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Manufacture of Ultra-Dense Knitted Superelastic Structures

[+] Author Affiliations
Henry Koon, Jack Laven, Julianna Abel

University of Minnesota, Minneapolis, MN

Paper No. SMASIS2018-8225, pp. V002T08A013; 9 pages
  • ASME 2018 Conference on Smart Materials, Adaptive Structures and Intelligent Systems
  • Volume 2: Mechanics and Behavior of Active Materials; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies
  • San Antonio, Texas, USA, September 10–12, 2018
  • Conference Sponsors: Aerospace Division
  • ISBN: 978-0-7918-5195-1
  • Copyright © 2018 by ASME


Knitted Textiles made from Nickel-Titanium (NiTi) shape memory alloy wires are a new structural element with enhanced properties for a variety of applications. Potential advantages of this structural form include enhanced bending flexibility, tailorable in-plane, and through-thickness mechanical performance, and energy absorption and damping. Inspection of the knit pattern reveals a repeating cell structure of interlocking loops. Because of this repeating structure, knits can be evaluated as cellular structures that leverage their loop-based architecture for mechanical robustness and flexibility. The flexibility and robustness of the structure can be further enhanced by manufacturing with superelastic NiTi. The stiffness of superelastic NiTi, however, makes traditional knit manufacturing techniques inadequate, so knit manufacturing in this research is aided by shape setting the superelastic wire to a predefined pattern mimicking the natural curve of a strand within a knit fabric. This predefined shape-set geometry determines the outcome of the knit’s mechanical performance and tunes the mechanical properties. In this research, the impact of the shape setting process on the material itself is explored through axial loading tests to quantify the effect that heat treatment has on a knit sample. A means of continuously shape setting and feeding the wire into traditional knitting machines is described. These processes lend themselves to mass production and build upon previous textile manufacturing technologies. This research also proposes an empirical exploration of superelastic NiTi knit mechanical performance and several new techniques for manufacturing such knits with adjustable knit parameters. Displacement-controlled axial loading tests in the vertical (wale) direction determined the recoverability of each knit sample in the research and were iteratively increased until failure resulted. Knit samples showed recoverable axial strains of 65–140%, which could be moderately altered based on knit pattern and loop parameters. Furthermore, this research demonstrates that improving the density of the knit increases the stiffness of the knit without any loss in recoverable strains. These results highlight the potential of this unique structural architecture that could be used to design fabrics with adjustable mechanical properties, expanding the design space for aerospace structures, medical devices, and consumer products.

Copyright © 2018 by ASME



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