Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2016 (149) (entfernen)
Dokumenttyp
- Beitrag zu einem Tagungsband (149) (entfernen)
Sprache
- Englisch (123)
- Deutsch (25)
- Mehrsprachig (1)
Schlagworte
- NDT (8)
- Reliability (8)
- Building materials (6)
- Baustoffe (5)
- CFRP (4)
- Corrosion (4)
- POD (4)
- Rheology (4)
- Active thermography (3)
- CO2 (3)
The environmental concerns about availability of fossil fuels and greenhouse gas effect increase and alternative renewable fuels for power plants are gaining significantly of importance. One of the alternative renewable fuels is biomass but it is a difficult fuel because of its diversity and complexity. It can contain high percentages of K and Cl responsible for corrosion together with sand that have additionally an abrasive effect during combustion. Because of permanently extending the surface reaction due to abrasion the corrosion of the materials increases. In particular in power plants, the superheater tubes are exposed to a corrosive abrasive attack that is one of the main sources of concern. The development of new alloys for multilayer surface, which combines corrosive and abrasive resistance is therefore of high importance. Those new technical approaches must be at the same time cost-effective to be an alternative to conventional materials. This paper presents the principle of experimental methods developed for the investigations of high temperature corrosion combined with abrasion in thermochemical processes with high hydrochloric acid concentrations like during biomass combustion. The aim of the presented investigation methods it to test and develop suitable alloys for coatings for the super heater tubes of biomass power plants. First results of abrasion investigations show improved abrasion resistance compared to the multi-component reference material Alloy 625.
In the presentation different zinc coatings are presented and investigated. Their naturally formed protective layers are electrochemically characterized and corrosion relevant values are determined by using a gel pad based on polysaccharide. The corrosion relevant values allow the differentiation of various zinc coating systems and can describe the current protective effect provided by the coating. It is shown that gel-type electrolytes influence protective layers and coatings considerably less than corresponding bulk electrolytes. From the results it is evident that gel-type electrolytes represent a viable and promising field in corrosion research.
Korrosionsuntersuchungen mit gelartigen Elektrolyten an natürlich gebildeten Zinkdeckschichten
(2016)
Ein neuer Ansatz bei elektrochemischen Korrosionsuntersuchungen kann durch den Einsatz von gelartigen Elektrolyten als Alternative zu wässrigen Prüfelektrolyten beschritten werden. Gelartige Elektrolyte ermöglichen minimalinvasive Untersuchungen an natürlich gebildeten Zinkdeckschichten.
Dadurch können korrosionsrelevante Kennwerte ermittelt werden, die Aussagen zur Deckschichtbildung und zur Stabilität der gebildeten Deckschichten erlauben. In diesem Beitrag wird anhand verschiedener Deckschichtzustände an Zink der Mehrwert von gelartigen Elektrolyten für die Korrosionsforschung verdeutlicht.
This contribution will show that gel-type electrolytes influence protective layers on zinc coatings considerably less than typical bulk electrolytes. Different zinc coatings are investigated, their naturally formed protective layers are electrochemically characterized and corrosion relevant values are determined by using a gel pad based on polysaccharide. From the results it is evident that gel-type electrolytes represent a viable and promising field in corrosion research.
Bei elektrochemischen Untersuchungen von atmosphärischen Korrosionsreaktionen an deckschicht- und passivschichtbildenden Werkstoffen stößt man elektrolytseitig an Grenzen. So erweisen sich sowohl das Nachempfinden eines dünnen Feuchtfilms als auch die Interpretation von elektrochemischen Messungen in so genannten Bulk-Lösungen (eine „Masse“ an Elektrolyt) hinsichtlich des Korrosionsverhaltens unter atmosphärischen Bedingungen häufig als schwierig. Eine neue Herangehensweise an diese Problemstellung in der Korrosionsforschung beinhaltet den Einsatz von gelartigen Elektrolyten als Alternative zu den Bulk-Elektrolyten. Gelartige Elektrolyte bilden einen dünnen Feuchtfilm auf der Werkstoffoberfläche aus, wodurch die natürlich gebildete Deckschicht ähnlich wie an Atmosphäre beeinflusst wird und nahezu zerstörungsfrei untersucht werden kann. Durch eine elektrochemische Instrumentierung können geeignete Kennwerte wie Polarisationswiderstände und Korrosionsströme ermittelt werden, die Aussagen zur Kinetik der Deckschichtbildung und zur Stabilität der gebildeten Deckschichten unter Einwirkung eines dünnen Feuchtfilms ermöglichen.
Anhand von auf Polysaccharid basierenden Gelpads werden im vorliegenden Beitrag verschiedene Zinkschichtsysteme und Aluminiumlegierungen untersucht, die natürlich gebildeten Deckschichten elektrochemisch charakterisiert und korrosionsrelevante Kennwerte bestimmt. Die ermittelten Kennwerte erlauben eine Differenzierung verschiedener Schichtsysteme und beschreiben die momentane Schutzwirkung der Deckschichten unter atmosphärischen Bedingungen.
High-power laser beam welding became new stimuli within the last 10 years due to the availability of a new generation of high brightness multi kilowatt solid state lasers. In the welding research new approaches have been developed to establish reliable and praxis oriented welding processes meeting the demands of modern industrial applications during this time. The paper focuses on some of the current scientific and technological aspects in this research field like hybrid laser arc welding, simulation techniques, utilization of electromagnetic fields or reduced pressure environment for laser beam welding processes, which contributed to the further development of this technology or will play a crucial role in its further industrial implementation.
In dieser Studie wurde die Heißrissanfälligkeit beim Laserstrahlschweißen für die Werkstoffe 1.4376, 1.4301 und 1.4828 mit Hilfe des CTW Test quantifiziert. Bei den Versuchen konnten Erstarrungsrisse in den Proben generiert werden. Zusätzlich können mit der Bildkorrelations-Technik die lokalen Dehnungen und Dehnungsraten während des Heißrisstests gemessen wer den. In Verbindung mit einem externen Diodenlaser zum Beleuchten der zu messende Oberfläche und lnterferenzfiltern an den Kameras konnten die DIC Messungen ohne optische Störungen durchgeführt werden.
Die Ergebnisse zeigen, dass die Heißrissbildung bei einer externen Belastung von 3 % für die Stahlsorte 1.4376 zu erwarten ist. Für die Stahls orte 1.4301 beträgt dieser Grenzwert 2 % und 1,5 % für die Stahlgüte 1.4828. Außerdem ist zu beobachten, dass die Gesamtrisslänge mit zu nehmender äußerer Zugbeanspruchung steigt
The validation of the plasma compatibility of particles is a prerequisite for their application in plasma dispersion layers. The goal is the realization of functional add-on features on surfaces, in films and coatings. Although intended applications primarily address nanoparticles, the compatibility tests were carried out at first with particles in the lower micrometer range in order to investigate material-, fluorescent marker- or surface-based degradation effects in a simple manner.
Plasma compatibility implies at least the short-term acceptance of charged species, plasma-UV radiation, vacuum and elevated temperatures. Otherwise, effects on geometrical dimensions, chemical bonds, fluorescence efficiency and plastic-elastic properties are expected.
The plasma compatibility of monodisperse fluorescent-labeled particles to microwave excitation was evaluated by means of microscopic and spectroscopic investigation methods (light, fluorescence, confocal, atomic force microscopy and FTIR). This study comprises particles of different materials (SiO2, PMMA, PS, MF) and sizes (from 50 nm to 10 μm).
A special preparation technique ensures that smallest geometry changes of particles can be measured by atomic force microscopy. For the selected plasma conditions (P = 600 W, f = 2.46 GHz, d = 10 cm) and an exposure time of 10 minutes, the geometry of SiO2 particles (approx. 1.7 μm) remains nearly unchanged, whereas PS particles shrink in diameter by 6% and PMMA particles by 11%. For selected core-particles (SiO2, MF) with fluorescencemarked (rhodamine) shell-polyelectrolytes no remarkable plasma degradation of the fluorescence intensity was observed for the above mentioned plasma conditions, however a doubling of exposure time already results in a significant decrease in intensity. Two different injection systems have been studied for the particle injection into the plasma deposition process.
One of the selected systems also proves process compatibility regarding the expected pressure differences upon injection.
The multiple-sample approach by means of centrifugal adhesion testing (CAT-technology) allows the determination of bonding strength of adhesive-bonded joints on a statistical basis of up to eight samples. Therefore, it is obvious to ensure the continuous handling and identical processing of an octet of samples within the entire process chain of wet-chemical cleaning, plasma-chemical pre-treatment, bonding of samples, and testing of bonding strength. Within the multiple-sample bonding set-up (MPKV-technology) a defined bonding pressure can be adjusted regardless the actual number of samples. A comparison of single- and multiple-sample approach is made for bonding strength of selected adhesives, double-sided adhesive tapes and different material combinations [stainless steel (V2A) vs. stainless steel, polyamide (PA), or polypropylene (PP)]. It is shown that both technologies improve reliability of results
Over the past couple of decades Non-Destructive Testing (NDT) has seen a significant increase in the use of automation. In addition to increased reliability, objectivity, consistency, repeatability, productivity, and so on, automating parts of the process is expected to decrease the potential for human error. However, the literature on human-automation interaction suggests that automation is not only associated with benefits, but also with new risks and risk sources. First, this paper will present the methodology used to identify—for the first time—possible risks associated with mechanised data acquisition and corresponding data evaluation. Moreover, it will highlight possible risks, their causes, consequences, and ways of preventing them. Second, those preventive measures will be further analysed by examining new risks that can arise from their implementation, i.e. potential for failure that can arise from (a) working with automated defect-detection and sizing aids, (b) implementing human redundancy, and (c) improvement of the inspection procedures without due consideration of the procedure users. And third, some optimisations strategies will be provided. The purpose of this work is to show that mechanised testing is associated with potential for failure and that the sources of those risks go beyond single inspectors and need to be looked at in the interaction of people with other systems, i.e. the technology, the team and, most importantly, the organisation.
Aufbau einer Wissensbasis zu Bruchflächen und Gefüge in der fraktographischen online-Datenbank
(2016)
In einer fraktographischen online-Datenbank werden Informationen zum Bruchverhalten von technischen Werkstoffen zusammengetragen. Primäres Ziel ist die kontrollierte Erzeugung von Brüchen und deren anschließende Analyse, aber auch Beispiele aus Schadensfällen werden eingestellt. Die makroskopischen und mikroskopischen Merkmale von Bruchflächen, die Art der Beanspruchung und die dazugehörigen Werkstoffgefüge werden in Datensätzen zusammengefasst, die der interessierten Fachöffentlichkeit zu Verfügung stehen.
The burning behaviour and thermal radiation of pool fires of organic peroxides (OP) have been studied by several authors in the past. It was shown that mass burning rates, flame temperatures and thus the Surface Emissive Power (SEP) of OP exceed to that of hydrocarbons considerably. These facts lead to further investigations of even dangerous worst case scenarios i.e. related to storage and transportation. A metal drum containing 200 l of DTBP (Di-tert-butyl peroxide) is investigated under a surrounding wood fire. Due to a higher heat flux to the substance, the mass burning rate reaches multiples of an equivalent pool fire and results in several fireballs. The analyses of thermographic camera images and radiometer measurements show higher flame lengths, higher temperatures and thereforeincreased thermal radiation compared to OP pool fires. The resulting greater safety distances for a DTBP fireball event are discussed.
The current state in the field of laser-induced periodic surface structures (LIPSS, ripples) is reviewed. Their formation mechanisms are analyzed in ultrafast experiments (time-resolved diffraction and polarization controlled double-pulse experiments) and technological applications are demonstrated.
Durch den stetig steigenden Einsatz von Plastikprodukten sind unerwünschte Kunststofffunde in verschiedenen Umweltmatrices mittlerweile allgegenwärtig. Besonderes Interesse erfahren die Kunststoffpartikel von einer Größe kleiner 5 mm, sogenannte Mikroplastik (MP) Partikel. Es werden aktuell Risiken für Mensch und Umwelt diskutiert, die von diesen Partikeln ausgehen.
