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It is well known that the development of persistent slipbands plays an important role in the initiation of fatigue cracks. This paper describes the application of photoelectron microscopy to measure the kinetics of the early stages of growth of persistent slipbands in 6061-T6 aluminum. The persistent slipbands (PSBs) are shown to consist of a periodic array of approximately semicircular extrusions 1 to 2 μm in diameter. Initially a single extrusion appears. The PSB elongates by the addition of further extrusions. The lengths of individual PSBs increase as the square root of the number of fatigue cycles. A model is proposed based upon an array of cells similar to the dislocation structure which has been observed in the PSBs of other materials. The cyclic strain within these cells is shown to be 10 to 100 times greater than the applied macroscopic strain.
persistent slipbands, extrusions, photoelectron microscopy
Senior staff research scientist, General Motors Research Laboratories, Warren, MI