TY - JOUR A1 - Cabeza, Sandra A1 - Mishurova, Tatiana A1 - Bruno, Giovanni A1 - Garcés, G. T1 - The role of reinforcement orientation on the damage evolution of AlSi12CuMgNi + 15% Al2O3 under compression N2 - Internal damage of an AlSi12CuMgNi alloy reinforced with planar random short fibres has been investigated after compression. This damage strongly influences the load partition between matrix and reinforcement. For fibres perpendicular to the applied load, breakage and interconnected cracks appear in significantly higher volume fraction than with fibres parallel to load. KW - Neutron Diffraction KW - Damage KW - Metal Matrix Composites KW - Load Partition KW - Synchrotron CT PY - 2016 U6 - https://doi.org/10.1016/j.scriptamat.2016.05.023 SN - 1359-6462 VL - 122 SP - 115 EP - 118 PB - Elsevier B.V. CY - Amsterdam, Netherlands AN - OPUS4-36357 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bruno, Giovanni A1 - Onel, Yener A1 - Cooper, R. C. A1 - Lange, A. A1 - Watkins, T. R. A1 - Shyam, A. T1 - Young's modulus and Poisson's ratio changes due to machining in porous microcracked cordierite N2 - Microstructural changes in porous cordierite caused by machining were characterized using microtensile testing, X-ray computed tomography, and scanning electron microscopy. Young's moduli and Poisson's ratios were determined on similar to 215- to 380-mu m-thick machined samples by combining digital image correlation and microtensile loading. The results provide evidence for an increase in microcrack density and decrease of Young's modulus due to machining of the thin samples extracted from diesel particulate filter honeycombs. This result is in contrast to the known effect of machining on the strength distribution of bulk, monolithic ceramics. KW - Stress KW - Beta-Eucryptite KW - Brittle materials KW - Ceramic materials KW - Thermal-Expansion KW - Fracture-Toughness KW - Composite materials KW - Differential scheme KW - Elastic-moduli KW - Representative volume element PY - 2016 U6 - https://doi.org/10.1007/s10853-016-0209-9 SN - 0022-2461 VL - 51 IS - 21 SP - 9749 EP - 9760 PB - Springer, NY, USA AN - OPUS4-37867 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bruno, Giovanni A1 - Sevostianov, I. A1 - Cabeza, Sandra A1 - Mishurova, Tatiana T1 - Average phase stress concentrations in multiphase metal matrix composites under compressive loading N2 - We develop a model to predict average over individual phases stress concentrations in a multiphase metal matrix composite under compressive loading. The model accounts for matrix plasticity through variation of the shear modulus with applied stress and for frac- ture of filler through change in the shape of the particles. Three micromechanical models are compared –non interaction approximation, Mori–Tanaka–Benveniste (MTB) scheme, and Maxwell scheme. Comparison with the experimental measurements of Cabeza et al. (2016) shows that Maxwell scheme generally predicts the stress concentration with satis- factory accuracy. Results of MTB scheme vary depending on the loading case and ignoring of the interaction leads to substantial overestimation of the stresses. KW - Average phase stress concentrations KW - metal matrix composite KW - multiphase composite PY - 2016 U6 - https://doi.org/10.1016/j.ijengsci.2016.06.004 SN - 0020-7225 VL - 106 SP - 245 EP - 261 PB - Elsevier Ltd. AN - OPUS4-37738 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shashev, Yury A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Müller, Bernd R. A1 - Bruno, Giovanni T1 - Improving the visibility of phase gratings for Talbot-Lau X-ray imaging N2 - Talbot-Lau interferometry provides X-ray imaging techniques with significant enhancement of the radiographic contrast of weakly absorbing objects. The grating based technique allows separation of absorption, refraction and small angle scattering effects. The different efficiency of rectangular and triangular shaped phase gratings at varying detector distances is investigated. The interference patterns (Talbot carpets) are modeled for parallel monochromatic radiation and measured by synchrotron radiation. In comparison to rectangular shapes of phase gratings much higher visibility is obtained for triangular shapes which yield enhanced contrast of a glass capillary test specimen. KW - Visibility KW - Talbot-Lau interferometry KW - Phase grating KW - Synchrotron imaging KW - X-ray reefraction PY - 2016 U6 - https://doi.org/10.3139/120.110948 SN - 0025-5300 VL - 58 IS - 11-12 SP - 970 EP - 974 PB - Carl Hanser Verlag CY - München AN - OPUS4-38422 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bruno, Giovanni A1 - Kachanov, Mark T1 - Microstructure-property connections for porous ceramics: The possibilities