Materials

Question 1

Describe the manufacturing process for a modern jet engine turbine blade, which allows for operation in a gas stream that exceeds the melting temperature of the turbine blade.

Answer 1

• Made out of a Nickel alloy
• Made out of a Single Crystal
• In-built cooling parts in the Fan
• Thermal barriers to protect from extreme heat

Question 2

In order to save further weight in the gas turbine engine, designers are considering the use of ‘blisks’ and ‘blings’. What are these components and what are the manufacturing methods and materials which allow them to be
used in service?

Answer 2

• Manufacturing blades and discs as a single structure (blisk ) removes the need for leakage paths and blade fixings, resulting in weight savings of up to 30 per cent.
• Bladed rings ( blings ) can save even more weight.
• Blisks have better life cycle value due to better manufacture and repair techniques
• Smaller Blisks are manufactured from a solid block whilst larger Blisks are made by friction welding a forged aerofoil onto the disk.
• Titanium Metal matrix composite with embodied silicon carbide fibres

Question 3

What materials would typically be used in a piston engine and what part of the engine is likely to operate at the highest temperature?

Answer 3

• Highest temperature at the cylinder head.
• Steel due to cost and constant changes between hot and cold

Question 4

Explain how upper temperature limits in a ramjet can be avoided if supersonic combustion is utilised.

Answer 4

At high speeds,high stagnation pressure and temperatures are experienced by an engine. To combust at subsonic velocities, the reduction in gas speed leads to high static pressures and temperatures which might exceed the material properties of the engine or lead to energy loss in dissociation reactions.

By allowing combustion at supersonic speeds, this reduces the static temperatures and pressures on the engine.

Question 5

Why are composite materials likely to be used in future jet engine production?

Describe two potential areas of use and what some of the limitations may be.

Answer 5

Composite materials could be used in fan blades or the compressor disk. They are likely to be used in future jet engine production due to being stiffer, stronger and lighter than conventional materials.

However, the cost of producing the composite in addition to the complexities of manufacturing them could act as limitations.