Functionalized Shape Memory Alloy Microfilament Twisted Yarn Structures

Abstract

The materials available to society define the substance of civilization. Continuous innovations in material science through history have enabled groundbreaking applications and technologies. The emergence of smart materials is revolutionizing the way we interact with everyday objects by providing additional functionalities to previously conventional devices. Of the smart material technologies, shape memory alloys (SMA) exhibit significant strain recoverability, large actuation deformations and forces, and multipurpose damping abilities through thermally dependent solid-state phase transformations. Monofilament-based SMA systems have immense potential in artificial muscle, energy absorbing, tactile surface, and wearable applications, but remain limited by obstacles in manufacturing, wearability, and tunability. This thesis provides the fundamental understanding of SMA microfilament twisted yarns to enable the design, manufacture, analysis, and synthesis of predictable and tunable functionalized microfilament fabric systems. SMA yarns are manufactured from a bundle of microfilaments through twist insertion. The nonlinear material within the nonlinear yarn geometry dictates the unique multifunctional performances across the hierarchical multi-level manufacturing of textiles. Detailed experiments conducted in this research identify key geometric, manufacturing, and processing parameters for mapping hierarchical interrelationships and improving the tunability of SMA performance. Key parameters function as inputs in a semi-analytical model that was derived from traditional yarn and SMA material models to predict the performance of SMA microfilament twisted yarns. The model accounts for superelastic recovery, shape memory actuation, and dynamic contraction phenomena to accurately capture the microfilament response to macroscopic loading in experimentally validated simulations. The twist-based geometric leveraging of SMA in the microfilament yarns, understood through this research, is expanded to manufacture over-twisted coiled yarn architectures that demonstrate strong artificial muscle actuator performance through moderately bounded thermal stimuli. The benefits of the highly compliant yarn structure are highlighted in cloth-like fabrics to demonstrate application-specific desired behaviors in both active and passive functionalized systems. This research establishes an understanding of SMA within microfilament twisted yarn structures for optimized performance, predictive modeling, expanded architectures, improved wearability in textiles, as well as a roadmap for integration of other smart material systems within yarn structures.