offered by micromechanics N2 - Microstructure of porous ceramics is highly “irregular”: it comprises pores and microcracks of diverse shapes and orientations. This makes their quantitative modeling challenging, and one often resorts to empirical relations containing Fitting Parameters and having somewhat uncertain range of applicability. We review the substantial progress made in modeling of “irregular” microstructures that does not seem to have been sufficiently utilized in the context of ceramics. We discuss the possibilities offered by micromechanics in developing microstructure–property relations for porous microcracked ceramics. After an overview of relevant micromechanics topics, we focus on several issues of specific interest for ceramics: nonlinear stress–strain behavior, effective elastic properties, and thermally induced microcracking. We discuss extraction of microscale Parameters (such as strength of the intergranular cohesion, density of cracks and pores, etc.) from macroscopic data and identify the extent of uncertainty in this process. We also argue that there is no quantitative correlation between fracturing process and the loss of elastic stiffness. KW - Ceramics KW - Microcracking KW - Pores KW - Microstructure KW - Micromechanics KW - Intergranular strength KW - Nonlinearity KW - Stress– strain curves PY - 2016 U6 - https://doi.org/10.1111/jace.14624 SN - 0002-7820 SN - 1551-2916 VL - 99 IS - 12 SP - 3829 EP - 3852 AN - OPUS4-39355 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stegemann, Robert A1 - Cabeza, Sandra A1 - Lyamkin, V. A1 - Bruno, Giovanni A1 - Pittner, Andreas A1 - Wimpory, Robert A1 - Boin, M. A1 - Kreutzbruck, Marc T1 - Residual stress characterization of steel TIG welds by neutron diffraction and by residual magnetic stray field mappings N2 - The residual stress distribution of tungsten inert gas welded S235JRC+C plates was determined by means of neutron diffraction(ND). Large longitudinal residual stresses with maxima around 600 MPa were found. With these results as reference, the evaluation of residual stress with high spatial resolution GMR (giant magneto resistance) sensors was discussed. The experiments performed indicate a correlation between changes in residual stresses (ND) and the normal component of local residual magnetic stray fields (GMR). Spatial variations in the magnetic field strength perpendicular to the welds are in the order of the magnetic field of the earth. KW - GMR KW - Magnetic stray field KW - Neutron diffraction KW - Residual stress KW - TIG-welding PY - 2017 U6 - https://doi.org/10.1016/j.jmmm.2016.11.102 SN - 0304-8853 SN - 1873-4766 VL - 426 SP - 580 EP - 587 PB - Elsevier CY - Amsterdam AN - OPUS4-38678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kupsch, Andreas A1 - Müller, Bernd R. A1 - Lange, Axel A1 - Bruno, Giovanni T1 - Microstructure Characterization of Ceramics via 2D and 3D X-Ray Refraction Techniques N2 - 3D imaging techniques are very fashionable nowadays, and allow enormous progress in understanding ceramic microstructure, its evolution, and its link to mechanical, thermal, and transport properties. In this feature article, we report the use of a powerful, yet not so wide-spread, set of X-ray techniques based on refraction effects. X-ray refraction allows determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with a nanometric detectability. While the techniques are limited by the X-ray absorption of the material under investigation, we demonstrate showcases of ceramics and composite materials, where understanding of process parameter influence or simply of microstructural parameters could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography. KW - X-ray refraction KW - Porosity KW - Specific surface KW - Crack detection KW - Composites PY - 2017 U6 - https://doi.org/10.1016/j.jeurceramsoc.2016.12.031 SN - 0955-2219 SN - 1873-619X VL - 37 IS - 5 SP - 1879 EP - 1889 PB - Elsevier CY - Amsterdam AN - OPUS4-39094 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shashev, Yury A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Evsevleev, Sergei A1 - Müller, Bernd R. A1 - Osenberg, Markus A1 - Manke, Ingo A1 - Hentschel, Manfred P. A1 - Bruno, Giovanni T1 - Optimizing the visibility of X-ray phase grating interferometry N2 - The performance of grating interferometers coming up now for Imaging interfaces within materials depends on the efficiency (visibility) of their main component, namely the phase grating. Therefore, experiments with monochromatic synchrotron radiation and corresponding simulations are carried out. The visibility of a Phase grating is optimized by different photon energies, varying detector to grating distances and continuous rotation of the phase