Damage mechanisms in unidirectional SiC/Ti composites under transverse creep loading:: Experiments and modeling

The damage mechanisms under transverse creep of two unidirectional metal matrix composites are investigated. This paper is based on a two-scale approach, and on experimental and numerical studies. On the macroscopic scale, the global response of the composite subjected to a constant transverse load is analyzed. On the microscopic scale, the influence of each component (matrix, fibre and interface) on the global behavior is investigated. In the experimental part of the study, creep tests have been performed at different temperatures under vacuum, and scanning electron microscope (SEM) observations have allowed the investigation of the damage evolution under different applied loads. In the numerical work, the creep tests were simulated on a representative unit cell using the finite element method and taking into account the various nonlincarities (matrix viscoplasticity coupled with interface damage). The experimental and numerical results show that the global behavior of the composite depends on the local interfacial behavior. Two domains are evidenced as a function of the applied stress, a critical stress being thus determined. Below the critical stress, the interfaces remain undamaged, leading to a low creep rate and a long duration test. Above the critical stress, the interfaces are totally debonded, thereby increasing the secondary creep rate and leading to a possible specimen failure.