occurrence of delayed hydrogen assisted cracking (HAC) must be anticipated. HAC is a critical combination of the local hydrogen concentration within a susceptible microstructure under certain mechanical load, i.e., the occurring (welding) residual stresses. The welding sequence of the thick-walled plates complicate the residual stress distribution due to the necessary repeated thermal cycling, i.e., welding seam / layer deposition to fill the joint. For that purpose, SAW with two-wire-technique was used to weld a specially designed and prototype-like mock-up of a real component with a thickness of 50 mm, filled more than 20 passes and a seam length of 1,000 mm. Additional welded stiffeners simulated the effect of a high restraint, to stimulate critical HAC conditions. The necessity of a minimum waiting time (MWT) before the NDT can be conducted (to exclude HAC) was critically verified by the application of ultrasonic testing of the welded joint at different time-steps of the NDT of 48 h after welding. The residual stresses were determined by a robot XRD goniometer. Tensile residual stresses up to the yield limit are found both in the weld metal and in the heat-affected zone. Numerical modelling allowed the qualitative estimation of the hydrogen diffusion in the weld. A remarkable HAC occurrence was not identified and proves both, a certain resistance of the weld joint to HAC and the (questionable) duration of the MWT.
This presentation summarizes the latest results on the microalloying influence on the preciptitation behavior on the mechanical properties of welded high-strength steel with a design yield strength of 690 MPa and above. For that reason, Charpy tests were performed for the pure weld metal and different heat-affected zones. Thermodynamic phase field modeling showed the usefulness of calculations in Thermocalc to predict the preciptiation behavior and (finally) to conclude the mechanistic behavior of the welded joint.
High entropy alloys (HEA) are a new class of materials that have been investigated since the early 2000s and offer great potential to replace conventional alloys. However, since they sometimes have significant contents of expensive alloying elements such as Co or Ni, their use is only conceivable in highly stressed areas of components. For this purpose, the weldability with conventional alloys such as high-alloy austenitic steels must be investigated. In addition to the resulting microstructure, the mechanical properties are also fundamental for the usability of HEAs in DMWs. For this purpose, TIG welds of CoCrFeMnNi HEA (cold rolled and recrystallized state) with AISI 304 austenitic steel are investigated. These mechanical properties are analyzed in this work by means of tensile tests and local hardness measurement. The local strain behavior of the welded joints is also characterized by means of Digital Image Correlation (DIC). The results of the local hardness measurement show a clear influence of the initial condition of the HEA on the HAZ. Thus, the HEA in the cold-rolled condition shows a clear softening because of recrystallization processes in the HAZ. On the other hand, there is no influence on the hardness of the weld metal, which is approx. 200 HV0.1 in both cases. The tensile tests show a consistent failure of the weld in the weld metal. However, regardless of the HEA condition, strengths in the range of the recrystallized HEA (RM ~ 550–600 MPa) are achieved, although with significantly reduced fracture elongations.
Iron is arguably the most essential metal in living organisms. For rock-inhabiting fungi its acquisition might be unconventional as they (1) tend to inhabit iron-deficient, oxygen-rich surfaces like marble monuments and solar panels and (2) produce the black, iron-adsorbing pigment melanin. We used a range of analytical methods, ongoing mineral dissolution experiments and gene deletion mutants of the model rock-inhabiting fungus Knufia petricola to figure out the mechanisms and substrate deteriorating effects of iron uptake by these organisms. To study both siderophore-mediated and reductive iron assimilation (RIA), genes like sidC, encoding a putative siderophore synthetase and ftr1 and fet3 encoding the subunits of an iron permease-oxidase were deleted.
At iron deficient conditions, growth of the wild type (WT) and ΔsidC mutant was similar, whereas growth of the Δftr1-fet3 mutant and the double mutant ΔsidC/Δftr1-fet3 was diminished and absent, respectively. We were not able to detect the siderophore of K. petricola and the WT and mutants were not able to grow at low concentrations of strong iron chelators. However, in a cross-feeding experiment, an overexpression strain of sidC allowed more growth of ΔsidC/Δftr1-fet3 on iron deficient medium than the WT, whereas the ΔsidC mutant could not do so at all. Compared to the WT, the sidC overexpression strain also withstood oxidative stress better and had a shorter lag time and higher growth rate. Combined, these results indicate that K. petricola relies more on RIA than siderophore-mediated uptake as it likely excretes low quantities of a primarily intracellular siderophore. Interestingly, Δftr1-fet3 had a higher iron content than the WT at iron deficient conditions. This difference disappeared upon deletion of melanin synthesis (Δpks1 vs. Δpks1/Δftr1-fet3): melanin-bound iron can likely not be used without RIA. K. petricola’s chelation incapacity implies a habitat free of competition for iron while offering us a mitigation strategy.
