Si-Ti-C-O系繊維強化アルミニウム複合材の疲労挙動とき裂進展特性

The push-pull fatigue test and crack propagation tests were performed on aluminum-metal-matrix/continuous Si-Ti-C-O fiber composites. The fatigue behaviour of a smooth cylindrical specimen reinforced with longitudinally directed fibers and fatigue crack growth behaviour of a C.T. specimen reinforced with transversely directed fibers were then examined. The fatigue strength of the composites at the life of Nf=107 cycles was about twelve and one-half times that of the matrix metal. This is slightly higher than that of the static tensile strength ratio of either materials. The crack growth rate, da/dN, plotted against stress intensity factor range, ΔK, forms a linear line on a double logarithmic scale, which depends on stress ratio. The stress-ratio-dependent threshold stress intensity factor range, ΔKth, was also recognized. The stress-ratio-dependence of the crack growth rate becomes slight in the low stress intensity regime, and remains slight in the high stress intensity regime when da/dN is plotted against the effective stress intensity factor range, ΔKeff. The energy release rate, ΔK2/E, may be an effective fracture mechanics parameter controlling the crack growth rates of both the composites and matrix metal.