Numerical simulation of ductile fracture in pipeline steels under bending and tensile loading conditions

In this paper, the effect of loading mode, and the resulting crack tip constraint, on the crack tip opening angle (CTOA) was investigated. This was achieved through a comparative analysis of a standard drop weight tear test (DWTT) specimen, and a variation whereby it is placed in a tensile loading mode. The tensile loading mode is similar to that of a clamped single edge notch tensile (SENT) specimen. Both models are examined under a quasi-static loading rate. In all analyses the same materials were used, namely, API standard X70 and X100 pipeline steels. A cohesive zone model (CZM) was used to simulate ductile fracture, and it was assumed that the cohesive parameters were constant for both loading modes. The results show that there is a weak dependence of the CTOA on the loading mode. Moreover, this work reinforces the notion of the transferability of the CTOA from the DWTT (bending) to a more representative loading mode for pipeline applications (tensile).