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

• A 40 kJ pendulum machine for DWTT tests with well traceability and reproducibility.
• Analytical regression method to estimate CTOA over stable cracking of specimens.
• Key-curve method to monitor the dynamic crack extension of standard DWTT samples.
• Experimental solution to obtain material parameters (A*σf) for DWTT-like 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.