The future of fabrics and clothing includes tailorable mechanical interaction with the human body for applications such as wearable robotics, self-fitting wearables, dynamic compression garments, and responsive haptic feedback garments. Actuating fabric structures are large, distributed mechanical actuators that take the form of traditional fabrics structures, such as thin-sheet, woven, or knit structures, and have been shown to produce complex motions, such as bending, torsion, and contraction. Shape memory alloy (SMA) knitted actuators are one type of actuating fabric structure that have previously been made of a single SMA filament deformed into a variety of weft knit patterns, which produce complex and programmable, surface wide actuation. Prior work shows these actuator fabrics can accomplish up to 50% uniaxial actuation contraction to self-fit around the body. Additionally, local manipulation of the knit pattern was shown to produce functionally graded, non-planar actuation to accomplish tailored conformity around non-cylindrical body forms. SMA knitted actuators also exhibit recovery forces up to 211 N/m, demonstrating their flexibility in applications that require large displacements as well as large force delivery.

This work expands prior SMA knitted actuator investigations by introducing SMA yarn geometries used in place of a SMA monofilament to produce new levels of kinematic tailorability within the knitted actuator. Other researchers have explored smart materials in yarn geometries to produce powerful torsional actuators, notably twisted SMA, carbon nanotube (CNT), polymer, or silk bundles. Limited work has leveraged the capabilities of actuator yarns within a fabric structure to enhance or modify large and distributed mechanical performance. This study experimentally investigates torque-unbalanced NiTi yarn structures and their contribution to the macroscopic performance of SMA knitted actuators. Through strategic modification of traditional geometric yarn variables, such as (1) SMA filament diameter, (2) number of SMA filaments within a yarn bundle, and (3) twist per unit length of yarn, performance of SMA knitted actuators composed of torque-unbalanced NiTi yarns is mapped. Results will be reported for both yarn and knitted actuator geometries to characterize their actuation contraction and force generation capabilities. In addition to wearable applications, this new level of actuator tunability has implications broadly in aerospace, industrial, biomedical, and consumer spheres.


Design and Experimental Investigation of Mechanical Actuator Fabrics Composed of Torque-Unbalanced Sma Yarns

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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