Interaction of Slip Bands in High-Cycle Fatigue Crack Initiation
A number of fatigue bands spaced 3 microns apart are assumed to exist in a most favorably oriented crystal at a free surface of a polycrystal. Each fatigue band is taken to consist of three thin slices P, Q, and R with R sandwiched in P and Q. P and Q in each band are assumed to have equal and opposite initial resolved shear stresses. Plastic strain distributions in the fatigue bands under cyclic loading were calculated.
The maximum shear strain at this free surface is a measure of the height of extrusion or depth of intrusion, which in turn is taken as a measure of crack initiation and hence the level of fatigue damage. The applied cyclic shear stress versus the number of cycles to yield different levels of fatigue damage were calculated. The shape of these curves seems to be similar to that of Wohler’s diagram and that of the Coffin-Mansan equations. It is hoped that this analysis gives some physical explanations to the Wohler and the Coffin-Mason relations.
KeywordsPlastic Strain Slip Band Fatigue Damage Resolve Shear Stress Fatigue Crack Initiation
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