Correcting for Residual Stress Effects on Fatigue Crack Growth Measurements: A Validation Study

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 test 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. The present study focused on validating the on-line crack compliance method to support its implementation into standard fatigue tests. Test specimens with well-controlled residual stress states were fabricated and tested. Conventional slitting measurements on duplicate specimens provided preliminary measurements of residual stress on the crack plane and the expected K_res values during fatigue crack growth testing. Constant applied alternating stress intensity factor tests, with the on-line crack compliance analysis technique, provided FCGR data at low growth rates with the corresponding K_res values. Corrections of observed FCGR data using K_res values from slitting and from the on-line crack compliance test method were compared to evaluate the on-line crack compliance method as a reliable means of supplying FCGR data independent of residual stress effects.