Damage Proportion Analysis of the Combined High and Low Cycle Fatigue Based on the Continuum Damage Mechanics

A combined high and low cycle fatigue (CCF) life prediction model, considering creep, low-cycle fatigue (LCF), high-cycle fatigue (HCF) at the maximum LCF nominal stress (HLCF) damages, and the interaction damage between LCF and HLCF, is proposed. The proportions for these four types of damage in total CCF damage are quantified. Compared with the existing CCF models, the CCF model proposed in this paper considers creep damage in CCF and has higher accuracy. The escalation in HCF stress amplitudes leads to reduced CCF life owing to the augmentation of HLCF and interaction damages. The increase in the cycle ratio of HCF to LCF, causing a reduction in CCF life is ascribed to elevated HLCF and creep damages. The calculated damage proportion results from the proposed model are consistent with the observations of the fracture characteristics using a scanning electron microscope (SEM), indicating the necessity of considering creep damage in CCF life prediction at high temperatures.