Explaining the mechanics of metallic sliding friction and wear in terms of slipline field models of asperity deformation

It is shown that the force which opposes the sliding of a hard relatively smooth surface over a softer surface can be explained as the force needed to push waves of plastically deformed material along the soft surface ahead of asperities on the hard surface. For rougher surfaces and/or poorer lubrication it is shown how the wave can be torn off or material removed by a chip formation process and wear particles formed. Coefficients of friction predicted from the corresponding asperity deformation models are shown to give good agreement with experimental results. For smooth well lubricated surfaces the wear of the softer surface is shown to occur as a result of the progressive damage to this surface brought about by the repeated passage of waves across it. Equations for predicting wear are derived from the asperity deformation models and a comparison made between predicted and experimental wear results. The paper ends by considering possible future trends in research into the mechanics of friction and wear.