Experimental Study On Cyclic Deformation Of Polytetrafluoroethylene (PTFE) Under Uniaxial And Multiaxial Loading At Room Temperature

Due to their tribological characteristics, electrical resistance, chemical inertness and temperature stability, polytetrafluoroethylene (PTFE) have been widely used in mechanical, chemical and electrical industries. Research on the mechanical behavior of PTFE is one of the basic jobs to improve the reliability of the materials.In this paper, an experimental study was carried out on the uniaxial and multiaxial cyclic deformation on cylindrical specimens of PTFE by extrusion forming. The cyclic stress-strain hysteresis loops were investigated with different shear ranges, shear rates and their loading histories under shear strain controlled tests at room temperature. The cyclic ratcheting tests were conducted for the stable stress, proportional, circular and rhombic paths of multiaxial loading with different axial mean stresses, shear strain amplitudes, shear strain rates and their histories.The experimental results show that the PTFE is a rate-dependent material. Cyclic softening is found to exist under pure torsion loadings, and the PTFE has noticeable non-Masing behavior. At room temperature, it is shown that the multiaxial ratcheting behavior depends significantly on the shape of loading path, and on the magnitude of mean stresses, shear strain amplitudes, shear rates and their histories. The ratcheting strain increases more rapidly as the steady stress or strain range become larger, or the strain rate become lower. The prior cycling with higher axial stress, larger strain range or lower strain rate greatly restrains ratcheting strain of subsequent cycling with lower ones. Such phenomenon is due to the enhancement of the material deformation resistance caused by the prior loadings.