grating about the grid lines. Such kind of rotation changes the projected grating shapes, and thereby the distribution profiles of phase shifts. This yields higher visibilities than derived from ideal rectangular shapes. By continuous grating rotation and variation of the propagation distance, we achieve 2D visibility maps. Such maps provide the visibility for a certain combination of grating orientation and detector position. Optimum visibilities occur at considerably smaller distances than in the standard setup. KW - Synchrotron, BAMline KW - Talbot-Lau interferometer KW - X-ray imaging KW - X-ray refraction KW - Grating interferometry KW - X-ray phase contrast PY - 2017 U6 - https://doi.org/10.3139/120.111097 SN - 0025-5300 VL - 59 IS - 11-12 SP - 974 EP - 980 PB - Hanser Verlag AN - OPUS4-42955 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cabeza, Sandra A1 - Mishurova, Tatiana A1 - Garces, G. A1 - Requena, G. A1 - Bruno, Giovanni A1 - Sevostianov, I. T1 - Stress-induced damage evolution in cast AlSi12CuMgNi alloy with one- and two ceramic reinforcements N2 - Two composites, consisting of an as-cast AlSi12CuMgNi alloy reinforced with 15%vol. Al2O3 short fibres and with 7%vol. Al2O3 short fibres + 15%vol. SiC particles were studied. Synchrotron computed tomography disclosed distribution, orientation, and volume fraction of the different phases. In-situ compression tests during neutron diffraction in direction parallel to the fibres plane revealed the load partition between phases. Internal damage (fragmentation) of the Si phase and Al2O3 fibres was directly observed in CT reconstructions. Significant debonding between Al-matrix and SiC particles was also found. Finally, based on the Maxwell scheme, a micro-mechanical model was utilized for the new composite with two ceramic reinforcements; it rationalizes the experimental data, and predicts the evolution of all internal stress components in each phase. KW - Computed tomography KW - Metal matrix composite KW - Load partition KW - Neutron diffraction PY - 2017 U6 - https://doi.org/10.1007/s10853-017-1182-7 SN - 0022-2461 SN - 1573-4803 VL - 52 IS - 17 SP - 10198 EP - 10216 PB - Springer AN - OPUS4-40572 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Stegemann, Robert A1 - Cabeza, Sandra A1 - Pelkner, Matthias A1 - Lyamkin, Viktor A1 - Sonntag, Nadja A1 - Bruno, Giovanni A1 - Skrotzki, Birgit A1 - Kreutzbruck, Marc T1 - Evaluation of high spatial resolution imaging of magnetic stray fields for early damage detection N2 - The paper discusses the evaluation of elastic and plastic strain states in two low-carbon steels of the same steel group with high spatial resolution GMR (giant magneto resistance) sensors. The residual stress distributions of tungsten inert gas welded plates were determined by means of neutron diffraction as a reference. The normal component of local residual magnetic stray fields arise in the vicinity of the positions of maximum stress. The experiments performed on flat tensile specimen indicate that the boundaries of plastic deformations are a source of stray fields. The spatial variations of magnetic stray fields for both the weld and the tensile samples are in the order of the earths magnetic field. T2 - 43rd Annual Review of Progress in Quantitative Nondestructive Evaluation, Volume 36 CY - Atlanta, Georgia, USA DA - 17.07.2016 KW - Plastic deformation KW - GMR KW - Neutron diffraction KW - Residual stress KW - Microstructure KW - Low carbon steel KW - TIG weld PY - 2017 SN - 978-0-7354-1474-7 U6 - https://doi.org/10.1063/1.4974688 SN - 0094-243X VL - 1806 IS - 1 SP - Article UNSP 110010-1 EP - 10 PB - AIP Publishing CY - Melville, NY 11747 AN - OPUS4-39279 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Cabeza, Sandra A1 - Artzt, Katia A1 - Haubrich, J. A1 - Klaus, M. A1 - Genzel, Ch. A1 - Requena, G. A1 - Bruno, Giovanni T1 - An Assessment of Subsurface Residual Stress Analysis in SLM Ti-6Al-4V N2 - Ti-6Al-4V bridges were additively fabricated by selective laser melting (SLM) under different scanning speed conditions, to compare the effect of process energy density on the residual stress state. Subsurface lattice strain characterization was conducted by means of synchrotron diffraction in energy dispersive mode. High tensile strain gradients were found at the frontal surface for samples in an as-built condition. The geometry of the samples promotes increasing strains towards the pillar of the bridges. We observed that the higher the laser energy density during fabrication, the lower the lattice strains. A relief of lattice strains takes place after heat treatment. KW - Selective laser melting KW - Additive manufacturing KW - Heat treatment KW - Ti-6Al-4V KW - Synchrotron X-ray