Nonlinear increase of the real contact area of PMMA blocks and the related contact model

Abstract Many experiments have proved the contact models, such as GW model, MB model, however, most of past validations are under light load. In this paper, based on total reflection method, we performed direct measurements of the real contact area between two polymethylmethacrylate (PMMA) blocks under heavy load, and utilized the image processing method to analyze the contact area. The results shows that the real contact area increase with normal load linearly in light load, but non-linearly under heavy load; the number of contact spots increase with load linearly in light load, but also nonlinearly under heavy load, synchronous with the changing of real contact area. We used GW and MB model to predict the experiment result, and found that both models failed to predict the nonlinear stage. Finally, we proposed a revised GW model based on the hypothesis of bulk deformation to predict the non-linear stage.