The Effect of Pressure induced Hoop Stress on Bi-axially Loaded Through wall Cracked Cylindrical Structures - A Strain Based Method

This paper presents a simplified strain-based fracture mechanics approach to study the effect of pressure induced hoop stress on bi-axially loaded through walled cracked (TWC) pipes subjected to an external bending load in combination with internal pressure. Elastic-plastic finite element analyses are conducted to establish the relation between global strain and Crack tip opening displacement (CTOD). In the finite element model X65 pipeline steel is considered using power-law idealization of stress-strain, and the inelastic deformations, including ductile tearing effects, are accounted for by use of the Gurson-Tvergaard-Needleman model. Several parameters are taken into account, such as crack length, internal pressure and material hardening. Strain based crack driving force equation is used and maximum load criterion is adopted to determine the critical strain from ductile tearing in the cracked pipeline. The results suggest that presence of pressure-induced hoop stresses increases the fracture response in high-hardening materials and their effects are significant due to large plastic-zone size.