Surface fatigue crack propagation behavior in a residual stress field. Fatigue crack growth law and evaluation of fatigue crack propagation rate.

Abstract

Fatigue lives of plain carbon steel with residual stress were studied with special reference to the initiation and the propagation of surface cracks. Tensile residual stresses did not have influences on crack initiation lives, but increased the fatigue crack propagation rate for surface fatigue cracks. The propagation rate of a surface fatigue crack was controlled by the parameter of {(ΔK)0.5(Kmax)0.5} in which ΔK and Kmax were, respectively, the stress intensity factor range and stress intensity factor calculated from the maximum stress distribution containing residual stress measured at the stress cycles of the initiation of surface cracks. This parameter also served to help understand surface fatigue crack shape in a residual stress field. Finally, the equation of (ΔK)p(Kmax)q≒Kmax-p·Kmin was derived under condition of both p+q=1 and minimum stress intensity factor |Kmin|<Kmax, which enabled us to discuss effects of Kmin (<0) on fatigue crack propagation from the point of mechanical behavior of the plastically deformed layer left in the wake of the advancing crack.