Mechanical Characterisation of Woven Pneumatic Active Textile

Abstract

Active textiles have shown promising applications in soft robotics owing to their tunable stiffness and design flexibility. Given the breadth of the design space for planar and spatial arrangements of these woven structures, a rigorous and generalizable characterisation of these systems is not yet available. In order to characterize the response of a stereotypical woven pattern to actuation, we undertake a parametric study of plain weave active fabrics and characterise their mechanical properties in accordance with the relevant ISO standards for varying muscle densities and both monotonically increasing/decreasing pressures. Tensile and flexural tests were undertaken on five plain weave samples made of a nylon 6 (polyamide) warp and EM20 McKibben S-muscle weft, for input pressures ranging from 0.00 MPa to 0.60 MPa, at three muscle densities, namely 100 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> , 74.26 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> and 47.62 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> . Contrary to intuition, we find that a lower muscle density has a more prominent impact on the thickness, but a significantly lesser one on length, highlighting a critical dependency on the relative orientation among the loading, the passive textile and the muscle filaments. Hysteretic behaviour as large as 10% of the longitudinal contraction is observed on individual filaments and woven textiles, and its onset is identified in the shear between the rubber tube and the outer sleeve of the artificial muscle. Hysteresis is shown to be muscle density-dependent and responsible for a strongly asymmetrical response upon different pressure inputs. These findings provide new insights into the mechanical properties of active textiles with tunable stiffness, and may contribute to future developments in wearable technologies and biomedical devices.