Elastic-Plastic Fracture of Cylindrical Shells Containing a Part-Through Circumferential Crack

Abstract

In this paper the problem of fatigue crack propagation and ductile fracture of a cylindrical shell containing a macroscopic circumferential flaw is considered. The main interest in the study is in applications to line pipes and other cylindrical containers under secondary axial stresses in addition to the primary stresses coming from the internal pressure. The stress intensity factor for the part-through crack used in analyzing and correlating the fatigue crack propagation rate is obtained by using a line spring model in conjunction with Reissner’s shell theory. To analyze the ductile fracture instability and to correlate the experimental and theoretical results, the crack mouth opening displacement is used as the parameter. The experiments were performed on 20-in-dia (o.d.) and 0.34-in-thick X60 steel pipes. A 0.025-in-wide part-through circumferential flaw was introduced into the pipes as a crack starter which were then tested under four-point bending. The limited data on fatigue crack propagation give the expected result, namely that the crack propagation rate in pipes may be predicted from the fatigue results performed on simpler geometries provided the stress intensity factors in pipes are calculated with sufficient accuracy. The ductile fracture results show that the technique based on the asymptotic behavior of COD may be quite useful to determine a conservative estimate of the fracture instability load.