Abstract
Fatigue-life tests were performed with notched bend specimens of ASTM A723 steel with three types of notch treatment and resulting residual stress; shot peening, hole swaging, and tensile overload. The three notch treatments produced widely different depths and surface values of residual stress near the notch root and different fatigue lives, depndent mainly on the notch root surface value of compressive residual stress. The highest life was measured from overload specimens, which had both the deepest and the highest surface-value residual-stress distribution.
Fracture-mechanics-based calculations of fatigue life agree well with measurements. The calculations account for the following factors which affect fatigue life: the crack-growth properties of the material; the shallow surface-crack configuration; the applied loading; and the depth and surface magnitude of the residual-stress distribution. A consistent description of fatigue life was obtained from a ΔK versus calculated life plot, where the ΔK is that for a shallow crack near the notch root and in the region of compressive residual stress. A power-law relationship between ΔK and life agrees well with the results from both the untreated notches and those with the three types of residual stress, indicating that life predictions could be made with some confidence for tests under generally similar conditions.
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References
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Underwood, J.H. Residual-stress effects at a notch root in A723 steel to extend fatigue life. Experimental Mechanics 35, 61–65 (1995). https://doi.org/10.1007/BF02325836
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DOI: https://doi.org/10.1007/BF02325836