Hollow Titanium Fan Blade Flashcards
List a hollow titanium fan blade’s main functions.
- Used to generate 85% of the total propulsive thrust and intake air into the compressor system.
- Capable of moving a tonne of air per second; 3300rpm, tip speed of 1730km/hr, centripetal force of 900N.
- High specific strength for fuel efficiency.
- High impact fracture toughness; bird strikes.
- High specific stiffness to endure tensile load from rotation.
- Corrosion resistant due to inlet air temperature, pressure and composition. Therefore, must have a high endurance limit, high fracture toughness, high Young’s Modulus and low density.
What is the most suitable alloy for this application?
Titanium Ti6Al4V. The Vanadium improves the hot working performance during the super-forming manufacturing process and the Aluminium provides high strength properties.
It has suitable strength ductility, fracture toughness, corrosion resistance and work-ability for use at the operating temperatures of the fan (up to 300 degrees C).
What are the disadvantages of using Aluminium alloys for this application?
They have higher specific strengths and stiffness; however, they are less reliable and more prone to high-cycle fatigue failure, making them less suitable for critical components of the engine operation.
Why is Steel not used for this application?
Lower specific strength and stiffness which leads to higher operational costs.
Why is CFRP not used for this application?
Undesirable impact behaviour; irreparable internal damage to the matrix from impacts can lead to sudden catastrophic failure. Leading and trailing edges are weak and can be easily damaged by foreign objects.
Describe the first manufacturing process of making a hollow titanium fan blade.
Diffusion Bonding: the atoms of two layers of metals intersperse themselves over time.
- 3 sheets of titanium alloy, two have ‘stop-off’ material that prevents the sheets from joining in the regions during the bonding.
- Sheets are then stuck together and placed in a furnace at moderate temperatures and high pressures; this is where the diffusion bonding takes place.
- A single flat sheet is produced where it is joined in all areas apart from where the stop-off material was used.
Describe the second manufacturing process for making a hollow titanium fan blade.
Super Plastic Forming:
- Bonded sheets are placed in a die and heated to a temperature within the titanium plastic temperature range.
- The bond at one end is opened to allow for pressurised blow forming of the cavity between the outer sheets. The internal sheet becomes crinkled as it acts as a stiff corrugated structure within the blade. air is then removed and an inert gas (Argon) is introduced to return the pressure and prevent corrosion.
- The process is highly compatible with Ti alloys due to their high ductility and yield quality as well as their moderate elastic modulus.
Give the first suitable inspection method.
Vibrothermographic inspection:
Blades are excited using an ultrasonic emitting device. Friction between the moving crack surfaces leads to local increases in temperatures that can be recorded using infrared sensors.
It is difficult to detect fine defects or structural weaknesses that aren’t cracks or inner damage.
Give the second suitable inspection method.
Eddy Current Testing:
A probe that generates an electromagnetic field is placed close to the conductive component. This induces eddy currents within the component that generate their own magnetic field. The interaction between the magnetic fields can be detected and used to determine whether a defect exists.
It is highly accurate, highly effective and cost efficient and can read through paint and other surface coatings. Depth of penetration is limited so it can only be used for surface checks. Also, it cannot detect defects that run parallel to the material surface.
