アルミナ粒子強化複合材料のモードI表面き裂の進展に及ぼす第二主応力の影響

概要

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Using a plate made of A2017-T6 metal matrix composites reinforced with 10 vol. % and 20 vol. % Al_2O_3 particles, crack propagation rate da/dN of a mode I suface crack by the simultaneous action of plane bending and cyclic torsion is sought. And the effects of crack tip opening stress σ_<top>, crack opening displacement COD and biaxial stress ratio C on da/dN are examined. When ⊿K is lower than the peculiar level, da/dN decreases with the increase of volume fraction of Al_2O_3 in C=0 and C=-0.55. But da/dN of Al alloy becomes minimum in C=-1 and the effect of Al_2O_3 particles disappears. σ_<top> increases with Al_2O_3 particles and the decrease of C. On the other hand, COD not always increases with the decrease of C. These phenomena can be explained by the residual compressive stress formed at the surface layer of the specimen by the fatigue test and the surface roughness of crack section.
1999-03-25