窒化けい素のせん断応力下におけるき裂進展挙動と転がり疲労下におけるき裂進展挙動

モードIIで進展する表面き裂の特徴

抄録

Surface crack growth behavior from pre-indentations of HIP-Si₃N₄ was observed under Rolling contact fatigue (RCF), and also under cyclic shear load. Near surface contact stress distributions were calculated by Hanson's analytical method, and the crack growth behavior was discussed in terms of stress intensity factors under rolling contact fatigue. It was found that the cracks grew in Mode II by shear stress (ΔK_II=3.0MPa·m^1/2, K_IImax= 1.5MPa·m^1/2 stress ratio R=-1). In order to confirm the effects of shear stress on surface crack growth, crack propagation tests under cyclic shear stress were carried out when the ΔK_II=2.4MPa·m^1/2 was lower than that of RCF. We found the following three features concerning Mode II crack growth. (1) The cracks grew by cyclic shear stress in Mode II (ΔK_II=2.4MPa·m^1/2). (2) Under the same ΔK_II=2.4MPa·m^1/2, the cracks grow more when K_{II max}=2.4 MPa·m^1/2 (R=0) than when K_IImax=1.2 (R=-1), (3) The cracks tend to stop growing when ΔK_II is lower than 1.2 MPa·m^1/2 (R=0). Comparing the features of Mode II crack growth obtained from the torsion fatigue tests and the RCF cracks, we conclude that the surface cracks are propagated in mode II (ΔK_II=3.0 MPa·m^1/2) under rolling contact fatigue.