Quantifying and Correcting for Residual Stress Effects on Fatigue Crack Growth Rate Measurements

Fatigue crack growth rate (FCGR) test data play a critical role in the design and reliability of engineering structural components. However, residual stress, a common side effect of many manufacturing techniques, can significantly impact the fatigue crack growth rates observed in standard tests. The on-line crack compliance method is an emerging analysis technique that quantifies the stress intensity factor caused by residual stress in FCGR test specimens. The measured residual stress intensity factor, K_res, can then be used to correct the observed FCGR data to more useful values that are free of the influence of residual stress. In the present study, Al7050-T74 specimens with well-controlled residual stress states were fabricated and tested. Constant applied alternating stress intensity factor and increasing applied alternating stress intensity factor tests provided FCGR data. Corresponding K_res values enabled the effects of residual stress on the FCGR data to be removed, and the corrected data to be compared to FCGR behavior of stress relieved Al7050-T7451.