Adhesion modelling by finite elements of three-dimensional fretting

摘要

This work builds a comprehensive adhesion model by finite elements (FEA) for a deformable hemisphere subject to fretting. The hemisphere is constrained between two rigid and frictionless plates as it is loaded in the normal direction and followed by prescribe oscillatory tangential motions. The material for the deformable hemisphere is gold (Au). The normal direction adhesion contact is based on the classic JKR model; however, the tangential resistance is based on the definition of the shear strength and the surface free energy. That is manifested into interfacial bilinear springs where detachment or reattachment of the two contacting surfaces occur when the springs "break" or "snap-back" at the interface. It is shown that the breakage of the springs may be gradual or avalanching. The tangential resistance effect is robust, that is, it is not influenced by the choice of meshing or the spring settings. When the two surfaces are about to detach, the most part of the contact region deforms plastically. At small fretting amplitudes (with no springs breakage), the fretting loop behaves similarly to that of full stick conditions. Hence, the von-Mises stress distributions, plastic strain distributions, and fretting loops, are similar to those of full stick condition. However, the current adhesion model is structurally less stiff because of the bilinear spring. Conversely, at a large oscillation amplitude, the fretting loop exhibits large energy losses, and yet it does not resemble those of gross slip conditions.