In the DARE Minor the team was given the task of investigating the storage of liquid oxygen as an oxidiser for a potential future DARE rocket launch and to simulate the thermal behaviour of the oxidiser in the storage tank. The tank is required to have an operating pressure of 60Bar and to be compatible with liquid oxygen.The team focused on two different main concepts a aluminium type design and a composite type design. Aluminium was a suitable choice due to its high yield strength of 155 MPa, as well as having acceptable weight properties. Its cost is suitable for the budget allowed for this years minor. Another challenge for the team was to design an adequate sealing method, to seal the tanks. The team investigated two different sealant methods, welding and o-ring seals.

Welded and Bolted Tank Designs

The welding method investigated both arc welding and electron beam welding, two different methods were investigated to find which created a stronger weld. The tanks are to be pressure tested to 90Bar to verify the welds can withstand the high stresses and to analyse the deformation of the tank. A further possible test is to test the tank till failure to analyse the failure mode. The other sealing method incorporated a FEP spring o-ring seal. The method used a bulkhead which is bolted to the tank shell and uses the FEP o-ring to seal the tank. A prototype of this tank will also be tested to a pressure of 90 Bar to verify the design. The failure of this method was modelled using a software developed in house by DARE.  The bolted design requires a sealing ring compatbile with cryogenic oxygen. The sealing ring is a new material which has never been used by DARE and is avery promising sealing method. The lower tank is the bolted design which incorporates the FEP spring o-ring. Another focus for the team was investigating the possibility of using a composite type tank. A full 3D model of the tank was created which modelled both the structural and thermal properties of the tank when loaded by a pressure and a thermal load. The composite design has a thin inner linerof aluminium and uses carbon fibres wrapped around the tank to provide the strength needed to withstand the pressure loads. Figure 2 is a complete 3D model of the stresss the tank would be put under when fully pressurised. This model was created to assist in the design procedure and validate the design. The team created a software tool which had the capability to model the thermal behaviour of the tank, both during filling but also incorporated the case when the tank would be filled and bleeding oxygen. Another model was created to analyse the structure of both the aluminium and the composite design as to verify the design. The team concluded that both design are feasible, the composite design is a better option, due to its higher strength and lower weight, however its costs are significantly higher and manufacturability might lead to more challenges.

Finite Element Analysis of the Composite Design