Experimental and Modeling Study on Stress Memory Effect of Shape Memory Polymers
Master of Science in Engineering Science (MSES)
Engineering Science (Interdepartmental Program)
As an important class of smart materials, thermal-induced shape memory polymers can store and release deformation energy on demand, in terms of recovery strain or recovery stress. Consequently, shape (strain) memory effect and stress memory effect can be identified. However, owning to some engineering and biomedical applications, stress memory effect sometimes can play an even more important role. In this work, stress memory effect is experimentally studied via two examples, namely, styrene-based bulky SMP by compression programming and polyurethane-based SMP fiber by stretch programming. Experimental results indicate that stress memory effect is closely related to programming temperature. In addition, “stress overshoot” and “temperature memory effect” are observed. We believed that at lower temperature the stress memory effect is primarily enthalpy driven, whereas at higher temperature it mainly driven by entropy, which provides a key clue for better understanding the origin of stress memory behavior programmed at different temperatures. We also proposed a multi-mechanism phase transition based phenomenological model, which includes shape memory effect, thermal expansion, mechanical relaxation and damage effect, to more accurately capture the recovery stress. In addition, a new concept of a fourth-order anisotropic stress memory effect tensor is introduced to help quantifying the general stress memory phenomena.
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Wang, Anqi, "Experimental and Modeling Study on Stress Memory Effect of Shape Memory Polymers" (2016). LSU Master's Theses. 2166.