Crack Tip Opening Angle: Measurement and Modeling of Fracture Resistance in Low and High Strength Pipeline Steels

Published

September 1, 2006

Author(s)

Philippe P. Darcis, Joseph D. McColskey, Christopher N. McCowan, Thomas A. Siewert, Gabriel Kohn, Arry Bussiba, Richard J. Fields

Abstract

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. This type of steady-state fracture resistance takes place when the CTOA in a material reaches a critical value, as typically occurs in low-constraint configurations. Our current research has applied the CTOA concept as an alternative or an addition to the Charpy V-notch and the drop weight tear test (DWTT) fracture energy in pipeline characterization. A test technique for direct measurement of CTOA was developed, using a modified double cantilever beam (MDCB) specimen. A digital camera and software are used to record the progression of the crack tip and to estimate CTOA using the crack edges adjacent to the crack tip. A steady-state CTOA has been successfully measured on five different strength grades of gas pipeline steel (four low strength grades and one high strength grade: X100). In addition, two dimensional finite element models (2D FEM) are used to demonstrate the sequence of the fracture process and the deformation mechanisms involved. The CTOA measurements and models are correlated and agree well.

Proceedings Title

IPC 2006 Proceedings

Conference Location

Calgary, 1, CA

Conference Title

Internal Pipeline Conference 2006

Pub Type

Conferences

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Keywords

Crack Tip Opening Angle (CTOA), Fracture, Testing, FEM Modeling, Low Strength Steels, High Strength Steels, Pipeline

Citation

Darcis, P. , McColskey, J. , McCowan, C. , Siewert, T. , Kohn, G. , Bussiba, A. and Fields, R. (2006), Crack Tip Opening Angle: Measurement and Modeling of Fracture Resistance in Low and High Strength Pipeline Steels, IPC 2006 Proceedings, Calgary, 1, CA, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50312 (Accessed October 13, 2025)