Topology morphing in composite helical lattices

Morphing composite structures present a departure from traditional engineering structures due  to their inherent shape changing nature, which can be tailored and optimised in order to reduce  structural mass whilst maintaining and even increasing structural stiffness, where desirable.  This thesis describes two such morphing structures, the bistable composite helix and the  multistable composite cylindrical lattice. While the two structures are similar in composition,  both consisting of carbon fibre reinforced polymer strips manufactured to an initial curvature  and constrained to a smaller curvature, introducing prestress, they differ in the method in which  they are fastened and hence their method of morphing. The bistable composite helix structure consists of composite strips joined by rigid spokes, fixing the helix to a constant radius, thus,  as the helix morphs, its radius remains constant and its twist varies. The cylindrical lattice  however comprises composite strips, fastened to each other, in a manner whereby as the lattice  deploys, its radius decreases and its twist remains constant.

The analytical modelling capabilities of both structures is enhanced upon by incorporating  thermal strain to the strain energy profile, which allows the morphing behaviour of these  structures to be more accurately predicted. Finite element analysis and experimental testing of  both structures are performed in order to test the validity of the analytical models developed.  This improvement of the modelling capabilities facilitates further morphing behaviours to be  enabled within these structures. This thesis focuses on developing a topological morphing  mechanism within the composite cylindrical lattice structure. Mechanical fasteners are replaced with permanent magnets in order to enable a reconfigurable joint within the cylindrical lattice structure, hence introducing manually actuated topological morphing. This mechanism  is further developed by replacing a set of permanent magnets with electromagnets in order to  introduce semi-autonomy of morphing to the system. Extensive characterisation of the cylindrical lattice is performed, focusing on the site of topology morphing, and on the structure  globally both pre- and post-topology change, through experimental testing and finite element  analysis in order to represent the effects of topology morphing on the cylindrical lattice.