Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Zhou, Wenxing

Abstract

The fracture toughness resistance curve (e.g. J-R curve) is widely used in integrity assessment and strain-based design of oil and gas pipelines with respect to planar defects (i.e. cracks). This thesis includes two-dimensional (2D) and three-dimensional (3D) finite element analyses (FEA) of ductile crack growth of X80-grade pipeline steel based on the Gurson-Tvergaard-Needleman (GTN) constitutive model, and investigation of the normalization (NM) method to generate the J-R curve for the single-edge tension (SE(T)) specimen.

First, the GTN model implemented in the computational cell is adopted in the commercial software ABAQUS to calibrate the micromechanical parameters for the pipeline steel. Subsequently, the stable fracture process of six SE(T) and four single-edge bend (SE(B)) specimens tested are simulated in 3D and 2D FEA. Results have shown that the GTN model is a viable tool to predict the fracture behavior of the specimens, in terms of predicting the load-displacement curve, J-R curve and crack front profile of the fracture specimen. In addition, the stress field near the crack-tip as well as various constraint parameters are examined.

Second, based on the calibrated micromechanical parameters, a series of SE(T) specimens with various geometric configurations are modelled. The applicability of the NM method to generate J-R curves for SE(T) specimens is investigated, followed by the proposal of the so-called ‘k factor-based NM method’ based on the J-CMOD relationship, to improve the computational efficiency of the conventional NM method.

The outcomes of this study will facilitate and improve the evaluation of J-R curves for the SE(T) specimen using the NM method.

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