A unification of small- and large-crack growth laws

A generalized model enhancement is proposed to link small- and large-crack growth laws. The enhancement is based on crack growth rate laws with crack tip plastic zone size formulations. Transition functions are used to transf orm small-crack plastic zone sizes and crack growth law exponents to those predicted by linear-elastic fracture mechanics. In doing so, influences on crack growth, e.g. constraint, crack aspect ratio and specimen geometry are accounted for. The applicability of the enhancement is directed toward ins tances where small cracks start from geometric features and grow through st ress gradients to eventually become large cracks under nominal LEFM conditi ons. The enhancement is applied to the Wang model, and crack growth rate an d fatigue lifetime predictions are made. The enhancement is shown to provid e a good correlation to experimental results for Ti-6AL-4V under various ma ximum stresses at a stress ratio of R = 0.4.