ADHESIVE CONTACT BETWEEN SILICON-BASED MEMS TOOTH SURFACES MODELLED BY THE MULTISCALE MULTI-BLOCK MODEL

Abstract

The contact interactions between microgear silicon-based MEMS teeth working in a clean and a vacuum environment are under consideration. A new approach has used to determine the friction force and the coefficient of friction over the whole meshing surfaces of the teeth. In this approach, the dry friction force is calculated through the energy dissipated during sliding contact between two meshed micro-tooth elastic rough surfaces. The energy dissipated may be caused by the different physical and chemical interactions between the counterparts surfaces. Due to the vacuum environment, these mechanisms reduced to the energy lost due to the dissociation of chemical and van der Waals bonds, and the energy lost through the elastic interlocking between the asperities located on the meshing micro-tooth surfaces. There is no plastic deformation of the microgear tooth surface asperities due to their size and the Polonsky-Keer effect. A multiscale hierarchical elastic structure (a multiscale block) is used to model the surface asperities. The tooth block roughness has modelled at two scales specified by the character of interactions: atomic level, where chemical interactions occur, and adhesive subscale, where van der Waals interactions are significant. The adhesion layer is defined similarly to Maugis approximation. The adhesion force of each nanoasperity has assumed to be equal to the pull-off force in the Boussinesq-Kendall model and corrected by the Borodich no-slip coefficient. Atomic Force Microscopy (AFM) techniques have been used to measure the tooth roughness. It is argued that there be a high probability for stiction between the clean silicon surfaces due to very high values of the friction force between the micro-conjunctions. On the other hand, the tooth surfaces having functionalized carbon-based layers are much less prone to stiction. However, due to wear of the functionalized coating the probability of stiction will start to increase. The results of the simulation for both the non-functionalized and functionalized micro-tooth surfaces (silicon-based MEMS surfaces) are presented.