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

•Back-face strain is suitable for measuring deformation in the OLCC method.•Multiple OLCC data analysis methods are appropriate for determining Kres.•Comparison to slitting results validated the OLCC method.•A data analysis method based on an influence function was chosen for best practice.•Limitations are present due to plasticity effects in the remaining ligament. 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, Kres, 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 Kres as a function of crack size. The OLCC method quantifies Kres 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 Kres during fatigue crack growth rate testing.