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Crack Tip Opening Angle Optical Measurement Methods in Five Pipeline Steels



Philippe P. Darcis, Christopher N. McCowan, H. Windhoff, Joseph D. McColskey, Thomas A. Siewert


Crack tip opening angle (CTOA) is becoming one of the more widely accepted properties for characterizing fully plastic fracture. In fact, it has been recognized as a measure of the resistance of a material to fracture in cases where there is a large degree of stable-tearing crack extension during the fracture process. Our current pipeline research uses the CTOA concept as an alternative or an addition to the fracture energy characterizations provided by the Charpy V-notch (CVN) and drop weight tear test (DWTT). A test technique for direct measurement of CTOA was developed, using a modified double cantilever beam (MDCB) specimen. A digital camera and image analysis software are used to record the progression of the crack tip and to estimate CTOA. In this report, different optical measurement methods are compared, three using the crack edges adjacent to the crack tip (defined in the ISO draft standard and ASTM standard) and one using the specimen surface grid lines. Differences in CTOA resulting from the various measurement methods are evaluated. The CTOA's for five different grades of gas pipeline steel are reported, and the effect of microstructure on CTOA is discussed.
Engineering Fracture Mechanics


Crack tip opening angle, Modified double cantilever beam CTOA test set-up, Optical angle measurement methods, Pipeline steels


Darcis, P. , McCowan, C. , Windhoff, H. , McColskey, J. and Siewert, T. (2007), Crack Tip Opening Angle Optical Measurement Methods in Five Pipeline Steels, Engineering Fracture Mechanics (Accessed May 26, 2024)


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Created October 15, 2007, Updated October 12, 2021