| A structure with the ability to change its shape has an increased range of operational uses and performance traits over a conventional fixed-design structure. A common example of this is an aircraft wing with moving control surfaces that change the lift and drag characteristics. Traditional actuation systems for generating shape changes in such a structure, however, are often encumbered by mechanical systems and devices that make the structure heavier and more complex. In general, a simple actuation mechanism is easier to manufacture and more robust. Consequently, this thesis uses a computation design methodology that allows actuation systems to be integrally designed into the structure by using topology optimization. The forces that generate the shape changing strains, for instance strains resulting from shape memory alloys, photomechanical effects, or pressure sources, are treated as eigenstrains. Eigenstrains are arbitrarily generated strains that are characteristic of the method of actuation. Using this eigenstrain approach, topology optimization is used to pattern the spatial layout of strains throughout a structure to produce a predetermined target shape. This methodology is applied to design self-assembling or shape changing structures using inelastic and incompressible eigenstrain concepts. The problems involving inelastic eigenstrains are assumed to hold their shape upon actuation. Geometrically nonlinear deformations are considered in the finite element model used for the topology optimization for these problems. The incompressible eigenstrain approach uses topology optimization to pattern fluid channels within a structure that, when pressurized, results in the target shape. A mixed displacement/pressure finite element approach is used to interpolate between solid and fluid regions in the structure. |
