Construction of J-R curve for X80 steel based on constraint level

Since the constraint level at crack tip is lower in pipeline cracks, the results of fracture assessment for pipelines are conservative by adopting the J-R curves determined by the traditional single edge bend specimens and compact tension specimens. In this paper, we investigated the effect of crack depth on the J-R curve by adopting the single notch tension specimen with different crack depths. Based on finite element analyses, we calculated the constraint of crack tip for single notch tension specimens with different crack depths. The J-R curve constructed based on the constraint level at the crack tip can accurately characterize the J-R curve for cracks in X80 pipeline steel.