Doctor of Philosophy (PhD)


Mechanical Engineering

Document Type



In this dissertation, the application of smart polymers as actuators was investigated, with focuses on shape memory polymers and twisted-then-coiled artificial muscles. Thermomechanical models have been developed for various polymeric actuators, so as to facilitate interpretation of the underlying mechanisms and to provide guidance for future design. The classical one-way shape memory effect in amorphous shape memory polymers was first reproduced. The amorphous shape memory polymer was treated as a frozen-phase matrix with active-phase inclusions embedded in it. A phase evolution law was proposed from the physics perspective and the Mori-Tanaka approach was used to predict the effective mechanical properties. Then, a phenomenological constitutive model was developed based on the multiple natural configurations framework for the semi-crystalline two-way shape memory effect. The model elucidated how the programming procedure affect the crystallization behavior and eventually determine the two-way shape memory effect via storage of internal stress. Artificial muscles with hierarchical chiral structure that can offer a hundredfold increase in power over natural muscles of equivalent lengths have recently been demonstrated experimentally. To investigate the physical origin behind the remarkable tensile actuation behavior and, therefore, the correlation between the actuation performance and the intrinsic material parameters, a multi-scale modeling framework from macro-scale helical spring structure top-down to the molecular chain interaction has been developed Then, based on the prediction results of the multi-scale model, a new type of hierarchical chiral structured artificial muscle was fabricated using two-way shape memory polymer fiber. The usual improvement in the axial actuation of the twisted-then-coiled muscles were demonstrated both experimentally and theoretically.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Li, Guoqiang