Besides measurement of VOC emissions also the evaluation of odour emissions and the perceived intensity of odours gains in importance. Due to difficulties detected in the measurement method of the perceived intensity described in (ISO 16000-28, 2012) the introduction of “reference” odours will be recommended for the training of panellists and as basis for interlaboratory comparisons.
In order to generate the “reference” odours standard liquid substances were directly injected into the main gas flow provided to the panellists. One of the substances tested was ethyl acetate. A pre-evaluation was conducted with six untrained panellists and has shown that ethyl acetate is potentially suitable as reference odour. For further validation of those “reference” odours they additionally will be provided to and evaluated by trained panellists of well established-measurement institutes.
Der Einsatz von nichtrostenden Duplexstählen im Bauwesen findet in den letzten Jahren zu-nehmende Verbreitung. Insbesondere die Lean-Duplexstähle sind aufgrund geringerer not-wendiger Legierungszuschläge von Nickel und Molybdän eine kostengünstigere Alternative zu den jahrzehntelang etablierten austenitischen Stahlsorten. Verschiedene Korrosionsuntersu-chungen an der BAM sowie Erfahrungen aus der Anwendung konnten nachweisen, dass Lean-Duplexstähle unter verschiedenen Einsatzbedingungen ein vergleichbar gutes, in man-chen Fällen sogar besseres Korrosionsverhalten aufweisen als austenitische Referenzwerkstoffe der gleichen Korrosionswiderstandsklasse. Im Hinblick auf die technisch-mechanischen Eigenschaften konnten von der Fa. Modersohn initiierte Untersuchungen zeigen, dass unter Beachtung der gefügebedingten Einsatzgrenzen eine gute Verarbeitbarkeit und mechanische Sicherheit bei gleichzeitiger Materialeinsparung gewährleistet werden kann. Die positiven Ver-suchsergebnisse haben wesentlich zur Akzeptanz und einer damit einhergehenden Erweiterung der Einsatzgebiete dieser alternativen Werkstoffe im Bauwesen beigetragen.
Since geothermal wells are a feasible energy source to replace fossil fuel supply, many technologies have been developed to take advantage of geothermal energy. Nevertheless, service conditions in geothermal facilities are due to the chemical composition of hydrothermal fluids and temperatures, in many cases, extreme in terms of corrosion. Therefore, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of the facilities.
The corrosion behavior of different high-alloyed metals including duplex and austenitic stainless steels as well as a nickel alloy have been evaluated in artificial geothermal fluids simulating the conditions in some locations with geothermal potential in Germany as well as two sites in Indonesia.
The suitability of carbon steel 25CrMo4, stainless steels X2CrNiMo17-12-2, X2CrNiMo-22-5, X2CrNiMoCuWN25-7-4 and super austenitic steel X1CrNiMoCu32-28-7 in these geothermal fluids obtained by electrochemical measurements and exposure tests is limited. The nickel alloy NiCr23Mo16Al shows an excellent corrosion resistance against pitting corrosion. Excluding its high cost, it is a very good alternative to be used in the construction of geothermal facilities having highly saline brines. Stainless and duplex steels exhibit a limited corrosion resistance concerning pitting and crevice corrosion.
Beside of the higher alloyed materials, also the low-alloyed steel 25CrMo4 could be employed as a constructional material for the geothermal power plant in stagnant highly acidic non saline environments, as long as the wall thickness of the material vs. corrosion rate is taken into account.
Since geothermal wells are a feasible energy source to replace fossil fuel supply, many technologies have been developed to take advantage of geothermal energy. Nevertheless, service conditions in geothermal facilities are due to the chemical composition of hydrothermal fluids and temperatures, in many cases, extreme in terms of corrosion. Therefore, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of the facilities.
This contribution deals with the evaluation of the corrosion behavior of duplex steel S31803 (318LN, X2CrNiMoN22-5-3, 1.4462) conducted by electrochemical measurements and exposure tests in artificial geothermal waters simulating the conditions in different locations with geothermal potential in Germany.
The duplex steel S31803 shows limited suitability for applications in artificial geothermal waters due to its susceptibility to pitting and crevice corrosion.
For low saline geothermal waters it can be considered suitable at moderate temperatures. Slight crevice corrosion susceptibility needs to be considered.
Results are being incorporated into a materials catalogue for geothermal applications which shall provide basic information for designers and users of geothermal facilities.
Within the last years the use of feasible alternative energy sources has risen and is going to replace fossil resources more and more. Nevertheless, service conditions in solar facilities are due to the chemical composition of heat transmission media and temperatures, in many cases, extreme in terms of corrosion. Since the construction of power plants shall be economical with maximum life service, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of those facilities.
The materials selection depends on the operation temperature of a power plant on the chemical composition of the transmission fluid used. In high corrosive environments Ni-based alloys are often used as an all-round solution for the construction of corrosion resistant parts, because of their good corrosion properties. However, there might be limits for their use regarding their corrosion behavior, with which this contribution deals.
By means of electrochemical measurements and exposure tests the suitability of two high alloyed materials X8NiCrSi38 18 and NiCr25FeAlYB in molten nitrate salt (60 % NaNO3/40 % KNO3) was characterized at 600 °C.
Characterization of multiphase metal matrix composites by means of CT and neutron diffraction
(2016)
The present study examines the relationship between the microstructure of multiphase metal matrix composites and their damage mechanisms. The matrix AlSi12CuMgNi was combined with 15% vol. Al₂O₃ (short fibers), and with 7% vol. Al₂O₃ + 15% vol. SiC (short fibers and whiskers, respectively). The experimental approach encompasses 3D microstructure characterization by means of computed tomography of samples (a) as-cast, (b) after heat treatment, and (c) after compression tests at room temperature. The volume fraction of different phases, their distribution, their orientation, and the presence of defects and damage are studied.
The influence of the addition of SiC particles on mechanical properties of composite was investigated. Phase-specific load partition analysis for samples with fiber plane parallel to load was performed by using neutron diffraction (ND) during in-situ compression. ND results show damage in the Si phase, while Al₂O₃ short fibers carry load without damage until failure. The computed tomography observations confirm the load partition analysis.
Pre-Inca civilizations like the coastal cultures Moche and Nazca (Early Intermediate) and the inland culture Wari (Middle Horizon) were agrarian societies which supported indigenous elites of impressive wealth, power, and organization. With the expansion of the Wari Empire, the polychrome style and technique of Nazca propagated to the other cultures. High status burials, most of the Late Moche Fine Line ceramics and a large corpus of ceramics with Wari-derived decoration have been recovered in San José de Moro since 1991. The degree of transfer of procedures in this highly interactive scenario is of special interest: is there a limitation to decoration or is it adopted by the local potters also regarding the formulation of the ceramic bodies? In this context the relative amount, size and type of incorporated non-plastic inclusions as temper are important.
The current paper presents residual stress analyses of large scale LTT (Low Transformation Temperature) welds. LTT filler materials are specially designed for residual stress engineering by means of an adjusted martensite phase transformation. Controlling the level of mostly detrimental residual stresses already during the welding process would be highly attractive as time and cost consuming post processing may be prevented. In large scale welds the residual stress state is influenced by the heat control (e.g. interpass temperature) during welding. Therefore, welding residual stresses are studied here putting the focus on the influence of welding process parameters while joining heavy steel sections with a thickness of 25 mm. The residual stress state was determined at the top surface using X-ray diffraction as well as in the bulk by neutron diffraction. The results show that control of the interpass temperature is vital for the residual stresses present in the joints. This accounts for the top surface but is most pronounced for the bulk of the welds. While high interpass temperatures are appropriate to induce compressive residual stresses in the weld metal, low interpass temperatures favor unwanted tensile residual stresses instead.
Copper is one of the most important components in brake pads and its amount can reach up to 14%. In spite of a number of positive features copper usage in brake pad formulations has recently become the subject of considerable discussions, primarily due to concerns about potential risks related to environmental impacts of copper particles. So, for developing new pad formulations with possible replacements of copper content, it is very important to understand the functionality of copper additions to brake friction materials. In the paper theoretical investigation of the role of copper as a pad ingredient was carried out on the basis of modelling by the method of movable cellular automata (MCA). In the study the concentration of copper particles in a Fe3O4-matrix was varied. The sliding simulations were performed while assuming material properties at 500 degrees C in order to assess the beneficial role of copper during severe braking conditions corresponding to fading cycles during dynamometer testing.
The method of movable cellular automata (MCA) and method of molecular dynamics (MD) were applied to simulate the friction and sliding behavior of model-tribofilms formed from a nanocomposite consisting of an epoxy matrix, 10 vol % micron-sized carbon fibers and 5 vol. % silica nanoparticles. Whereas MCA considered the tribofilm as an agglomerate of silica nanoparticles released from the composite and mixed with graphite particles, MD simulated the sliding behavior of an amorphous silica layer supported by stiff crystalline substrates on both sides. The MCA model provided reasonable quantitative results which corroborate experimental findings at moderate stressing conditions. The very low coefficient of friction observed experimentally under severe stressing conditions was not explained by this model. This could be attributed to the lack of mechanical data at the high temperature expected under these conditions. Although based on a simpler assumption of the tribofilm composition, MD-modelling could be easily applied to the expected high flash temperature and was able to predict friction reduction and smooth sliding under these conditions.
Copper is one of the most important components in brake pads and its amount can reach up to 14%. In spite of a number of positive features copper usage in brake pad formulations has recently become the subject of considerable discussions, primarily due to concerns about potential risks related to environmental impacts of copper particles. So, for developing new pad formulations with possible replacements of copper content, it is very important to understand the functionality of copper additions to brake friction materials. In the paper theoretical investigation of the role of copper as a pad ingredient was carried out on the basis of modelling by the method of movable cellular automata (MCA). Our previous studies show that copper as a constituent of the tribofilm formed during braking provides smooth sliding by forming a granular layer of mechanically mixed materials from the friction layers. In the present study the concentration of copper particles in a Fe3O4-matrix was varied systematically in the range 5.5-28 vol. % and compared to mixtures with the same amount of graphite nanoparticles. The sliding simulations were performed while assuming material properties at 500°C in order to assess the beneficial role of copper during severe braking conditions corresponding to fading cycles during dynamometer testing.
The generation of active disinfectants by electrochemical processes gains market share due to the lack of need for transportation and storage of dangerous goods as well as the ease of operation. Usually the process involves the use of specific electrodes for electrolysis of water to produce active chlorine species, sometimes supported by addition of chlorides to the process water. The resulting ECA (ElectroChemically Activated) solutions can cause corrosion due to the content of free active chlorine (FAC) or due to the chloride content of the process solution. These fluids are widely used because they show a good chemical and microbiological stability, are well suited for the standard cleaning procedures and allow reducing germ concentrations to meet hygienic standards. The influence of the respective agents to alloy 1.4301 is investigated by storage experiments and by electrochemical investigations. The results show, that the influence of chlorides is higher for short-term experiments. ECA-Fluids with low chloride concentrations are preferable. The goal of the investigations is to creat evaluation guidelines for the application parameters to provide a sufficient cleansing effect without causing corrosion of the surfaces.
Accurate and reliable detection of subsea Pipeline corrosion is required in order to verify the integrity of the pipeline. A laboratory trial was conducted with a representative pipe sample. The accurate measurement of the wall thickness and corrosion was performed with high energy X-rays and a digital detector array. A 7.5 MV betatron was used to penetrate a stepped pipe and a welded test pipe of 3 m length and 327 mm outer diameter, with different artificial corrosion areas in the 24 mm thick steel wall. The radiographs were taken with a 40 x 40 cm² digital detector array, which was not large enough to cover the complete pipe diameter after magnification. A C-arm based geometry was tested to evaluate the potential for automated inspection in field. The primary goal was the accurate measurement of wall thickness conforming to the standard. The same geometry was used to explore the ability of a C-arm based scanner in asymmetric mode for computed tomography (CT) measurement, taking projections covering only two thirds of the pipe diameter. The technique was optimized with the modelling Software aRTist. A full volume of the pipe was reconstructed and the CT data set was used for reverse engineering, providing a CAD file for further aRTist simulations to explore the technique for subsea inspections.
