Effects of prior aging at 288°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

Abstract

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.

Computational Viscoplasticity Based on Overstress (CVBO) Model

“…Figure 12 shows the comparison between the experimental and predicted stressstrain curves for the PMR-15 neat resin subjected to prior aging for 250 h. Figures 13 and 14 show the comparison between the experimental and predicted stress-strain curves obtained for the PMR-15 polymer subjected to prior aging for 500 and 2000 h, respectively. Note that the solid lines in black from [32] were obtained with a one-dimensional implementation of the VBO The second type of test simulated is a creep test of 6 h duration conducted at 21 MPa (naturally, in stress control), preceded by strain controlled loading at 10 −4 s −1 . The specimens were subjected to four different prior aging times.…”

“…Ryther and Ruggles-Wrenn [30] have demonstrated the adaptation of VBO to include temperature dependence. McClung and Ruggles-Wrenn [31,32] have augmented the VBO to account for the effects of thermal aging on polymer deformation behavior.…”

Mechanical response of two polyimides through coarse-grained molecular dynamics simulations

“…The mechanical behaviour of PMR15 and its composites has been particularly well characterised [21][22][23][24], while recently, experimental results on HFPE52 have also been reported [40]. In particular, the stress-strain curves of the two polyimides that have been characterised, among others, by [23] and [40], throw up subtle differences.…”

“…The mechanical behaviour of PMR15 and its composites has been particularly well characterised [21][22][23][24], while recently, experimental results on HFPE52 have also been reported [40]. In particular, the stress-strain curves of the two polyimides that have been characterised, among others, by [23] and [40], throw up subtle differences. The experimentally obtained uniaxial tensile responses for PMR15 at strain rates ranging between 10 10 s  = --˙, both have a comparable yield stress of around 35 45 MPa -, the stress carrying capacity of HFPE52 being somewhat lower than PMR15.…”