Experimental validation of relationship between fracture parameters J and CTOD for SE(B) and SE(T) specimens during ductile crack growth

Abstract

In structural assessments, the crack driving force is usually estimated numerically based on the \(J\)-Integral definition because its determination is well established in many finite element codes. The nuclear industry has extensive fracture toughness data expressed in terms of \(J\)-Integral and huge experience with its applications and limitations. On the other hand, the material fracture toughness is typically measured by CTOD parameter using the plastic hinge model or double-clip gauge technique. The parameter CTOD has a wide acceptance in the Oil and Gas Industry (OGI). Also, the OGI has a lot of past data expressed in terms of CTOD, and the people involved are very familiar with this parameter. Furthermore, CTOD parameter is based on the physical deformation of the crack faces and can be visualized and understood in an easy way. There is a unique relationship between \(J\) and CTOD beyond the validity limits of linear elastic fracture mechanics for stationary cracks. However, if ductile crack propagation happens, the crack tip deformation profile and stress–strain fields ahead of the crack tip will change significantly when compared to the static case. Thus, the stable crack propagation may change the well-established relationship between \(J\) and CTOD for stationary cracks compromising the construction of resistance curves \(J\)-\(\Delta a\) from CTOD-\(\Delta a\) data or vice versa. A search in the open literature was undertaken to get experimental measurements of \(J\)-Integral and CTOD data including ductile crack growth. Then, using theoretical relations developed in previous work, predictions for CTOD values from \(J\) values are performed and directly compared with the experimental values. The present results provide additional understanding of the effects of ductile crack growth on the relationship between \(J\)-Integral and CTOD for standard fracture specimens. Specific procedures for the evaluation of CTOD-R curves using SE(T) and SE(B) specimens are proposed.