Durch ein thermodynamisch konsistentes Phasenfeldmodell kann die Rißinitiierung sowie das Rißwachstum in einem spröden Material mit Hilfe der Finite-Elemente-Methode simuliert werden. Ein diskreter scharfer Riß wird durch einen Regularisierungsansatz in ein Phasenfeld überführt, das einen kontinuierlichen Übergang zwischen Riß und Restmaterial abbildet. Modelle von C(T) - Bruchmechanikproben konnten unter monoton wachsender Belastung simuliert werden. Die Ergebnisse konnten mit analytischen Ergebnissen der linear-elastischen Bruchmechanik verglichen werden. Ablenkungen des Rißpfades konnten durch Modelle von gelochten Proben simuliert werden. An dem Modell eines Dreipunktbiegeversuchs konnte die Rißinitiierung demonstriert werden. Die Kenntnis und Modellierung eines vordefinierten Rißpfades ist bei Verwendung dieses Modells nicht erforderlich, was insbesondere zur Untersuchung von komplexen Rißpfaden von Vorteil sein kann.
We describe the fabrication of a polycarbonate (PC) micro-structured polymer optical fiber (mPOF) and the writing of fiber Bragg gratings (FBGs) in it to enable strain and temperature measurements. We demonstrate the photosensitivity of a dopant-free PC fiber by grating inscription using a UV laser. We further show that PC Bragg gratings can be extended up to at least 3% without affecting the initial functionality of the micro-structured fiber. The response of PC FBGs to temperature up to 125°C is also investigated. Polycarbonate has good mechanical properties and its high temperatureresistance might extend the range of application of polymeric FBGs.
Modeling the lifetime reduction due to the superposition of TMF and HCF loadings in cast iron alloys
(2016)
The superposition of small amplitude, high frequency loading cycles (HCF) to slow, large amplitude loading cycles (TMF) can significantly reduce the fatigue life. In this work, the combined TMF+HCF loading has been experimentally investigated for a cast iron alloy. In particular, the influence of the HCF frequency of the HCF amplitude and of the location of the superposed HCF cycles has been assessed. It was observed that the HCF frequency has a limited impact on the TMF fatigue life. On the other side, the HCF-strain amplitude has a highly non-linear influence on the TMF fatigue life. A simple estimate for the fatigue life reduction due to the superposed HCF cycles has been derived from fracture mechanics considerations. It is assumed that the number of propagation cycles up to failure can be neglected after a threshold for the HCF loading has been reached. The model contains only two adjustable parameters and can be combined with any TMF life prediction model. The model predictions are compared with the test results for a large range of TMF+HCF loading conditions.
The recent experience of Italian seismic events provided wide observational information about typical behaviour, damage patterns and intrinsic vulnerability of monumental buildings. Evidence indicates that historical constructions are by far the most vulnerable from the seismic point of view. As a consequence, they demand for the definition of urgent strategies for the protection of cultural heritage from seismic hazard. The main goal of an in-depth knowledge of the structure should help to avoid inadequate, unsuitable or dangerous rehabilitation operations, as well as to select non-invasive and reversible techniques for the best exploitation of material and technology features. The definition of reliable models and methods for seismic risk assessment of historical constructions is today a very important topic. Typical problems of masonry structures concern aspects like inherent structural lacks, material degradation, geotechnical problems, buckling behaviour of slender elements and dynamic loading vulnerability. Modelling the mechanical behaviour of masonry may play an important role, due to both inherent material complexity and great scatter in mechanical properties. Effective procedures for the identification of the structural parameters from static and dynamic testing are thus required. In particular, dynamic measurements may be very useful for the identification of mechanical properties and soil restraints and, consequently, for the calibration of advanced numerical finite element models. The paper addresses two case studies of structural monitoring and seismic assessment of medieval masonry towers in Italy: the bell tower of Aversa and the bell tower of Capua. These monuments, placed in the Campania region, were monitored by means of full-scale environmental vibration testing. Measured responses are then used for modal identification with a typical finite element model updating technique based on vibration test results. Parameters optimization is carried out on the basis of a criterion which minimises a weighted error on modal properties. A satisfactory improvement in the determination of modal parameters is thus obtained, resulting in a close agreement between the modal properties observed in dynamic tests and those calculated from numerical model. Seismic assessment is finally performed based on nonlinear static analysis of the tower under multimodal distributions of lateral loads. Results from nonlinear analysis indicate the potential collapse mechanisms and evidence dangerous structural weakness which may play a role in the seismic vulnerability of the towers.
This paper presents an innovative way to combine an external ultra-high performance concrete (UHPC) supporting layer with an insulation layer of autoclaved aerated concrete (AAC) or cellular lightweight concrete (CLC) to create light-weight façade elements, which are improved in functionality and in energy efficiency. The durability of the façade elements is improved by developing UHPC with self-cleaning properties. One approach is based on the photocatalytic activation of the external UHPC shell by incorporation of TiO2 particles. The second approach consists of the modification of the UHPC surface by micro structuring in combination with the application of water-repellent agents to create durable super hydrophobicity. The current results obtained from laboratory testing are promising and demonstrate the feasibility of the approaches.
The complex microstructure and the advanced mechanical properties of AHSS steel types lead to an increased susceptibility to weld cracking, especially during resistance spot welding under ‘rough’ manufacturing conditions.
Various activities have been conducted in recent years at the Federal Institute for Materials Research and Testing (BAM) and the Fraunhofer IPK on this matter. Understandings about the safe spot weldability and the process of crack-forming itself were gained, and solutions for handling this issue given.
The performed work includes investigations on the influence of initial gaps as well as restraint intensity. An experimental method for the determination of the general cracking susceptibility, i.e. a material ranking of AHSS in respective to current restraints was developed. Coupled mechanical and thermal simulations of the welding process show the present internal stress-strain-conditions and values responsible for the formation of cracks, deepening the understanding of the process.
By using this easy to perform and material-independent method for the determination of the cracking susceptibility in resistance spot welded joints, small and medium sized companies can profit by rapidly evaluating the joinability of their handled material combinations as well as OEMs.
Radiation in the spectral ranges of UV and VIS are environmental impact factors that can cause ageing of many materials or products. The reason for this is that especially organic materials, such as food or many pharmaceutical, are subject to photochemical degradation. Of course, suited transparent packaging material may give protection against such impact for radiation sensitive fillings. But for this, it is necessary to know about the spectral range of the fillings sensitivity as well as about the radiation impact of the radiation sources that are relevant during the life time of the product.
The spectral irradiance for characterizing the emission of various radiation sources is easily measured by means of a spectroradiometer. The spectral sensitivity of a filling's property can be determined by spectrally dispersed irradiation, where the positions on a sample are related to the different wavelengths. Thus, the damaging effect of the different wavelengths can be directly evaluated. A lateral measurement of the relevant property change shows the activation spectrum, which is the product of the spectral radiant exposure and the spectral sensitivity. By measuring the spectral irradiance for each sample position, the spectral sensitivity of the ageing property can be calculated.
Comparing the fillings spectral sensitivity and the spectral irradiance of a potential radiation source during later transport and storage, conclusions can be drawn about necessary spectral absorption of a (partly) transparent packaging to give sufficient protection.
The setup for such investigation will be shown and several illustrating samples from daily food experience will be given.
A commonly used way of minimizing the occurrence of hot cracks, especially solidification cracks during component welding, is mainly to analyse and vary process parameters such as welding speed and consequently the heat input. Metallurgy and component design are however hardly ever considered due to special production requirements and therefore, restricted flexibility in material selection and design. Such conditions, especially crack-critical welding positions are given by slot-welds or welds near pre-deformed areas, for instance bending edges. Hence, it follows that increased local and global residual component stress caused cracking on reaching a solidification crack critical level, which is characterised by solidification crack initiation.
Metal additive manufacturing is often based on laser beam processes like Laser Metal Fusion (LMF) or Laser Metal Deposition (LMD). The LMF process is in particular suitable for very complex geometries. However build rate, part volume and material flexibility are limited in LMF. In contrast, LMD achieves higher deposition rates, less restricted part sizes and the possibility to change the material composition during the build-up process. On the other hand, due to the lower spatial precision of the material deposition process, the complexity of geometries is limited. Therefore, combined manufacturing with both LMF and LMD has the potential to utilize the respective advantages of both technologies.
In this paper, combined additive manufacturing with LMF and LMD is described for Ti-6Al-4V and Inconel 718. First, lattice structures with different wall thickness and void sizes are built with LMF. The influence of LMD material deposition on these LMF-structures is examined regarding metallurgical impact and distortion. Cross-sections, x-ray computer tomography and 3D-scanning results are shown.
For the titanium alloy specimen, oxygen and Nitrogen content in the deposited material are analysed to evaluate the LMD shielding gas atmosphere. The results are used to develop guidelines for a LMD build-up strategy on LMF substrates. With these findings, a gas turbine burner is manufactured as reality test for the combined approach.
Experimentelle Untersuchungen zu streifenden Schlägen mit verschiedenen Edelstahlsorten in explosionsfähigen Atmosphären, jeweils bestehend aus Wasserstoff, Acetylen, Ethylen bzw. Propan mit Luft, haben gezeigt, dass deren Zündwahrscheinlichkeit sowohl von der Art des Brenngas-Gemisches als auch der Höhe der kinetischen Schlagenergie abhängt. Ein Einfluss des Chromgehaltes im Edelstahl auf die Zündwahrscheinlichkeit durch mechanisch erzeugte Schlagvorgänge konnte in dem untersuchten Bereich des Chromgehaltes nicht nachgewiesen werden, obwohl ein steigender Chromgehalt die Oxidationsfähigkeit abgetrennter Partikel erhöhter Temperatur tatsächlich senkt. Ferner haben weitere Werkstoffeigenschaften wie die Wärmeleitfähigkeit, spezifische Wärmekapazität, Dichte und Härte einen Einfluss auf die Zündwahrscheinlichkeit mechanischer Edelstahl-Schlagvorgänge bei Wasserstoff/Luft-Gemischen. Mit steigender Wärmeleitfähigkeit des Edelstahls sinkt die Zündwahrscheinlichkeit. Für die spezifische Wärmekapazität, Dichte und Härte konnte kein Einfluss nachgewiesen werden. Für Schlagvorgänge wurden in der Norm EN 13463-1:2009 Grenzwerte für die maximale kinetische Schlagenergie festgelegt, unterhalb derer die Entstehung einer wirksamen Zündquelle als unwahrscheinlich angenommen werden kann. Dabei wurde zwischen Schlagvorgängen mit funkenarmen Metallen, wie z. B. Kupfer, Messing, und Schlagvorgängen mit sogenannten „sonstigen Werkstoffen“ unterschieden. Die Grenzwerte dieser sonstigen Werkstoffe resultieren aus Versuchen der BAM mit unlegiertem Baustahl. Bei solchen Schlagvorgängen wird von Oxidationsprozessen einzelner Partikel mit dem Luftsauerstoff ausgegangen, die das Gasgemisch aufgrund des hohen Temperaturanstiegs entzünden. In industriellen Anwendungen wie zum Beispiel der chemischen Industrie wird jedoch statt ferritischem Stahl überwiegend Edelstahl verwendet. Im Allgemeinen gilt mit Chrom hochlegierter Edelstahl bei Schlagvorgängen gegenüber ferritischem Stahl als funkenärmer, da die Oxidationsfähigkeit von Edelstahlpartikeln mit steigendem Chromgehalt abnimmt. Aufgrund der abnehmenden Oxidationsfähigkeit postulierte Voigtsberger, dass abgetrennte Edelstahlpartikel mit einem Anteil von 18,11 % Chrom nicht mehr oxidieren können. Bei den eigenen Schlagversuchen der BAM konnte zwar eine sinkende Oxidationsfähigkeit der Partikel, aber keine abnehmende Zündwirksamkeit von Edelstählen mit steigendem Chromgehalt beobachtet werden.
Sliding wear of martensitic steels in hydrogen – X30CrMoN15-1 and 100Cr6 – the role of water traces
(2016)
Initially the primary objective of the project has been the investigation of the influence of gaseous hydrogen on the wear of martensitic steels under heavy tribological stress. As a counter body an Al2O3 ball has been used because the material is inert and hard so that a low amount of wear was expected. If only the gas pressure is responsible for the absorption of hydrogen from the gas to pure α-iron it would require 15·105 MPa (~15 Mbar) to press 1 ppm into the material.
