Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Mechanical Engineering

First Advisor

Dr. Y. Charles Lu

Second Advisor

Dr. Haluk E. Karaca

Abstract

Shape memory polymers (SMPs) are an emerging class of active polymers that can be used on a wide range of reconfigurable structures and actuation devices. The present study comprehensively examines the unconstrained shape recovery abilities of an epoxy-based SMP. In doing so, epoxy based SMP is synthesized and thermo-mechanically characterized. Results show that the present SMP exhibits excellent shape recoveries under unconstraint conditions, for a range of fixing strains and temperatures. Additionally, the stress-strain behavior of the SMP is determined to be nonlinear, finite deformation at all regions. The strain energy based models have been used to capture the complicate stress-strain behavior and shape recovery process of the SMPs.

Further SMP based composites are considered to obtain a smart material that is suitable for applications at both above and below the glass transition temperature of the polymer. A smart composite made of SMP and SMA would allow many design possibilities due to their controllable temperature-dependent mechanical properties. In this study, the shape memory composites (SMCs) are created by embedding SMA components (particles and fibers) into SMP matrices, which take advantage of the complementary properties of SMAs and SMPs. The SMA-particle and SMA-fiber reinforced SMP composites are designed through numerical simulations for different weight fractions of the SMA fillers were varied from 0-50%. Addition of SMA fillers significantly increased modulus across the temperature regimes while maintaining the large actuation strain. In addition to the simulations, SMA-Particle + SMP composites are synthesized and tested using DMA in compression. The obtained modulus results from the simulations for SMA-Particle + SMP composite is comparable with the experimentally determined results. However, since SMP matrix is not conductive these composites often require external stimuli such as external heaters which limit their applications. To overcome this limitation, multi-functional Shape memory polymer based composites are thus fabricated in the present study by embedding CNT fibers and Ni particles in SMP matrix that resulted in electrically conductive and thermally stable SMP based composites.

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