A B S T R A C T A new mechanism modelling is proposed in this paper to explain the shot peening effect on fatigue life predictions of mechanical components. The proposed methodology is based on the crack growth analysis of shot peened specimens, which are affected by the interaction of surface roughness and residual stress produced during the shot peening process. An asymptotic stress intensity factor solution is used to include the surface roughness effect and a time-varying residual stress function is used to change the crack tip stress ratio during the crack propagation. Parametric studies are performed to investigate the effects of surface roughness and the residual stress relaxation rate. Following this, a simplified effective residual stress model is proposed based on the developed mechanism modelling. A wide range of experimental data is used to validate the proposed mechanism modelling. Very good agreement is observed between experimental data and model predictions.a, a i , a c = crack length, initial crack length, critical crack length, respectively A, α, β = material-dependent parameters C, m, p = material parameters in fatigue crack growth criteria d = motch depth g, b = parameters to include stress ratios into fatigue crack growth K t = stress concentration factor N = number of fatigue cycle R = stress ratio R RS = the applied stress ratio R tm , S m = mean to peak valley heights and spacing of adjacent peaks, respectively Y , Y = crack geometry factor without and with plasticity correction, respectively K, K th = stress intensity factor and threshold stress intensity factor σ f = uniaxial fatigue stress limit σ = stress range in one cycle respectively λ,λ = residual stress reduction factor and effective residual stress reduction factor, respectively ρ = plastic zone size σ max , σ 0 = maximum stress in one cycle and cyclic ultimate strength, respectively σ a , σ RS = stress amplitude and surface residual stress, respectively σ RS = effective residual stress
I N T R O D U C T I O NPeening is a manufacturing process to increase the fatigue strength of materials, in which the surface of mechanical component is blasted by small media, such as shot peeing, laser peening and water cavitation peening. 1,2 It iswidely used in many industries to enhance the fatigue life for some critical components, such as transmission gear, crankcase, and so on. 3,4 Shot peening is a very effective way to relieve tensile stress built up in the manufacturing process and to produce very high compressive residual stress near the specimen's surface. Both fatigue limit and fatigue life can be greatly increased. 5 The effect of shot 116