Mechanical responses of Semi-crystalline thermoplastic polymers at various temperatures

This study examines the mechanical responses of three semi-crystalline POM polymers under uniaxial tension and compression loadings with various loading histories and at different temperatures. The studied POM polymers show variations in their molecular weight and degree of crystallinity with insignificant differences in the lamella thickness. Experimental results indicate that mechanical loadings, even at relatively low strain levels, cause permanent deformations and hysteretic responses, which are attributed to changes in the microstructures of polymers. Tensile and compressive loadings lead to different microstructural changes and elevated temperatures accelerate the changes. The POM polymers also show pronounced viscoelastic responses. A new mathematical model, based on a multi-network approach, is formulated to describe the macroscopic thermo-mechanical response of viscoelastic POM polymers incorporating the net effect of microstructural changes. The model assumes that the polymer has different stress-free configurations associated with different microstructures and the microstructural changes are governed by the deformations of the polymers. The model is shown capable of describing mechanical responses of POM polymers under various loading conditions, loading histories, and temperatures.