Identification of elastic material parameters from experimental kinematic fields.

The aim of this thesis is to find the mechanical properties of a non-homogeneous material in the hypothesis of elastic behaviour. To overcome the problems of conventional testing, in which the macroscopic properties are determined, and identify the real Poisson’ s ratio of a material, the spatial distribution of dis-placements has been measured. To obtain, what is called, a displacement field, Digital Image Correlation (DVC), is used. Thanks to the DVC it has been possible to obtain displacement field measurements from a 3D image series (from initial to deformed), results of a test.The 3D images treated in this thesis are either synthetically generated, or as a result of x-ray tomography on a real experiment.In both cases the initial configuration of the specimens has been chosen with increasingly complicated morphologies. Starting from the homogeneous configuration, up to a specimen with many void spherical defects.In the synthetic case, once the image of the initial configuration is generated, it is deformed with a displacement field resulting from a Finite Element simulation.In the case where the campaign of experiments is carried out once the material has been chosen with the desired configuration, the images are obtained thanks to in-situ tomography, combining x-ray tomography and uniaxial compression testing. Once the images are generated, these are correlated to produce the real displacement field, from which the boundary conditions are extracted.The boundary conditions are then applied in Finite Element simulations. The FE meshes are representative of the initial configuration of the material. In the simulation the linear elastic behaviour is assumed, and in each of them different values are chosen for the elastic constants of the material (output of the treatment). The result of each simulation is a simulated displacement field.By searching which simulated displacement field is the most similar to the real displacement field it has been possible to identify Poisson’s ratio of the material tested.