MICROCRACK CLOSURE PHENOMENA FOR AL 2219-T851

The effect of maximum cyclic stress, σmax, on the closure behavior of surface microcracks is studied for Al 2219-T851 subjected to fatigue for fully reversed cyclic loading. The relationship between σmax and the crack closure stress σcc, is found to change as the noncrystallographic transgranular microcracks grow from intermetallic particles at the alloy surface (where they initiate) to the grain boundaries. After crack initiation, with crack lengths just slightly greater than the width of the intermetallics from which they have propagated, σcc is found to be independent of σmax· For longer microcracks with lengths of approximately the grain size, σcc∞ σmax. Crack closure mechanisms which can explain this behavior are discussed. © 1979 American Society for Metals and the Metallurgical Society of AIME.