TY - JOUR A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Vormwald, M. T1 - Fatigue strength and fracture mechanics N2 - If fracture mechanics shall be applied to the total lifetime respectively the fatigue limit of components (within the meaning of the S-N curve approach) it has to address four challenges: (a) It has to adequately describe so-called short crack propagation, which cannot be based on the common long crack concepts for principle reasons. Since the crack size is in the order of the plastic zone size, the modelling of short crack propagation cannot be based on the common linear elastic Delta K concept. Instead, an elastic-plastic parameter such as the cyclic J integral has to be applied. A second point is that the crack closure concept has to be modified in that the crack opening stress is not a constant, crack size- independent parameter but shows a transient behaviour with increasing short crack size. (b) It has to provide a meaningful definition of the initial crack dimensions as the starting point for an S-N curve relevant (residual) lifetime analysis. This can be based either on the (statistical) size of material defects which can be treated as cracks or by the size of the crack which would arrest subsequent to early crack propagation, whatever is larger. (c) It has to cope with the problem of multiple cracks for load levels higher than the fatigue limit such as it occurs in many applications in the absence of very large initial defects. (d) This requires consequent statistical treatment taking into account variations in the local geometry of the area where crack initiation has to be expected as well as the scatter in the initial crack size and in the material data used for the analyses. T2 - 2nd International Conference on Structural Integrity CY - Funchal, Madeira, Portugal DA - 04.09.2017 KW - Fatigue strength KW - Fracture mechanics KW - Initial crack size KW - Short crack propagation KW - Multiple crack propagation PY - 2017 DO - https://doi.org/10.1016/j.prostr.2017.07.065 SN - 2452-3216 VL - 5 SP - 745 EP - 752 AN - OPUS4-42545 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hertwig, Andreas A1 - Hinrichs, K. A1 - Beck, Uwe A1 - Esser, N. T1 - Editorial to the proceedings of the 7th conference on spectroscopic N2 - The 7th International Conference on Spectroscopic Ellipsometry (ICSE-7) was held in Berlin in June 2016, jointly organised by ICSE and BAM. The publication of the proceedings special issue in Applied Surface Science follows this event. In the special issue, about 100 articles on current topics of optics and surface science related to ellipsometry, polarimetry, and similar techniques are presented, underpinning the high significance of these techniques for many fields of materials science. T2 - 7th International Conference on Spectroscopic Ellipsometry, ICSE-7 CY - Berlin, Germany DA - 06.06.2016 KW - Spectroscopic ellipsomety PY - 2017 DO - https://doi.org/10.1016/j.apsusc.2017.04.081 SN - 0169-4332 VL - 2017 IS - 421 SP - 269 EP - 270 PB - Elsevier B.V. AN - OPUS4-42554 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Léonard, Fabien A1 - Stein, J. A1 - Soutis, C. A1 - Withers, P. J. T1 - The quantification of impact damage distribution in composite laminates by analysis of X-ray computed tomograms N2 - One of the great strengths of X-ray computed tomography over conventional inspection methods (ultrasound, thermography, radiography) is that it can image damage in 3D. However for curved ordeformed composite panels it can be difficult to automatically ascribe the damage to specific plies or inter-ply interfaces. An X-ray computed tomography (CT) data processing methodology is developed to extract the through-thickness distribution of damage in curved or deformed composite panels. The method is applied to [(0°/90°)2]s carbon fibre reinforced polymer (CFRP) panels subjected low velocity impact damage (5 J up to 20 J) providing 3D ply-by-ply damage visualisation and analysis. Our distance transform approach allows slices to be taken that approximately follow the composite curvature allowing the impact damage to be separated, visualised and quantified in 3D on a ply-by-ply basis. In this way the interply delaminations have been mapped, showing characteristic peanut shaped delaminations with the major axis oriented with the fibres in the ply below the interface. This registry to the profile of the panel constitutes a significant improvement in our ability to characterise impact damage in composite laminates and extract relevant measurements from X-ray CT datasets. KW - Delamination KW - Impact behaviour KW - Non-destructive testing KW - X-ray computed tomography KW - Distance transform PY - 2017 UR - http://www.sciencedirect.com/science/article/pii/S0266353817307157?via%3Dihub DO - https://doi.org/10.1016/j.compscitech.2017.08.034 SN - 0266-3538 SN - 1879-1050 VL - 152 SP - 139 EP - 148 PB - Elsevier Ltd. AN - OPUS4-42556 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madia, Mauro A1 - Zerbst, Uwe A1 - Beier, T. A1 - Tchoffo Ngoula, D. T1 - Approximation of the crack driving force for cracks at notches under static and cyclic loading N2 - The work deals with the efficient calculation of the elastic-plastic crack driving force (J-integral for monotonic loading andΔJ-integral