Materials Flashcards
Stiffness
Young’s Modulus
Early elastic deformation
Strength
Ultimate load bearing capacity prior to failure
Toughness
Energy absorbed before fracture
Ductility
Ability to deform
Brittle
Opposite to ductile
Low deformation before fracture
Hardness
Resistance to surface deformation
Ductility test
A bar of the material is bent in the middle with force applied in the middle and at the ends.
Fatigue test
A cyclic load is applied below UTS
Tests crack initiation, growth and tensile overload failure
Steel- pros and cons
Pros
UTS
Good elevated temperature properties
Cheap and readily available
Cons Relatively high density Poor Strength/weight Corrosion problematic Difficult to fabricate
Aluminium
Pros Low density Good strength/weight Easily fabricated by many routes Relatively inexpensive
Cons
Low hardness
Poor Corrosion resistance
Relatively poor fatigue performance
Titanium
Pros Relatively lightweight Excellent corrosion resistance High strength/weight Good high temperature properties Demonstrates super-plasticity-complex forms
Cons
Relatively high price
Difficult to form at room temp
Expensive to machine
Types of Composites
Fibreglass Carbon fibre reinforced polymer Wood MMC's CMC's
Fibre orientation and loading
Fibre orientation matched to principal stresses
GLARE Technology
Hybrid material
Alternating layers of aluminium foils and unidirectional glass fibres
Impregnated with adhesive
Jet engine work cycle
Suck-Squeeze-Bang-Blow
Fan in a jet engine
Intakes a large volume of air
Compressor
Reduces air volume and raises pressure
Combustor
Air+Fuel mixed and ignited
Turbine
Exhaust gases expelled, turbines rotates fan and compressor via shaft/gears
How much thrust is produced by air directly expelled around the outside of a high bypass gas turbine?
Up to 50%
How many flight cycles are engines typically designed for?
30,000 flights
Temperature at fan intake
-60 degrees celsius
Temperature at IP compressor
300 degrees celsius
Temperature at the HP compressor
600 degrees celsius
Temperature at the combustor
1200 degrees celsius
Temperature at the turbine/exhaust
> 1200 degrees celsius
Fan/Compressor material
Titanium
Combustor/Turbine material
Nickel
Why is having a single crystal turbine blade desired?
Excellent mechanical properties in longitudinal axis and improved heat resistance
How are the HP turbine blades cooled?
Blade temperature would exceed melting point of Nickel so cooling air plus ceramic thermal barrier coatings are used to prevent this
Engine Tests
Bird strike (impact)
Fan blade off (containment)
Hail and water ingestion
