Fatigue Crack Propagation of Al Alloy 2017-T4 under Mixed Mode of Modes I and III and Modes I, II and III

摘要

Fatigue crack propagation behavior under the mixed-mode condition which combined modes I and III and modes I, II and III was investigated in a push-pull fatigue test of notched specimen. The notch inclined in the thickness direction was cut at the center of the specimen. Four values were selected for the notch length 2b, that is, 2b=9,15, 25, 35 mm. In the present study, the crack propagation behavior under the mixed modes is assumed to be dominated by the maximum principal stress criterion. The stress intensity factor K_p of mode I was calculated with the projected crack length along the load direction and the crack propagation rate da/dN under the mixed modes was evaluated using it. This stress intensity factor K_p can approximate relatively well the stress intensity factor determined on the basis of the maximum principal stress criterion in the case of the specimen used in the present experiment. The crack propagation rate da/dN can reasonably be evaluated with the effective stress intensity factor range of K_p independent of the applied mean stress.