Ratcheting testing of polytetrafluoroethylene (PTFE) under multiple-step compression

Abstract

Abstract Uniaxial stress-controlled ratcheting experiments of PTFE (polytetrafluoroethylene) under cyclic compressive loads with multiple load steps were performed. The influence of stress rate, temperature, stress amplitude, loading sequence and peak holding on the compressive ratcheting behavior have been discussed systematically. Results indicate that ratcheting deformation increases significantly when enhancing temperature and stress amplitude and reducing stress rate. Only a slight, accumulated deformation occurs during the first 20 or so cycles at room temperature (RT), but it always turns to shakedown. Moreover, ratcheting strain is clearly influenced by the loading sequence. When greater compressive deformation was obtained during the prior load step due to a greater stress level (such as higher temperature or a lesser stress rate), increased compressive strain hardening and deformation resistance could be produced, which in turn restricts or even reduces ratcheting deformation in the pursuing load step. It is of great interest that no initial cyclic stress strain curve was observed under cyclic compression at peak holding time. This indicates that creep recovery due to anelastic relaxation decreases the ratcheting rate of PTFE material under compressive creep-fatigue conditions. This research provides an important testing approach and data for PTFE material subjected to repeated compressive loads influenced by temperature modulation.