Browsing by Subject "shape memory alloys"

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    Bear Hug: The Design and Development of an Active Deep Touch Pressure Garment for Sensory Processing Disorder
    (2017-08) Duvall, Julia
    Many medical conditions, including sensory processing disorder (SPD), employ compression therapy as a form of treatment. SPD patients often wear weighted or elastic vests to produce compression, deep touch pressure (DTP), on the body, which have been shown to have a calming effect on the wearer. Unfortunately, current products (weighted vests and blankets, pneumatic garments, and negative ease stretch garments) are unable to meet their wearers’ needs, in that they are unable to both provide the dynamic compression required, while also meeting the user’s comfort needs by being unobtrusive. Recent advances in compression garment technology incorporate active materials to produce dynamic, low bulk compression garments that can be remotely controlled. The purpose of this thesis is twofold, first, to identify requirements for a DTP therapy garment, and second, to a build a dynamic garment for DTP therapy. A literature review, a qualitative investigation with experts and occupational therapists, and a quantitative study of current DTP garments were used to build a problem variable framework for a more optimal DTP therapy garment. The variables that were identified fell into two major categories; system variables, which encompass the basic important features needed in order to provide DTP on the body, and usability variables, which are the other important features required for an effective and efficient system. Following this investigation, an active compression vest using shape memory alloy (SMA) spring actuators was developed in order to better meet these requirements than existing DTP products. The vest prototype incorporates 16 SMA spring actuators (1.25 mm diameter, spring index = 3) that constrict when heated, producing large forces and displacements that can be controlled via an applied current. When power is applied (up to 43.8 W), the prototype vest generates increasing magnitudes of pressure (up to 37.6 mmHg, spatially averaged across the front of the torso) on a representative child-sized form. Average pressure generated was measured up to 71.6% of the modeled pressure, and spatial pressure non-uniformities were observed that can be traced to specific garment architectural features. Although there are no consistent standards in magnitude of applied force in compression therapy garments, it is clear from comparative benchmarks that the compression produced by this garment exceeds the demands of the target application. Additionally, the garment can produce a dynamic and controllable pressure durations and magnitudes within a low and unobtrusive form factor, which are identified as important requirements for DTP therapy. There are several variables that require further investigation, including thermal comfort of the garment. This study demonstrates the viability of SMA-based compression garments as an enabling technology for individualized and enhanced SPD (and other compression-based) treatment. Additionally, the technology can be used as a tool to determine and standardize optimal treatment parameters.
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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.