Analysis of residual stress relaxation under mechanical cyclic loading of shot-peened trip780 steel until fatigue lifetime

Abstract

TRIP aided steels are used in the automotive industry due to their high strength, ductility and toughness properties. Typical parts made of TRIP steels (as engine sub-frame for instance) are submitted to cyclic loading during their lifetime. Those parts could be also shot-peened to minimise the risk of fatigue failure. Studies have investigated the fatigue life of non-treated TRIP aided steels [1-3], the shot peening of TRIP steels [4-9] but very few [10] have investigated the mechanical residual stress stability after shot peening on TRIP steels and the impact on fatigue life. TRIP steels exhibit a multiphased microstructure of ferrite, bainite, residual austenite and martensite created after thermomechanical loading/straining. Shot peening on TRIP steel generates austenite to martensite phase transformation and a gradient of microstructure and residual stresses from the surface as characterized by Guiheux [9]. The aim of this study is to analyse the evolution of residual stresses (RS) generated by shot-peening during cycling and the effects of shot peening on fatigue life of a cold rolled TRIP780 steel. The stability of RS was assessed using X-ray diffraction techniques. Macroscopic finite element simulation of fatigue life.