Tests have been performed in an effort to gain understanding of electrical and mechanical properties of silver-coated nylon fibers subjected to stresses and strains and exposed to various environmental conditions. This effort is part of a larger effort to develop electro-textiles ("e-textiles") [electrically conductive textiles] that could be incorporated into future Army combat uniforms and used therein to couple electrical power and signals between electronic devices. Understanding of the effects of stresses, strains, and environmental conditions is important because of a need to ensure adequate performance of e-textiles under the widely varying, harsh conditions to which military uniforms are exposed when worn in extreme climates, during laundering, and during storage at high temperatures.

The Fractional Change in Electrical Resistance of a silver-coated nylon fiber was determined from measurements of electrical resistance immediately after application of tensile strain.
The nylon fibers included single filaments and 34-continuous- filament yarns. Before the tests, the fibers were coated with thin layers of silver by electroless deposition. The tests included standard measurements of stress versus strain, strength, and elongation to break in a tensile testing machine, and measurements of electrical resistance in the presence of tensile stress and strain and in post-strain and post-damage conditions. Electrical resistances were also measured after immersion in aqueous solutions of various degrees of acidity and alkalinity, after exposure to high temperatures, and after thermal cycling. Morphological examinations of the silver coats on the fibers were performed by means of scanning electron mi cros - copy.

The conclusions drawn from the measurement data acquired in the tests include the following:

  • As expected, electrical resistances of fibers increased with applied strains (see figure). In general, the piezoresistant behavior of a fiber of the type tested depends on the mechanical behavior of the base fiber as well as on the microstructure of the silver coat: changes in electrical resistance can be attributed to both changes in dimensions and changes in separation of silver particles.
  • Following removal of applied strains, fibers recovered mechanically and their electrical conductivities were almost completely restored. However, the response times (times for viscoelastic recovery and concomitant recovery of electrical conductivity) were found to be so long — of the order of minutes or longer — that one could not rely on such recovery in practical applications.
  • Electrical conductivities of fibers after thermal cycling and after exposure to high temperature were not diminished.
  • Although fibers in clothing are not normally subjected to large induced strains, any such strains and the associated changes in electrical resistance are of concern with respect to reliability of electrical connections. A plausible solution to the reliability problem may lie in the design of novel yarns or fabric structures to eliminate most or all induced strains.

This work was done by Suzanne Bosselman of the U. S. Army Natick Soldier Research, Development and Engineering Center.

ARL-0043


This Brief includes a Technical Support Package (TSP).
Testing Silver-Coated Nylon Fibers as Electrical Conductors

(reference ARL-0043) is currently available for download from the TSP library.

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