Material BehaviourThe rate (time)-dependent mechanical behavior of the PMR-15 thermoset polymer at elevated temperature

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 288 °C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behavior. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain-controlled loading were examined. The material exhibits positive, nonlinear strain rate sensitivity in monotonic loading. Nonlinear, “curved” stress-strain behavior during unloading is observed at all strain rates. The recovery of strain at zero stress is strongly affected by prior strain rate. The prior strain rate also has a profound influence on relaxation behavior. The rest stresses measured at the termination of relaxation tests form the relaxation boundary which resembles a nonlinear stress-strain curve. Likewise, creep response is significantly influenced by prior strain rate.