Shear Mode Growth and Threshold of Small Fatigue Cracks in SUJ2 Bearing Steel
Hisao MATSUNAGA, Satoshi MURAMOTO, Naoya SHOMURA and Masahiro ENDO
Abstract:The shear mode propagation and threshold behaviors of small, semi-elliptical fatigue cracks were investigated in the JIS-SUJ2 bearing steel. Fully-reversed torsional loading was combined with a static axial compressive load to obtain crack growth in the longitudinal direction of cylindrical specimens. Non-propagating cracks smaller than ˜1 mm in size were obtained (I) by decreasing the stress amplitude in tests using notched specimens, and (ii) by using smooth specimens in constant stress amplitude tests. The Mode Ⅱ and Mode Ⅲ threshold stress intensity factor ranges, ΔKⅡth and ΔKⅢth, were estimated from the shapes and dimensions of non-propagating cracks. The threshold values decreased with a decrease in crack size, and there was no significant difference between ΔKⅡth and ΔKⅢth. Wear on the crack faces was inferred by a powder and also by changes in microstructure in the wake of a crack. The ΔKⅡth in the absence of interference of crack faces was estimated to be approximately 13 MPa m1/2 for a 1mm long crack Key Words:ΔKⅡth, ΔKⅢth, Shear mode fatigue cracks, Small cracks, Bearing steel, Torsional fatigue test under static axial compressive stress