Improvement of ASTM compliance offset method for precise determination of crack opening load

There are two serious drawbacks to the ASTM offset method for determination of crack opening load, discontinuity and inconsistency problems. The former is the lack of opening load value in the lower 5% load range due to the procedure that the compliance offset is plotted against the mean load of the segment span of 10% of the cyclic load range. The latter is that the ASTM method underestimates, estimates accurately, or overestimates the opening load, depending on the maximum compliance offset value and the stress ratio. To overcome the two drawbacks, the so-called normalized-extended ASTM method is proposed and evaluated quantitatively in detail using the data of 7475-T7351 and 2024-T351 aluminum alloys. The normalized-extended ASTM method improves the standard ASTM method significantly and provides very good correlation of crack growth rate stress ratio effects. The normalized-extended ASTM method is strongly recommended for crack opening load determination.