Plastic deformation and fracture behavior of X65 pipeline steel: Experiments and modeling

Abstract

In order to respond to the increasing demand of oil and gas, pipeline steel has been noticeably developed to enhance both efficiency and performance of fuel transportation. Hereby, metallurgical and mechanical properties of such steel have been continuously improved. Due to the complex microstructure of advanced pipelines more accurate failure prediction is thus necessary. In this work, the plastic deformation and damage behavior of pipeline steel grade X65 were investigated experimentally and numerically by means of the Gurson-Tvergaard-Needleman (GTN) damage mechanics approach. The differences between observed microstructure characteristics of the center and skin region of examined pipe were taken into account. Initially, FE simulations of tensile test for materials in both pipe regions were conducted using representative volume element (RVE) models, in which the characteristics of existing phases could be incorporated. It was seen that the effective true stress-strain responses calculated by the RVE simulations agreed well with the experimental results. Subsequently, the GTN model parameters were determined by metallographic considerations and RVE simulations. The engineering stress-strain curves until fracture of the steel were fairly predicted by the macroscopic simulations coupled with the damage model. Furthermore, the obtained GTN parameters were verified by a quasi-static fracture mechanics test, in which the single edge notch tension (SENT) specimens taken from both longitudinal and transverse direction of pipe were investigated. Experimental and predicted local stress and strain distributions of SENT specimens for different pipe regions were compared and analyzed.