TOUGHENING BY CRACK PINNING AND CRACK DEFLECTION IN PARTICLE-DISPERSED COMPOSITES

An analysis is conducted on the toughening mechanisms in composite materials reinforced with spherical particles in terms of pinning and deflection. The requisite for a crack to be deflected at particle/matrix interface depends both on the fracture toughness of the interface and on the impinging angle. According to the cracking behavior at the interface, dispersed particles are classified into two types of particles for crack-pinning and for crack-deflection. The respective toughening mechanisms are analyzed by introducing the equivalent crack closure stresses. The crack deflection has a little effect on the enhancement of the fracture toughness compared with that of the crack pinning, and can be neglected in the case of the higher interface toughness. The apparent fracture toughness of the composites increases with both the interface toughness and the volume fraction of particles. Various dependencies of the apparent fracture toughness on the volume fraction are derived by varying the interface toughness, which substantiate well experimental results. The value of the interface toughness is also estimated indirectly from the comparison of the theoretical prediction with the experimental results.