Prediction of residual stress relaxations in shot-peened specimens and its application for the rotor disc assessment

Quantification of shot peening effects in fatigue life prediction becomes increasingly important in industry. The goal of the present work is to find out an engineering method for predicting the residual stress variations and to give a quantitative conservative estimate about the improvement from shot peening. The variations of residual stress caused by shot peening can be described by three sets of ordinary differential equations which have to be solved with the initial residual stresses and the initial plastic strain. It is shown that the equations are valid for materials on free surface and in position where the residual stress reaches maximum value. The equations provide the basis for predicting residual stress variations in the whole shot-peened layer. The nonlinear residual stress variations can be replaced by a multi-linear uniaxial method introduced in the present work. The accuracy of the multi-linear method is verified by detailed finite element computations for uniaxial tension bars and notched specimens. The applicability of the present method to rotor disc is investigated. Discrepancy between the finite element analysis and the multi-linear method is trivial for engine design if the maximum loading strain is limited by 2.5%.