In the test series the Al2O3 balls showed in N2 and H2 atmosphere a higher wear compared to aerial experiments which showed a smaller wear track and a severer wear for the disc. Because of scattering and thereof following investigations it was shown that hydrogen has no noticeable influence but water traces in the gas are manipulating the outcome of the tests distinctly.
Carbon-fiber reinforced composites are becoming more and more important in the production of light-weight structures, e.g., in the automotive and aerospace industry. Thermography is often used for non-destructive testing of These products, especially to detect delaminations between different layers of the composite.
In this presentation, we aim at methods for defect reconstruction from thermographic measurements of such carbon-fiber reinforced composites. The reconstruction results shall not only allow to locate defects, but also give a quantitative characterization of the defect properties. We discuss the simulation of the measurement process using finite element methods, as well as the experimental validation on flat bottom holes.
Especially in pulse thermography, thin boundary layers with steep temperature gradients occurring at the heated surface need to be resolved. Here we use the combination of a 1D analytical solution combined with numerical solution of the remaining defect equation. We use the simulations to identify material Parameters from the measurements.
Finally, fast heuristics for reconstructing defect geometries are applied to the acquired data, and compared for their accuracy and utility in detecting different defects like back surface defects or delaminations.
This work presents the use of limited experimental measurements to develop a set of calibrated Simulation parameters that can then be used for reliable simulation of subsea pipeline inspections. The modelling software aRTist is used as the simulation tool, and the calibration is through comparison with experimental images of a well characterised sample in a water tank. Image Quality parameters such as signal-to-noise ratio, contrast and basic spatial resolution are compared with the aim of matching simulated values to experimental results. Currently the model is partially calibrated, with signal-to-noise ratio successfully matched while differences are still found in contrast-to-noise ratio comparisons. This means that measurements depending on absolute intensity are not accurate enough in the simulation at this stage. However, the simulation is found to be accurate for wall thickness measurements in tangential images, which are not based on absolute intensity, with simulated and experimental cases producing similar results.
The friction and wear properties of polyetherimide composites under dry oscillating sliding condition at room temperature (RT) as well as at elevated temperature (120 °C) was investigated. The polymer specimens were made to oscillate against steel cylinder as a counterpart. The friction and wear properties of PEI and composites were strongly influenced by the temperature. In case of carbon fiber composite abrasive action of carbon fibers has severely damaged the counterpart and resulted in accelerated wear of the composite at RT. Solid lubricants filled (PTFE, MoS2, graphite) along with glass fiber is beneficial in improving the friction and wear performance of the PEI composite at RT, whereas at elevated temperature wear performance was deteriorated.
Compared to the designated European upper reference level of 300 Bq/m³ for indoor radon concentrations, the contribution of building materials appears to be low. Taking into account the recommended limit of 100 Bq/m³ by WHO as well as the increased dose conversion factor, the contribution of building products is quite relevant, especially at low air change rates. Therefore in Germany a maximum contribution of building materials to the indoor radon concentration of 20 Bq/m³ is discussed.
Because measurements of low concentrations are associated with high uncertainties, radon exhalation rates are often determined in chambers without air exchange and indoor conditions are extrapolated.
This study investigated the suitability of direct low level radon measurement under simulated indoor conditions with commercially available instruments, based on the preliminary EU standard for the determination of the emission of volatile organic compounds (VOC) from building materials in test chambers.
Measurements are possible with a relative uncertainty ranging from 7 to 18%. Four major problems were identified:
1. Detector sensitivity: Two of four instruments were identified to determine low radon concentrations in a sufficiently short measuring time.
2. Thoron discrimination: Thoron was discriminated by aging the sampled air in a hose before the detector.
3. Sampling setup: An external chamber measurement was feasible as long as all main system parts were under slight overpressure.
4. Blank value: For VOC-emission testing ambient air, conditioned by filtration and sorption, is used to generate an air exchange. Regarding radon, this treatment is non-effective. If all instrument background levels have been characterized, the blank value must be measured with a second detector in parallel.
Analyzing the reliability of non-destructive tests using the modular modell - a practical approach
(2016)
Non-destructive testing is an important tool to guarantee the safety of railway traffic.
The infrastructure with tracks, switches and sleepers is regularly tested, the
locomotives and wagons with their wheels, bogies and axles as well. Many years of experience and some events lead in Germany to a good practice in testing the railway components. Now, European authorities are drafting a system of common requirements and standards for the European Railway Market. The German practice combines an intensive training of the NDT-personnel including sufficient time for practical exercises with organizational measures of the companies, responsible for rolling stock and infrastructure. Through the example of UT-testing of railway axles it will be shown, how training and organizational measures influence the reliability of such testing.
Rubber is widely used as sealing material in various applications. In many fields the function of seal materials at low temperatures is necessary. Therefore the understanding of failure mechanisms that lead to leakage at low temperatures is of high importance. It is known that the material properties of rubbers are strongly temperature dependent. At low temperatures this is caused by the rubber-glass transition (abbr. glass transition). During continuous cooling the material changes from rubber-like entropy-elastic behaviour to stiff energy-elastic behaviour, that allows nearly no strain or retraction, due to the glass transition. Hence rubbers are normally used above their glass transition but the minimum working temperature limit is not defined precisely, what can cause problems during application. Therefore the lower operation temperature limit of rubber seals should be determined in dependence of the material properties. In the past we investigated the material properties and sealing behaviour of elastomeric seals at low temperatures. Additionally we started to study the effect of a small partial release of elastomer seals at low temperatures. To study the influence of dynamic events on seal performance and to enhance the understanding of occurring seal failure, a setup for a fast partial seal release was designed. In this contribution we focus on the correlation of material properties and component behaviour under different application conditions. It is desired to widen the understanding of the process of seal failure at low temperature.
Spot welding is one of the most important joining technologies, especially in the automotive industry. Hitherto,the quality of spot welded joints is tested mainly by random destructive tests. A nondestructive testing technique offers the benefit of cost reduction of the testing procedure and optimization of the fabrication process, because every joint could be examined. This would lead to a reduced number of spot welded joints, as redundancies could be avoided. In the procedure described here, the spot welded joint between two zinc-coated steel sheets (HX340LAD+Z100MB or HC340LA+ZE 50/50) is heated optically on one side. Laser radiation and flash light are used as heat sources. The melted zone, the so called “weld nugget” provides the mechanical stability of the connection, but also constitutes a thermal bridge between the sheets. Due to the better thermal contact, the spot welded joint reveals a thermal behavior different from the surrounding material, where the heat transfer between the two sheets is much lower. The difference in the transient thermal behavior is measured with time resolved thermography. Hence, the size of the thermal contact between the two sheets is determined, which is directly correlated to the size of the weld nugget, indicating the quality of the spot weld. The method performs well in transmission with laser radiation and flash light. With laser radiation, it works even in reflection geometry, thus offering the possibility of testing with just one-sided accessibility. By using heating with collimated laser radiation, not only contactfree, but also remote testing is feasible. A further convenience compared to similar thermographic approaches is the applicability on bare steel sheets without any optical coating for emissivity correction. For this purpose, a proper way of emissivity correction was established.
The usefulness and purpose of evaluating nondestructive testing (NDT) systems and their capabilities has changed in the last decade. The conventional method of simply applying a familiar statistical algorithm to say whether the system is usable for the tasks is history.
Nowadays, multiple parameter methods which describe the probabilities of detection (POD) of different systems or real defects need new characteristics and a broader variety of statistical models to describe the true system behaviour. The appraisal of the NDT system involves diverse departments within a company (engineering, NDT-operators, and statisticians), but is, at the same time, more needed and requested than in the past. In this article, an approach is discussed in which professionals from different fields worked well together, accomplishing cost-intensive metallographic studies in correlation with well-understood physical behaviour of NDT-methods as well as deep-discussed mathematical methods to create a holistic evaluation of the technical reliability for a specific radiographic testing (RT) equipment. The first part of the publication will show the comparison between metallographic grinding and the RT indications. An essential innovation over past evaluation methods was the use of a multi-scale smoothing algorithm, which describes physical parameters, which were not used in evaluation like the POD in this way in the past.
In the second part the statistical requirements for the POD take the focus. It can often be hard to make significant statements; especially in the case where only a small amount of data is available. The combination of data and the use of knowledge from simulations are essential. One possible solution will be shown for the RT evaluation. The methodology is used for evaluating the digital RT system for the inspection of electron-beam welds, which was method considered to seal the Finnish copper canisters for the final deposit of spent nuclear fuel.
Multi residential buildings, developed as highly energy-efficient and airtight are nowadays often fitted with mechanical Ventilation Systems as a way to overcome shortcomings and even defects tinked to indoor climate. The presented study investigates the potential of low-emitting. natural building materials with hygroscopic properties to contribute to a healthy and comfortable indoor environment, while reducing the need for mechanical Ventilation.
A selection of natural building materials suitable for application as internal partition walls has been investigated with regards to their water vapour adsorption capacity.
Special emphasis was placed on the investigation of modified earth plasters as well as wood-based materials, used as wall lining to provide increased adsorption capacities.
In addition, tests on materials emissions (formaldehyde, VOCs, SVOCs and radon) as well as adsorption tests of airborne pollutants have been conducted in specially-designed fest chambers. All tests were performed at either the material or the component tevel.
Overall results to date suggest that natural materials contribute to an improved indoor environment quality through an increased moisture-buffering capacity, low emissions and the potential to adsorb airborne pollutants, therefore reducing the need for mechanical Ventilation.
Die größten Ressourcenverbraucher unserer Zeit sind die Gebäude oder Behausungen des Menschen sowohl in der Phase der Errichtung als auch im Betrieb. Der Gebäudesektor und damit auch die Architektur verbrauchen in Deutschland ca. 50 % der fossilen Energieressourcen und verursachen ca. 60 % des gesamten Müllaufkommens mit dem zugehörigen Bedarf an Ressourcen in der Errichtung. Öl, Stahl und Beton haben uns Glauben gemacht die natürlichen Begebenheiten bei der Gestaltung von Gebäuden wenig beachten zu müssen. Immer neue Techniken zum Betrieb und zur Klimatisierung von Gebäuden waren die Zukunft. Der Klimawandel und die Ressourcenknappheit sind Aufforderungen zur Veränderung. Das Voranschreiten der Reform des Bauwesens hat somit zentrale Bedeutung zur Erreichung der Nachhaltigkeitsziele und um unsere Gesellschaft zukunftsfähig zu machen. Klimaangepasste Architekturkonzepte und die Verwendung von klimaaktiven Naturbaustoffen werden einen wesentlichen Beitrag zum Ressourcenschutz erbringen.
Earth, timber, fibre boards and insulation materials based on wooden and other natural fibres offer a variety of properties beneficial for eco innovative constructions that are able to improve the energy and resource efficiency of buildings.
Due to their porosity, natural building materials are vapour active and are able to buffer moisture. In combination with highly insulated and airtight but vapour permeable building envelopes, modern earth-timber constructions provide stable indoor humidity levels and can therefore be naturally ventilated while achieving highest energy efficiency standards. Experimental evidence suggests that monitored pilot buildings in Berlin do show healthy indoor air humidity levels (around 50%) in wintertime, while mechanically ventilated buildings demonstrate significantly lower values (around 25%), which have to be considered as uncomfortable and unhealthy.
The application of building materials being poor in chemical emissions, particularly volatile organic compounds (VOC) and radon, improves the indoor air quality further, so that intermittent ventilation twice a day will be sufficient to provide healthy indoor air quality. The air quality in critical rooms (e.g. small bedrooms), demonstrating a smaller air volume, should be monitored if appropriate ratios of room size to occupancy level cannot be realised.
Through night time ventilation in summer, vapour active earth-timber constructions provide evaporative cooling (humidity adsorption at night time and desorption during the day). As a result, indoor temperatures of earth-timber buildings range around 8 °C below the outside temperature peak, when an appropriate glazing ratio is reflected. The EU funded research project H-house is investigating various construction materials regarding water vapour adsorption as well as emission and absorption of harmful substances. Based on this investigation new wall constructions are designed to provide a healthier indoor environment.