In this workpackage of the ELENA project, we develop a way to express the measurement uncertainty of nanoscale determination of electrical propserties. The method developed aims to be usable for industrial contexts and described in technical documents and standards drafts. Standards and reference samples are used to make traceable measurements available for the end user.
Hydrogen-induced stress corrosion cracking (HSCC) is well known, and highly sensitive pre-stressing steels are normally not available on the market. But in the case of existing structures, it could be necessary to ensure their safety through special kinds of investigations. Those kinds of investigations are often not applicable in a non-destructive way.
Therefore, a once in a lifetime project was initiated.
In the course of the deconstruction of the "Bridge of the 20th anniversary of the GDR" at the Altstädter Bahnhof in Brandenburg a. d. Havel, new information on the initiation of hydrogen-induced stress cracks could obtained. The initial observation to do several investigations at this bridge are several meters long longitudinal cracks in the concrete web of the box girder above and below the tension duct. The BAM was commissioned by the Brandenburg State Road Administration to participate in a corresponding joint project which is financed by the Federal Ministry for Digital and Transport. The added value of the new information gained in this project goes beyond the specific structure. It describes unexpected new damage patterns that can be transferred to other structures with concentrated tendons (tendon block method and Baur-Leonhardt method) and were previously unknown in this form. These should be made known to other developers to enable them to initiate any necessary actions.
One of the major results is, the wire breaks observed at this bridge can be attributed to cracking as a result of HSCC and subsequent crack growth until breakage, due to cyclic loading from traffic and alternating restraint stresses. The probable trigger here was crevice corrosion processes at the contact points of the wires to the spacer plates in superposition with high tensile stresses due to prestressing after or with in grouting the duct. Tension wire breaks, which may have occurred before grouting and during prestressing, were not detected. The unfavorable gap situation at the spacer plates occurs over the entire cross-section of the prestressing channel and can thus affect each individual prestressing wire. Losses in the load-bearing capacity of the prestressed concrete structure can then be the result. A disadvantage of the prestressing block method in this respect is that a large number of individual wires can be affected at the same time (theoretically all wires), which can reduce the prestressing effect of the concentrated tendon accordingly. With the usual use of only one tendon per web, the possibility of load transfer to other tendons is thus not given (lack of redundancy).
This presentation deals with the phenomenology and design of pile foundations for offshore wind turbines, and is divided into two lectures.
The first lecture presents a brief introduction to the context and peculiarities of such foundations, and then focuses on the particular case of axially loaded piles. This part is most relevant for the relatively slender piles of the multi-pile substructures (i.e. jackets and tripods). A clear distinction between physical phenomenology and practical design is drawn here.
The change of DNA radiation damage upon hydration: In-situ observations by near-ambient-pressure XPS
(2023)
Ionizing radiation damage to DNA plays a fundamental role in cancer therapy. X-ray photoelectron-spectroscopy (XPS) allows simultaneous irradiation and damage monitoring. Although water radiolysis is essential for radiation damage, all previous XPS studies were performed in vacuum. Here we present near-ambient-pressure XPS experiments to directly measure DNA damage under water atmosphere. They permit in-situ monitoring of the effects of radicals on fully hydrated double-stranded DNA. The results allow us to distinguish direct damage, by photons and secondary low-energy electrons (LEE), from damage by hydroxyl radicals or hydration induced modifications of damage pathways. The exposure of dry DNA to x-rays leads to strand-breaks at the sugar-phosphate backbone, while deoxyribose and nucleobases are less affected. In contrast, a strong increase of DNA damage is observed in water, where OH-radicals are produced. In consequence, base damage and base release become predominant, even though the number of strand-breaks increases further.
Small-angle X-ray scattering (SAXS) can be used for structural determination of biological macromolecules and polymers in their native states (e.g. liquid phase). This means that the structural changes of (bio-)polymers, such as proteins and DNA, can be monitored in situ to understand their sensitivity to changes in chemical environments. In an attempt to improve the reliability of such experiments, the reduction of radiation damage occurring from exposure to X-rays is required. One such method, is to use scavenger molecules to protect macromolecules against radicals produced during radiation exposure, such as reactive oxygen species (ROS). In this study we investigate the feasibility of applying the compatible solute, osmolyte and radiation protector Ectoine (THP(B)), as a scavenger molecule during SAXS measurements of the single-stranded DNA-binding protein Gene-V Protein (G5P/GVP). In this case, we monitor the radiation induced changes of G5P during bio-SAXS measurments and the resulting microscopic energy-damage relation was determined from microdosimetric calculations by Monte-Carlo based particle scattering simulations with TOPAS/Geant4 and a custom target-model. This resulted in a median-lethal energy deposit of pure G5P at 4 mg mL−1 of E1/2 = 7 ± 5 eV, whereas a threefold increase of energy-deposit was needed under the presence of Ectoine to reach the same level of damage. This indicates that Ectoine increases the possible exposure time before radiation-damage to G5P is observed. Furthermore, the dominant type of damage shifted from aggregation in pure solutions towards a fragmentation for solutions containing Ectoine as a cosolute. These results are interpreted in terms of indirect radiation damage by reactive secondary species, as well as post-irradiation effects, related to preferential-exclusion of the cosolute from the protein surface. Hence, Ectoine is shown to provide a non-disturbing way to improve structure-determination of proteins via bio-SAXS in future studies.
