MICROMECHANICS BASED CREEP DAMAGE ANALYSIS OF UNIDIRECTIONAL METAL MATRIX COMPOSITES

摘要

Experimental results shown the classical creep curves with the primary, secondary and tertiary phases. Both the linear secondary creep and the tertiary one are dependent on the amount of damage initiated at the interface during the primary creep. Two main evolutions could be arose: the first one, for loads under a given threshold, leads to long life tests (some of them without tertiary creep or stopping during the secondary creep), and the second one, for loads over the threshold, inducing an important damage at the beginning of the secondary creep, leads to the tertiary creep and the failure of the specimen. The numerical micromechanical analysis, using the finite element method, performed to simulate the creep tests, helped to understand the influence of the damaging process, evolving at the interface, on the macroscopic response. In order to improve the lifetime under creep loads, it is important that the interface remains safe as long as possible in order to share the load between the fiber and the matrix. It has been shown that once the interface begins to break, the crack continues to propagate until the complete decohesion, then, a macroscopic crack leads to the failure of the specimen, the load being only carried by the unreinforced matrix. These are just qualitative observations, and an effort is devoted to improve the modeling in order to be able to reproduce quantitatively the experimental results.