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Fractographic Measurements of Crack-Tip Closure

Relative changes in striation spacing resulting from a sudden change of the load range were used to measure crack-tip closure under plane-strain conditions. The tests were performed in a 2124-T351 aluminum alloy. The difference between the opening and closure rates of the crack tip was quantitatively measured by comparing striation spacings for two different programmed load blocks. It is concluded that crack-tip closure occurs principally in the plane-stress region of the crack front. In the center of the specimen, under plane strain, the average value of K o p /K m a x is less than 0.20 for ΔK varying from 10 to 35 MPa√m.