Recent work by the authors have shown that a subcritical surface crack (SC) can transition to a through-wall crack (TWC) with significant differences between the inner diameter (ID) and outer diameter (OD) crack lengths. In the current versions of the xLPR code (Ver. 1.0), an idealized through-wall crack (which has the same area as the final surface crack) is formed once the surface crack penetrates the wall thickness. This type of crack transition was selected since no general stress intensity factor (K) and crack-opening displacement (COD) solutions were available for crack shapes that would form during the transitioning stages, i.e., non-idealized through-wall cracks. However, it has been demonstrated that this idealized through-wall crack may result in an overestimate of the leak rate. Thus, it is necessary to further investigate and develop a model that can handle the surface crack to through-wall crack transition.
In this paper, a surface to through-wall crack transition model was proposed using existing K and COD solutions for non-idealized through-wall cracks. This model includes a criterion for transitioning the final surface crack to the initial non-idealized through-wall crack which determines when the transition should occur (based on surface crack depth) and determines the two crack lengths (at ID and OD surfaces) of the initial non-idealized through-wall crack. Furthermore non-idealized through-wall crack growth can be conducted using the proposed model. Example results (crack shape and COD) obtained from the proposed model were compared to those obtained from the natural crack growth simulations for a circumferential crack. Results presented in this paper demonstrated the applicability of the proposed model for simulating crack transition. Limitation of the present model and plans for future work are also discussed in the paper.
