THE STRAIN RATE- AND TEMPERATURE-DEPENDENT MECHANICAL BEHAVIOR OF VERIFLEX-E IN TENSION

In this study, the inelastic deformation behavior of Veriflex-E, a thermally-triggered shape memory polymer resin, was investigated. The experimental program was designed to explore the influence of strain rate on monotonic loading at various temperatures. In addition, the creep behavior of specimens at various temperatures was evaluated. The time-dependent mechanical behavior of the Veriflex-E resin is strongly influenced by the temperature as well as the deformation rate. Thermally-actuated shape memory polymers can be thought of as having two phases separated by the glass transition temperature (T-g). At temperatures well below the T-g (room temperature), the Veriflex-E exhibits a high elastic modulus and positive, nonlinear strain rate sensitivity in monotonic loading. Likewise, the room temperature creep response is significantly influenced by the prior strain rate. The Poisson's ratio at room temperature is independent of the strain rate, but dependent upon the strain magnitude. As the temperature is increased, the strain rate sensitivity in monotonic loading decreases. Well above the T-g, the elastic modulus drops by several orders of magnitude, and strong strain rate sensitivity is no longer observed in the path of the stress-strain curve. In this high temperature region, the material achieves strain levels well above 100% and the Poisson's ratio is constant at 0.5 regardless of strain rate or strain magnitude. The creep strain, on the other hand; is significantly influenced by the prior strain rate at the elevated temperature. A slight hysteresis is observed during unloading, while recovery following unloading shows a permanent strain.