Pressurized nonlinear elastic tubular membranes reinforced with ultraviolet-activated contractile fibers

Azobenzene is a photoresponsive material whose stress-free configuration changes when exposed to ultraviolet light, allowing ultraviolet light to act as a non-mechanical trigger for deformation. This work investigates the mechanics of a fluid-filled tubular membrane formed from a homogeneous incompressible nonlinear elastic material reinforced by an axisymmetric distribution of photoresponsive fibers. The fibers lie parallel to the membrane midsurface and are helically wound. The tube contains an incompressible fluid and has closed ends. Fiber contraction induced by ultraviolet light can alter the tube geometry and generate changes in internal pressure. A constitutive model is developed to account for the nonlinear elastic response of the membrane and the activation-induced contraction of the fibers. Using force balance equations, the governing equations for tube deformation and equilibrium are formulated for two loading conditions: contraction at constant fluid pressure and contraction at constant fluid volume. Numerical solutions are obtained both by solving the formulated system of nonlinear algebraic equations directly and by finite element analysis. Results quantify the influence of fiber contraction and fiber orientation on tube deformation, the radius-to-length ratio, and pressure generation. The enclosed fluid is shown to strongly influence the mechanical response, leading to distinct behaviors under constant pressure and constant volume conditions. Numerical results obtained by the two methods are in good agreement.