BOUNDARY ELEMENT ANALYSIS OF ADHESION CONSIDERING VAN DER WAALS FORCE

Recently, micro- and nano-machine for microelectromechanical systems (MEMS) and the mechanism of bioadhesive pads and sensors attract great interest. Forces such as the van der Waals force affect the adhesion in nanoscale structures. Even if two bodies does not really contact, adhesion will happen as they approach each other. The adhesion occurs easily in micromachines, so several devices are required to prevent the adhesion. In the present paper, the van der Waals force is introduced into a boundary integral method (BEM) program for analyzing the adhesion in arbitrarily shaped bodies. The van der Waals force is described by a nonlinear function of the distance between two surfaces in close proximity, and the adhesion and repulsion forces vary greatly within the atom equilibrium distance, so the solution for the simultaneous equation in the BEM is hard to converge to an exact solution. In the present paper, we propose a method for converging to a solution, apply it to the adhesion problem between a cylinder and a flat substrate, and compare the solution with the previously published theoretical result. Furthermore, adhesive contact of a semicircular cylinder and a half domain with a wavy surface is analyzed, and the semicircular cylinder is moved to the horizontal direction of the domain. Then, stick-slip phenomenon can be observed and a variation of friction coefficient is discussed. In our analysis, a repeated boundary condition is introduced like a molecular dynamics analysis. So, the program can be used for evaluating the adhesion in a large system.