Development of Viscoelastic-viscoplastic Model based on Transient Network Theory for Polyamides with Different Thermal Histories

Abstract

Polyamide (PA) is a semi-crystalline polymer in which the main chain is configured by repeating units of amide bonds (NHCO). The strength of PA is achieved by intermolecular hydrogen bonds between hydrogen and oxygen atoms of amide bonds. Previous studies have indicated that the thermal history conditions influent the crystallization rate and crystalline structure of PA, which affects the macroscopic mechanical properties. In this study, the relationship between the nano-micro structure of PAs and their macroscopic plastic deformation behavior was investigated. PA6 specimens were prepared with different microstructures obtained from two different crystallization processes, called the “isothermal” and “annealing” conditions, respectively. The microstructures were investigated using polarized optical microscopy and small angle X-ray scattering (SAXS), and the mechanical behaviors were evaluated using uniaxial tensile test. The SAXS measurement revealed the difference of nano-micro structures in PA6 with different thermal histories. In this study, we introduced parameters characterizing the nano-micro structure to the transient behaviors of PAs with different thermal histories. The proposed model can express the large plastic deformation behaviors of PAs with different thermal histories. We also performed the finite element (FE) simulations based on the proposed model to investigate the local plastic deformation of semi-crystalline PA. The simulation results reproduced the effects of viscoelastic-viscoplastic mechanical model based on the transient network (TN) theory.