抄録
Notched specimens of porous silicon carbide with porosity 37% were fatigued under four-point bending at frequencies of 30 and 0.3Hz. The fatigue life expressed in terms of time was rather insensitive to the test frequency, while that expressed in terms of cycles was much shorter for the case of 0.3Hz than for 30Hz. The relation between the load and the compressive strain was recorded at prescribed cycles during fatigue tests. At the beginning of fatigue cycling, the relation between load and strain was linear. As the number of cycles increases, the hysteresis loop moved toward the right side and also expanded. The crack extension from the notch was determined from the compliance change by FEM method. The crack propagation curve was divided into Stages I, II and III. In Stage I, the crack propagation rate decreased even though the applied stress intensity factor got larger with crack extension. The rate was rather constant in Stage II, and then increased in Stage III. This anomalous behavior is caused by crack-tip shielding due to asperity contact and bridging by SiC particles. Fractographic observations showed that the fracture path was along the binder phase between SiC particles, more precisely along the interface between particles and binders.
