Synergistic effect of axial-torsional-radial deformation on the multi-strand helical filament artificial muscles

Multi-strand helical structures have attracted increasing attention in artificial intelligence materials due to their large deformation in axial, torsional, and radial directions. Such novel materials as artificial muscles with multi-strand helical structures hold a promising potential application in aerospace and biological engineering. Understanding the mechanical response of helical artificial muscles in these three typical directions is not only essential for tactically designing microstructures to improve the mechanical performance, but also significant for promoting the energy conversion efficiency of intelligent structures. In this paper, a bottom-up theoretical model is proposed to predict the mechanical behavior of multi-strand helical filament artificial muscles. The synergistic effect of axial torsional-radial deformation is demonstrated by the stiffness matrix of the helical structures, in which the interaction between adjacent filaments is involved. The result shows that the axial-radial and torsional-radial coupling responses are dominant in the moderate and high helical angular configurations, and the increase of radial strain may weaken the axial strength and heighten the torsional strength of artificial muscles. The dependence of mechanical properties on the microstructural parameters with different deformation modes is analyzed, which agrees well with the numerical calculations. This work would help explore the physical origin behind the remarkable abilities of deformation and elastic property of the helical artificial muscles and could present inspirations for the optimal design of advanced artificial intelligence materials with helical configurations.