Residual Stresses in Shot Peened Components

Author:  Dr. David Kirk, Coventry University, U.K.
Source:  The Shot Peener magazine, Vol 18 / Issue 4, Fall 2004
Doc ID:  2004054
Year of Publication:  2004
Abstract:  
INTRODUCTION Shot peening of components produces a 'magic skin' containing compressive residual macrostress. This skin has a thickness that is largely determined by the size of the shot particles that have been used. The level of compressive residual stress in the skin is a large fraction of the yield strength of the as-peened surface material. Residual and applied stresses super-impose themselves, so that compressive surface residual stresses offset tensile applied surface stresses. It is that lowering of net surface stress that improves the service performance of shot peened components. Residual stresses are produced whenever inhomogeneous plastic deformation is applied to a component. Shot peening is a prime example of inhomogeneous plastic deformation. Peening involves tensile plastic deformation of a surface layer - produced as the sum of numerous indentation expansions. Compressive residual stresses are generated at the surface because of this tensile deformation. Peening can impose huge amounts of deformation without cracking because of the hydrostatic compression that is involved. Gold has a tensile ductility of 40% but can be hammered until it is almost transparent. The imposed stored energy is so great, however, that gold leaf (normal M.Pt. 1064