Deep rolling and shot-peening to improve the tribological response of connecting rod screws

This work deals with an experimental study on the frictional properties of connecting rod high strength screws. Considering that friction has a significant impact on the achievable preload for fixed and controlled tightening torque, the question of friction reduction was tackled by suitable surface treatments. Deep-rolling and shot-peening were involved in the campaign that proved the latter has a highly beneficial effect at reducing friction. Moreover, bearing friction coefficient is made barely steady versus repeated tightening in both lubricated and dry conditions.