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Languages : en
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Book Description
Cyclic tension-tension experiments were conducted on a ceramic matrix composite of continuous Nicalon SiC-fibers in a calcium-aluminosilicate matrix. Two different stress ratios (R = sigma(min)/sigma(max)) were studied (R = 0.5 and R = 0.05) at a loading frequency of 200 Hz. Specimens tested at R = 0.05 were found to have a shorter fatigue life than specimens tested at R = 0.5. The fatigue limit (defined as run-out at 10(exp 8) cycles) increased from 212 MPa for R = 0.05 to 240 MPa for R = 0.5. Microstructural investigations revealed an internal zone with no fiber pull-out at the fracture surface, suggesting that the fatigue failures occur due to internal embrittlement. The loading condition with smallest stress range (i.e., the largest stress ratio) has the lowest amount of interfacial sliding (and thus the lowest frictional energy dissipation). It is therefore plausible that the fatigue damage is related to the amount of interfacial sliding.