Determination method of equivalent initial flaw size for crack initiated at hole chamfering

Cracks often initiate at the chamfering for sagging holes. The initial fatigue quality (IFQ) of this type of crack needs to be determined prior to economic life assessment. Firstly, finite element models with and without chamfering are developed so as to investigate the effect of chamfering on the stress intensity factors at the crack front. The results show that the chamfering imposes great influence on the stress intensity factors of relatively small crack. Secondly, in order to characterize the IFQ of sagging holes, a circular-front crack initiated at the intersection of the chamfering and specimen surface is taken as the initial flaw, with the radial distance of crack front from the initiation site as the crack size. Finally, the crack growth equation for relatively small cracks is employed to characterize the crack growth behavior, and the equivalent initial flaw size (EIFS) distribution is obtained through back-extrapolation. Statistical analyses show that the EIFS distribution parameters obtained by using the proposed crack size definition are independent of stress levels.