| Deployable structures play an important role in space applications as they minimise the volume required by large structures such as antennas, solar panels, reflectors or de-orbiters. A low cost and mass option, relies on the use of airtight inflatable structures. Over the years several rigidization methods have been developed, each with their strengths and weaknesses, however due to the simplicity of aluminium based metal-polymer laminates, this class of shells have been successfully flown on a series of legacy missions. Metal polymer laminates are typically three-ply constructions where two foils of ductile annealed aluminium sandwich a polymer core. Structures such as sphere and columns may be constructed from flat sheets of material. The envelopes are then packaged. Pressurised gas, typically nitrogen is realised into the envelope to achieve deployment. To rigidize the structure the pressure is further increased to a value slightly higher than the yield point of the metal foils. By conducting repeated rigidization experiments it was observed that residual fold creases remain present in metallic shell. As metal laminates rely on the structural integrity of the shell for strength, it is important that the extent of the initial imperfections is known. The collapse load of laminate columns is significantly reduced by this effect. If care is taken during packaging and construction of these structures, packaging residual creases remain the largest source of imperfections.;To observe closely the folding process, a 3D laser and SEM images have been taken at various steps during folding. To understand this mechanism these results were compared against the results from literature. It has been found that for a 'Z' folded column the longitudinal creases flatten more than the circumferential creases. A numerical model has been derived for the elastic-plastic bending and springback of a metal film and metal-polymer-metal laminate. In the presented work this approach replicates the introduction of a typical 'V' fold and relaxation once the load has been removed. The system of differential equations was solved in MATLAB using ode45. To simplify the analysis a bilinear stress-strain profile with plane strain has been attributed to the metal film. The results have been validated with good agreement against experimental results and FEA analysis conducted in ABAQUS. Two three ply aluminium-polymer-aluminium flight ready laminates have been used as the experimental benchmark. The derived model may be adapted for different laminate configurations. It is known that it is difficult to quantify the mechanical properties of thin aluminium films, in particular the Young's modulus. Several results from literature are discussed and the solutions proposed is outlined. The lessons learn from this research project have been applied to the development of a novel rigidizable aluminium-BoPET based deployable structure. The structure consists of six laminate booms to connect to form a cuboid structure with a cross-sectional are of 0.5 m2. The structure and support systems were design to occupy the volume of single CubeSat Unit. The deployable will be flown on the RemoveDebris ADR technology demonstrator. |
