Numerical Investigation of Ductile Crack Propagation of Circumferentially Cracked Pipes Subjected to Multiaxial Loading at Room and Low Temperatures

Failure in pipes containing an initial crack under multi-axial loading condition is of common occurrence in industry and engineering applications. Current fitness-for-service codes and design standards cover partially part of this complex type of failure mode where the stress states may change abruptly from one state to another due to the combinatory nature of the applied loads. However, the torsional moment is mostly disregarded in the analysis for being apparently negligible in front of the bending moment and axial force, whose combined effects on crack-tip stress-strain fields have been very well investigated in the past. Based on recent research efforts to understand its effect, it has found that torsion in combination with axial force and bending moment, in fact, increases structural strength and delay fracture propagation, whose intensity varies depending on the crack configurations. Inspired by previous observations, this work takes a step forward in understanding effects of combined torsion with bending and axial force under harsh environments such as low temperature levels. A comprehensive numerical investigation is carried out using a newly developed constitutive model to describe failure at low temperatures on multi-axially loaded cracked pipes made of 316L stainless steel. Kinetic phase transformation and temperature dependent fracture criterion are implemented to accurately capture mechanical response at different temperature levels. Even though, experimental observations of these simulations were not available, their outcomes were quite consistent with some already published results performed on similar materials and loading conditions.