Stress memory of a thermoset shape memory polymer

The performance of stress recovery and shape recovery are equally important for high performance shape memory polymers (SMPs) in emerging applications. However, unlike shape recovery, stress recovery does not always follow a monotonic behavior, i.e., “stress plateau,” “stress overshoot,” and “stress undershoot” can be observed. In order to reveal the complicated stress memorization and recovery behavior, this study employs a phenomenological model which considers the recovery stress as the sum of residual programming stress, memorized stress, thermal stress, and relaxed stress for amorphous crosslinked SMPs. This model is demonstrated by a stress recovery experiment in which a polystyrene based SMP was programmed at two prestrain levels above the glass transition temperature, i.e., 20% (neo‐Hookean hyperelastic region) and 50% (strain‐hardening region), and two fixation temperatures, i.e., 20°C (below T g ) and 45°C (within the T g region), respectively. In addition, a clear distinction between the memorized stress and recovery stress is presented.