A New Fatigue Life Prediction Model for Variable Amplitude Loading

摘要

A cumulative fatigue damage model for metals subjected to variable amplitude loading is presented. The model is based on the observed crack-closure behaviour of short fatigue cracks in cyclically loaded fatigue specimens. A damage parameter that accounts for the effects of mean stress and overloads on damage accumulation especially for cycles below the constant amplitude fatigue limit is developed. The damage parameter takes the form: Etriangle openepsilon, where E is the elastic modulus and triangle openepsilon is an effective strain range. The material resistance to fatigue is represented by a simple expression of the form: Etriangle openepsilon, where E is the elastic modulsu and triangle openepsilon is an effective strain range. The material resistance to fatigue is represented by a simple expression of the form: Etriangle openepsilon = A (N_f)~b where A and b are material constants and N_f is the number of cycles to failure. The model is incorporated into existing computer software for fatigue analysis and is shown to give very good life predictions for axial coupons subjected to variable amplitude service strain histories.