TY - JOUR A1 - Straub, D. A1 - Schneider, Ronald A1 - Bismut, E. A1 - Kim, H.-J. T1 - Reliability analysis of deteriorating structural systems N2 - Reliability analysis of deteriorating structural systems requires the solution of time-variant reliability problems. In the general case, both the capacity of and the loads on the structure vary with time. This analysis can be approached by approximation through a series of time-invariant reliability problems, which is a potentially effective strategy for cases where direct solutions of the time-variant reliability problem are challenging, e.g. for structural systems with many elements or arbitrary load processes. In this contribution, we thoroughly Review the formulation of the equivalent time-invariant reliability problems and extend this approximation to structures for which inspection and monitoring data is available. Thereafter, we present methods for efficiently evaluating the reliability over time. In particular, we propose the combination of sampling-based methods with a FORM (first-order reliability method) approximation of the series system reliability problem that arises in the computation of the lifetime reliability. The framework and algorithms are demonstrated on a set of numerical examples, which include the computation of the reliability conditional on inspection data. KW - Monitoring KW - Reliability KW - Deterioration KW - Structural systems KW - Bayesian analysis KW - Inspection PY - 2020 U6 - https://doi.org/10.1016/j.strusafe.2019.101877 VL - 82 SP - Paper 101877, 1 PB - Elsevier Ltd. AN - OPUS4-48952 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Omidalizarandi, M. A1 - Herrmann, Ralf A1 - Kargoll, B. A1 - Marx, S. A1 - Paffenholz, J. A1 - Neumann, I. T1 - A validated robust and automatic procedure for vibration analysis of bridge structures using MEMS accelerometers N2 - Today, short- and long-term structural health monitoring (SHM) of bridge infrastructures and their safe, reliable and cost-effective maintenance has received considerable attention. From a surveying or civil engineer’s point of view, vibration-based SHM can be conducted by inspecting the changes in the global dynamic behaviour of a structure, such as natural frequencies (i. e. eigenfrequencies), mode shapes (i. e. eigenforms) and modal damping, which are known as modal parameters. This research work aims to propose a robust and automatic vibration analysis procedure that is so-called robust time domain modal parameter identification (RT-MPI) technique. It is novel in the sense of automatic and reliable identification of initial eigenfrequencies even closely spaced ones as well as robustly and accurately estimating the modal parameters of a bridge structure using low numbers of cost-effective micro-electro-mechanical systems (MEMS) accelerometers. To estimate amplitude, frequency, phase shift and damping ratio coefficients, an observation model consisting of: (1) a damped harmonic oscillation model, (2) an autoregressive model of coloured measurement noise and (3) a stochastic model in the form of the heavy-tailed family of scaled t-distributions is employed and jointly adjusted by means of a generalised expectation maximisation algorithm. Multiple MEMS as part of a geo-sensor network were mounted at different positions of a bridge structure which is precalculated by means of a finite element model (FEM) analysis. At the end, the estimated eigenfrequencies and eigenforms are compared and validated by the estimated parameters obtained from acceleration measurements of high-end accelerometers of type PCB ICP quartz, velocity measurements from a geophone and the FEM analysis. Additionally, the estimated eigenfrequencies and modal damping are compared with a well-known covariance driven stochastic subspace identification approach, which reveals the superiority of our proposed approach. We performed an experiment in two case studies with simulated data and real applications of a footbridge structure and a synthetic bridge. The results show that MEMS accelerometers are suitable for detecting all occurring eigenfrequencies depending on a sampling frequency specified. Moreover, the vibration analysis procedure demonstrates that amplitudes can be estimated in submillimetre range accuracy, frequencies with an accuracy better than 0.1 Hz and damping ratio coefficients with an accuracy better than 0.1 and 0.2 % for modal and system damping, respectively. KW - Vibration analysis KW - Automatic modal parameters identification KW - MEMS KW - FEM analysis KW - Bridge monitoring PY - 2020 UR - https://www.degruyter.com/view/journals/jag/14/3/article-p327.xml