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 ‡U and Mode ‡V threshold stress intensity factor ranges, ƒ¢K‡Uth and ƒ¢K‡Vth, 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 ƒ¢K‡Uth and ƒ¢K‡Vth. Wear on the crack faces was inferred by a powder and also by changes in microstructure in the wake of a crack. The ƒ¢K‡Uth in the absence of interference of crack faces was estimated to be approximately 13 MPa m1/2 for a 1mm long crack Key Words:ƒ¢K‡Uth, ƒ¢K‡Vth, Shear mode fatigue cracks, Small cracks, Bearing steel, Torsional fatigue test under static axial compressive stress