A numerical study of the mechanisms of cyclic strain hardening in metal-ceramic composites

Abstract

A numerical study of the mechanical behaviour of discontinously-reinforced metal-matrix composites under uniaxial fully-reversed cyclic deformation is presented. The analyses are carried out within the framework of the finite element analysis of a unit cell. Three reinforcement shapes (whiskers, particulates, and spheres) and two different reinforcement volume fractions (10 and 20%) are studied. The composites exhibit cyclic hardening, which is mainly due to the progressive accumulation of plastic deformations in the matrix upon loading and unloading, and which is very sensitive to the matrix strain hardening capacity. Monotonic and cyclic strain hardening are maxima for the materials containing whiskers and minima in the case of spherical reinforcements, and increase with the volume fraction of reinforcement. However, it was found that the effect of reinforcement shape and volume fraction is more pronounced under monotonic deformation than in fatigue. The differences and similitudes in the strengthening mechanisms during monotonic and cyclic deformation are indicated, and the possible sources of cyclic softening (matrix cavitation, reinforcement fracture and interfacial decohesion) are discussed from the evolution of the plastic strains in the matrix and of the stresses acting on the ceramic reinforcements and at the interfaces.