Elastic–plastic analysis of off-center cracks in cylindrical structures

Abstract

This paper presents new elastic and elastic–plastic finite element solutions of the J-integral for a pipe containing off-center through-wall cracks under pure bending. The analysis is based on a three-dimensional nonlinear finite element method and small-strain theory. One hundred and five analyses were performed using the ABAQUS commercial code for a wide variety of crack sizes, off-center crack angles, and material hardening exponents. The results from these analyses show that the J-integral values at the two crack fronts of an off-center crack are unequal due to the loss of symmetry with respect to the bending plane of the pipe. In addition, the J-integral is larger, and hence, critical at the crack front which is farther away from the bending axis of the pipe. This is because, at that crack front, the tensile stress is larger and the component of the applied bending moment about the crack centerline has a further crack-opening effect. Also at this crack front, the J values can be lower or slightly higher than those of a symmetrically centered crack, depending on the crack size and off-centered angle. For the crack front that is closer to the bending axis, the J values are always lower than those of a symmetrically centered crack. This implies that the load-carrying capacity of a pipe is usually larger for an off-center crack than that for a symmetrically centered crack. Finally, based on these finite element solutions, new analytical expressions of J-integral were developed for fracture analysis of pipes containing off-center cracks.