Contact mechanics of zinc-coated steel sheets

Contact mechanics of zinc coated steel sheets in contact with smooth tools are treated from the viewpoint of plastic deformation phenomena in the asperities of the coating and its matrix material. A plane strain deformation of the asperity model is proposed and analysed by using the upper bound method for the cases of non-deforming bulk materials. Compression tests are performed without lubrication (dry) and with two paraffinic mineral oils of low and high viscosity. The surface texture of these sheets and micro-structural changes are recorded using a video recorder and a stylus instrument. Changes in surface roughness and ratio of real to apparent area of contact with normal pressure, surface texture, thickness and hardness of the coating and lubricant viscosity are clarified. The upper bound analysis is shown to be quantitatively in a good agreement with experimental results. It is suggested that the cracks which develop in hard coatings might have a great influence on the lubrication process.