The effect of specimen thickness on the experimental characterization of critical crack-tip-opening angle in 2024-T351 aluminum alloy

Although the crack-tip-opening angle (CTOA) has been shown to be well suited for modeling stable crack growth and instability for thin sheet aluminum alloys, its behavior for increasing thickness has not been thoroughly evaluated. To investigate this behavior, fracture tests were performed on specimens made of 2024-T351 aluminum alloy with thicknesses of 2.3, 6.35, 12.7, and 25.4 mm. The surface CTOA exhibited an initially high value followed by a transition to a “constant” value after a short amount of crack extension, with this transition decreasing significantly with increasing specimen thickness. The critical CTOA was shown to decrease with increasing specimen thickness and appears to possibly be approaching a lower limiting value.