Improved damage mechanics method for fatigue life prediction

The stress concentration factor is introduced to modify the fatigue limit and a practical damage evolution equation is established. According to the theory of conservative integral in damage mechanics, the damage coupling effect of stress and strain concentration in notched specimen can be expressed in closed form solution. Then, integrating the damage evolution equation by means of variable separation method, an integral expression of stress-life relation can be established. The material parameters of damage evolution equation are obtained by fatigue curves of standard plane specimens with K_T = 1 and K_T = 3. The correctness of damage evolution equation and the fatigue life prediction method are verified through the results of fatigue experiment with K_T = 5. Hence a practical method to predict the fatigue life of structures can be provided by using damage mechanics. Finally, this method is applied to provide the theoretical fatigue curves for K_T = 4 and K_T = 2.