An experimental failure model based on triaxiality factor and Lode angle for X-100 pipeline steel

X-100 steel is one of the most recently developed materials for production of gas transportation pipelines. In order to extract the failure properties of this material a series of experiments on smooth and notched round bars with different notch radius and flat notched specimens with different notch radius and notch depth in tension are done. Whereas this material is severely anisotropic (Lanckford ratio around 0.5), specimens are cut in different directions within the plane of rolling. Lode angle, which is a recently introduced parameter in the fracture of ductile materials and contains the effect of third invariant of deviatoric stress tensor, along with triaxiality factor, showing the effect of hydrostatic stress, are studied in the fracture of this material. The load-displacement curves and pictures taken by 2 photo camera are used to study the effects of anisotropy, triaxiality factor and Lode angle on the failure of this material. Finally an experimental failure criterion is developed to model the failure of this material. In this failure criterion, strain at fracture initiation is a function of X and TF. Models that take into account the effect of Lode angle, Triaxiality factor and anisotropy in plasticity and damage are the current state of the art in the research of ductile materials.