Folding of a Bistable Composite Tape-Spring Structure

A bistable composite tape-spring is a thin-walled, laminated open slit tube, which is stable in both extended and coiled configurations. The governing factors of its bistability depend on the material constitutive behaviour, initial geometrical proportions, and geometrically non-linear structural behaviour. This inherent behaviour is similar to the lock-stay or side-stay assemblies within an aircraft landing gear: these extend and retract with the gear, but remain in a fixed position when the gear is stowed in the bay or locked in the down position. Thus, it is envisaged that by using bistable composite tape-springs, it may reduce further the weight, complexity and maintenance, compared to conventional lock-link assemblies. The lock-stays are selected as the first potential application of bistable tape-spring structures. Both stays are mainly subjected to relatively low compressive loads, and are static in two different positions - when the gear is locked in the deployed or retracted position. Here, we present our investigations in folding of bistable composite tape-springs through experiments, finite element analysis (FEA) and theoretical analysis.