Effect of the stress level on the fatigue strengthening behavior of 2D needled C/SiC CMCs at room temperature.

The fatigue behavior of 2D needled C/SiC CMCs at room temperature was studied. The residual tensile properties were determined for the run-out condition set for the fatigue testing. It is noted that the 2D needled C/SiC CMCs achieve ~ 20% enhancement of the ultimate tensile strength after fatigue loading with fiber pull-out present. This enhancement of residual properties is not widely observed and reported for CMCs. The increase in residual tensile properties correlates with the applied fatigue stress. The procedures for testing and the mechanics for the increased strength after fatigue testing are discussed. This is supplemented with microstructure observations. The prior fatigue loading results in more full-developed micro-damage and a more uniform stress state in the fibers of needled C/SiC CMCs, so the load capability of post-fatigue specimens is stronger than the as-received ones with extremely uneven pre-loading in fibers. [ABSTRACT FROM AUTHOR]