Etude du comportement et de l'endommagement des composites à matrice aluminium et à renforts particulaires

Abstract
Tensile tests were performed on two MMC materials : a recast Duralcan composite (A356+20% SiCp), and another composite elaborated by powder metallurgy (2124+15% SiCp). These composites increased their specific properties such as their Young's modulus, however these improvements were accompanied by a degradation of strain at failure, moreover σ-ε curves were observed with a non linear behavior. In discontinuously reinforced metal matrix composites, microvoid nucleation is the predominant fracture mode. The failure mechanism consist of void nucleation, growth and coalescence stages. The RICE-TRACEY law used to illustrate growth stage was not checked by MMC materials, but WEIBULL'S theory was successful ; the very low WEIBULL's modulus confirmed the predominant stage of void nucleation by cracking particles. Nucleation of voids is studies numerically. Results of finite element calculation were compared with fracture surfaces. The microscopic observations confirmed the different initiation mechanisms predicted by modeling : cracking for particulate with sharp corner and microvoid in the matrix (A356+20% SiCp), and debonding for sphere (2124+15% SiCp). Acoustic emission tests were carried out simultaneously with tensile tests, and showed the damage appearation and his increasement.