Evaluation of cracking behavior and critical CTOA values of pipeline steel from DWTT specimens

A regression based algorithm, load-line displacement method has been developed from the Martinelli–Venzi ductile fracture model to measure the crack-tip-opening-angle (CTOA) of high strength and toughness pipeline steels. Key-curve method is employed on the instrument force–displacement curve to estimate the dynamic cracking behavior of a standard pressed-notch DWTT specimen, also conveniently to identify the stable fracture propagation. From the above laboratory procedure, the critical CTOA is found to be constant over the steady-state stage, independence of the thickness in the range 19–31 mm as studied.