Schadensteil: PME-Kraftstoffleitung
Schadensmechanismus: Reibverschleiß und Schwingbruch
Schadensursachen: Nichtbeständigkeit der Elastomereinlage in Befestigungsschelle gegen unplanmäßig ausgetretenen Biodiesel (PME); Schwingungen der Kraftstoffleitungen
Schadensablauf: Elastomer versprödet, Schwingungen der Kraftstoffanlage, Reibverschleiß an der Befestigungsschelle, äußerliche oberflächliche Korrosion der Leitung; Schwingbruch der Kraftstoffleitung; Brand am Motor eines BHKWs
The phenomenon of creep of structural steel in fire engineering is gaining more and more interest. Due to shortcomings of the EC3 constitutive model and other approaches based on classical creep theory an alternative approach mainly based on the ideas of Krempl is proposed. Due to this so-called operator approach the material as well as the constitutive model is looked upon as an operator. The application of this view serves as a guide through the analysis of the relationship between experimental facts and constitutive theory especially in the context of transient creep.
With increased usage of highly demanded, modern materials on safety
relevant parts (e.g. railway wheel sets, generator shafts, turbine disks, medical
implants, etc.) comprehensive analyses regarding the quality of the material are
requested. This gives a focus to non-destructive methods using ultrasound immersion
tank testing for classifying the degree of purity. Two autonomous standards,
ASTM E588 and SEP 1927, have been established for the definition, execution and
evaluation for this high resolution ultrasonic measurements on steel products.
The propagation of ultrasonic waves and the resulting sound field are strongly
dependent on the acoustical properties of the inspected material and the geometry
of probes and specimen. The definition of the measurement setup and the evaluation
methods appear to differ significantly in the given standards. ASTM E588 and
SEP 1927 prescribe the requirement for surface roughness and probe selection, are
using threshold based methods for cleanliness detection, but differ in computation
for the degree of purity. This has been the motivation for a comparison between
both standards with the main focus on amplitude depth dependency and overall spatial
resolution taking the influence of different material characteristics, geometry of
the specimen and sound fields into account.
A performance comparison between the use of non-focusing and focusing probes
respective to the threshold based detection will be presented in this contribution. In
addition, the usage of complex reconstruction algorithms (e.g. SAFT, echo tomography)
is compared with the traditional approaches of inclusion detection and
estimation of the degree of purity
In respect of modern approaches in material sciences and highly increased
requirements on materials on safety relevant components, quality management
and non-destructive testing reclaims a steadily increased meaning. The
destructive meaning of measuring the degree of purity is defined in DIN EN 10247
through metallurgical investigations, especially microsections.
For and comparable, but non-destructive testing due ultrasonic testing, the material
the SEP 1927 is a well-defined industry standard. A novel and alternative way
of reference block construction was focused by this work. The proposed amendments,
regarding the manufacturing and machining, are less time and cost consuming.
Verified by measurements the presented reference block fits the same acoustical
characteristics and the requirements of the guideline.
Carbon arc-air gouging is a common technology when repairing defects in welded structures. Often this technique is applied in repeated cycles even on the same location of the joint. Due to the multiple heat input by gouging and subsequent re-welding, the residual stresses are strongly influenced. This can become crucial when microstructure and mechanical properties are adversely affected by multiple weld reparations. Knowledge about the relation of gouging and residual stresses is scarce but important when high strength steels, which are sensitive to residual stresses, are processed. The present study shows the effect of repair welding on a high strength steel structural element. The weld and the heat affected zone were subjected to multiple thermal cycles by gouging and subsequent repair welding. The residual stresses were determined by X-ray diffraction at different positions along the joint. The results showed that the residual stress level has increased by the repair cycles. This is most pronounced for the heat affected zone. Adapted welding procedures may prevent detrimental residual stress distributions.
The most substantial innovations in radiographic imaging techniques of the last two decades aim at enhanced image contrast of weakly absorbing micro and nano structures by taking advantage of X-ray refraction effects occurring at outer and inner surfaces. The applications range from fibre reinforced plastics to biological tissues. These techniques comprise, among others, X-ray refraction topography, diffraction enhanced imaging, phase contrast imaging, Talbot-Lau grating interferometry, and refraction enhanced imaging. They all make use of selective beam deflections up to a few minutes of arc: the X-ray refraction effect. In contrast to diffraction, this type of interaction has a 100 % scattering cross section, as shown experimentally. Since X-ray refraction is very sensitive to the orientation of interfaces, it is additionally a tool to detect, e.g., fibre or pore orientation. If the detector resolution exceeds the size of (small) individual features, one detects the integral information (of inner surfaces) within the gauge volume. We describe the above-mentioned techniques, and show their experimental implementation in the lab and at a synchrotron source. We also show strategies for data processing and quantitative analysis.
At BAM, which is the federal institute for materials research and testing in Germany, it is one of our tasks to evaluate the safety of casks designed for transport and/or storage of radioactive material. This includes assessment of elastomeric seals applied in the containers. Besides examining the low-temperature behaviour and irradiation effects of elastomeric seals, it is our goal to evaluate the service lifetime of the seals with regard to the requirements for long-term safety (40 years and more) of the containers. Therefore, we started an accelerated ageing programme with selected rubbers often used for seals (HNBR, EPDM and FKM) which are aged at four different temperatures (75 °C, 100 °C, 125 °C and 150 °C) up to 1 year. In order to assess sealability, O-rings are aged in compression by 25 % (corresponding to the compression during service) between plates as well as in flanges that allow leakage rate measurements. For comparison, uncompressed O-rings are aged as well. Further methods characterising seal performance are compression stress relaxation (CSR) reflecting the loss of sealing force of a compressed seal over time, and compression set (CS) which represents the recovery behaviour of a seal after release from compression. Additionally, hardness is measured for information about the change of mechanical properties. The experimental results indicate that while hardness, CSR and CS show considerable degradation effects, the leakage rate stays constant or even decreases until shrinkage and the loss of resilience of the aged seal leads to the formation of a leakage path. This indicates that static leakage rate, which is the only available direct seal performance criterion, has only limited sensitivity for the degradation of the seal material.
BAM is the federal institute for materials research and testing in Germany. One of our tasks is to evaluate the safety of casks designed for transport and/or storage of radioactive waste. As elastomeric seals are used in the containers as safety-relevant parts, it is our goal to be able to evaluate the service lifetime of the seals with regard to the requirements for long-term safety (40 years and more) of the containers. For this reason, an accelerated ageing programme with selected rubbers often used for seals (HNBR, EPDM and FKM) was started. Ageing was performed at four different temperatures (75 °C, 100 °C, 125 °C and 150 °C) for up to 2 years. For assessing properties related to the sealability, O-rings were aged in compression by 25 % (corresponding to the compression during service) between plates. For comparison, uncompressed O-rings were aged as well. The aged materials were characterized with conventional polymer analysis methods such as hardness and tensile tests, but also with more seal-specific methods such as compression stress relaxation (CSR, reflecting the loss of sealing force of a compressed seal over time), and compression set (CS, representing the recovery behaviour of a seal after release from compression). CS is chosen as the property for lifetime prediction as it is both sensitive to degradation and related to the seal performance. CS data is extrapolated to 60 °C, which yields lifetimes of approximately 5 years for HNBR and 64 years for EPDM for a criterion of 85 % CS respectively, and approx. 40 years for FKM for a criterion of 65 % CS (the highest value measured so far).
3D Crack analysis in hydrogen charged lean duplex stainless steel with synchrotron refraction CT
(2016)
Hydrogen in metals can cause a degradation of the mechanical properties, the so-called hydrogen embrittlement. In combination with internal stresses, hydrogen assisted cracking (HAC) can occur. This phenomenon is not completely understood yet. To better characterise the cracking behaviour, it is important to gain information about the evolution of the 3D crack network. For this purpose samples of lean duplex stainless steel were loaded with hydrogen by means of electrochemical charging and investigated by means of synchrotron refraction CT and SEM fractography after uniaxial tensile loading. Synchrotron refraction CT is an analyser-based imaging (ABI) technique. It uses a Si (111) single crystal as analyser, which is placed into the beam path between sample and detector. According to Bragg’s law only incident x-rays within a narrow range around the Bragg-angle are diffracted from the analyser into the detector. Hence, the analyser acts as an angular filter for the transmitted beam. This filtering allows to turn the refraction and scattering of x-rays into image contrast. Refraction occurs at all interfaces, where the density of the material changes and is more sensitive to density changes than the attenuation. Therefore, it is possible to detect smaller cracks than with classical x-ray imaging techniques, like CT, with comparable spacial resolution. It also visualises the 3D structure of the cracks and gains quantitative information about their morphology and distribution. Since cracks introduced by HAC are usually very small and have a small opening displacement, synchrotron refraction CT is expected to be well suited for imaging this cracking mechanism and can be a valuable tool to characterise the formation and the evolution of a 3D crack network.
The nonlinear analysis became a common tool to precisely assess the load-bearing behavior of steel beam and column members. The failure level is significantly influenced by different types of imperfections, among geometric also structural imperfections (residual stresses). Here are still gaps in the knowledge. Nowadays, 3-D welding simulation developed to a level where it could provide reliable estimation of weld-induced distortion and residual stresses. Nevertheless, modelling and computational effort are still in a less practicable range. In this study a simplified procedure to implement residual welding stresses in continuous large scale members is proposed and the influence on the ultimate limit state of slender members in compression is evaluated for two common structural steel grades. The results showed significant improvements in the utilization of load bearing capacity compared with simplified design methods. The comparatively general approach in this study offers
potential for future optimization.
This article presents the latest results of an ongoing national research project on improved models for the prediction of welding residual stresses of thick-plated welded I-girders. The experimental program is presented and the importance of different influencing factors on the residual stresses is discussed in detail. All results are compared for mild (S355J2+N) and high strength (S690QL) steel. Finally, conclusions for further works are drawn.
Carbon Capture, Utilization and Storage (CCUS) has been proposed as a promising technology for the mitigation of CO2 emissions into the atmosphere from fossil-fuel-operated power generation plants. As the reliability and cost effectiveness of the pipeline transport network is crucial to the overall operability and resilience of the CCUS system, it is vital to realize the possible corrosion risks of the employed pipeline steels corresponding to the impurity level of the gas source.
Recent studies have shown that even the high alloyed materials might be susceptible to general and/or localized corrosion by the condensates forming from the impurities such as SOx, NOx, CO, O2 and water [1]. Up to now, however, there is no regulation procedure which defines the maximum acceptable level of impurities and the combination of them for each employed pipeline steels. Herein, systematic experiment series were conducted by mixing pure CO2 gas with varying concentration of each impurity and with the varying combination of them. Each time, the mixture was then fed (1 L/min) into the reactor containing 12 specimens for 120-600 h at 5°C (to simulate the sub-level pipeline transport). The resulted condensate was collected and analyzed by ionic chromatography and atomic absorption spectroscopy to determine the chemical composition. In this study, the “worst-case scenario” gas mixture, containing 2.5 % H2O, 1.8 % O2, 1000 ppm NO2, and 220 ppm SO2 as impurities, resulted in the condensate containing H2SO4 0.114 M and HNO3 0.0184 M (pH 2.13). This “original” condensate was then re-produced to carry out exposure tests and electrochemical characterization including corrosion potentials and impedance spectroscopy in CO2 saturated condition for 7-14 days at the same temperature. The corrosion rate was also measured by mass loss method.
We can conclude that, at the initial stage, HNO3 plays the dominant role in Fe dissolution process, while H2SO4 is responsible for the pit initiation followed by pitting corrosion. Future studies will be focused on the combination effect from the impurities and the exposure test under the regularly changing condensate to mimic the real CO2 pipeline system.
