The 8 PhD projects of the early-stage researchers led to the following salient results:
ESR 1. A crystal plasticity model to analyze the effect of Triaxiality, Lode angle and crystal orientation in the mechanical response of metallic materials was developed. A key point was the generation of prescribed boundary conditions such that the external Triaxiality and Lode angle could be controlled considering periodicity and using a multipoint constraint subroutine. Numerical calculations were developed with different boundary conditions to study the mechanical response of single crystals with voids, bicrystals with voids at the grain boundaries and polycrystals with voids.
ESR 2. A constitutive model to describe the dynamic response of porous metallic materials under plane strain condition was developed. The approach consists of considering a cylindrical void of circular section embedded in a cylindrical shell made of viscoplastic matrix. The key point was to show that the length of the cylinder plays an important role in the macroscopic response of the material. Micro-inertia effects were investigated, considering various cases of loading conditions including spherical loading, plane stress loading and uniaxial loading paths. The analytical model was validated against numerical simulations.
ESR 3. A constitutive model to study material’s rate sensitivity on interfacial crack growth in brittle materials was developed and validated with experiments. The tests showed that a weak interface under static loading conditions can be transformed into a strong interface under dynamic loads, thus diverting the crack trajectory. The interaction of a dynamically loaded crack with different pre-existing flaws was also studied. While similar problems were previously investigated in the literature, it was shown that much of the experimental results concerning the effect of a pre-existing hole’s size are in fact a result of stress wave scattering from the hole, prior to any crack growth.
ESR 4. A two-scale damage model with distributed heat sources resulting from energy dissipation during rapid evolutions of microcracks in brittle materials has been developed. The model has been obtained by asymptotic homogenization, extending a procedure available in the literature to thermo-elastic media with dynamically propagating microcracks having heat sources at their tips. The model is implemented in a finite element code and numerical simulations of the Compact Compression Test showed good agreement with the experimental temperature evolutions.
ESR 5. Development of a perturbation model to assess the joint effect that inertia, strain rate, loading path, porosity, tension-compression asymmetry and anisotropy have on the onset and development of necking instabilities in ductile metals subjected to dynamic loading. The distinctive feature of this work is to consider material anisotropy, tension-compression asymmetry and porosity. The results of the analytical model were compared with finite element calculations and specific experiments that we performed for this task.
ESR 6. Formulation of a multi-scale dislocation-based constitutive model to define the thermomechanical response of metallic materials under dynamic loading. Based on the evolution of the microstructure during deformation, the model can predict the material response at the macroscopic level. The thermal evolution is estimated by considering the heat dissipation related with internal features of the material structure. This model will establish the base for future models for material instabilities, such as those considering shear localization.
ESR 7. Development of an operating system to measure surface imperfections and damage on aircraft structures. This procedure further developed to investigate the characteristics of fracture surfaces at a lower scale. To do so, an algorithm was created based on Deep Learning and Artificial Intelligence methods that can automatically perform topographic characterization of the fracture surface for ceramic materials.
ESR 8. Development of a methodology to extract the delamination energy of composite structures from peel tests. The methodology, which combines experimental data and modeling, has been applied to obtain new guidelines for the mechanical design of Printed Circuit Boards.
