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Influence of strain rate and temperature on necking transition in a polydomain smectic main chain elastomer Part B Polymer physics

Lentz, Daniel M., Chen, Huipeng, Yu, Ziniu, Patil, Harshad P., Crane, Charles A., Hedden, Ronald C.
Journal of polymer science 2011 v.49 no.8 pp. 591-598
cold, deformation, heat, image analysis, polymers, temperature
Smectic main-chain liquid crystalline elastomers (MCLCE) with polydomain morphology are rare examples of elastomers that can form a neck and undergo cold drawing under tension. However, not all previous studies of the mechanical behavior of smectic MCLCE reported neck formation. The mechanical response of a polydomain smectic MCLCE has therefore been characterized by elongation at varying strain rates and temperatures to identify factors favoring mechanical instability. Yielding and neck formation are increasingly favored as the strain rate increases at constant temperature, or as the temperature decreases toward Tg. As cold drawing proceeds, significant creep occurs continuously within the neck, in contrast to the behavior of certain linear polymers that exhibit a “natural” draw ratio. Thermal imaging during elongation indicates that viscous heating is not a prerequisite for neck formation. Rather, inherent softening of the material during yielding due to morphological changes leads to an enhanced rate of deformation and contraction at the neck.