Interior microscopic cracking behavior and microstructure-fatigue based damage evaluation of case-hardened steels under variable amplitude loading

Abstract Variable amplitude loading tests were performed to clarify the interior cracking behavior for three case-hardened steels under stress ratios in high-cycle and very-high-cycle regimes, and to develop a microstructure-fatigue based damage evaluation approach. The round beach marks are observable within fisheye, and the fine granular area is more obvious under compressive stress. The microcrack effect is responsible for fatigue cracking in very-high-cycle regime. The approach mainly involves: (i) definition of remaining life factor, (ii) conversion of correlation function and (iii) reconstruction of stress-life curve with failure behavior. The agreement between predicted and experimental results is good within factor-of-two boundaries.