Passive thermal driving mechanics of a bistable composite tape-spring

Abstract

A bistable composite tape-spring (CTS) structure is a thin-walled open slit tube with fibres oriented at ±45°, which is stable at both the extended and fully coiled configurations. Owning to its positive Gaussian curvature deformation mechanics and high stowage-to-pack ratio, it has been successfully applied and launched to International Space Station and microsatellites to construct deployable solar sails. Intelligent driving designs of the CTS-based deployable structures are becoming more and more important to further reduce weight and complexities for space applications. Here, we presented novel findings on the passive thermal driving mechanics of the bistable CTS structure. This is achieved by exploring the thermal energy-induced microstructural expansion and contraction, which would change the structural curvature, and thus regulating the strain energy within the CTS. An analytical model on the strain energy evolution under thermal effects was established to predict the minimum stable shape transition paths, as well as to determine the critical boundary conditions for thermal driving. Both experiments and finite element model were then carried out to reveal underlying mechanisms. It is found that a CTS is able to be passively deployed under thermal energy, there is a minimum energy constraint to initiate the shape morphing process, and the critical boundaries are dependent on the thermal expansion of the structural material. These findings provide a novel low cost, simple and reversed smart morphing design principle of the CTS structure, enriching the theoretical analysis and deployable control of the bistable composites to benefit future deep space explorations.