Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dr. Wenxing Zhou

Abstract

The fracture toughness resistance curve such as the J-integral resistance curve (J-R curve) is widely used in the integrity assessment and strain-based design of energy pipelines with respect to planar defects (i.e. cracks). Two studies about the development of the J-R curve are carried out and reported in this thesis. In the first study, the plastic geometry factor, i.e. the ηpl factor, used to evaluate J in a J-R curve test based on the single-edge bend (SE(B)) specimen is developed based on the three-dimensional (3D) finite element analysis (FEA). The main finding of this study is that besides the crack length, both the thickness and side grooves of the specimens have observable impacts on the ηpl factor. The ηpl factors obtained from 3D FEA are different from those obtained from two-dimensional (2D) FEA. The results of this study can improve the accuracy of the experimentally determined J-R curve and facilitate the use of non-standard (e.g. shallow-cracked) SE(B) specimens for the J-R curves testing. In the second study, 3D FEA is carried out on SE(B) specimens for which the J-R curves have been experimentally determined to develop the constraint-corrected J-R curves for X80 grade pipe steels. The constraint parameters considered in this study include Q, A2, h and Tz. Several different forms of the Q parameter that account for the correction for the load and/or bending stresses are considered. It is observed that three constraint parameters, namely QBM1, Tz and A2, lead to reasonably accurate constraint-corrected J-R curve for a wide range of crack extension compared with the J-R curves experimentally determined from two shallow cracked SE(B) specimens. On the other hand, the constraint-corrected J-R curve based on constraint parameters QHRR, QBM2 and Qm lead to a relatively large error of prediction. The approach for constructing the constrain-corrected J-R curve can be used to develop the structure-specific J-R curve based on those obtained from small-scale test specimens to improve the accuracy of the structural integrity assessment.

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