diffraction KW - Residual stress PY - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-395759 SN - 1996-1944 VL - 10 IS - 4 SP - Article 348, 1 EP - 14 AN - OPUS4-39575 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cooper, R. A1 - Bruno, Giovanni A1 - Shyam, A. A1 - Watkins, T. A1 - Pandey, A. A1 - Wheeler, M. T1 - Effect of microcracking on the uniaxial tensile response of beta-eucryptite ceramics: Experiments and constitutive model N2 - A constitutive model for the nonlinear or “pseudoplastic” mechanical behavior in a linear-elastic solid with thermally induced microcracks is developed and applied to experimental results. The model is termed strain dependent microcrack density approximation (SDMDA) and is an extension of the modified differential scheme that describes the slope of the stress-strain curves of microcracked solids. SDMDA allows a continuous variation in the microcrack density with tensile loading. Experimental uniaxial tensile response of β-eucryptite glass and ceramics with controlled levels of microcracking is reported. It is demonstrated that SDMDA can well describe the extent of non-linearity in the experimental uniaxial tensile response of β-eucryptite with varying levels of microcracking. The advantages of the SDMDA are discussed in regard to tensile loading. KW - Microcracking KW - β-eucryptite KW - Young's modulus KW - Modeling KW - Tensile behavior PY - 2017 U6 - https://doi.org/10.1016/j.actamat.2017.06.033 SN - 1359-6454 SN - 1873-2453 VL - 135 SP - 361 EP - 371 PB - Elsevier Ltd. AN - OPUS4-40859 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Obaton, A-F. A1 - Fain, J. A1 - Djemaï, M. A1 - Meinel, Dietmar A1 - Léonard, Fabien A1 - Mahé, E. A1 - Lécuelle, B. A1 - Fouchet, J-J. A1 - Bruno, Giovanni T1 - In vivo XCT bone characterization of lattice structured implants fabricated by additive manufacturing N2 - Several cylindrical specimens and dental implants, presenting diagonal lattice structures with different cell sizes (600, 900 and 1200 µm) were additively manufactured by selective laser melting process. Then they were implanted for two months in a sheep. After removal, they were studied by Archimedes’ method as well as X-ray computed tomography in order to assess the penetration of bone into the lattice. We observed that the additive manufactured parts were geometrically conform to the theoretical specifications. However, several particles were left adhering to the surface of the lattice, thereby partly or entirely obstructing the cells. Nevertheless, bone penetration was clearly visible. We conclude that the 900 µm lattice cell size is more favourable to bone penetration than the 1200 µm lattice cell size, as the bone penetration is 84 % for 900 µm against 54 % for 1200 µm cell structures. The lower bone penetration value for the 1200 µm lattice cell could possibly be attributed to the short residence time in the sheep. Our results lead to the conclusion that lattice implants additively manufactured by selective laser melting enable better bone integration. KW - Biomedical engineering KW - Dentistry KW - Medical imaging KW - X-ray computer tomography PY - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-418648 SN - 2405-8440 IS - 3 SP - Article e00374, 1 EP - 21 PB - Elsevier Limited CY - 125 London Wall London, EC2Y 5AS United Kingdom AN - OPUS4-41864 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nadammal, Naresh A1 - Cabeza, Sandra A1 - Mishurova, Tatiana A1 - Thiede, Tobias A1 - Kromm, Arne A1 - Seyfert, Christoph A1 - Farahbod, Lena A1 - Haberland, Christoph A1 - Schneider, Judith Ann A1 - Portella, Pedro Dolabella A1 - Bruno, Giovanni T1 - Effect of hatch length on the development of microstructure, texture and residual stresses in selective laser melted superalloy Inconel 718 N2 - In the present study, samples fabricated by varying the deposition hatch length during selective laser melting of nickel based superalloy Inconel 718 were investigated. Microstructure and texture of these samples was characterized using scanning electron microscopy, combined with electron back-scattered diffraction, and residual stress assessment, using neutron diffraction method. Textured columnar grains oriented along the sample building direction were observed in the shorter hatch length processed sample. A ten-fold increase in the hatch length reduced the texture intensity by a factor of two attributed to the formation of finer grains in the longer hatch length sample. Larger gradients of transverse residual stress in the longer hatch length sample were also observed. Along the build direction, compressive stresses in the shorter hatch length and negligible stresses for the longer hatch length specimen were observed. Changes to the temperature gradient (G) in response to the hatch length variation, influenced the G to growth rate (R) ratio and the product G × R, in agreement with the microstructures and textures formed. For the residual stress development, geometry of the part also played an important role. In summary, tailored isotropy could be induced in Inconel 718 by a careful selection of parameters during selective laser melting. KW - Additive manufacturing KW - Nickel-based superalloy KW - Microstructure and texture KW - Residual stress KW - Electron back-scattered diffraction KW - Neutron diffraction PY - 2017 UR - http://www.sciencedirect.com/science/article/pii/S0264127517308018 U6 - https://doi.org/10.1016/j.matdes.2017.08.049 SN - 0264-1275 VL - 134 SP - 139 EP - 150 PB - Elsevier CY - Oxford, UK AN - OPUS4-41606 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nellesen, J. A1 - Laquai, René A1 - Müller, Bernd R. A1 - Kupsch, Andreas A1 - Hentschel, M. P. A1 - Anar, N. B. A1 - Soppa, E. A1 - Tillmann, W. A1 - Bruno, Giovanni T1 - In situ analysis of damage evolution in an Al/Al2O3 MMC under tensile load by synchrotron X-ray refraction imaging N2 - The in situ analysis of the damage evolution in a metal Matrix composite (MMC) using synchrotron X-ray refraction radiography (SXRR) is presented. The investigated material is an Al alloy (6061)/10 vol% Al2O3 MMC after T6 heat treatment. In an interrupted tensile test the gauge section of dog bone-shaped specimens is imaged in different states of tensile loading. On the basis of the SXRR images, the relative change of the specific surface (proportional to the amount of damage) in the course of tensile loading was analyzed. It could be shown that the damage can be detected by SXRR already at a stage of tensile loading, in which no Observation of damage is possible with radiographic absorption-based imaging methods. Moreover, the quantitative analysis of the SXRR images reveals that the amount of damage increases homogeneously by an average of 25% with respect to the Initial state. To corroborate the experimental findings, the damage distribution was imaged in 3D after the final tensile loading by synchrotron X-ray refraction computed tomography (SXRCT) and absorption-based synchrotron X-ray computed tomography (SXCT). It could be evidenced that defects and damages cause pronounced indications in the SXRCT images. KW - Composite materials KW - Defects KW - Micro analysis PY - 2018 U6 - https://doi.org/10.1007/s10853-017-1957-x SN - 0022-2461 SN - 1573-4803 VL - 53 IS - 8 SP - 6021 EP - 6032 PB - Springer US AN - OPUS4-44241 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bruno, Giovanni A1 - Fernández, R. A1 - Gonzáles-Doncel, G. T1 - Fractal nature of aluminum alloys substructures under creep and its implications N2 - The present work offers an explanation for the variation of the power-law stress exponent, n, with the stress r normalized to the shear modulus G in aluminum alloys. The approach is based on the assumption that the dislocation structure generated with deformation has a fractal nature. It fully explains the evolution of n with r/G even beyond the so-called power law breakdown region. Creep data from commercially pure Al99.8%, Al-3.85%Mg, and ingot AA6061 alloy tested at different temperatures and stresses are used to validate the proposed ideas. Finally, it is also shown that the fractal description of the dislocation structure agrees well with current knowledge. KW - SSTC Model KW - Creep KW - Aluminum Alloys KW - Fractal Microstructure PY - 2018 U6 - https://doi.org/10.1063/1.5012035 SN - 0021-8979 VL - 123 IS - 14 SP - 145108-1 EP - 145108-8 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-44779 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fernández, R. A1 - Cabeza, Sandra A1 - Mishurova, Tatiana A1 - Fernández-Castrillo, P. A1 - González-Doncel, G. A1 - Bruno, Giovanni T1 - Residual stress and yield strength evolution with annealing treatments in an age-hardenable aluminum alloy matrix composite N2 - We investigated the possibility of minimizing tensile matrix residual stresses in age hardenable aluminum alloy metal matrix composites without detrimentally affect their mechanical properties (such as yield strength). Specifically, we performed thermal treatments at different temperatures and times in an age-hardenable aluminum matrix composite 2014Al-15vol%Al2O3. Using X-ray synchrotron radiation diffraction and mechanical tests, we show that below a certain treatment temperature (250 °C) it is possible to identify an appropriate thermal treatment capable of relaxing residual stress in this composite while even increasing its yield strength, with respect to the as processed conditions. KW - Residual