Fast ductile fracture: Effect of inertia on propagation resistance and CTOA in pipe steels

In this paper, the effect of inertia on the steady-state velocity of propagating cracks in modern high toughness pipeline steel was investigated. The steel grades examined in this work were American Petroleum Institute Standard X70 and X100. A tensile plate model, simplified from the geometry of a pipe, was studied using the finite element code ABAQUS 6.14-2. The cohesive zone model (CZM) was used to simulate crack propagation. The CZM parameters were calibrated based on matching the crack tip opening angle (CTOA) measured from a drop-weight tear test (DWTT) finite element model to the experimental CTOA of the material. The CZM parameters were then applied to the tensile plate model. The effect of inertia on the steady-state crack velocity was systematically assessed by altering the density of the material used with the plate model. To isolate the influence of inertia, the effect of strain rate on the fracture process and material hardening was neglected and the CZM parameters were assumed constant. It was found that the steady-state crack velocity decreased with increasing mass density; this is consistent with the effect of backfill in pipeline burst tests. The CTOA extracted from the FE model was not affected by the density.