Thermomechanical recovery couplings of shape memory polymers in flexure

Shape memory polymers (SMPs) have the capacity to recover large strains when pre-deformed at an elevated temperature, cooled to a lower temperature and reheated. The thermomechanical recovery behavior of an SMP is examined in three-point flexure for various pre-deformation and recovery conditions. Results indicate that when pre-deformed well above the glass transition temperature, T-g, the stress-strain response at the pre-deformation temperature governs the relationship between the recovery stress/strain and the corresponding pre-deformation strain/stress. When pre-deformed at a temperature below T-g, the relationship between recoverable stress and strain level in the SMP is not governed by the stress-strain response of the material at the pre-deformation temperature. Rather, a peak recovery stress, which is less than the applied pre-deformation stress, appears near T-g. Higher cooling rates during constraint lower the temperature necessary for complete shape fixity, but increase the recoverable stress level. Higher heating rates during recovery raise the recovery onset temperature and decrease the peak recoverable stress. Ramifications of the results on future research efforts and emerging applications of SMPs are discussed.