Crack-tip fields under generalized-plane-strain conditions

Abstract

Quantitative determination of crack-tip stress and strain fields under generalized-plane-strain conditions is a necessary first step toward estimating the potential decrease in crack-initiation toughness, from a reference plane strain value, due to positive straining along the crack front of a circumferential flaw in a reactor pressure vessel. Two methods for estimating the stress and strain fields within a distance of a few crack-tip-opening displacements ahead of a two-dimensional crack front under generalized-plane-strain conditions are summarized in this study. The first method requires little computational effort and involves an analytical description of the near-crack-tip region based on generalized-plane-strain slip-line equations. The second method requires much greater computational effort and involves a finite-strain, boundary-layer description of the near-crack-tip region based on the finite element method. The scope of the investigation described here is limited to crack-front-constraint conditions that can be described in terms of the conventional one-parameter in-plane K-fields and the transverse strain. Results from this study indicate that crack-tip fields determined using the slip-line approach compare favorably with those determined using the finite element method. Implications of these results toward crack initiation under generalized-plane-strain conditions are discussed.