| In an effort to understand the fatigue behavior of carbon-carbon composites, high cycle (107 cycles) uniaxial fatigue experiments were performed. A variety of specialized experimental techniques were developed to identify the mechanisms underlying the fatigue response. In-situ optical microscopy combined with image processing was used to evaluate microcrack morphology and damage evolution as a function of cycle number. Likewise, mercury porosimitry was used to quantify the pore size distributions. Load and extensometer data was recorded to evaluate the cycle dependent mechanical behavior. Stress-life data was compiled and post cyclic residual strengths were compared.; To investigate the hypothesis that interfacial wear is the mechanism of fatigue damage propagation in carbon-carbon composites, internal surface lubrication experiments were designed and conducted. Results show that wear was not the dominant fatigue mechanism. Fatigue performance was found to be dependent upon an initially damaging load history and subsequent cyclic stress amplitude. |
