Fracture Toughness Evaluation of High Strength Steel Pipe

Abstract

Stress fields and constraint parameters (Q and A2) of circumferentially-cracked high strength pipe in displacement-controlled tension are compared with those of small-scale single-edge notched samples tested in tension (SE(T)) and bending (SE(B)). The factors affecting transferability of fracture toughness (J-resistance) data from small-scale laboratory tests to cracked high strength pipe are discussed. The crack-tip stress field is of similar form for a circumferential crack in a pipe and a SE(T) test specimen, while for a SE(B) specimen there is a significant gradient in the crack-tip stress field. Hence, the fracture toughness can be characterized by only two parameters (J and Q or J and A2) for tension-loaded pipe and SE(T) tests, but for SE(B) tests one more parameter is needed to describe the bending term. It is concluded that the constraint in a SE(T) test with ratio of span between load points to width H/W = 10 provides a reasonable match to that for a circumferential crack in a pipe subjected to tensile loading.