A fatigue model based on M-integral in notched elastic–plastic material

Abstract

In this paper, an innovative fatigue model is investigated based on the concept of M-integral in notched elastic–plastic material. The contribution of notch and plastic zone damage to the lifetime of material are taken into account in the present fatigue model. The new form of fatigue damage evolution rate (dAD/dN) and fatigue driving force (ΔM) are introduced, where AD deontes the equivalent damage area of notch, plastic zone and cracks, N is the number of cycles, and ΔM corresponds to the M-integral range per load cycle. The fatigue experimental evaluations of a typically elastic–plastic material (e.g., No. 45 steel) with a circular notch have been carried out to validate the effectiveness of the present fatigue model. For experimental study, the change of the total potential energy (CTPE) is introduced to measure the value of M-integral. The results demonstrate that dAD/dN shows an apparent power law relation with ΔM in notched elastic–plastic material. The slope n and intercept λ of lg(dAD/dN)-lg(ΔM) curve has linear correlation with the initial notch radius R, but not with applied stress σ. Moreover, the model can clearly describe the two-stage process from the initiation of microcracks to the growth of macrocracks in notched body. It is concluded that the proposed fatigue model based on M-integral can accurately predict the fatigue lifetime of the notched elastic–plastic material.