Validation of on-line crack compliance data analysis methods for the residual stress intensity factor

Residual stress can significantly impact the fatigue crack growth rate (FCGR) observed in standard tests. In the present study, implementation of the on-line crack compliance (OLCC) method for determining the residual stress intensity factor, K-res, in FCGR tests is supported by validation data, details of novel data analysis methods, and strategies for data reduction. Slitting measurements on C(T) specimens of quenched (but not stress relieved) and aged aluminum alloy 7050-T74 provide reference profiles of K-res as a function of crack size. The OLCC method quantifies K-res profiles from stress intensity factor control and load control FCGR tests over a range of residual stress states. Novel OLCC data reduction techniques are developed, and data analysis attributes and limitations explored, contributing to an improved methodology for standardization. The results demonstrate that the on-line crack compliance method is a valid means of quantifying K-res during fatigue crack growth rate testing.