Structural optimisation of bistable deployable structures

Scissor structures are transportable, reusable and transformable from a compact bundle of elements to a deployed configuration, offering a huge volume expansion. They can behave as mechanisms during deployment, and in this case need additional members in order to be stable in the deployed configuration.
Other designs, the so-called self-locking scissor structures, avoid this need for external manipulation. By the satisfaction of certain geometric constraints, scissors structures can have straight members in the folded and the deployed configuration while geometric incompatibilities exist during transformation.
Because of these incompatibilities, some specific members bend during transformation, resulting in a bistable structural response which is characterised by a controlled snap-through behaviour that ’locks’ the structure and assures instantaneously some structural stability in the deployed configuration.

Due to the transformable bistable nature the design requires assessing both the non-linear transformation behaviour, as well as the service state in the deployed configuration. The requirement of a low peak force during transformation can be shown to oppose the high stiffness requirement in the deployed state;
the design can therefore be formulated as a multi-objective non-linear optimisation problem. A size and shape optimisation method is elaborated by choosing the best material combinations, the optimal geometry of the structure and beam cross-sections. The originality of this contribution is the use of
a multi-objective evolutionary algorithm to structurally optimise bistable scissor structures taking into account the deployed state as well as the transformation phase. First, the method is applied to optimize a single bistable scissor module. Next, a multi-module bistable scissor structure is optimised and the
single module and full structure based approaches are critically compared.