Shaping exponent in wheeler model under a single overload

Abstract A process was proposed in this study to calibrate the Wheeler m-exponent by fitting the number of delay cycles in a single overload test. A formula was also provided to determine the plastic zone size constant α, by employing the overload affected crack length. The number of delay cycles and the overload affected crack length are two main experimental parameters of the single overload test. This process was performed for 5083-O and 6061-T651 aluminium alloys, respectively, so as to investigate the behaviour of the exponent at various overload ratios and initial crack lengths. The m-value was found to be dependent on materials, overload ratios and initial crack lengths; in addition, its ranges extended from 0.94 to 2.19 for 5083-O and from 1.36 to 1.98 for 6061-T651. For both of these materials, the regressions m and α were established with respect to the overload ratio and initial crack length. By applying these regressions, the Wheeler predictions for the retarded crack growth after a single overload were found to sufficiently correlate with the experimental results.