Application Of Shot Peening

Author:  Almen, J. O.
Source:  p. 20-40 thru 20-49
Doc ID:  1964000
Year of Publication:  1964
Abstract:  
Shot peening is coming into extensive use as the most versatile of the several prestressing processes for strengthening metal machine parts against cohesive failure. Cohesive failures that are characterized by brittle fracture are caused only by tensile stresses and result from (1) impact loads on brittle metals in which the tensile stress acting at the surface is greatly magnified by various forms of stress raisers, (2) stress corrosion in which cracks (usually intercrystalline) propagate through metal that is stressed in tension, and (3) fatigue failures in which, because of the magnification of surface tensile stresses, fractures occur from repeated loads that stress the metals less than their nominal yield stress. Shot peening is effective against these forms of cohesive failure because it induces residual compressive stress in the surface of the metal being peened. The surface tensile stresses from externally applied loads will be reduced by the amount of the residual conpressive stress. The quality of the peening is determined by (1) the magnitude of the induced residual stress, which is a function of the yield stress of the peened metal and the state of strain in the metal at the time of peening, (2) the depth of the induced residual stress, which is a function of the hardness and ductility of the peened metal, the state of strain in the metal at the time of peening, and the characteristics of the shot and the shot stream, and (3) the degree of coverage, by which is meant the number of shot impacts per unit of area.