U6 - https://doi.org/10.1515/jag-2020-0010 SN - 1862-9016 VL - 14 IS - 3 SP - 1 EP - 28 PB - De Gruyter CY - Berlin AN - OPUS4-51338 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nerger, Deborah A1 - Moosavi, Robabeh A1 - Bracklow, F. A1 - Hering, M. A1 - Kühn, T. A1 - Curbach, M. A1 - Hille, Falk A1 - Rogge, Andreas T1 - Planar tomography and numerical analysis for damage characterization of impact loaded RC plates N2 - The damage analysis of reinforced concrete (RC) is of high interest for reasons of effective maintenance and structural safe-ty of buildings. The damage structures of RC plates loaded by an impact were investigated, applying X-ray planar tomogra-phy and finite element method (FEM). Planar tomography allows getting three-dimensional information of the RC elements and the damage including crack, spalling and scabbing. The FEM model validated on the tomography data justifies the appli-cation for further predictions of the damage description. In this study, we investigated concrete plates of three different thick-ness subjected to impacts at different low- and medium-velocity, whereby the used impactor had a flat tip, which resulted in small penetrations on the front side and scabbing on the rear side. In order to quantify the damage, the damage volume and its distribution through the plate were computed and the correlations between degree of damage and impact velocity were found out. KW - Impact KW - Damage characterization KW - Planar tomography KW - Numeric simulation KW - Reinforced concrete structure PY - 2020 U6 - https://doi.org/10.1002/cend.202000017 VL - 8 SP - 1 EP - 19 PB - Wiley AN - OPUS4-51117 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nerger, Deborah A1 - Hille, Falk A1 - Moosavi, Robabeh A1 - Grunwald, Marcel A1 - Redmer, Bernhard A1 - Kühn, T. A1 - Hering, M. A1 - Bracklow, F. T1 - Post-impact evaluation at RC plates with planar tomography and FEM N2 - Due to the wide range of applications, the easy production and the large field of use, reinforced concrete (RC) is a widespread building material. This variety of applications is reflected in a wide range of physical material properties. Not only therefor it still is a technical challenge to provide all necessary test conditions for experimentally reproducing dynamic effects under impact loading of RC structures. In this paper we present investigations on the thicknesses of RC plates under low and medium high velocity impact loading by a flat-tipped impactor. The planar tomography setup at BAM is used to visualize the impact damage and to characterize the damage features such as cracks, scabbing and spalling. Further, the comparison of tomography results with those of an applied numeric simulation analysis is used to verify the numeric models for future damage prognosis under impact loading. Using the results of both, the tomographic as well as the FE analysis, different damage features were investigated and compared regarding their validity. Crack damage plays a leading part and the significance of summarized crack values as well as their distribution is analyzed. The total damage value but also the determined damage distribution both provide an input for describing damage as a function of the impactor velocity and plate thickness. KW - Reinforced concrete structure KW - Post-impact evaluation KW - Damage characterization KW - Ansys Autodyn KW - Drucker-Prager KW - Planar tomography PY - 2020 U6 - https://doi.org/10.1016/j.matpr.2020.05.671 SP - 1 EP - 10 PB - Elsevier AN - OPUS4-51115 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hu, W.-H. A1 - Xu, Z.-M. A1 - Liu, M.-Y. A1 - Tang, D.-H. A1 - Lu, W. A1 - Li, Z.-H. A1 - Teng, J. A1 - Han, X.-H. A1 - Said, Samir A1 - Rohrmann, R. G. T1 - Estimation of the Lateral Dynamic Displacement of High-Rise Buildings underWind Load Based on Fusion of a Remote Sensing Vibrometer and an Inclinometer N2 - This paper proposes a novel method to estimate the lateral displacement of high-rise structures under wind loads. The coefficient β(x) is firstly derived, reflecting the relation between the structural lateral dynamic displacement and the inclination angle at the height x of a structure. If the angle is small, it is the ratio between the structural fundamental mode shape and its first-order derivative without influence of external loads. Several dynamic experiments of structures are performed based on a laser remote sensing vibrometer and an inclinometer, which shows that the fundamental mode is dominated in the structural displacement response under different types of excitations. Once