Fractographic Analysis of the Crack Growth Rate and the Shear Lip Development of 2024-T3 Speciments under Simple Variable-Amplitude Loading

摘要

The purpose of the present investigation is to study sequence effects on fatigue crack growth under variable amplitude (VA) load histories. The crack surfaces of 2024 sheet materials obtained in fatigue tests under two simple VA load sequences were studied under the electron microscopes (TEM and SEM). Phenomena, like the giant striation induced by the first overload cycle, the delayed retardation after applying overload(s) etc., were observed and evaluated. The crack growth rates during and after the overload(s) and underload(s) were measured and compared with the predictions. Possible effects of the shear lip width on the crack growth were estimated by new crack growth data. Comparisons between the test results and the CA data obtained with the corresponding shear lip width were provided.