Shape of a bistable composite tape-spring in folding

A composite tape-spring structure is a thin-walled, laminated open slit tube. With fibres oriented at ±45˚, it is stable in both the extended and coiled configurations. In this research, we devise a simple ‘free’ bending system with minimal constraints to evaluate the folding nature of composite tape-springs. The shape of the tape-spring is characterised by considering both the shape during folding and the final folded shape. Experiments are carried out on composite tapes with different geometries: a finite element model is established and calibrated using the experimental results; a parametric study on the folded tape shape is performed based on a theoretical model to evaluate the effects of the initial geometry. Torsional buckling is clearly observed, and complemented with details from the FE model. Here, we show good agreement between experiments, simulation and theoretical analysis