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

This paper presents new elastic and elastic-plastic finite element solution s of the J-integral for a pipe containing off-center through-wall cracks un der pure bending. The analysis is based on a three-dimensional nonlinear fi nite 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 resu lts from these analyses show that the J-integral values at the two crack fr onts of an off-center crack are unequal due to the loss of symmetry with re spect to the bending plane of the pipe. In addition, the J-integral is larg er, and hence, critical at the crack front which is farther away from the b ending 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 fro nt, the J values can be lower or slightly higher than those of a symmetrica lly 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 alway s 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 fini te element solutions, new analytical expressions of J-integral were develop ed for fracture analysis of pipes containing off-center cracks. (C) 2000 El sevier Science Ltd. All rights reserved.