Precise determination of fatigue crack closure in Al alloys

The crack closure phenomenon is important when evaluating the effective driving force for crack growth. Hence, the precise measurement of the crack closure load is an essential preprequisite for the determination of the effective stress intensity factor range (ΔKeff). In the present investigation, an acoustic emission (AE) technique was employed to measure crack closure during the fatigue cycling of Al alloys and the results are compared with those obtained by the crack opening displacement (COD) method, the back face strain (BFS) gauge method and the surface strain (SS) gauge method. Results show that the intrinsic fatigue crack growth rates (da/dN vs. ΔKeff) obtained by the AE technique gave the best fit for the high stress ratio (R = 0.8) test, which implies that the AE technique should be considered as a reliable crack closure measurement method.