Experimental and Numerical Investigation on Ductile Fracture of Steel Pipelines

Abstract

Rupture of steel pipelines leads to the loss-of-containment that may be accompanied with loss of life or damage to property and environment. Therefore, the understanding of the fracture characteristics of steel grades used in the pipelines is essential for a safe and reliable design. In this study, a set of small-scale fracture tests was designed and conducted in order to characterize the fracture of X65 steel grade. The experimental results show that not only is the fracture strain dependent on the triaxial stress condition but also the three-dimensional nature of the stress field considerably affects the ductile fracture toughness. Moreover, parallel finite element (FE) simulation of experiments were conducted and a hybrid experimental–numerical approach was used to calibrate the Mohr–Coulomb fracture criterion and obtain the equivalent plastic strain to fracture of X65 steel as a three-dimensional function of stress triaxiality and Lode angle. An engineering application friendly ductile fracture model is proposed for X65 steel pipelines.