On tailoring deployable mechanism of a bistable composite tape-spring structure

A bistable composite tape-spring (CTS) structure is a thin-walled open slit tube with fibres oriented at +/- 45 degrees, which is stable at both its extended and coiled configurations. The traditionally manufactured CTS is effectively self-deploying. Here, we devise a novel manufacturing method to tailor the deployable mechanism of a CTS. This is achieved through adjusting the internal stress levels by subjecting the fully coiled as-manufactured CTS samples to additional heat treatment process. Their deploying performance were then characterised through a bespoke axial load monitoring rig, in order to reveal the underlying mechanics. It is demonstrated three different deployable mechanisms can be manufactured based on the same CTS, namely self-deploying, neutrally stable and self-coiling CTS structures. The processed CTS samples also show specialised stabilities, varying from monostability to multi-stability. The tailoring mechanism is then proposed. Since the CTS sample is in a highly strained state when coiled, the polymeric composite material would slowly deform due to viscoelasticity. According to the time-temperature superposition principle, the custom heat treatment of a fully coiled tape is equivalent to acceleration of the viscoelastic deformation, where local stress relaxation occurs on both the outer and inner tape surfaces, which in turn altering the internal stress levels. Thereby, the heat treatment processing is able to tailor the deployable mechanism of the CTS structure. These enrich the deployment diversity of the CTS to better fit the requirements for various deployable mechanisms in order to further promote the applications of CTS structures to aerospace explorations.