Étude des mécanismes d'endommagement de deux composites à matrice métallique A356 + 20%SiC_p et 2124 + 15%SiC_p

Study of the damage mechanisms of two metal matrix composites A356 + 20%SIC_p and 2124 + 15%SIC_p

¹ CETIM, Sentis, France, actuellement à l'U.T.C.
² CETIM, Sentis, France
³ Université de Technologie de Compiègne, Centre de Recherches de Royallieu, LG2MS, URA 1505 CNRS, Compiègne, France
⁴ Canmet, Ottawa, Ontario, Canada

Abstract

Tensile tests were performed on two MMC materials : a recast Duralcan composite (A356+20% SiC_p), and another composite elaborated by powder metallurgy (2124+15% SiC_p). These composites increased their specific properties as their Young’s modulus, however these improvements have been accompanied by a degradation of strain to failure.

The failure mechanism consist of void nucleation, growth and coalescence stages. In discontinuously reinforced metal matrix composites, microvoid nucleation is the predominant fracture mode. The microscopic observations shown the different initiation mechanisms : cracking for particulate with sharp corner and microvoid in the matrix (A356 + 20% SiC), and debonding for sphere (2124 + 15% SiC_p).

Acoustic emission tests have been carried out simultaneously with tensile tests, and showed that damage appeared and rapidly increased during elastic loading : this was due to premature and progressive damage of composite. Unloading cycles during tensile test confirmed this damage by a decrease of the Young’s modulus.