Effect of crack closure in a specially-orthotropic cylindrical shell containing an axial or a circumferential crack

This article presents a theoretical analysis of the crack-face closure behaviors of an axial or a circumferential crack in a specially orthotropic cylindrical shell, emphasizing the influence of material orthotropy on crack-tip stress field. The shallow shell theory developed by Delale and Erdogan is extended to incorporate the effect of crack-face closure. In the present analysis the crack-face closure is modeled by a line contact at the compressive edges of the crack faces. The unknown contact force is then computed by solving a mixed-boundary value problem iteratively to ensure that either the normal displacement of the crack face at the compressive edges equals zero or the contact pressure equals zero along the crack length. The results show that the curvature effect causes the closure behavior in cylindrical shells to differ considerably from that in flat plates. Instead of complete closure over the entire crack length in flat plates, only partial closure occurs along the crack length in shells with large curvatures. Material orthotropy is also found to strongly influence the closure behavior of an axial crack but not that of a circumferential crack. In both cases the crack closure is found to reduce the maximum stress intensity factors, which is the most pronounced for shells with large radii for a given crack length and shell thickness.