Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor(s)

Dr. Wenxing Zhou

Abstract

This thesis deals with issues related to the experimental determination of the fracture toughness resistance curves, i.e. the J-integral (J)-R curve and crack tip opening displacement (CTOD)-R curves, using the single-edge bend (SE(B)) and single-edge tension (SE(T)) specimens. First, the impact of the crack front curvature on the J-R curve measured from the SE(B) specimen is investigated through systematic linear-elastic and elastic-plastic three-dimensional (3D) finite element analyses (FEA) of SE(B) specimens containing both straight and curved crack fronts. Three average relative crack lengths are considered, namely 0.3, 0.5 and 0.7, and three specimen width-to-thickness ratios are considered: 0.25, 0.5 and 1. The curved crack fronts are characterized by a power-law expression. The analysis results suggest that the crack length evaluated from the CMOD compliance of the SE(B) specimen is insensitive to the crack front curvature and that the impact of the crack front curvature on the experimentally-evaluated J values varies with the specimen configurations. For a given specimen configuration, as the crack front curvature increases, the value of J evaluated based on the test standard ASTM E1820-11 without considering the crack front curvature becomes less conservative and tends to overestimate the actual J. New crack front straightness criteria that are in most cases less stringent than ASTM E1820-11, are recommended. The accuracy of the double clip-on gauge method for experimentally determining CTOD is examined through systematic 3D elastic-plastic large-strain FEA of clamped SE(T) specimens. The relative crack lengths of the specimens range from 0.3 to 0.7, and the thickness-to-width ratios are 0.5, 1 and 2. It is observed that the CTOD values determined from the double clip-on gauge method may involve significant errors. This error primarily depends on the crack length, the material property and the loading level. Based on the analysis results, a modified CTOD evaluation equation is developed to improve the accuracy of CTOD evaluated using the double-clip on gauge method.


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