Aircraft materials Flashcards
What is duty cycle?
consideration of aircraft demands/requirements for material selection
describe duty cycle with regards to military and civil aircraft
- military aircraft have a service life of 100s hrs; civil airline > 30,000 hrs thus civil requires allow with lower fatigue and corrosion resistance
- military aircraft are v.agile and will be subject to high aerodynamic forces thus must be considered
describe the casting process
- 3 forms of casting: sand; permanent or die
- either heat treated or not
- gives 9 international series of allows Y1xx.x-Y9xx.x
- cost effective due to low boiling point BUT not as strong as Forming (wrought) process
describe the forming (wrought) process
- 2 forms: rolled sheet or extrusion
- either heat treated or not
- gives 8 international series of alloys 1xxx-8xxx
- strength is the key quality (higher than casting process)
describe the super plastic forming process
- high pressured air is blown at carefully controlled velocities to form shape and geometry
- process can be used on aluminium and titanium
- reduces cost and weight
what is carbon fibre reinforced plastic (CFRP)
CFRP consists of carbon fibres set into a matrix of plastic or epoxy resin (mechanically and chemically protective)
- CFRP sheets are sandwiched together to give enhanced load bearing properties in a chosen direction
- a sheet of CFRP is anisotropic
what is anisotropic
strength is dependent on direction of fibres
what are the advantages of CFRP
- high performance but cheaper
- 3x stronger than Al
- lighter than Al; 40% replacement of Al alloy would reduce weight by 13%
what are the disavantages of CFRP
- brittleness: tends to lost strength dramatically after impact (prone to imvisible impact damage)
- absorbs water of long periods –> reduces compressive strength
- doesn’t yield plastically
what are the 5 main aircraft material groups
- wood
- steel
- aluminium alloys
- titanium alloys
- fibre reinforced alloys
what features of pure aluminium means it has to be alloyed
- soft and flexible
- but: low strength –> not useful unalloyed
what are the 3 main aluminium alloy groups
- Aluminium, alloyed with copper, magnesium, manganese,
silicon, and iron. - Aluminium alloyed with all the above, plus nickel as well.
- Aluminium alloyed with copper, magnesium, zinc, and nickel.
Group 1 has trace elements of manganese, silicon, iron, copper and magnesium which give it properties such as
trace elements radically improve the
performance of the aluminium and make it capable of the
following:
-better at resisting fatigue but lower static strength
Tensile strength of not less than 390 N/mm2
Elongation at fracture of 15%
0.1% proof stress of at least 230 N/mm2
We can make this even better by using high temperature
‘ageing’, to get the tensile strength up to a minimum of 460
N/mm2 and the 0.1% proof stress up to not less than 370
N/mm2.
Group 2 has trace elements of manganese, silicon, iron, copper, magnesium (same as group 1) and nickel
This
group is particularly good for high temperature work and can
also be found in engine applications
-high strength at high temp
give an example of a commercially successful example of a specialised aluminium alloy
RR alloys - special mixtures from the 2nd group of al allows
- proposed by Rolls Royce plc & High Duty Alloys ltf
- widely used for forgings and extrusions in both aero engines & airframes where high temp work is necessary
