Numerical modeling of the effective ductile damage of macroporous alumina

Macroporous γ-alumina ceramics is a granular-like medium composed of agglomerated mesoporous grains allowing inter-granular macroporosity. Macropores, whose equivalent diameter is larger than 1 µm, represent a volume fraction of 14.5%. The mechanical properties of the macroporous material are very low compared with the mesoporous matrix. In this work, the ductile damage mechanisms of the considered porous alumina are numerically investigated on a wider range of stress triaxiality ratio than experimentally thanks to a full-field homogenization approach based on a 2D Finite Element Method (FEM). The microstructure geometry is extracted from Scanning Electron Microscopy (SEM). The complexity of the macropores shape is closely transcribed from image treatment process to meshing. The matrix behavior is considered elastic-plastic and follows a Drucker-Prager yield surface. A reference plastic dissipation, adjusted on experimental uniaxial compression tests is used to approximate the plastic domain under negative mean stress. The calculated yield surface of the porous Drucker-Prager matrix presents a cap-form which is consistent with the shape identified experimentally. The overall yield surface is qualitatively the same cap-form as those obtained in literature for isotropic porous media containing spherical voids embedded in a Drucker-Prager matrix, which seems to show that the pore shape does not strongly affect this cap-form since the overall isotropy is respected.