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5 April 2007Thermomechanical characterization of shape memory polymers
Data from comprehensive thermomechanical tests of shape memory polymers are reported, with specimens tested up to
75% strain and between 30-120°C temperatures. The data is analyzed and key observations are drawn. The stress/strain
behavior during loading at temperatures above glass transition for the Veriflex shape memory polymer tested was
linear and did not show much variation with the actual temperature. When the polymer is cooled with end constraints,
thermally induced tensile stresses developed, but only after the temperature reduced below glass transition and the
material stiffened. When the constraints were then released, 97-98% of the original strain was locked in. Reheating the
shape memory polymer beyond the glass transition temperature resulted in shape recovery (shape memory effect). When
the polymer was reheated while constraining the strain, the full recovery stress developed was about the stress the
polymer was initially loaded to during deformation at high temperature. Examining the Young's modulus at elevated
temperature and low temperature showed that Veriflex softened by around 40-60 times when heated through glass
transition.