Abstract
A modified linear-elastic method of analysis was proposed for the estimation of fatigue lifetimes of biaxially loaded components containing cracks. The following constitutive relation was used as a basis for the analysis: (da)/(dN)=A(ΔK_<eff>-ΔK_<effth>)^2 where a is the half crack length, N is the number of cycles, A is a material constant, ΔK_<eff> is the effective range of the stress intensity factor (SIF) given by K_<max>-K_<op>, where K_<max> is the maximum value of SIF and K_<op> is the SIF at the crack opening level; and ΔK_<effth> is the effective range of the SIF at the threshold level. A modified LEFM approach was used in the analysis. The modifications included a correction for elastic-plastic behavior, consideration of Kitagawa effect, and consideration of the development of crack closure in the wake of a newly formed crack. An analysis was made using the proposed method of the da/dN data obtained by Brown and Miller for different biaxial stress states. The effects of stress ratio were also investigated. It was found that the difference in elastic-plastic behavior and effects of stress ratio accounted for the effect of biaxial stress on da/dN.
