Unloading compliance correlations for throughwall circumferentially cracked elbow to measure crack growth during fracture tests

The unloading compliance technique is very commonly used to measure crack growth during fracture experiment. The pre-requisite of this technique is an equation correlating crack length with unloading compliance. Such correlations are easily available for small specimens. But no such correlation exists for elbows. Unlike conventional geometries, elbow cross section ovalises during deformation which makes the problem non-linear. Considering these complexities, new compliance correlations are proposed based on non-linear FEA for throughwall circumferentially cracked elbow under in-plane bending moment. The proposed correlations are expressed in terms of normalized parameters to make them independent of specific values of geometric dimensions.