Experimental and theoretical investigation of running-in

► Results of running-in experiments are presented to establish the evolution of wear depth, worn weight and surface roughness. ► The wear depth and worn weight exhibit similar trend during the running-in stage, i.e. they both initially increase with a relatively sharp slope. As the asperities polish and the number of plastically deformed asperities reduce, the slope of wear depth and worn weight decreases. ► In lubricated contact of rollers, keeping the sliding speed constant and increasing the rolling speed in the mixed regime results in a better protecting film and therefore a decrease in traction coefficient.