Observation on Failure Process of Fiber-Reinforced-Composites in High Temperature Fatigue

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Delamination behavior of carbon fiber reinforced polymer at high temperatures was investigated in order to elucidate the effect of matrix creep using double cantilever beam specimens of CF/PEEK and CF/PMR-15 laminates. The propagation of delamination crack was observed by means of optical microscope and it revealed that the creep accelerated the propagation rate of CF/PEEK in fatigue at 473K while the creep scarcely took place in the tests of CF/PMR-15 at 573K.The experimental results was successfully analyzed on the basis of linear fracture mechanics concept. The tests were also conducted under constant stress intensity factor range in order to examine the shielding effect of fiber bridging. The propagation rate was decelerated as the crack propagated because of the fiber bridging. The micro-morphology of bridging was observed by means of microscopes.The fatigue tests of SiC-whisker reinforced aluminum alloy were carried out at 573K.The focus of this study was put on the observation on the failure life and the cracking morphology in high temperature fatigue. The fatigue life was shortened by creep deformation. Few cracks were observed during the fatigue and one of them, which initiated at the middle stage of life, brought about the failure. As the tensile strength and the creep life of the material at high temperatures was examined by a joint research project (Report on High Temperature Strength of SiC-whisker reinforced aluminum alloy, Society of Materials Science, Japan, 1993), the results obtained in this study were analyzed on the basis of the fundamental data.