Turn-assisted deep cold rolling: An innovative manufacturing method for the improvement of fatigue life

It is well recognized that mechanical surface enhancement methods, such as shot peening, laser shock peening, roller burnishing and deep cold rolling can significantly improve the fatigue performance of highly-stressed metallic components. Deep cold rolling is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In this paper, the effect of turn-assisted deep cold rolling on the fatigue behavior of AISI 4140 steel is examined. In the present study, the parameters which have significant effect on turn-assisted deep cold rolling process are identified. Fatigue experiments are performed using rotating beam fatigue testing machine. The data is plotted as cyclic stress versus number of cycles to failure. It is found that ball diameter and rolling force has significant influence on fatigue performance of 4140 steel and it exhibits well-defined fatigue limit below which continued loading does not lead to failure. It is further established that the higher the cyclic stress the shorter the life. A second order regression model is developed to predict the fatigue life using response surface methodology and central composite design. Based on cyclic deformation and stress/life (S/N) fatigue behavior, it is found that turn-assisted deep cold rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in AISI 4140 steel.