Stress Distribution at PTFE Interface in Cylindrical Bearing

Abstract

Two analytical methods capable of evaluating stresses at the curved polytetrafluoroethylene (PTFE) metal sliding interface in a cylindrical bearing subjected to combined vertical and horizontal loads are described. One method is based on a finite-element approach incorporating contact elements to model the sliding PTFE/metal interface, while the other, referred to as the displacement method, is based on an approach that assumes all displacement in the bearing under load is confined to the PTFE. Both methods are shown to give similar results. Basic equations for the displacement method are derived assuming a bilinear stress-displacement relationship for the PTFE, and this method is used to produce design curves for cylindrical bearings, based on criteria relating to prevention of separation of the interface and limitation of maximum stress level in the PTFE under service load. The displacement model shows that the common design practice of assuming linear elastic material behavior and a plane surface is conservative. The design charts presented in this paper provide an effective tool for taking advantage of the extra horizontal load resistance resulting from the bilinear behavior of the PTFE and the curved interface of the bearing.