A statistical model of elastic-plastic contact between rough surfaces

In a mechanical interface, the contact surface topography has an important influence on the contact stiffness. In the contact processes of asperities, elastic-plastic change can lead to discontinuity and lack of smoothness at a critical contact point. The result is a large difference between the elastic-plastic deformation and the actual asperity deformation. Based on Hertz contact theory, the heights of asperities on a rough surface obey a Gaussian distribution. To take into consideration the continuity of elastic-plastic asperity deformation, we divide the elastic-plastic deformation into three stages: pre-elastic-plastic, mid-elastic-plastic, and post-elastic-plastic deformation. This establishes an elastic-plastic contact model of asperity at a continuous critical point. The contact model of a single asperity fits well with the Kogut–Etsion model and the Zhao–Maietta–Chang model, and the variation trend is consistent. At a lower plastic index, the present model coincides with classical models of contact area and contact load. At a higher plastic index, the simulation results of the present model differ from the Greenwood–Williamson model and the Chang–Etsion–Bogy model but are similar to results from the Kogut–Etsion and Zhao–Maietta–Chang models. This study provides a more accurate microscopic contact model for rough surfaces and a theoretical framework for interface design and analysis.

Motion Analysis of Micropart in Dry Friction Environment Due to Surface Excitation Considering Microscale Forces

This manuscript investigates the motion of a micropart on a dry nonlubricated controlled deformable surface considering the dynamically changing microforces while in contact with the surface. The motion analysis of a micropart on a flexible surface under controlled deformation is the first step to initiate feasibility of a micromanipulation device. At the micro/nanoscale, the surface force of attraction becomes more significant than the inertia force; thus motion analysis requires estimating and accommodating these forces in a dynamic model. The model considers microscale forces and surface roughness conditions (asperity deformation), while dynamically evaluating the friction coefficient and attraction force due to the dynamic asperity deformation as the micropart moves on a controlled deformation active surface. The parameters considered in the model include the micropart mass and size, the relative roughness between the micropart and surface, the surface and micropart material, and input actuator frequency, stroke, and deformation profile. The simulation results indicate that predictable micropart motion could be achieved but only within a certain range of input actuator frequencies. At lower frequencies no motion is possible while at higher frequencies the micropart detaches from the surface. The understanding of the effects of the microforces on the dynamic model and micropart motion would pave the way towards controlled micropart translocation and manipulation employing a flexible surface for microassembly or for processes requiring controlled micropart handling for heterogeneous microdevice mass production.