Benchtop 1H-NMR and FTIR have both been successfully developed for size-exclusion chromatography (SEC) applications. The latest implementations of these methods by Wilhelm and collaborators[1-3] have taken advantage of commerically available low-cost equipment, and a provide a means to obtain slice-by-slice spectra for the monitoring of functional groups in polymer separations. Demonstrated applications include the detection of highly diluted chains in a polymer blend (e.g., PS/PMMA), copolymer content determination (e.g., styrene-methyl methacrylate), and butadiene isomer detection. To synthesize and characterize an end-labelled low molecular wt. poly(ethylene glycol) as a model polymer to aid in the development and validation of spectroscopic detection (FTIR and 1H-NMR) for SEC applications. A particular focus is to improve quantitation and/or detection of highly diluted funtional groups (e.g., polymer chain ends or sparsely functionalized chains) In the first approach, an isocyanate with IR- and NMR-active functional groups was reacted with PEG (4000 and 10000 g/mol) to form end-functionalized chains by means of an addition reaction. The functionalization of the 10000 g/mol PEG was found to be non-homogeneous (not discussed further). The 4000 g/mol PEG was successfully functionalized to 100%, found to be homogeneous across the molecular weight distribution and could therefore serve as a model polymer for analysis by the coupled methods.
Germany has concluded energy partnerships with various countries, including Japan. During the 3rd meeting of the Hydrogen Working Group, the strategic approach of both countries on developments of hydrogen guidelines, certification and safety was presented and discussed. BAM gave a presentation on important topics in the field of safety research and on safety-related issues along the value chain. Furthermore, the work program and selected projects of the competence center H2Safety@BAM were presented.
It was found that there is a systematic dependence of the crack growth on the welding parameters as well as on the load. Decreasing welding speeds with simultaneously higher heat input promote crack formation with increasing strain rate.
Based on the results, a new crack criterion was finally selected which allows an extended assessment of the material behavior during the MVT-test. The threshold introduced can quantify the dependencies of the crack formation on the welding and testing parameters, which could not be comprehensively described with the conventional evaluation. In principle, the evaluation routine can also be transferred to other Varestraint or externally loaded hot cracking tests.
This presentation summarizes the latest research results of the influence of the post weld heat treatment (PWHT) rate and
the global mechanical stress conditions on the stress relief cracking (SRC) susceptibility of low-alloyed and creep-resistant CrMoV steel submerged arc weld joints. It was found that a certain effect of very low heating rates could be confirmed. In addition, the interlinking of SRC susceptibility increasing effects during the PWHT and the ex-post indentification in metallographic cross-section via microstructure characterization is very complex.
Since there is a continuously growing demand for complex, frequently heavy-sectioned spheroidal graphite cast iron (SGI) castings it is worth paying attention to the chunky graphite (CHG) degeneration which may occur under certain technological circumstances. Although a reference line for preventive actions in terms of general metallurgical and process measures could be drawn to avoid CHG in heavy-sectioned ferritic SGI castings, a broad majority of experts claim the avoidance of CHG in heavy sections cannot yet be rated a hundred percent process safe. A major reason may be seen in the fact that a universal, generally accepted explanation of CHG formation and growth has not yet been established, although several theories have been proposed. Nevertheless, metallurgical aspects are not in the focus of this paper.
This paper is about the current state of methods to detect CHG in SGI on the laboratory and component scales. Capabilities and limits of different metallographic, fractographic and non-destructive computer tomographic methods to recognize and quantify CHG are discussed. With respect to the characteristic fili-gree three-dimensional string-like, multi-branched CHG structure, which is non-isometric and non-dispersed, serious implications on the possibility to quantitatively characterize the amount of CHG must be considered.
In contrary to the metallurgical aspects, the knowledge about the impact of CHG on the materials and com-ponents properties is still surprisingly limited. Therefore, special emphasis of this paper is on the impact of CHG degeneration on the properties of ferritic SGI. Experimental results are reviewed to illustrate the effect of CHG on mechanical strength and ductility properties as well as fracture mechanics properties in terms of crack resistance and fracture toughness.
The present situation is characterized by discussions and uncertainty about the acceptance or rejection of SGI components containing CHG. Addressing this, conclusions from the materials engineering point of view are drawn for quality control, a safe operational strategy in the foundry and component safety.