Cumulative Fatigue Damage: CDM-Based Engineering Rule and Life Prediction Aspect

Cumulative fatigue damage analysis plays a key role in life prediction of elements and structures subjected to field loading histories. A general methodology for fatigue life prediction of metallic materials under variable amplitude loading is proposed in this paper. A novel theory of cumulative fatigue damage is presented. It is based on Continuum Damage Mechanics approach which relates the damage rate to that of cyclic loading through the damage function. A new damage function related to isodamage lines and remaining life aspects is analyzed. The final result is a nonlinear fatigue damage rule. The nonlinear damage accumulation rule proposed in this paper improves the deficiencies inherent in other rules and still maintains its simplicity in the application. The relationship with other formulations is pointed out together with the advantages of the proposed model. A number of fatigue damage rules can be derived as a special case of the model developed herein. A wide range of fatigue data available in the literature as well as from the laboratory are used to validate the proposed rule. The agreement between prediction and experiment is found to be excellent. The prediction results are also compared with existing fatigue rules.