A CTOD-Based Mixed-Mode Fracture Criterion

ABSTRACT: This paper presents a mixed-mode fracture criterion that uses the crack-tip opening displacement (CTOD) at a fixed distance behind the crack tip as the fracture parameter. This criterion is developed based on a detailed analysis of crack kinking in arbitrary directions. In essence, the proposed criterion states that crack growth occurs when the current CTOD reaches a critical value and the direction of crack growth is the direction that causes either the opening or the shearing CTOD component at the new crack tip to be the absolute maximum. Under linearly elastic conditions, it is shown that this criterion is equivalent to several commonly accepted mixed-mode criteria and predicts that crack growth will occur in a locally Mode I manner. Under elastic-plastic conditions, the mixed-mode CTOD criterion predicts that crack growth will be along either a local Mode I or a local Mode II direction. The prediction of the abrupt transition from Mode I-dominated crack growth to Mode II-dominated crack is in good agreement with the observation of the mixed-mode fracture test results from the Arcan specimens. Alternative forms or extensions of this criterion are also discussed.

A representative finite element mesh for the continuous specimen-fixture system, where F is the loading angle. Predicted and measured crack growth direction dc(degrees) as a function of the local mode mixity a.
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