Mit dem KorroPad Verfahren ist es dem Anwender möglich den Zustand der Passivschicht nichtrostender Stähle auf sehr einfache und schnelle Weise einschätzen zu können. Das Verfahren eignet sich dazu, den Grad der Passivität in Abhängigkeit der Umgebungsbedingungen und der Zeit nachzuvollziehen. Dies ermöglicht dem Anwender und Verarbeiter von nichtrostenden Stählen, die Lagerungsbedingungen und –zeiten einer frisch bearbeiteten Stahloberfläche zu ermitteln, welche für die Ausbildung einer stabilen Passivschicht notwendig sind, bevor diese risikoarm eingesetzt werden kann. Wie die hier dargestellten Beispiele und auch weitere zahlreiche praktische Anwendungen gezeigt haben, eignet sich das KorroPad ebenfalls für die Identifikation kritischer Prozessparameter bei der Verarbeitung nichtrostender Stähle. Mit dem Verfahren lassen sich viele prozessbedingte Einflussfaktoren auf die Oberflächengüte wie auch auf den Werkstoff charakterisieren. Aufgrund der schnellen und einfachen Auswertung der Prüfergebnisse können positive wie auch negative Veränderungen hinsichtlich der Passivschichtstabilität zügig erkannt werden. Dies ermöglicht es dem Anwender schnell zu reagieren, um kritische Einflüsse zu korrigieren und um eine Optimierung von Inhouse-Prozessen durchzuführen. Weitere Einsatzgebiete sind im Bereich der Wareneingangs- und/oder Warenausgangskontrolle denkbar, überall wo es um die Frage der Passivschichtstabilität einer nichtrostenden Stahloberfläche geht.
One of the unique advantages of polymer optical fibres (POF) is that they can be used to measure very high strain values up to 100 % and beyond exceeding the strain limits of silica fibre-based sensor principles. In this paper the distributed strain measurement capabilities of POF based on backscatter change evaluation are summarized and distributed backscatter measurement technologies are intro-duced. Application examples in the structural health monitoring (SHM) field are presented: a promising approach is the integration into technical textiles for high-strain measurement in earthwork structures and crack detection in buildings. The potential of POF for future applications in SHM such as distributed relative humidity sensing is discussed.
Bei der Bewertung der Verlässlichkeit der im Labor gewonnenen Prüfergebnisse spielen Ringversuche eine entscheidende Rolle. Die Bundesanstalt für Materialforschung und -prüfung (BAM) unterstützt deshalb den weiteren Ausbau des Ringversuchsprogramms des im Jahr 2007 gegründeten Kompetenzzentrums zur Qualitätssicherung für Prüfungen von Gefahrgütern und Gefahrstoffen auf physikalische Gefahren (Centre for quality assurance for testing of dangerous goods and hazardous substances, CEQAT-DGHS).
Bei allen bisher untersuchten Prüfmethoden besteht ein Verbesserungsbedarf. Die RV müssen daher zunächst auf die Methodenentwicklung, -verbesserung und -validierung abzielen und nicht auf Leistungstests.
IBESS steht für „Integrale Bruchmechanische Ermittlung der Schwingfestigkeit von Schweißverbindungen“ und ist das Ergebnis eines DFG-AiF-Clusters, an dem acht Partner beteiligt waren. Kernstück ist eine analytische Methode zur bruchmechanischen Beschreibung der Rissausbreitung unter Schwingbelastung, die im IBESS-Teilprojekt A3 entwickelt wurde. Da man es im Bereich der Schwingfes-tigkeit mit kurzen Rissen zu tun hat, auf die die etablierten Methoden der Langriss-bruchmechanik nicht anwendbar sind, wurden Lösungen entwickelt, die es erlauben, sowohl die rissnahen Plastizitätsverhältnisse als auch die mit wachsendem Riss gra-duell zunehmenden Rissschließeffekte quantitativ zu beschreiben. Unter Einbeziehung der sogenannten „zyklischen R-Kurve“, deren experimentelle Methodik ebenfalls im Rahmen des Projekts weiterentwickelt wurde, ist es zudem möglich, Ausgangsrissgrö-ßen vorherzusagen, die auf Dauerfestigkeitsniveau gerade so noch arretieren würden. Dies erlaubt umgekehrt eine Abschätzung der Dauerfestigkeit an den Schweißverbin-dungen sowie die statistisch basierte, analytische Vorhersagen des Zeitfestigkeitsas-tes der Wöhlerkurve. In diesem Aufsatz wird die Methodik vorgestellt und ihre Validie-rung an einem ausgewählten Beispiel diskutiert.
In diesem Aufsatz wird eine analytische Prozedur zur bruchmechanischen Beschreibung des Schwingverhaltens von Schweißverbindungen beschrieben, die im Rahmen des DFG-AiF-Clusters IBESS entwickelt wurde. Es wurden drei Verbindungen untersucht (Stumpfstöße, Kreuzstöße und Längssteifen), die aus warmgewalzten Stahlplatten produziert wurden. Die analytische Modellierung basierte auf drei wichtigen Aspekten: Quantitative Beschreibung der Rissausbreitung mechanisch-kurzer Risse; Statistische Effekte infolge der Variabilität der lokalen Schweißnahtgeometrie; Modellierung der Mehrfachrissinitiierung und des Mehrfachrisswachstums. Im Folgenden wird die Methodik vorgestellt und ihre Validierung an einem ausgewählten Beispiel diskutiert.
The increased use of fibre-reinforced plastic (FRP) composites for improved efficiency and reliability in energy related applications e.g. wind and marine turbine blades, nacelles, oil and gas flexible risers, also increases the demand for innovative non-destructive testing technologies. Thus, in order to achieve increased acceptance of suited and optimized non-destructive testing (NDT) methods in industry, the European Metrology Research Programme (EMRP) project ENG57 Validated Inspection Techniques for Composites in Energy Applications (VITCEA) deals with the development and validation of innovative NDT technologies. In this contribution, results concerning thermographic investigations at test specimens during tensile loading and active thermography testing after tensile loading are presented. Additionally, the determination of the optical properties (relative transmittance and directional spectral emissivity) of CFRP and GFRP test specimens is described.
Amongst various other NDT methods, within the EMRP-project
‘VITCEA’ active thermography is validated for testing of CFRP and
GFRP structures constructed for energy application. In this
contribution, the optical and thermal properties of CFRP and GFRP
reference defect artefact (RDA) and natural defects artefact (NDA)
test specimens are characterized. Different excitation techniques
and techniques for data analysis are compared for optimizing the
number of detected defects.
For pulse laser materials processing often optical step index and gradient index multimode fibers with core diameters ranging from 100 to 600 μm are used. The design of a high power fiber transmission system must take into account limitations resulting from both surface and volume damage effects. Especially, breakdown at the fiber end faces and self-focusing in the fiber volume critically influence the fiber performance. At least operation charts are desirable to select the appropriate fiber type for given laser parameters.
In industry-relevant studies the influence of fiber core diameter and end face preparation on laser-induced (surface) damage thresholds (LIDT) was investigated for frequently used all-silica fiber types (manufacturer LEONI). Experiments on preform material (initial fiber material) and compact specimens (models of the cladding and coating material) accompanied the tests performed in accordance with the relevant LIDT standards ISO 21254-1 and ISO 21254 2 for 1-on-1 and S-on-1 irradiation conditions, respectively. The relation beam diameter vs. LIDT was investigated for fused silica fibers. Additionally, laser-induced (bulk) damage thresholds of fused silica preform material F300 (manufacturer Heraeus) in dependence on external mechanical stress simulating fiber bending were measured. All experiments were performed with 10-ns laser pulses at 1064 and 532 nm wavelength with a Gaussian beam profile.
The premise for the development of improved failure criteria for fiber reinforced composites is the understanding of the failure processes on microscale. On microscale the local behaviour of the matrix polymer is crucial. It significantly differs from that found in macroscopic measurements. The present study is focused on the plastic material behaviour of a standard epoxy resin. Local plastic strains are measured in tensile test by using digital image correlation. A multilinear plastic law is implemented by the experimental data. The stress field arising in an idealised representative volume element of a unidirectional ply is analysed by finite element calculations. The change of the stress and strain field due to plastic deformation according to the multilinear plastic law is shown. The change leads to a shift of the critical locations where failure is likely to initiate. In addition, the failure type changes from stress based to strain based failure. The dominant role of the shear strains is shown.
The failure of composites is initiated by imperfections on microscale. The interface between fiber and matrix is a key parameter concerning failure initiation. In order to get an improved understanding of local failure processes a fracture mechanical analysis of interfacial failure in a composite ply under transverse stresses is performed. The mixed mode energy release rate is calculated. In addition the failure of interfaces under cyclic loading is studied on a single fiber model. The quasistatic debonding process is compared with the interfacial failure under fatigue loading. It is shown that the tan delta can be used as an indicator for the damage propagation.
The nonlinear behaviour of epoxy resins is studied on standard tensile tests. A strain field measurement system is applied (Aramis) in order to monitor local strains. The residual strain is measured by recovering the specimens for up to 68 hours after unloading. The time span the specimen is exposed to load has a large influence on the creeping process and the residual strain after recovering. This is studied by comparison of instantaneous unloading with keeping the specimen under permanent load for thirty minutes. It is shown that moderate differences in the initial strain can lead to large differences in the creep behaviour as well as in the residual strain.
Ultrasonic phased array is, currently, the technology which is being applied as the solution to a lot of inspection problems. The perceived benefits are seen to be worth the outlay on equipment and specialised personnel. Yet, there is a source of knowledge, freely available, which can also deliver immediate benefits, through more reliable inspection results, and consequently increased client confidence, but which is largely ignored by the greater part of the NDT community. This talk will review the latest Human Factors knowledge and provide practical illustrations of how companies can use it to improve their competitive edge.
In-plane shear behaviour of earthen materials panels strengthened with polyester fabric strips
(2016)
An experimental investigation was carried out to study the in-plane shear behaviour of earthen material Panels strengthened with polyester fabric strips. Strengthened panels were developed to exploit the strength potential of earthen materials and to solve its lack of tensile strength, significantly improving not only strength but also ductility. Three earthen materials were considered: cob, earth block masonry (EBM) and rammed earth (RE). As first approach the strengthening configuration, based on different adhesive materials, was tested only for cob panels. As part of the study the results of a big testing campaign of unstrengthened Panels were considered. Seven strengthened panels were tested in diagonal compression/shear.A unique reinforcement orientation was used. The results of these tests are presented in this paper, and include the load-displacement behaviours, crack patterns, failure modes. The results showed that the reinforcement was the most effective in EBM panels, with increase in strength and ductility observed. In RE and cob panels the reinforcement did not likely contribute significantly to the shear resistance, due to a lack of embedment length of the strips. Instead, in EBM it was likely that the vertical reinforcement acted in tension to restrain shear induced dilation and to restrain sliding.
UHPC-AAC/CLC composite panels with self-cleaning properties. Materials and production technology
(2016)
The aim of this study is to show the development of a façade composite panel combining either an autoclaved aerated concrete or a cellular lightweight concrete insulation layer with a box-type external ultra-high performance concrete (UHPC) supporting layer. The paper presents the materials characteristics of the different components and the production technology of the panel. The efficiency of surface modifications of the materials forming the external shell of the panel is reported. The activation of self-cleaning properties is described. The test results showed that the most efficient way to use the water-repellent agent is its application on the substrate before the concrete cast. Concerning the production technology, the preliminary studies showed more advantages of a twostep manufacturing procedure of the UHPC boxes than a one-step procedure.
The goal of the present study is to assess the feasibility to develop a first reliable database of materials parameters for Earth Block Masonry (EBM). The database is crucial when defining the materials safety factors. In the first part an experimental campaign of compressive tests were carried out on two types of earth block and two types of earth mortar. The results showed that the mean variation of the compressive strength was remarkably less than expected. This low variation is related to a production with high quality standards of the materials employed. In the second part a partial safety factor for EBM under uniaxial compression was determined through the reliability method. The results proved the reliability of a common calculation method for EBM based on partial safety factors following the current standards.
The paper presents a comparison between two different numerical modelling approaches aimed to simulate the in-plain behaviour of rammed earth walls, namely under axial, diagonal and cyclic shearcompression loading. In the first part of the study the mechanical characterisation of wallets tested under uniaxial compression and diagonal compression and walls tested under in-plane cyclic shear-compression loading is presented. The results were used to implement and validate the finite element simulations.
The numerical modelling of the rammed earth samples tested is then discussed in the second part. A non-linear constitutive law based on the total strain rotating crack model (TSRCM) was employed as implemented in the DIANA® software. The aim of the numerical analyses presented here is to simulate the behaviour of rammed earth under different inplane loading conditions. For the wallets, tests under static loading both macro- and micro-modelling
approaches were considered for the simulation of the experimental tests. For the walls subjected to cyclic loading only the micro-modelling approach was applied for the simulation of the experimental tests.
