New concept on fatigue crack growth characteristics under combined stress conditions

Using thin walled cylindrical specimens subjected cyclic tension and torsion, fatigue crack growth tests under combined stress conditions were carried out. The characteristics of the fatigue crack growth rate (FCGR) and morphology of the fatigue crack were identified.By comparing the experimental results with the results of finite element analyses, it was found that the experimental characteristics of FCGR were related to fatigue damage accumulation before initial crack growth. Damage mechanics approach is indispensable to characterize the fatigue crack growth under combined stress conditions.