Study on bi-variable fatigue damage model of metal components

Constitutive relation of bi-variable damage was introduced. Based on irreversible thermodynamics, damage driving force was introduced and damage evolution criterion was constructed. Furthermore, damage evolution equation of time form and cycle form was constructed. The fatigue life prediction method for smooth specimen under the repeated loading with constant strain amplitude was obtained by the method of variables separation. By the theory of conservative integral in damage mechanics, the fatigue life prediction method for notched specimen under the repeated loading with constant amplitude was obtained by numerical method. Using these methods, the material parameters in the damage evolution equation are obtained by the mean value experimental fatigue lives of standard specimens with K_T=1 and K_T=3. On the basis of above methods, theoritical mean fatigue curves for different values of K_T are drawn. This research provides the possibility for predicting the fatigue lives of structure members through the methodology of damage mechanics.