Proposal of modified (normalized) ASTM offset method for determination of fatigue crack opening load

For determination of crack opening load, a modified ASTM compliance offset method called the normalized ASTM offset method is proposed, which utilizes the relative compliance offset normalized by the maximum offset obtained by the ASTM offset method. The normalized ASTM offset method is evaluated in a quantitative manner for the conventional ΔKeff estimation and also for the 2/π(2/PI) ΔKeff estimation method proposed by Paris et al. The normalized ASTM offset method improves remarkably correlation of crack growth rate stress ratio effects, in comparison with the ASTM offset method. Quantitative evaluation results indicate that the normalized ASTM offset method is very promising as a precise, simple and practical Kop determination method alternative to the ASTM method, and also the use of the 2/PI (ΔKeff) estimation method is recommended.