A FINITE-ELEMENT ANALYSIS OF PLASTIC RELAXATION AND PLASTIC ACCUMULATION AT 2ND-PHASE PARTICLES

An elastic-plastic FE analysis has been used to examine the plastic be haviour of the metal matrix within an Al/(SiC)(p) MMC system subjected to tensile loading. It aims to understand the following basic aspects : (1) how does the plastic behaviour of the aluminium matrix affect th e stress gathering capability of the particles? (2) does the stress co ncentration increase with further plastic strain? (3) what factors are responsible for the low ductility of Al/(SiC)(p) MMCs? The stress gat hering capability is defined as the ratio of the axial stress within t he particle to the far field value. It has been found that plastic def ormation leads to stress relaxation only at the early stages of strain . Just after stress relaxation, both the stress gathering capability o f the particles and the stress concentration are reduced, compared wit h those for elastic deformation. However, during further plastic accum ulation, strain hardening overcomes the plastic relaxation and the con centration then increases. Eventually, this concentration may even exc eed the ratio that existed before plastic relaxation. Concurrently, th e stress gathering capability of the particles increases. The conseque nces of these effects of plastic behaviour on the strength and the duc tility of the composite is discussed.