Mode II surface crack growth under rolling contact fatigue and cyclic shear stress in Si_3N_4

摘要

The effects of friction on surface crack growth behavior from pre-indentations of HIP-Si3N4 were investigated under rolling contact fatigue (RCF). 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 friction promoted surface crack growth and the cracks grew in mode II by shear stress (ΔK_(II) = 3.6 MPam~(1/2), K_(II max) = 1.8 MPam~(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. We found the features concerning Mode II crack growth: 1) The cracks grew by cyclic shear stress in Mode II (initial value of ΔK_(II) is 3.0 MPam~(1/2)); 2) Under the same ΔK_(II)= 3.0 MPam~(1/2), the cracks grow more when K_(II max) = 3.0 MPam~(1/2) (R = 0) than when K_(II max) = 1.5 (R =-1). Comparing the features of mode II crack growth obtained from the crack propagation tests under cyclic shear stress and the RCF cracks, we conclude that the increase in values of stress intensity factors of mode II explains that the cracks under frictional contact are promoted by friction.