Effects of Prior Aging at 288 degrees C in Argon Environment on Time-Dependent Deformation Behavior of a Thermoset Polymer at Elevated Temperature, Part 2: Modeling with Viscoplasticity Theory Based on Overstress

摘要

The viscoplasticity based on overstress (VBO) is augmented to model the effects of prior isothermal aging in an argon environment on the inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer. VBO is a unified state variable theory with growth laws for three state variables: the equilibrium stress, the kinematic stress and the isotropic stress. A systematic model characterization procedure based on a limited number of well defined experiments is employed to determine the VBO parameters. Experimental findings presented in Part I reveal the equilibrium stress and the kinematic stress to be affected by prior aging. Based on the experimental results, the isotropic stress is developed as a function of prior aging time. In addition, several VBO model parameters are made dependent on prior aging time. Comparison with experimental data demonstrates that the modified VBO successfully predicts the inelastic deformation behavior of the PMR-15 polymer subjected to prior isothermal aging for up to 2000 h. (C) 2009 Wiley Periodicals, Inc(dagger). J Appl Polym Sci 114: 3389-3395, 2009