Browsing by Subject "smart materials"

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    Multiscale Mechanics of Shape Memory Alloy Knitted Architectures
    (2020-08) Eschen, Kevin
    Fully-integrated, wearable garments with intrinsic active properties and a small form factor are bound to replace wearable designs with attached actuators and sensors in the next years. One of the promising intrinsically-active garment implementations is the shape memory alloy (SMA) knitted architecture. SMA knitted architectures provide spatially-distributed, three-dimensional actuation deformations and forces upon thermal stimuli. This thesis provides the fundamental understanding of the contractile shape memory alloy knitted architecture mechanics, which enables the predictable design of these novel intrinsically-active garments. SMA knitted architectures are manufactured from a single shape memory filament which is assembled into a network of interlacing loops. The connection of nonlinear geometry and material governs the SMA knitted architecture performance spanning from the macroscale (knit pattern) to the mesoscale (knitted loop) and microscale (SMA material). Macroscopic experiments are conducted to identify the dependence of force-extension properties on the number of loops in the knitted architecture, operation strategies and cyclic performance. The knitted architecture actuation and relaxation temperatures were defined and their variation was studied through variation of loop geometries and applied loading. Geometric loop properties were correlated to the knitted architecture thermo-mechanical performance on the mesoscale and microscopic phase fraction analysis was conducted to identify highly-stressed segments of the knitted loop and derive the primary deformation modes that contribute to the SMA knitted architecture performance. An empirical and a finite beam element method (FEM) model were implemented to provide predictive capabilities of the SMA knitted architecture performance. The FEM model includes textile specific modules and enables verification of simulation results by comparison to experimental results on all scales. The new understanding of the SMA knitted architecture mechanics was applied to design wearable garments with self-fitting and compression capabilities utilizing body heat for actuation through novel operation strategies. This research sets up the design of complex applications, optimization of SMA knitted architectures, and provides transfer knowledge that can be applied broadly in the up-and-coming intrinsically-active wearables space.