Plastic properties of polytetrafluoroethylene (PTFE) under conditions of high pressure and shear

We investigate experimentally the behavior of a thin sheet of PTFE between a steel plate and a cylindrical steel indenter under combined action of high normal force and torsion. Under these actions, the PTFE layer is partially squeezed out of the contact area. The thickness of the remaining layer is studied as function of the applied normal force, the torsion angle, and the radius of the indenter. We suggest a simple semi-empirical material model which describes both the process of squeezing out of the layer and the force of friction produced by the layer.