The respective FEM model was calibrated with the experimental results. The rammed earth layers were represented by continuum elements, the contact surfaces between layers by interface elements. This approach allowed assessing the influence of the apparent weakness of the interfaces between layers on the shear behaviour of rammed earth.
The goal of the numerical simulation of the cyclic tests was to establish the adequacy of common analytical methods (e. g. used for masonry) applied to the analysis of rammed earth. Rammed earth exhibits brittle characteristics similar to masonry materials and is used in geometrical typologies, such as walls, common in masonry construction.
Der Beitrag präsentiert einen Vergleich zwischen verschiedenen numerischen Modellierungsansätzen die dazu dienen sollen, das flächige Verhalten von Stampflehmwänden, genauer unter axialer, diagonaler und zyklischer Scherkraftbelastung zu simulieren.
Im ersten Teil der Studie werden die mechanischen Eigenschaften der Wandscheiben, die unter einachsiger und diagonaler Druckbelastung getestet wurde und der Wände, die in flächigen, zyklischen Scherkraftbelastung getestet wurden, dargestellt. Die Ergebnisse werden verwendet, um die Finite Elemente Simulation anzuwenden und zu bewerten. Die numerische Modellierung der getesteten Stampflehmproben
wird dann im zweiten Teil diskutiert. Ein nichtlineares Materialgesetz basierend auf dem Gesamtdehnungsrissmodell (total strain rotating crack model – TSRCM) wurde, wie durch die Software DIANA® verwendet, angesetzt. Ziel dieser hier präsentierten numerischen Analyse ist es, das Verhalten von Stampflehm unter verschiedenen Lasteinflüssen
zu simulieren. Für die Wandscheiben wurden Versuche unter linearer Last, sowohl in Makro- als auch Mikromodellansätze für die Simulation der experimentellen Versuche gewählt. Für die Wände, welche zyklischer Belastung ausgesetzt waren, wurden nur die Mikromodellansätze für die Simulation der experimentellen Versuche gewählt. Das betreffende FEM Modell wurde mit den experimentellen Ergebnissen kalibriert. Die Stampflehmlagen wurden mit durchgehenden Elementen, die Kontaktflächen zwischen den Lagen mit Oberflächenelementen repräsentiert.
Dieser Ansatz erlaubte die Bewertung des Einflusses der auftretenden Schwächung in den Oberflächen zwischen den Lagen auf das Scherverhalten des Stampflehms. Ziel der numerischen Simulation von zyklischen Versuchen war es, die Eignung allgemeiner Analysemethoden (z. B. für Mauerwerk) für die Analyse von Stampflehm einzuführen und anzuwenden. Stampflehm zeigt brüchige Eigenschaften vergleichbar zu Mauerwerksbaustoffen und wird in geometrischen Formen, wie Wänden, genutzt, die im Mauerwerk üblich sind.
The presentation will discuss the difference between EU and US standards for the determination of explosion (flammability) limits and limiting oxygen concentration. Small differences observed in measured values can be traced back to the different test apparatuses and criteria. The discrepancies can be much greater in the case of limiting oxygen concentration because of the high amount of inert gases and the corresponding low laminar burning velocities. The paper describes some examples and the influence of the chosen criteria on the results. The European and US standards use the criteria of flame propagation in open test vessels and of pressure rise in closed ones. The examples discussed show that flame propagation is still possible at very small pressure rise values, as observed much below the pressure rise criterion of usual standards. However, flame propagation in a process plant can cause an accident or explosion and must be avoided. Therefore, the flame propagation criterion is recommended to be used in chemical safety engineering. The European safety database CHEMSAFE contains expert-evaluated safety data for cases where the determination method and criteria are known. Flammability characteristics based on the pressure rise criterion may suffice in certain cases, e.g. for explosion protection in closed vessels without any connecting pipes.
In the beginning of the 1980s earth building has undergone a renaissance, which nowadays leads to an increasing use of load-bearing earth constructions and in particular, earth block masonry. At present, there are no common structural standards according to the semi-probabilistic design concept, which is the state-of-the-art in European standards.
A solid database is needed for the determination of the partial safety factor on the resistance side. Therefore, compressive strength tests were carried out with two types of earth blocks and two types of prefabricated earth mortar. The evaluation showed that the variation of the compressive strength was remarkably less than expected, which seems to indicate high quality standards of the components earth block and mortar with regard to industrial production.
On the basis of these results and together with the reliability method, a partial safety factor for earth block masonry subjected to compression was determined. The main aim of the research was the development of a first valid database for material parameters of earth block masonry with particular regard to statistical characteristics. The results showed that a common calculation method for earth block masonry based on partial safety factors following the valid masonry construction standard is feasible.
Die Instandsetzung von Lehmbauwerken ist keine einfache Aufgabe. Der Baustoff Lehm hat vergleichsweise schwache mechanische Eigenschaften. Er ist außerdem anfällig gegenüber eindringendem Wasser, wobei er sehr schnell seinen Zusammenhalt verlieren kann, wenn gewisse Feuchtegehalte überschritten werden. Instandsetzungskonzepte für Bauwerke aus solchen Materialien stellen deshalb eine Herausforderung dar. Historische Lehmbauwerke zeigen oft Schäden in Form von starker Rissbildung, die durch statische oder dynamische Lasten hervorgerufen sein kann. Häufig werden solche Risse wegen mangelnder Fachkenntnis und / oder fehlender Techniken nur ungenügend instandgesetzt. Die Rissinstandsetzung mit Einpressmörteln birgt insbesondere für Lehmbaustoffe eine Herausforderung und erfordert spezifische Anforderungen an den Einpressmörtel, wie z. B. niedriger Wassergehalt, gutes Wasserrückhaltevermögen, niedriges Schwindmaß, an das instandzusetzende Material angepasste Festigkeit und E-Modul sowie eine gute Haftung am Lehmuntergrund. Zusätzlich müssen Einpressmörtel eine ausreichende Fließfähigkeit aufweisen, um kleine Risse und Hohlräume ohne Entmischung zu füllen. Deshalb muss das rheologische Verhalten des Einpressmörtels gut untersucht und kontrolliert werden, um die gewünschte Wirkung zu erzielen. Die Rissinstandsetzung bei Lehmbauwerken erfolgt traditionell durch manuelles Stopfen mit einem Mörtel. Natürlich können auf diese Weise nur Risse mit einer großen Breite verfüllt werden. Ein weiterer Nachteil ist, dass Risse, die durch dickere Wände verlaufen, nicht vollständig mit den für das Stopfen verwendeten Werkzeugen erreicht werden können. Kalkgebundene Einpressmörtel für Lehmbaustoffe werden gewöhnlich für die Wiederbefestigung von Putzen und weniger aus statisch-konstruktiven Gründen eingesetzt.
Aufgrund der Eigenschaften von Lehm, müssen Einpressmörtel auf Basis von hydraulischem Kalk nach EN 459-1 [4] wesentliche Anforderungen an eine Reihe von Eigenschaften erfüllen, die sich auf die Verträglichkeit, die Dauerhaftigkeit und insbesondere die Injektionsfähigkeit beziehen. Das Ziel der vorgestellten Untersuchungen war einen Einpressmörtel zu herzustellen, mit dem die strukturelle Kontinuität in Lehmmauerwerk oder anderen massiven Lehmwänden (Stampf- und Wellerlehm) durch Rissverpressung wiederhergestellt werden kann. Das Material bestand aus Kalkhydrat mit Zusätzen von Puzzolanen und Kalksteinfüller.
Die Instandsetzung von Lehmbauwerken ist keine einfache Aufgabe. Der Baustoff Lehm hat vergleichsweise schwache mechanische Eigenschaften. Er ist außerdem anfällig gegenüber eindringendem Wasser, wobei er sehr schnell seinen Zusammenhalt verlieren kann, wenn gewisse Feuchtegehalte überschritten werden. Instandsetzungskonzepte für Bauwerke aus solchen Materialien stellen deshalb eine Herausforderung dar. Historische Lehmbauwerke zeigen oft Schäden in Form von starker Rissbildung, die durch statische oder dynamische Lasten hervorgerufen sein kann. Häufig werden solche Risse wegen mangelnder Fachkenntnis und / oder fehlender Techniken nur ungenügend instandgesetzt. Die Rissinstandsetzung mit Einpressmörteln birgt insbesondere für Lehmbaustoffe eine Herausforderung und erfordert spezifische Anforderungen an den Einpressmörtel, wie z. B. niedriger Wassergehalt, gutes Wasserrückhaltevermögen, niedriges Schwindmaß, an das instandzusetzende Material angepasste Festigkeit und E-Modul sowie eine gute Haftung am Lehmuntergrund. Zusätzlich müssen Einpressmörtel eine ausreichende Fließfähigkeit aufweisen, um kleine Risse und Hohlräume ohne Entmischung zu füllen. Deshalb muss das rheologische Verhalten des Einpressmörtels gut untersucht und kontrolliert werden, um die gewünschte Wirkung zu erzielen.
Die Rissinstandsetzung bei Lehmbauwerken erfolgt traditionell durch manuelles Stopfen mit einem Mörtel. Natürlich können auf diese Weise nur Risse mit einer großen Breite verfüllt werden. Ein weiterer Nachteil ist, dass Risse, die durch dickere Wände verlaufen, nicht vollständig mit den für das Stopfen verwendeten Werkzeugen erreicht werden können. Kalkgebundene Einpressmörtel für Lehmbaustoffe werden gewöhnlich für die Wiederbefestigung von Putzen und weniger aus statisch-konstruktiven Gründen eingesetzt Aufgrund der Eigenschaften von Lehm, müssen Einpressmörtel auf Basis von hydraulischem Kalk nach EN 459-1 wesentliche Anforderungen an eine Reihe von Eigenschaften erfüllen, die sich auf die Verträglichkeit, die Dauerhaftigkeit und insbesondere die Injektionsfähigkeit beziehen. Das Ziel der vorgestellten Untersuchungen war einen Einpressmörtel zu herzustellen, mit dem die strukturelle Kontinuität in Lehmmauerwerk oder anderen massiven Lehmwänden (Stampf- und Wellerlehm) durch Rissverpressung wiederhergestellt werden kann. Das Material bestand aus Kalkhydrat mit Zusätzen von Puzzolanen und Kalksteinfüller.
The repair of earthen structures is not an easy task. Earth as a construction material has comparatively weak mechanical properties. It is also susceptible towards liquid water, were it can lose cohesion very quickly if certain moisture contents are exceeded. Repair concepts of structures built with such materials are therefore challenging. Historical earthen structures often exhibit damages in form of extensive cracking, which may have been caused by static or dynamic loads. Frequently these cracks are insufficiently or inappropriately repaired because of lack of knowledge and / or technology. In particular, the behaviour of crack repair by grouting poses a challenge in earthen materials and demands specific requirements for the grouting mortar, such as low water content, good water retention, low shrinkage. Grouting materials require additional specifications such as compatible strengths and Young’s modulus as well as good adhesion to the earthen substrates. In addition, grouts have to be sufficiently flowable to fill small cracks and voids without segregation or bleeding. Therefore, the rheological behaviour has to be well understood and controlled to gain the desired effects.
The repair of cracks in earthen buildings is traditionally done by stuffing manually mortar into the gap. Naturally, this method is only usable for cracks with large widths. Another disadvantage is that cracks going through thicker walls cannot be completely reached by the tools used for stuffing the mortar into the crack. Lime based grouts for earthen materials were usually used for re-attachment of plasters but less for structural reasons. Due to the nature of earthen materials grouts based on formulated or hydraulic lime (according to the definition in EN 459-1) have to meet considerable demands on a variety of properties, which are related to compatibility, durability and in particular to the ability of being injected. The goal of this study was to create a grout, which can be used to re-establish structural continuity in cracked earthen masonry or other massive earth walls (rammed earth and cob) with the focus on grouting cracks. The grout material was based on hydrated lime (calcium hydroxide) with additions of pozzolana and lime stone filler.
