SHEAR-DRIVEN HIGH-TEMPERATURE FATIGUE-CRACK GROWTH IN POLYCRYSTALLINEALUMINA

High-temperature crack growth behavior of a polycrystalline alumina wa s examined under Mode-I tension-tension cyclic loading. Locally at the crack tip, the fatigue crack was found to advance in shear by frictio nal sliding of grains on alternating sets of planes of the maximum she ar. Evidence of a shear-driven crack growth was given in terms of topo logical and morphological analyses of the fatigue crack surface, grain sliding, frictional debris, and temperature-dependence of fatigue cra ck growth kinetics. Based on experimental observations, a new model of fatigue crack growth by alternating shear was proposed.