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  Title Modelling crack propagation and arrest in gas pipes using the CTOA criterion
  Author(s) Dr Mohamed Ben Amara, Prof. Guy Pluvinage, Dr Julien Capelle, and Prof. Zitouni Azari  
  Abstract ON THE ASSUMPTION THAT the fracture toughness and driving force can be expressed using the crack-propagation velocity and decompression wave speed, the gas pipeline standard codes, such as ASME B31.8, require a minimum toughness in term of the Charpy or DWTT energy to ensure ductile-fracture arrest. This approach involves the superposition of two curves: the gas-decompression-wave speed and the ductile characteristic fracture-propagation velocity, each as a function of the local gas pressure. For this reason, it is called the two-curve method (TCM). The most commonly used TCMs for crack-arrest problems are semi- empirical uncoupled models such as the Battelle method. This model is based on theoretical analysis and full-scale crack-arrest experiments. With the appearance of numerical simulations for ductile-crack extension based on the Gurson-Tvergaard-Needleman model, and critical damage given by strain-rate- dependent damage (SRDD) model or a critical crack-opening angle (CTOA), several authors tended to extend the TCM approach by using numerical analysis of pipeline crack-arrest-simulation results. Well known as a single parameter with low sensitivity to pipe geometry, the CTOA fracture criterion was used to perform a running-ductile-fracture simulation of pipeline made from API 5L X-65 steel. Then, a new arrest pressure equation base on critical CTOA, similar to the BTCM’s equation, was proposed and compared to a commonly used one, such as Battelle-TCM, HLP, and HLP-Sumitomo methods.  
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