Testing of the oxidative resistance of polyolefin based geosynthetics in
autoclaves at high oxygen pressure has been suggested as an alternative method to
conventional forced-air oven aging. The intention is to shorten considerably the testing
time and to ensure that aging is performed under the condition of rate-controlled
and not diffusion-limited oxidation. We compare data from high pressure autoclave
tests (HPAT) with data from oven aging and water immersion tests at 80 °C. For this,
the stabilization of the samples has to be taken into account. Polyolefin based geosynthetics
are usually stabilized by two types of “packages” of antioxidants (AO), designated
here as P1 and P2. P1 consists of phenols and phosphites, P2 of hindered amine
stabilizers (HAS) in addition to a marginal stabilization P1 of the resin for the manufacturing
process. Phenolic and phosphite AO are quickly consumed in the HPAT.
Failure time is tremendously reduced compared to forced-air oven aging or water
immersion. The results are discussed within the framework of a basic autoxidation
scheme (Wise et al., 1997). The reduction is much greater than expected from theoretical
considerations. Therefore, a direct and degrading reaction of oxygen with the AO
has to be assumed. In case of HAS, the time dependence of the degradation of tensile
properties in the HPAT is significantly different from the dependence observed in
conventional forced-air oven aging and their effectiveness is likewise strongly reduced.
A conclusive interpretation of HPAT results needs a better understanding of
what happens to the AO at high oxygen pressure.
The Bundesanstalt für Materialforschung und –prüfung (BAM) is a federal institute for materials research and testing in Germany and has been involved in the qualification and safety evaluation procedures of metal seals from the early beginning of the interim storage licensing procedures for radioactive materials, stored in dual purpose casks. Regarding this subject, BAM investigates the long-term behavior of metal seals under the influence of temperature using experimental data and analytical approaches. The development of numerical models is in progress as well. Systematic experimental investigations performed by BAM indicate a continuous decrease of the remaining seal force and the usable resilience considering the leak tightness. Hence, there is a fundamental interest of describing time and temperature dependency to gain predictable values for the long-term behavior and to achieve reliable results with help of short-term tests.
The paper gives an overview about the sealing principle, test program and test results of metal seals of the type HELICOFLEX® HN200. The aging effect, respectively the long-term behavior in dependency of time and temperature, are introduced for two different outer liner materials, aluminum and silver.
The modeling and prediction of the behavior of reinforced concrete under impact load is still an engineering challenge. The scientific community has put a lot of effort into the development of this knowledge, especially after the unfortunate events of 09/11 in Manhattan. The main concern is with nuclear power plants and how to design structures that can withstand such extreme situations. An experimental investigation has been carried out to collect fundamental data and to develop a deeper understanding of the effect of impact damage on the load capacity of concrete plates. The paper presents the process on the definition of procedures and the first results of an experimental investigation on the damage and residual load capacity of reinforced concrete plates after impact load. Two types of reinforced concrete plates measuring 1.5 x 1.5 x 0.3 m were subjected to the impact of a flat-nose hard projectile. The two types were casted with the same reinforcement and 80 or 40 MPa concrete. After the impact, the plates go through planar tomography, visual inspection and an ultimate load capacity test. The results showed that the planar tomography can be used for the assessment of internal damage on concrete plates, as long as the number of scans in each direction is more than four. The visual inspection gave a good. The formation of cone cracking after the impact load showed the highest influence on the remaining load capacity of the concrete plates. More plates will be tested to confirm the indications at different damage conditions.
Die in dieser Studie vorgestellte einfache Probengeometrie zeigt sich in Verbindung mit der
angewandten Versuchs- und Auswertemethodik geeignet, um den umwandlungsplastischen (TRIP)-Parameter K unter Verwendung des thermomechanischen Simulators Gleeble® 3500 experimentell zu bestimmen.
Der TRIP-Parameter K wurde für die Grundwerkstoffe S355J2+N und S960QL, sowie für den hochlegierten Zusatzwerkstoff CN13-4 -IG bestimmt.
Die numerische Einflussanalyse zeigt, dass bei der Berechnung von (Oberflächen-)Schweißeigen-spannungen die Vernachlässigung des TRIP-Effektes kaum einen Einfluss auf die Längseigenspannungen hat. Im Gegensatz da zu resultieren gegenüber dem Referenzfall signifikante Abweichungen der
Quereigenspannungen im und um den Schweißnahtbereich.
Die Verdopplung des TRIP-Parameters K gegenüber dem Referenzfall hat nur einen vernachlässigbaren Einfluss auf die Längs- sowie Quereigenspannungen auf der Oberfläche.
Für eine qualitative und quantitative numerische Nachbildung der experimentell bestimmten Längs- und Quereigenspannungen ist die Berücksichtigung der Größenordnung des material-abhängigen TRIP-Parameters K notwendig.
Numerical Sensitivity Analysis of TRIP-Parameter K on Weld Residual Stresses and Weld Distortion
(2016)
A combined experimental numerical approach is applied for a sensitivity analysis of the transformation induced plasticity (TRIP)-parameter K on welding residual stresses and welding distortion for the welding of the low-alloyed high-strength S960QOL with the high-alloyed hig-strength filler material CN13-4-IG. A thermo-mechanical FE model of a real GMA welding process was experimentally validated against termperature field, X-Ray stress measurments and optical distortion measurement. Within the sensititvity analysis K was varied and the influence on the calculated welding residual stresses and welding distortion is evaluated by performing corresponding FEA. The correct order of K magnitude is necessary in order to reproduce the residual stresses qualitatively and quantitatively. For the sufficient reproducing of the welding distortion the transformation induced plasticity can be neglected.
In the paper by using molecular dynamics method we investigate behavior of nickel-phosphorus compound in amorphous-like state under conditions of shear loading at the constant velocity. Samples with an amorphous layer of pure nickel and nickel-phosphorus compound were considered. The analysis showed that forces of shear resistance in the sample with an amorphous layer containing phosphorus in about 3 times less than the sample with a layer of pure nickel. Thus, it was shown that nickel-phosphorous coating in amorphous-like state may exhibit low friction properties, and, therefore, serve as the solid lubricant material.
The use of high-performance concretes holds great promise for many structural applications. This paper investigates the performance of these materials when used in combination with traditional reinforcing bars. An improved understanding of failure during reinforcing bar pull-out from high-performance concretes is needed in order to better predict the embedment length required to develop full reinforcing bar pull-out strength and the required thickness of reinforcing bar cover for adequate corrosion protection. The cracking structures surrounding the reinforcing bars were analyzed using x-ray computed tomography (CT) in order to determine the stress states causing failure. This was accomplished by conducting in-situ reinforcing bar pull-out experiments during CT scanning. A conventional concrete, a high-strength concrete, and a high-strength fiber reinforced concrete were all tested during the experiments. The results of these experiments showed that the levels of brittleness of the different concrete materials had a major impact on the failure mechanisms that they experienced during reinforcing bar pull-out. It was also clear that the specimen geometry and the casting method had a major impact on fiber orientation. The inclusion of fibers within concrete was also found to significantly improve strength and corrosion protection during reinforcing bar pull-out.
This article addresses the imperfections caused by the weld assembly in I-shape sections made of two structural steel grades. Load influencing imperfections are assumed as deviations from the ideal shape (e.g. bending distortion) and longitudinal residual stresses. The quality of a numerically aided design of components exposed to either compression and/or bending is significantly affected, depending on these parameters. The Eurocode (EC3) provides robust simplified models. As a result, the Ultimate Limit State (ULS) is approached on a conservative basis. The following investigations are aimed at providing further guidance on these values in component-like specimens. The long term goal is an improved understanding of the load-bearing capacity of such sections. As a first step in this process, the experimental and corresponding numerical studies are presented.
Die Anwendung von modernen Lehmbaustoffen hat in den letzten Jahren überdurchschnittliche Wachstumsraten erreicht. Für Bauherren und Planer ausschlaggebend ist häufig ihr extrem niedriger CO2-Äquivalentkennwert. Entsprechend wurden Lehmplatten in einem Projekt mit Pilotcharakter für den Umbau des alten Abgeordnetenhauses in Bonn zum Gebäude des Klimareferats der Vereinten Nationen verwendet. Bei der Entscheidung für die Bauweise mit Lehmplatten standen vor allem raumklimatische und schallschutztechnische, das heißt gesundheitliche Aspekte, aber auch der Wunsch nach erhöhter Nachhaltigkeit im Vordergrund. Durch das Fehlen einer Norm entstehen im Vergleich zu geregelten Bauprodukten jedoch noch deutliche Wettbewerbsnachteile für Produzenten von Lehmplatten. Planer und Anwender sehen aufgrund fehlender Prüfzertifikate nicht selten von der Anwendung dieser Lehmbaustoffe ab. Wie schon für Lehmsteine und Lehmmörtel sollen deshalb jetzt auch für Lehmplatten an der Bundesanstalt für Materialforschung und -prüfung (BAM) in dem Projekt StandardBoard Grundlagen für eine Produktnorm geschaffen werden. Darin ist als Projektpartner der Hersteller Conluto beteiligt. Zweck des in Erarbeitung befindlichen Regelwerks ist es, über die Festlegung von Qualitätsanforderungen und Prüfvorschriften die Gebrauchstauglichkeit von Lehmplatten sicherzustellen und somit einerseits Sicherheit für Planer und Anwender und andererseits Vergleichbarkeit und damit Konkurrenzfähigkeit zu konventionellen Plattenprodukten für gleiche Einbaubereiche zu erreichen. Darüber hinaus stellt sie ein Instrument dar, um die besonderen ökologischen und bauphysikalischen Eigenschaften der Lehmbaustoffe hervorzuheben. Die Erarbeitung des Regelwerks erfolgt in enger Abstimmung mit dem Dachverband Lehm e. V. (DVL).
Reliability analysis of the ultrasonic inspection system for the inspection of hollow railway axles
(2016)
Axles are safety critical train components that are subjected to significant cyclic loading during operation. If the crack is initiated in the axle, cyclic loading will lead to crack propagation. To maintain structural integrity, axles must be periodically inspected for fatigue cracks in the material. Deutsche Bahn uses mechanized ultrasonic inspection system to inspect hollow railway axles. The inspections are performed from the bore surface, using several conventional transducers with different incident angles, inspecting the axle along the entire length. As with the every safety critical system, the reliability of these inspections must be determined with regard to their flaw detection capabilities. Traditionally this is done according to the relevant standards for railway vehicles. To investigate the capability of the NDT system more thoroughly, we want to evaluate the capability of the inspection system to detect flaws by means of probability of detection (POD) curves. It will be shown that other parameters, beside the size of the crack, for example crack position in the axle, influence the detection of the crack. The influence of these parameters was evaluated using ultrasonic simulation. The evaluation served as an input for the manufacturing of the flaws in the real scale axle. Once these axles are inspected and the data evaluated, using data from both measurement and simulation, we will express the POD of the crack as function of influencing parameters using the multiparameter POD model.
The canister for the permanent storage of spent nuclear fuel used by SKB in Sweden consists of a cast iron insert surrounded by a five centimetre thick shell of copper. It is a safety critical component and in order to secure long-term structural integrity non-destructive methods are used to inspect 100% of the volume of each canister, before it is disposed of in the repository. One of the critical components that requires inspection is a sealing weld, joining the copper tube and the lid. The friction stir weld is inspected using an ultrasonic phased array system. The area of the weld is inspected with several inspection channels with different angles and varying coverage. To make sure that no defects that might occur in the weld are overseen, the reliability of the inspection must be quantified. The reliability of NDT is usually quantified with the probability of detection curves. The influence of the parameters that might influence the POD of the flaws in the weld is investigated analysing the experimental results, as well as with a help of a numerical simulation of the inspection.
Most VVOC were rarely considered in the evaluation of construction products. (Salthammer, 2014) In Germany this will change because the latest version of the German AgBB scheme for health evaluation (2015) now include VVOC, e.g. ethyl acetate and ethanol. In this study selected compounds were tested with the procedure described in ISO 16017 and a method for measuring VVOC with thermal desorption was developed.
Three different adsorbents Tenax TA, Carbograph 5TD and Carbopack X were tested to analyse VVOC according to ISO 16017. For the tested VVOC, Carbograph 5TD showed the best results under the chosen analytical conditions.