Mechanical Surface Treatments and Life Improvement

Mechanical surface treatments such as shot-peening, hammering, cold rolling are used in order to introduce compressive residual stresses in surface layers. These stresses usually induce significant life improvement. Optimization of these treatments might be more efficient if an analytical model is used to predict the induced residual stresses and their evolution under cycling loading. Such models have been settled by L. Castex, G. Inglebert and their students between 1984 and 1992. They used the MASSI method (Simplified Analysis of Inelastic Structures Method~– J. Zarka, G. Inglebert), the analytic knowledge of Hertzian contact stresses in the elastic case, and a specific behaviour law, MI2. The paper will sum up the predictive method and how it could be used for life improvement estimation using multiaxial life criteria. Accuracy of the results is strongly linked to the quality of the behaviour law; recent work of G. Inglebert, N. Point and D. Vial settled an optimization process to obtain the four material parameters for the MI2 law from a tensile test.