Uniaxial Time-Dependent Ratcheting Behavior of Bronze Powder Filled Polytetrafluoroethylene at Room and High Temperature

摘要

A series of tensile and ratcheting experiments for cold compaction polytetrafluoroethylene (PTFE) and bronze filled PTFE (PTFE/bronze) were conducted with Dynamic Mechanical Analyzer (DMA-Q800) at room and high temperature (473 K). The effects of peak stress-holding time, creep, recovery, mean stress history, stress-rate history, and pretension on the ratcheting behavior of PTFE/bronze were investigated. It is found that longer peak stress-holding time leads to larger ratcheting strain accumulation. In the meantime, the ratcheting strain accumulates more rapidly at high temperature and the influence of temperature is more obvious than that of the additive fraction of bronze. Creep strain produced during the uploading and the stress-holding time only partially recovers in the unloading process. Moreover, prior lower stress rate enhances the deformation resistance and restrains the ratcheting of subsequent cycling at higher stress rate. The ratcheting strain in the subsequent cyclic loading at lower mean stress is also restrained by previous cyclic loading at higher mean stress. Finally, the elastic modulus increases and the ratcheting strain is restrained apparently after the pretension. In addition, the elastic modulus and ratcheting strain of the PTFE/ bronze with both pretension and recovery are smaller than those with pretension but without recovery.