CONSTRAINT-BASED FAILURE ASSESSMENT OF COPLANAR CRACKS IN PLATES AND PIPES UNDER TENSION

Abstract

Detailed numerical investigations in this study found a plasticity-induced over-constraining effect on coplanar cracks in plates and pipes under tension. This over-constraining effect increases with increasing load level, biaxial stress and material hardening exponent. Using crack driving force of coplanar cracks could not account for this constraining effect hence underestimates the stresses near the coplanar crack fronts. A crack interaction factor is proposed by considering directly the change in near-tip stress field caused by the presence of an adjacent crack, and thus incorporates the variation on the high-order terms in the near-tip stress solution. The existing failure assessment diagram relies on the leading term characterizing the near-tip stress solutions, and ignores geometry or plasticity-induced constraint variations. A modified J solution is calculated based on the proposed crack interaction factor and integrated into the failure assessment procedure using the failure assessment curve in BS7910 engineering standard.