Joint surface model based on total reflection optical image

The joint contact characteristics of mechanical structures strongly influence the stiffness, damping and other dynamic characteristics. Many contact models have been developed, but they are based on different theoretical models with some even giving diametrically opposed physical interpretations. This study used the total reflection method and image processing to study the evolution of polymethyl methacrylate (PMMA) contact spots loaded with positive pressures. The observations show that the variation of contact spots under normal force has three stages: the first stage is the linear increasing region under light loads, the second and third stages are the nonlinear increasing region under heavy loads. With light loads, the number of contact spots and the contact area are consistent with those predicted by the Greenwood-Williamson (GW) model, but differ from those predicted by the Majumdar-Bhushan (MB) model. With heavy loads, the GW and MB models both cannot adequately predict the physical characteristics due to the bulk deformation with heavy loads leading to smaller actual contact areas. Thus, more accurate contact model would be obtained when the influence of the bulk deformation is considered.