A review of crack closure measurement by compliance technique and the normalized-extended ASTM method as a currently most refined, practical and simple one

The intrinsic drawbacks of the standard ASTM compliance offset method for determination of crack opening load is described and the normalized-extended ASTM method as an alternative is introduced and applied to random loading tests on 7475-T7351 aluminum alloy. Fatigue crack growth under random loading is successfully predicted by the effective stress intensity factor range based on the crack opening load determined by the normalized-extended ASTM method. Conclusively, it is strongly recommended to use the normalized-extended ASTM method. It is also found that the crack closure behavior of 7475-T7351 aluminum alloy under random loading is significantly different from that of 2024-T351.