Damage analysis of 2.5D C/C-SiC composites subjected to fatigue loadings

Damage analyses of a ceramic matrix composite during fatigue and quasi-static loads were performed by acoustic emission (A.E.) monitoring. The material studied was a 2.5D C/C-SiC composite produced by chemical vapor infiltration followed by liquid silicon infiltration. The analysis done during the first 200 cycles of a fatigue test showed that the number of A.E. hits is a good parameter for the quantification of damage. Furthermore, the A.E. hit energy was associated with the type of damage. In this sense, the damage developed during the fatigue loading was related to matrix crack initiation, propagation and re-opening, as well as fiber-matrix friction. Quasi-static tests on post-fatigue samples showed that the previous fatigue loadings increased the material's damage threshold and hindered the development of new damage. Particular attention was given to the sample after 2,000,000 cycles as this sample showed distinct A.E. signals that could be related to fiber debonding.