under cyclic loading) for short cracks at notches as essential parameter for the reliable static and fatigue assessment of notched structures. The J- or ΔJ-integral is calculated based on analytical solutions for stress intensity factors, estimated by means of well-known weight function solutions in the case of cracks under power-law stress distributions. A plasticity-correction function is applied to the stress intensity factors to obtain the final expression of the crack driving force. The comparison between analytical solutions and finite element calculations in case of cracks at the weld toe in welded joints shows good agreement. T2 - 2nd International Conference on Structural Integrity CY - Funchal, Madeira, Portugal DA - 04.09.2017 KW - Structural integrity KW - Fracture mechanics KW - Crack driving force KW - Notches PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-425577 DO - https://doi.org/10.1016/j.prostr.2017.07.111 SN - 2452-3216 VL - 5 SP - 875 EP - 882 PB - Elsevier B.V. AN - OPUS4-42557 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jensen, S. A. A1 - Rosu, Dana Maria A1 - Hertwig, Andreas A1 - Hansen, P.-E. T1 - Use of Rayleigh-Rice Theory for Analysis of Ellipsometry Data on Rough CIGS Films N2 - Ellipsometry is a useful tool for studying the optical properties of thin films such as photovoltaic devices. We employ Müller matrix ellipsometry to study the thin film photovoltaic material copper indium gallium selenide Cu(In,Ga) Se2 (CIGS), a commercially relevant material with high energy conversion efficiency. Confocal microscopy reveals an rms roughness of 68 nm, which greatly affects the ellipsometry data. Rayleigh-Rice theory is employed to account for the optical properties of the surface roughness in the ellipsometry experiment, and a library search method is used to compare Müller parameters calculated for various CIGS compositions, to the measured data. The Müller parameters calculated with the Rayleigh-Rice model are found to correspond well with the measured data, and a surface roughness of 37nm and a correlation length of 125nm are extracted. KW - Photovoltaics KW - Thin Films KW - Ellipsometry KW - Scattering Theory KW - Optical Wavefield KW - Simulation KW - Müller Polarimetry KW - Multidimensional Spectroscopy PY - 2017 DO - https://doi.org/10.1002/pssc.201700217 SN - 1862-6351 VL - 14 IS - 12 SP - 1700217, 1 EP - 5 PB - WILEY-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-43390 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Cheng-Chieh A1 - Weisbrich, S. A1 - Neitzel, F. ED - Emri, Igor T1 - Approximate model for geometrical complex structures N2 - Many engineering structures are nowadays made of composite materials or metal foam. These modern engineering materials contain very complex inner geometry. To simulate the deformational behaviour of these structures often requires a high number of discretisation elements. This in turn yields a very large system of linear equations that are extremely time and memory consuming or practically impossible to solve. It is therefore desirable to find an approach to overcome this obstacle. In this paper a numerical method is proposed to find an approximate substitute model for geometrical complex structures. T2 - 33rd Danubia Adria Symposium on Advances in Experimental Mechanics CY - Portorož, Slovenia DA - 20.09.2016 KW - Adjustment calculation KW - Finite element method KW - Substitute model KW - Complex structures PY - 2017 UR - http://www.sciencedirect.com/science/article/pii/S2214785317308593 DO - https://doi.org/10.1016/j.matpr.2017.06.084 SN - 2214-7853 VL - 4 IS - 5, Part 1 SP - 5995 EP - 6000 PB - Elsevier CY - Amsterdam, Netherlands AN - OPUS4-42794 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Le, Quynh Hoa A1 - Vestergaard, M.C. A1 - Tamiya, E T1 - Carbon-based nanomaterials in biomass-based fuel-fed fuel cells N2 - Environmental and sustainable economical concerns are generating a growing interest in biofuels predominantly produced from biomass. It would be ideal if an energy conversion device could directly extract energy from a sustainable energy resource such as biomass. Unfortunately, up to now, such a direct conversion device produces insufficient power to meet the demand of practical applications. To realize the future of biofuel-fed fuel cells as a green energy conversion device, efforts have been devoted to the development of carbon-based nanomaterials with tunable electronic and surface characteristics to act as efficient metal-free electrocatalysts and/or as supporting matrix for metal-based electrocatalysts. We present here a mini review on the recent advances in carbon-based catalysts for each type of biofuel-fed/biofuel cells that directly/indirectly extract energy from biomass resources, and discuss the challenges and perspectives in this developing field KW - Carbon-based nanomaterials KW - Biofuel cells KW - Biomass KW - Carbon nanotubes KW - Graphene KW - Carbon nanodots PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-428226 UR - http://www.mdpi.com/1424-8220/17/11/2587/htm DO - https://doi.org/10.3390/s17112587 SN - 1424-8220 VL - 17 IS - 11 SP - 2587, 1 EP - 2587, 21 PB - MDPI AG CY - Basel, Switzerland AN - OPUS4-42822 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Heitz, J. A1 - Plamadeala, C. A1 - Muck, M. A1 - Armbruster, O. A1 - Baumgartner, W. A1 - Weth, A. A1 - Steinwender, C. A1 - Plessberger, H. A1 - Kellermair, J. A1 - Kirner, Sabrina V. A1 - Krüger, Jörg A1 - Bonse, Jörn A1 - Guntner, A. S. A1 - Hassel, A. W. T1 - Femtosecond laser-induced microstructures on Ti substrates for reduced cell adhesion N2 - Miniaturized pacemakers with a surface consisting of a Ti alloy may have to be removed after several years from their implantation site in the heart and shall, therefore, not be completely overgrown by cells or tissue. A method to avoid this may be to create at the surface by laser-ablation self-organized sharp conical spikes, which provide too little surface for cells (i.e., fibroblasts) to grow on. For this purpose, Ti-alloy substrates were irradiated in the air by 790 nm Ti:sapphire femtosecond laser pulses at fluences above the ablation threshold. The laser irradiation resulted in pronounced microstructure formation with hierarchical surface morphologies. Murine fibroblasts were seeded onto the laser-patterned surface and the coverage by cells was evaluated after 3–21 days of cultivation by means of scanning electron microscopy. Compared to flat surfaces, the cell density on the microstructures was significantly lower, the coverage was incomplete, and the cells had a clearly different morphology. The best results regarding suppression of cell growth were obtained on spike structures which were additionally electrochemically oxidized under acidic conditions. Cell cultivation with additional shear stress could reduce further the number of adherent cells. KW - Laser Processing KW - Femtosecond laser KW - Titanium alloy KW - Cell adhesion KW - Anodic oxidation KW - Pacemaker PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-427681 UR - https://link.springer.com/article/10.1007/s00339-017-1352-0 DO - https://doi.org/10.1007/s00339-017-1352-0 SN - 0947-8396 SN - 1432-0630 VL - 123 IS - 12 SP - 734, 1 EP - 9 PB - Springer-Verlag CY - Berlin AN - OPUS4-42768 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lehmann, Jens A1 - Leonhard, H. T1 - Oberflächendetektive im Praxiseinsatz - Schnelltest auf Korrosionsgefahr an nichtrostenden Stählen N2 - Die Passivschicht von Behältern und Rohrsystemen aus nichtrostendem Stahl ist nicht nur durch den rauen Industriealltag gefährdet. Schon im Neuzustand können Schäden entstehen, etwa durch Schleifvorgänge oder ungenügende Entfernung von Anlauffarben. TÜV SÜD Chemie Service beteiligte sich an der Prüfung eines von der BAM entwickelten Schnelltests. Das Korropad-Verfahren liefert in nur 15 Minuten eine verlässliche Aussage zum Zustand der Passivschicht. KW - Nichtrostender Stahl KW - Korrosionsschnelltest KW - KorroPad KW - Passivschicht PY - 2017 SN - ISSN 0009-2800 VL - 50. Jahrgang IS - 10-2017 SP - 34 EP - 35 PB - Konradin-Verlag Robert Kohlhammer GmbH CY - Leinfelden-Echterdingen AN - OPUS4-42735 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Unger, Jörg F. A1 - Kindrachuk, Vitaliy T1 - A Fourier transformation-based temporal integration scheme for viscoplastic solids subjected to fatigue deterioration N2 - Using continuum damage mechanics (CDM) for lifetime prediction requires numerical integration of evolving damage until the onset of failure. The primary challenge for the simulation of structural fatigue failure is caused by the enormous computational costs due to cycle-by-cycle temporal integration throughout the whole loading history, which is in the order of 103–107 cycles. As a consequence, most approaches circumvent this problem and use empirical methods such as Wöhler curves. They are well suited for approximating the lifetime, but they are not capable to capture a realistic degradation of the material including redistribution of stresses. The main objective of the paper is to provide a technique for finite element (FE) simulations of structures under fatigue loading while reducing computational costs. A Fourier transformation-based temporal integration (FTTI) scheme is proposed, which adapts the conventional FE method for modeling the viscoplastic deterioration in a structure subjected to cyclic loading. The response fields are represented by a Fourier series which assumes a temporal scale separation: a microchronological (short time) scale arises from the oscillatory loading and a macrochronological (long time) scale is due to the slow material relaxation resulting from yielding and damage evolution. The original dynamic boundary value problem (BVP) is approximated by the stationary BVP on the microchronological scale. Alternation of the displacement field on the macrochronological scale is correlated with evolution of the history variables by means of a high order adaptive cycle jump method. Performance and significant acceleration of the FE simulations is demonstrated at different loading scenarios for a constitutive damage model where the progressive damage accumulation is driven by viscoplastic yielding. KW - Fatigue KW - Accelerated time integration KW - Continuum damage mechanics KW - Fourier series PY - 2017 DO - https://doi.org/10.1016/j.ijfatigue.2017.03.015 SN - 0142-1123 SN - 1879-3452 VL - 100 IS - 1 SP - 215 EP - 228 PB - Elsevier Ltd. AN - OPUS4-39616 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -