Computational Mechanics of Heterogeneous Materials: Influence of Residual Stresses

Abstract

Heterogeneous materials such as Metal Matrix Composites (MMCs) of the type Al/SiC contain significant residual stresses due to different thermal expansion coefficients from the metal and ceramic constituents. They are believed to influence the mechanical properties of these materials to some extent — including some changes in their failure behavior. In this contribution, a physically based micromechanical approach is applied in order to clarify the influence of residual stresses on local as well as global properties of MMCs. A representative microstructural cut-out of an Al/10% SiC-composite is meshed with finite elements in order to take phase boundaries into account. This mesovolume possesses all characteristic features of the material, such as volume fraction, distribution characteristics as well as shape of the particles. The deformation behavior of this microstructure is analyzed under large compressive external loading up to strains of about 10%. In addition, the failure behavior is modeled using Rice&Tracey’s failure criterion which was recently shown to model microstructural failure to a good approximation. It is found that although residual stresses do have some impact on failure initiation in the microstructure, strains due to external loading are much more of importance in this respect. In order to illuminate the influence of particle shape and arrangement, artificial two-dimensional microstructures are analyzed as well. It is found that irregular particle shapes are much more prone to fracture in the matrix as compared to regular shapes and that particle alignments are not beneficial with respect to failure aspects. The distribution and maximum values of the damage parameter are shown. It is found that in all cases analyzed, damage follows the pattern of plastic deformation and is much less influenced by hydrostatic stresses than expected. Nevertheless, damage nucleates between clusters of particles where shear deformation as well as hydrostatic tensile stresses are concentrated in the matrix.