Recent developments in design for crack arrest using the crack-tip opening angle (CTOA)

摘要

Adequate toughness is required to arrest a running crack. Prediction of the arrest toughness for a pipeline at given operating conditions, and availability of test methods to measure this toughness, are vital for design and materials selection. In this paper, test methods to measure fracture-propagation toughness in terms of the crack-tip opening angle (CTOA) are briefly reviewed. Development of a draft standard CTOA test suitable for pipe steel is outlined. Methodologies for prediction of fracture-arrest toughness based on CTOA are reviewed, including discussions of the effect of velocity on crack-driving force.The increase in apparent toughness with velocity is an inertial effect, reflecting the need to accelerate material in the process zone; for a propagating crack, there is also inertial resistance from the soil and opening flaps. For methodologies based on CTOA, it is important to develop finite-element modelling tools to predict crack-driving force and to investigate the transferability of CTOA from laboratory-scale specimens to full-scale pipe. Needs for full-scale burst tests to validate fracture-arrest methodologies based on CTOA are briefly discussed.