OHKLA Design/Oxidizer tank material
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[edit] Decision
A decision on this design task was made on 23/10/2010. The OHKLA oxidizer tank will be manufactured from 6061 T6 Aluminium
[edit] Summary
The purpose of this design task is to select a material from which to construct the OHKLA hybrid rocket engine's oxidiser tank.
[edit] Background
One of the two major components of a hybrid rocket engine is the oxidiser tank, which holds the gaseous or liquid oxidiser, ready to be injected into the combustion chamber. In the case of OHKLA, the oxidiser is nitrous oxide (N2O), which will be stored as a liquid, with a layer of gas on top providing the pressurisation which keeps the rest of the oxidiser liquid at room temperature and which is used to force the oxidiser into the combustion chamber.
[edit] Features/Considerations
[edit] Tank mass
A lighter oxidiser tank will contribute to a lighter dry mass of the entire rocket, and hence to a lower required propellant mass, making the rocket smaller and each launch cheaper. Thus, all else being equal, materials which result in lower tank masses should be preferred over those which result in heavier tanks. This point is particularly salient because the oxidiser tank is very often the heaviest single component of an N2O hybrid rocket.
[edit] Tensile strength
The oxidiser tank is a pressure vessel, and must be capable of safely containing the pressurised oxidiser at the expected pressures. In the case of liquid N2O at room temperature, this pressure is about 5.2 MPa.
[edit] Ease of construction
Since N2O cylinders of the required size and length to diameter ratio cannot be purchased as off-the-shelf components, the oxidiser tank will need to be manufactured from raw materials. Thus there needs to be a preference for materials which are easier to work with. For instance, steel is easier to weld than aluminium.
[edit] Cost
All else being equal, cheaper materials are preferred over more expensive materials.
[edit] Available Solutions
[edit] 304 Stainless Steel
Pros:
- High ultimate tensile strength (505 MPa)
- Easy to weld
Cons:
- High density (8.00 g/cc)
- Low yield tensile strength (215 MPa)
[edit] 6061 T6 Aluminium
Pros:
- High yield tensile strength (276 MPa)
- Low density (2.70 g/cc)
Cons:
- Less easy to weld
- Less ultimate tensile strength than 304 Stainless Steel (310 MPa)
[edit] Nickel Chromium Alloy
Pros:
- Extremely high yield tensile strength (875 MPa)
- Extremely high ultimate tensile strength 1275 MPa)
Cons:
- Extremely expensive
- High density (8.22 g/cc)
[edit] Carbon Composite
Pros:
- Extremely low density
Cons:
- Expensive
