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Detailing the visco-elastic origin of thermo-mechanical training of twisted and coiled polymer fiber artificial muscles

Journal Article


Abstract


  • Artificial muscles made be twisting and coiling polymer fibers provide outstanding performance. However, these materials show inconsistency in their non-loaded length that depends on their thermo-mechanical history. Typically, this behavior has been treated by “training” the samples before any actuation testing. A change in sample length occurs during training but remains consistent during subsequent heat/cool cycles at the same applied load. In this study, the training effect is investigated for a twisted and coiled nylon yarn heated over two temperature ranges: 25–50°C and 50–75°C. The training effect was most obvious in the lower temperature range, but nearly absent in the higher temperature range. When loaded below the glass transition temperature (Tg ~ 40°C) the viscoelastic strain occurs slowly but is rapidly released when the sample is first heated above Tg. The net effect of the first heating through Tg after loading is a small length change because the contraction due to actuation is offset by the expansion due to the release of the viscoelastic strain. A simple spring and dashpot model was developed and by changing only two relaxation times it was possible to simulate the observed training phenomena.

Publication Date


  • 2022

Citation


  • Nishimura, Y., & Spinks, G. M. (2022). Detailing the visco-elastic origin of thermo-mechanical training of twisted and coiled polymer fiber artificial muscles. Journal of Polymer Science, 60(8), 1360-1370. doi:10.1002/pol.20220024

Scopus Eid


  • 2-s2.0-85124723658

Start Page


  • 1360

End Page


  • 1370

Volume


  • 60

Issue


  • 8

Abstract


  • Artificial muscles made be twisting and coiling polymer fibers provide outstanding performance. However, these materials show inconsistency in their non-loaded length that depends on their thermo-mechanical history. Typically, this behavior has been treated by “training” the samples before any actuation testing. A change in sample length occurs during training but remains consistent during subsequent heat/cool cycles at the same applied load. In this study, the training effect is investigated for a twisted and coiled nylon yarn heated over two temperature ranges: 25–50°C and 50–75°C. The training effect was most obvious in the lower temperature range, but nearly absent in the higher temperature range. When loaded below the glass transition temperature (Tg ~ 40°C) the viscoelastic strain occurs slowly but is rapidly released when the sample is first heated above Tg. The net effect of the first heating through Tg after loading is a small length change because the contraction due to actuation is offset by the expansion due to the release of the viscoelastic strain. A simple spring and dashpot model was developed and by changing only two relaxation times it was possible to simulate the observed training phenomena.

Publication Date


  • 2022

Citation


  • Nishimura, Y., & Spinks, G. M. (2022). Detailing the visco-elastic origin of thermo-mechanical training of twisted and coiled polymer fiber artificial muscles. Journal of Polymer Science, 60(8), 1360-1370. doi:10.1002/pol.20220024

Scopus Eid


  • 2-s2.0-85124723658

Start Page


  • 1360

End Page


  • 1370

Volume


  • 60

Issue


  • 8