Optimum Peening Intensities

Author:  Fuchs, H. O.
Source:  Conf Proc: ICSP-3, (p.639-646)
Doc ID:  1987062
Year of Publication:  1987
Abstract:  
Shot peening improves fatigue resistance mainly by introducing self stresses (residual stresses). The compressive self stresses near the surface are balanced by tensile self stresses which decrease fatigue strength in the interior where stresses are usually lower. The magnitude and distribution of the peening stresses depend mainly on the materials, not on the intensity. The intensity (specified in Almen numbers) determines the depth to which the compressive stresses extend below the peened surface. A low peening intensity will not increase the fatigue resistance as much as a higher intensity. Very high peening intensities may not increase the fatigue resistance as much as a lower intensity, partly because the tensile stresses at the interior become too high and partly because the compressive stresses become less for great depth of peening than for shallow peening. The optimum intensity is defined by the depth at which both decreased intensity and increased intensity would decrease the fatigue resistance. Figure 1 gives an example of optimum depth, based on assumptions explained in the discussion.