New concept on fatigue crack growth characteristics under combined stress conditions

Using thin walled cylindrical specimens subjected cyclic tension and torsio n, fatigue crack growth tests under combined stress conditions were carried out. The characteristics of the fatigue crack growth rate (FCGR) and morph ology of the fatigue crack were identified. By comparing the experimental results with the results of finite element an alyses, it was found that the experimental characteristics of FCGR were rel ated to fatigue damage accumulation before initial crack growth. Damage mec hanics approach is indispensable to characterize the fatigue crack growth u nder combined stress conditions.