Swelling Induced Twist in Hyperelastic Tubes Due to Spiral Patterned Biasing Fibers in the Cross Section

Simple fiber reinforcing patterns can serve to guide deformations in specialized ways if the material experiences expansion due to some sort of swelling phenomenon. This occurs even when the only activation is via the material swelling itself; the fibers being a passive hyperelastic material embedded in a swellable hyperelastic matrix. Using anisotropic hyperelasticity where the usual incompressibility constraint is generalized to model swelling, we consider such fiber guided deformation in the context of a circular cylinder subject to uniform swelling. The material is taken to be transversely isotropic with a fiber pattern corresponding to helical spirals in each cross section. This paper extends previous work which had examined a traction free outer radius that expanded while the inner radius was held fixed. Because of the spiral pattern, the tube in these previous studies exhibited increasing twist as the swelling proceeded. The problem considered here takes both inner and outer radius as free surfaces, thus causing the amount of radial expansion itself to be unknown. It is found that the spiral fiber pattern again induces a twist, and that this pattern also influences the nature of the radial expansion.