Investigation of crack-tip plasticity in high volume fraction particulate metal matrix composites

Crack-tip strain fields in high volume fraction ceramic particle reinforced metal matrix composites are assessed using photoelastic measurements. It is shown that the size of the significant crack-tip plastic zones that form in these materials depends on the type and diameter of the reinforcement and on the matrix material. This plastic zone size correlates well with the macroscopic toughness values assessed through J-integral testing. The composites are thus "metallic" in the sense that their toughness is mostly composed of plastic energy dissipation around the crack tip. Plastic deformation also induces marked constraint effects that influence the shape of the surface strain fields. It is shown that finite element analysis must be three-dimensional to describe these strain fields, as two-dimensional plane-stress analysis fails to reproduce the experimental data.