Physically short fatigue crack growth from notch described by plasticity-corrected stress intensity factor

Abstract

When a physically short fatigue crack propagates from a notch root, the crack growth rate shows a “V-shaped” behavior; i.e., the rate firstly decreases and then increases as the crack propagates. In this study, a plasticity-corrected stress intensity factor (PC-SIF) is applied to describe the effects of both notch's plastic zone and crack-tip's plastic zone in ductile materials under cyclic loading. Experiments in previous study for disk-shaped compact tension (CT) specimens made of 1070 steel with different notch sizes and load ratios, as well as single-edged specimens made of low-carbon steel with U-shaped notches, are examined by numerical analysis in present paper. The V-shaped curves of fatigue crack growth data can be summarized by straight lines if the PC-SIF range is applied which considers the influence of plastic zone near the notch roots. The plastic zone near the notch root plays an important role in the V-shaped behavior for the physically fatigue short crack, and the evolution of the plastic zone is discussed in detail. The ratio of PC-SIF range to the stress intensity factor (SIF) range was fitted by the power functions and the fitting expressions before and after the turning point of the V-shaped curve exhibit a significant difference.