stress KW - X-ray diffraction KW - Annealing treatment KW - Metal matrix composite KW - Yield strength PY - 2018 U6 - https://doi.org/10.1016/j.msea.2018.06.031 SN - 0921-5093 SN - 1873-4936 VL - 731 SP - 344 EP - 350 PB - Elsevier CY - Amsterdam AN - OPUS4-45255 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cabeza, Sandra A1 - Müller, Bernd R. A1 - Pereyra, R. A1 - Fernández, R. A1 - González-Doncel, G. A1 - Bruno, Giovanni T1 - Evidence of damage evolution during creep of Al–Mg alloy using synchrotron X-ray refraction N2 - In order to provide further evidence of damage mechanisms predicted by the recent solid-state transformation creep (SSTC) model, direct observation of damage accumulation during creep of Al–3.85Mg was made using synchrotron X-ray refraction. X-ray refraction techniques detect the internal specific surface (i.e. surface per unit volume) on a length scale comparable to the specimen size, but with microscopic sensitivity. A significant rise in the internal specific surface with increasing creep time was observed, providing evidence for the creation of a fine grain substructure, as predicted by the SSTC model. This substructure was also observed by scanning electron microscopy KW - Aluminium alloys KW - Creep KW - Damage KW - Synchrotron X-ray refraction KW - Electron microscopy KW - subgrain structure PY - 2018 U6 - https://doi.org/10.1107/S1600576718001449 SN - 1600-5767 VL - 51 SP - 420 EP - 427 PB - Wiley AN - OPUS4-44619 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bruno, Giovanni A1 - Buljak, V. T1 - Numerical modeling of thermally induced microcracking in porous ceramics: An approach using cohesive elements N2 - A numerical framework is developed to study the hysteresis of elastic properties of porous ceramics as a function of temperature. The developed numerical model is capable of employing experimentally measured crystallographic orientation distribution and coefficient of thermal expansion values. For realistic modeling of the microstructure, Voronoi polygons are used to generate polycrystalline grains. Some grains are considered as voids, to simulate the material porosity. To model intercrystalline cracking, cohesive elements are inserted along grain boundaries. Crack healing (recovery of the initial properties) upon closure is taken into account with special cohesive elements implemented in the commercial code ABAQUS. The numerical model can be used to estimate fracture properties governing the cohesive behavior through inverse analysis procedure. The model is applied to a porous cordierite ceramic. The obtained fracture properties are further used to successfully simulate general non-linear macroscopic stress-strain curves of cordierite, thereby validating the model. KW - Interfacial strength KW - Cordierite KW - Young’s modulus KW - Thermal expansion KW - Hysteresis KW - Inverse analysis KW - Cohesive finite elements PY - 2018 U6 - https://doi.org/10.1016/j.jeurceramsoc.2018.03.041 SN - 0955-2219 VL - 38 IS - 11 SP - 4099 EP - 4108 PB - Elsevier Ltd. AN - OPUS4-45117 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mishurova, Tatiana A1 - Cabeza, Sandra A1 - Thiede, Tobias A1 - Nadammal, Naresh A1 - Kromm, Arne A1 - Klaus, Manuela A1 - Genzel, Christoph A1 - Haberland, Christoph A1 - Bruno, Giovanni T1 - The influence of the support structure on residual stress and distortion in SLM Inconel 718 parts N2 - The effect of support structure and of removal from the base plate on the residual stress state in selective laser melted IN718 parts was studied by means of synchrotron X-ray diffraction. The residual stresses in subsurface region of two elongated prisms in as-built condition and after removal from the base plate were determined. One sample was directly built on a base plate and another one on a support structure. Also, the distortion on the top surface due to stress release was measured by contact profilometry. High tensile residual stress values were found, with pronounced stress gradient along the hatching direction. In the sample on support, stress redistribution took place after removal from the base plate, as opposed to simple stress relaxation for the sample without support. The sample on support structure showed larger distortion compared to sample without support. We conclude that the use of a support decreases stress values but stress-relieving heat treatments are still needed. KW - Additive manufacturing KW - SLM KW - Residual stress KW - Synchrotron X-ray diffraction KW - IN718 PY - 2018 U6 - https://doi.org/10.1007/s11661-018-4653-9 SN - 1073-5623 VL - 49A IS - 7 SP - 3038 EP - 3046 PB - Springer Sciences & Business Media CY - New York, NY AN - OPUS4-45100 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -