The Effects of Temperature, Strain-rates and Loading Histories on the Inelastic Stress-Strain Behavior of a Biodegradable Nanocomposite Polymer nPLA and Numerical Simulations

摘要

Monotonic compressive deformation tests were conducted under time-varying strain rate and temperature conditions of 1.1 x 10~(-2) ~10~(-5) s~(-1) and 10~60°C in the full-digital servo-controlled testing system for nano-order clay particle dispersed composite nPLA (HV-6200, UNITIKA Ltd.)- Experimental stress-strain responses showed notable effects of the strain-rates and temperature, and they were compared with those of typical engineering polymers: PE, PP and PC, and some important deformation characteristics are revealed such as higher stiffness, work-hardening and softening m initial monotonic loadings, predominant overshoot phenomena in stress jumping of the strain-rate change tests, changes of stress-strain responses at elevated temperature, and inapplicability of time-temperature equivalence often shown for other polymers. The viscoplastic constitutive model based on overstress, VBO has been applied to simulate the experimental stress-strain behavior of nPLA. Numerical study has indicated that the modified VBO model has good modeling capability to reproduce observed basic responses including the overshoot phenomena with use of a newly proposed additional function which controls the viscosity in the model.