[en] This book summarizes the works carried out during a workshop that brought together European specialists of X-ray tomography. Different aspects are reviewed: global description of X-ray tomography, introduction to reconstruction algorithms, advantages of X-ray synchrotron sources on phase contrast images, and examples of X-ray tomography analyses of materials with an heterogenous microstructure. (J.S.)

[en] Effects of matrix elastoplastic properties and reinforcement volume fraction on damage initiation in model heterogeneous metals have been studied using in situ tensile tests coupled with high resolution X-ray tomography. The materials consisted in two kinds of aluminium matrices (commercially pure Al and Al2124 alloy) reinforced by 4 vol% or 20 vol% of spherical hard ceramic particles. The main damage mechanisms were found to change from particle/matrix interface decohesion to particle cracking as the matrix got harder. Quantitative analyses of experimental observations have been performed using the three dimensional images. These measurements were linked to a Weibull statistic based on different local mechanical quantities (stress, strain or energy) calculated by Finite Element in the particle or at the particle/matrix interface. The results obtained for particle cracking confirmed that this damage mechanism is intrinsic to the chosen ceramic reinforcement and the theoretical approach allowed to determine mechanical parameters such as the particle critical stress

[en] A simple model for describing the competition between interface decohesion and particle cracking as the elementary damage nucleation mechanisms in heterogeneous materials is proposed. It allows to rationalise the influence of the plastic behaviour of the ductile matrix and of the interfacial strength. The model is applied to analyse the dominant damage mechanisms in model composites with aluminium alloys matrix and spherical zirconia/silica reinforcement

[en] The third generation synchrotrons are very powerful X radiations sources. With these devices, it has been possible to develop a new high resolution version of the X radiation tomography, a non-destructive imaging technique. Then, for instance the internal microstructure of materials can be studied. (O.M.)

[en] X-ray microtomography is used to measure volume fraction and connectivity of the metallic phase in an alumina-chromium composite. Reconstructed images are used as input data for a finite element calculation of the residual thermal stresses. Results confirm the main trends shown by similar calculations previously performed on less-realistic finite element models

[en] The deformation mechanisms during indentation of aluminum-based metal foams are examined by use of X-ray tomography and the finite element method. The deformation was found to be almost totally restricted to a spherical cap-shape compacted zone under the indenter. An analytical expression is given which describes the changes in the size of the compacted zone as a function of the diameter of the indenter, the indentation depth and the relative density of the foam. Results of finite element simulations and the calculated function were found to be in reasonably good agreement

[en] High resolution synchrotron X-ray tomography has been used to image damage development during mechanical loading in model metallic materials. First, the initiation, growth and coalescence of porosities in the bulk of two metal matrix composites have been imaged at different stages of a tensile test (2 μm resolution). Quantitative data on damage development has been obtained and related to the nature of the composite matrix. Second, 3D images of one fatigue crack have been obtained post mortem for a cast Al alloy. Thanks to a special decoration technique, the shapes of the crystallographic grains surrounding the crack have also been imaged (0.7 μm resolution). Local deviations of the crack have been related to the presence of grain boundaries

[en] The aim of the paper is to study the partitioning of stress between bridging and broken fibres and the nearby matrix in the region around a fatigue crack in the matrix of a Ti-6Al-4V/SCS-6 SiC fibre composite. This was achieved by using synchrotron X-ray radiation to perform a combination of high spatial resolution tomographic imaging and strain mapping. The average elastic fibre strain for each ply was mapped with distance from the crack, ply by ply. Two samples were examined; one in which there were no broken fibres and one in which some fibres in ply 1 had broken. The contributions of broken and bridging fibres were separated using a double peak fitting routine. The interfacial stress variation and the extent of interfacial debonding were deduced from the fibre strain profiles. Contrary to most micromechanical models the interfacial frictional sliding stress was not found to be constant along the fibre length, but to decrease approximately linearly towards the crack plane. Upon unloading the fibres were found to undergo reverse sliding at the interface

[en] Crumpled foils are a new type of material with promising characteristics due to their interesting mechanical properties associated with their low weight. They are fabricated by dye compaction, resulting in a structure consisting of randomly arranged ridges and vertices, thus providing a lot of self-contact. Mechanical properties and internal complex mesostructures were investigated using non-destructive techniques in order to link the microstructure to mechanical properties. As regards the mechanical characteristics, the influence of different parameters was studied: volume fraction of solid, loading–unloading cycle, simple or closed die compression, pre-folding of foils, compaction rate and creation of local welding. It appears possible to significantly change the mechanical behavior of crumpled foils, especially by increasing the solid fraction but also by generating the local welding of foils in the microstructure. A study of relaxation was also performed, which showed that these materials are slightly sensitive to deformation rate. Finally, a qualitative and quantitative study of the microstructure by in situ tests using X-ray tomography was conducted. This resulted in a better understanding of the behavior and local organization of foils during compaction

[en] X-ray tomography is a non-destructive technique which provides 3D information of materials. It is consequently very attractive in Materials Science since the relation between macroscopic properties and the micro-structure of a material is very frequently required. The aim of this paper is to present selected results obtained in various investigations of metallic materials such as superplastic deformation, materials in the semi-solid state and metallic foams. Depending on the studied features, several tomography analysis modes were used: conventional absorption mode, phase contrast and holotomography, a new technique, which provides the 3D distribution of the electron density in the bulk of the material. Furthermore micro-tomography enables one to perform in situ experiments either by using a mechanical test machine or a furnace