the coefficient β(x) is curve-fitted by measuring both the structural lateral dynamic displacement and the inclination angle synchronously, the real-time structural lateral displacement under operational conditions is estimated by multiplying the coefficient β(x) with the inclination angle. The advantage of the proposed method is that the coefficient β(x) can be identified by lateral dynamic displacement measured in high resolution by the remote sensing vibrometer, which is useful to reconstruct the displacement accurately by the inclination angle under operational conditions KW - Inclination angle KW - High-rise building KW - Lateral dynamic displacement KW - Remote sensing vibrometer PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-506833 VL - 12 IS - 7 SP - 1120 PB - MDPI CY - 4052 Basel, Schweiz AN - OPUS4-50683 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hu, W.-H A1 - Tang, D.-H. A1 - Wang, M. A1 - Liu, J.-L. A1 - Li, Z.-H. A1 - Lu, W. A1 - Teng, J. A1 - Said, Samir A1 - Rohrmann, R. G. T1 - Resonance Monitoring of a Horizontal Wind Turbine by Strain-Based Automated Operational Modal Analysis N2 - A strain-based automated operational modal analysis algorithm is proposed to track the long-term dynamic behavior of a horizontal wind turbine under operational conditions. This algorithm is firstly validated by a scaled wind turbine model, and then it is applied to the dynamic strain responses recorded from a 5 MW wind turbine system. We observed variations in the fundamental frequency and 1f, 3f excitation frequencies due to the mass imbalance of the blades and aerodynamic excitation by the tower dam or tower wake. Inspection of the Campbell diagram revealed that the adverse resonance phenomenon and Sommerfeld effect causing excessive vibrations of the wind tower. KW - Strain KW - Automated operational modal analysis KW - Resonance KW - Horizontal wind turbine PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-503350 VL - 13 IS - 3 SP - 579 EP - 584 PB - MDPI CY - Schweiz, Basel AN - OPUS4-50335 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hille, Falk A1 - Sowietzki, D. A1 - Makris, R. T1 - Luminescence-based early detection of fatigue cracks N2 - Classic non-destructive fatigue crack detection methods reveal the state of the fatigue damage evolution at the moment of application, generally not under operational conditions. The here introduced crack luminescence method realizes a clear visibility of the occurred and growing crack in loaded components during operation. Different established experiments show that due to the sensitive coating a crack Formation can be detected even in early stage under the premise the crack reached the surface. The coating consists of two layers with different properties and functions. The bottom layer emits light as fluorescence under UV radiation. The top layer covers the fluorescing one and prevents the emitting of light in case of no damage at the surface. In case of surface crack occurrence, the luminescent light is clearly noticeable by visual observations and also by standard camera equipment which makes automated crack detection possible as well. It is expected that crack luminescence can increase structural safety as well as reduce costs and time for inspections and preventive maintenance. KW - Coating KW - Fatigue KW - Crack damage detection KW - Luminescence PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-510517 SN - 2214-7853 SP - 1 EP - 5 PB - Elsevier CY - Amsterdam AN - OPUS4-51051 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brunier-Coulin, F. A1 - Cuéllar, Pablo A1 - Philippe, P. T1 - Generalized Shields criterion for weakly cohesive granular materials N2 - The erosion of natural sediments by a superficial fluid flow is a generic situation in many usual geological or industrial contexts. However, there is still a lack of fundamental knowledge about erosional processes, especially concerning the role of internal cohesion and adhesive stresses on issues such as the critical flow conditions for the erosion onset or the kinetics of soil mass loss. This contribution investigates the influence of cohesion on the surface erosion by an impinging jet flow based on laboratory tests with artificially bonded granular materials. The model samples are made of spherical glass beads bonded either by solid bridges made of resin or by liquid bridges made of a highly viscous oil. To quantify the intergranular cohesion, the capillary forces of the liquid bridges are here estimated by measuring their main geometrical parameters with image-processing techniques and using well-known analytical expressions. For the solid bonds, the adhesive strength of the materials is estimated by direct measurement of the yield tensile forces and stresses at the particle and sample scales, respectively, with specific traction tests developed for this purpose. The proper erosion tests are then carried out in an optically adapted device that permits a direct visualization of the scouring process at the jet apex by means of the refractive index matching technique. On this basis, the article examines qualitatively the kinetics of the scour crater excavation for both scenarios, namely, for an intergranular cohesion induced by either liquid or solid bonds. From a quantitative perspective, the critical condition for the erosion onset is discussed specifically for the case of the solid bond cohesion. In this respect, we propose here a generalized form of the Shields criterion based on a common definition of a cohesion number from yield tensile values, derived at both micro- and macroscales. The article finally shows that the proposed form manages to reconcile the experimental data for cohesive and cohesionless materials, the latter in the form of the so-called Shields curve along with some previous results of the authors which have been appropriately revisited. KW - Hydraulic jet erosion KW - Cohesive granular materials KW - Jet erosion test PY - 2020 U6 - https://doi.org/10.1103/PhysRevFluids.5.034308 VL - 5 IS - 3 SP - 034308 PB - American Physical Society AN - OPUS4-50613 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Benseghier, Z. A1 - Cuéllar, Pablo A1 - Luu, L.-H. A1 - Delenne, J.-Y. A1 - Bonelli, S. A1 - Philippe, P. T1 - Relevance of Free Jet Model for Soil Erosion by Impinging Jets N2 - The surface erosion of soil samples caused by an impinging jet can be analyzed using the jet erosion test (JET), a standard experimental test to characterize the erosion resistance of soils. This paper specifically addresses the flow characteristics of a laminar impinging jet over the irregular surface of granular beds to discuss the pertinence and relevance of commonly used empirical estimations based on a selfsimilar model of a free jet. The JET is here investigated at the microscale with a coupled fluid-particle flow numerical odel featuring the lattice Boltzmann method (LBM) for the fluid phase combined with the discrete element method (DEM) for the mechanical behavior of the solid particles. The hydrodynamics of a laminar plane free jet are confronted with the results from a parametric study of jet impingement, both on solid smooth and fixed granular surfaces, that take into account variations in particle size, distance from jet origin, and jet Reynolds number. The flow characteristics at the bed surface are here quantified, including the maximal values in tangential velocity and wall shear stress, which can be regarded as the major cause of particle detachments under hydrodynamic solicitation. It is shown that the maximal velocity at the impinged surface can be described by the free jet self-similar model, provided that a simple empirical coefficient is introduced. Further, an expression is proposed for the maximal shear stress in laminar conditions, including a Blasius-like friction coefficient that is inversely proportional to the square root of the jet Reynolds number. To conclude, finally, the JET erosion of different cohesionless granular samples is analyzed, confirming that the threshold condition at the onset of granular motion is consistent with the Shields diagram and in close agreement with previous experimental results. KW - Lattice Boltzmann method KW - Soil erosion KW - Discrete element method KW - Laminar flow KW - Jet impingement PY - 2020 U6 - https://doi.org/10.1061/(ASCE)HY.1943-7900.0001652 VL - 146 IS - 1 SP - 04019047 PB - ASCE AN - OPUS4-49491 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Benseghier, Z. A1 - Cuéllar, Pablo A1 - Luu, L.-H. A1 - Bonelli, S. A1 - Philippe, P. T1 - A parallel GPU-based computational framework for the micromechanical analysis of geotechnical and erosion problems N2 - This article deals with the relevance and practical feasibility of micromechanical simulations for their application to general geomechanical problems involving fluid-saturated granular assemblies, whether frictional or cohesive. A set of conceptual and numerical tools is here presented, advocating for a parallel computation using graphical processing units (GPUs) to treat large numbers of degrees of freedom with conventional Desktop computers. The fluid phase is here simulated with a particle-resolved approach in the frame of the Lattice Botzmann Method (LBM) while the granular solid phase is modelled as a collection of discrete particles from a Molecular Dynamics DEM perspective. The range of possible material behaviours for the solid granular phase is intended here to cover a broad spectrum from purely frictional to viscous cohesive materials with either brittle or transient debonding features. Specific details of the implementation and some validation cases are put forward. Finally, some exemplary applications in the fields of soil erosion and geotechnical profile installation are provided along with a discussion on the parallel performance of the presented models. The results show that a micromechanical approach can be feasible and useful in practice, providing meaningful insights into complex engineering problems like the erosion kinetics of a soil under an impinging jet or the penetration resistance of a deep foundation in a layered soil profile. KW - Offshore geomechanics KW - Erosion KW - Micromechanical modelling KW - LBM-DEM KW - GPU Parallel computing PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-502309 VL - 120 SP - Paper 103404, 1 PB - Elsevier Ltd. AN - OPUS4-50230 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Auersch, Lutz A1 - Said, Samir T1 - Slab track behaviour under train passage and hammer impact – Measurements at different sites and calculated track interaction with continuous soils N2 - This contribution intends to give an overview on the vibration behaviour of slab tracks in comparison of measurements and calculations and also by comparison of different track types at more than ten different measuring sites. In theory, tracks on continuous soil are calculated by the frequency-wavenumber domain method. In experiment, geophone measurements are transformed to displacement results. Two aspects of track behaviour are considered, the frequency-dependant compliance of the track, measured by hammer impact, and the deflection under a passing axle load. In theory, the response to a single axle can be calculated, whereas in experiment, only the passage of the whole train can be measured. For comparison of theory and experiment, the calculated deflection under a single axle is superposed to get the response of the whole train. As a result, the slab track characteristics are completely different from the ballast track characteristics where each axle can be seen in the time histories. The slab track has a more global behaviour where only a whole bogie can be found in the track response and moreover, the two neighbouring bogies are not completely separated. The measurement of the different track elements (rail, sleeper, track plate, base layer) and the frequency-dependant compliances with possible resonances yield further information About the properties of the track elements. The calculations show that the soil has the dominant influence on the amplitudes and the width of the track-plate displacements. In the measurement results, the following parameters are analysed: slab track vs. ballast track, different types of slab tracks, damaged slab tracks, different trains, switches at different measuring points, voided sleepers, an elastic layer, the mortar layer, and different soils at different places. Finally, a good agreement between measured and calculated results is found for the normal and some special (damaged, floating) slab tracks. KW - Slab track KW - Train passage KW - Hammer impact KW - Compliance function KW - Track deflection PY - 2020 UR - https://iiav.org/ijav/index.php?va=viewpage&vaid=177&id_number=95 U6 - https://doi.org/10.20855/ijav.2020.25.31622 SN - 1027-5851 VL - 25 IS - 3 SP - 341 EP - 354 PB - International Institute of Acoustics and Vibration CY - Gliwice AN - OPUS4-51346 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Auersch, Lutz T1 - Simple and fast prediction of train-induced track forces, ground and building vibrations N2 - A simple and fast prediction scheme is presented for train induced ground and building vibrations. Simple models such as (1-dimensional) transfer matrices are used for the vehicle-track-soil interaction and for the building-soil interaction. The wave propagation through layered soils is approximated by a frequency-dependent homogeneous half-space. The prediction is divided into the parts “emission” (excitation by railway traffic), “transmission” (wave propagation through the soil) and “immission” (transfer into a building). The link between the modules is made by the excitation force between emission and transmission, and by the free-field vibration between transmission and immission. All formula for the simple vehicle-track, soil and building models are given in this article. The behaviour of the models is demonstrated by typical examples, that is the mitigation of train vibrations by elastic track elements, the low- and high-frequency cut-offs characteristic for layered soils, and the interacting soil, wall and floor resonances of multi-storey buildings. It is shown that the results of the simple prediction models can well represent the behaviour of the more time-consuming detailed models, the finite-element boundary-element models of the track, the wavenumber integrals for the soil, and the three-dimensional finite-element models of the building. In addition, measurement examples are given for each part of the prediction confirming that the methods provide reasonable results. As the prediction models are fast in calculation, many predictions can be done, for example to assess the environmental effect along a new railway line. The simple models have the additional advantage that the user needs to know only a minimum of parameters. So, the prediction is fast and user-friendly, but also theoretically and experimentally well-founded. KW - Railway induced vibration KW - Ground vibration KW - Layered soil KW - Building response KW - Excitation forces KW - Track and vehicle irregularities PY - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-513340 SN - 2662-4745 VL - 28 IS - 3 SP - 232 EP - 250 PB - Springer AN - OPUS4-51334 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Auersch, Lutz T1 - Vehicle-Track-Soil Interaction of Isolated, Un-isolated and Damaged Railway Tracks N2 - This article deals with two topics of vehicle-track-soil interaction, the mitigation of railway induced ground vibration by soft track elements, and the identification of track damage. Theoretical results have been achieved by a combined finite-element boundary-element method (FEBEM). The theoretical results are confronted with measurements at four sites. Improved mitigation effects have been found for soft rail pads under heavy sleepers. The insertion loss, however, can be too optimistic if a strong vehicle track resonance occurs for the un-isolated reference track. Two measurement sites show this strong vehicle-track resonance at about 80 Hz, which has been approximated by using the results of a wide parameter study including the rail pad, ballast, and soil stiffness, as well as the ballast model and the soil layering. – The detection of slab track damage is mainly based on the differences of the receptance or compliance functions. Theoretical results have been confirmed by measurements at one site where a loss of contact between track plate and base layer was visible. Measurements at a second site with a hidden damage have been compared with the theoretical results of a loose sleeper. The differences between intact (or repaired) and damaged tracks are strong enough to encourage the further development of this method for the identification of track damages. KW - Railway track KW - Track-soil interaction KW - Ground vibration KW - Mitigation KW - Under-sleeper pads KW - Track damage monitoring PY - 2020 U6 - https://doi.org/10.4203/ijrt.6.3.2 SN - 2049-5358 VL - 2 IS - 20 SP - 21 EP - 49 PB - Saxe-Coburg Publications CY - London AN - OPUS4-51257 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Auersch, Lutz T1 - Characteristics of train passages over slab tracks from measurements and different track-soil models - Damage detection and ground vibration reduction N2 - The train passages over intact or damaged slab tracks on different soils have been calculated by the finite-element boundary-element or the wavenumber-domain method. The influence of track and soil parameters on the distribution of the track displacements and the soil forces has been analysed. The measured and calculated displacement time histories of train passages could be used to identify track damages such as lose sleepers or a lose track plate. The time histories and spectra of the soil forces can explain the measured ground vibration reduction of slab tracks. The calculated displacement and force distributions of slab tracks on continuous soils do not fulfil the Winkler hypothesis and Winkler models should not be used for track analysis. KW - Wavenumber domain KW - Continuous soil KW - Slab track KW - Soil forces KW - Track displacements KW - Track filter KW - Vehicle–track interaction PY - 2020 U6 - https://doi.org/10.1177/0954409719835036 SN - 0954-4097 VL - 234 IS - 2 SP - 142 EP - 160 PB - Sage CY - London AN - OPUS4-50266 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -