Figure 2.

Twofold programming and stress recovery behavior of PEU. (a) Stress (solid line) and temperature (dashed line) vs. time protocols. Programming consisted of deformation and unloading both at 40 and 0 °C, followed by cooling to −20 °C. The stress recovery behavior was investigated during heating to 80 °C. Finally, the specimen was unloaded and cooled to 23 °C. Heating and cooling were accomplished with a rate of 3 °C·min⁻¹. (b) Stress-strain relation when applying two-step programming, including an elongation to 400% at 40 °C and unloading, same as the application of an absolute maximum strain of 225% at 0 °C and unloading. The associated loading and unloading rates were 3 × 10² and 1 × 10³% min⁻¹, respectively. (c) Stress recovery behavior of twofold programmed PEU during heating from −20 to 70 °C.