Fracture mechanics is the study of the nucleation and the propagation of cracks in materials, which includes both stable and unstable crack growth. The subject allows for the quantification of the relationships between material properties, stresses, the presence of crack-producing flaws, and crack propagation mechanisms. In modern materials science, fracture mechanics is an important tool used to improve the performance of mechanical components. Fracture mechanics is used in fitness-for-service assessments, which analyze flaws to determine which are safe and which are liable to propagate and cause failure of a flawed structure.
Fracture toughness is a material property which measures a material’s resistance to crack extension when an existing crack is present and is subjected to monotonic loading. There are various fracture toughness parameters that are measurable and used in engineering analysis. In practice, these parameters are generally narrowed down to 3 types: KIC, JIC, and CTOD.
Crack-Tip Opening Displacement (CTOD) testing measures the critical opening displacement of the crack-tip which drives crack extension. It is used for materials which display some plastic deformation before sudden brittle fracture occurs. CTOD is the most common fracture toughness parameter of choice for evaluating weldments in the oil & gas industry. Accu-Test Labs performs CTOD testing in accordance with BS 7448 Part 1 & 2, ISO 12135, ISO 15653, and ASTM E1820. Accu-Test Labs commonly performs CTOD testing as a part of weld qualification testing in accordance with industry standards such as API 1104 Appendix A, CSA Z662 Annex K, and DNV-OS-F101.
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