多孔質セラミックスの疲労破壊に及ぼす切欠きの影響

概要

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Smooth specimens, semi-circular notched and V-notched specimens of porous silicon carbide with porosity of 35% were fatigued under cyclic four-point bending at a stress ratio of 0.1. The reduction of the fatigue strength due to notches can be estimated from the reduction of the crack initiation stress in static bending fracture tests. The crack propagation curve in V-notched specimens 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 crack propagation rate was nearly constant in stage II, and then increased in stage III. The anomalous behavior in stages I and II was caused by crack-tip shielding due to microcracking and asperity contact, while the crack tip shielding was minimal in stage III. For the case of semi-circular notched specimens, stage I was followed by stage III without stage II. The crack length at the end of stage I took a constant value of about 0.068mm for semi-circular notched specimens and 0.12mm for V-notched specimens. The stress intensity factor at the onset of unstable fracture was about 1 MPa・m^<1/2> for both types of notched specimens.
2005-09-25