Modeling the Effect of Strain Rate on the Mechanical Properties of HDPE/Clay Nanocomposite Foams

Abstract

A constitutive model considering the effect of strain rate on the mechanical properties of semicrystalline polymer/clay nanocomposite foams was studied. Also, the influence of crystallinity on the effect of strain rate was incorporated in the model. High density polyethylene (HDPE)/clay nanocomposite foam was manufactured by a batch foaming process. Intercalated clay structures in the nanocomposite were investigated by means of transmission electron microscope (TEM), and the crystallinity of the material was measured using differential scanning calorimeter (DSC). Also, foam morphologies were studied by using scanning electron microscope (SEM). The favorable effect of nanoclay on the foaming was increased as crystallinity decreases. Also, the influence of crystallinity on the foaming decreased at high clay contents. The tensile strength of the foams increased linearly to the logarithmic scale of strain rate. The Young's modulus of the foams was reinforced by increasing the crystallinity. However, the rate of increase in the modulus was blunted as strain rate increases. Also, the Young's modulus increased gradually with increasing the strain rate, but the rate of increase diminished as crystallinity increases. This combining effect of strain rate and crystallinity on the Young's modulus was modeled and a viscoelastic stress-strain behavior of the foam was also proposed. The proposed constitutive model was validated by experiments.