Slide 1
Selection of materials for aircrafts
Introduction
The aerospace industry is in business to provide a means of
transport, and the broad service requirement to convey maximum
cargo at minimum cost is the same as for other forms of
transport.
However, the materials problems are greatly intensified by the
fact that failure in the air is much more likely to involve
catastrophic losses, including loss of life, than it is on the
surface.
Design Requirements
Lifting against gravity is a expensive task.
Design must be efficient and light weight.
The types of aircrafts makes different requirements of the
aircraft.
Big commercial passenger aircrafts (Airbus A380)
Small commercial passenger aircrafts (Hawker Jet)
Military aircrafts.
Agriculture Aircrafts
There are 4 important cycles in a aircraft life cycle
Ground
Takeoff
Cruise/operational
Landing
Design Requirements
Flying range (8000m 18000m)
Pressure will be low, moisture and air packets will cause
turbulence.
Life expected (6000 100000 hours)
Approx 25 years
Apart from fatigue corrosion and stress corrosion were
considered.
Three key factors
The three main constitutions of aircraft.
Payload (Passengers/Goods)
The carrier (The hull structure, control system & crew)
The power plant.
Considerations
We cant loose on the weight carried by the aircraft.
If the flight runs for a long time it must carry the required
fuel along with it. The fuel carried by it, is the main
constitution to the weight.
Power plant efficiency improvement
Improve weight to thrust ratio.
Improve the Blade design
Good elevated temp properties Nimonic series alloys
single crystal blade.
Blade cooling requires new techniques of manufacturing.
Oxidation resistant coating on blade.
Reinforced ceramics on blade.
Aircraft structure
As small as the structure as large you can adapt the payload.
(In terms of weight)
To reduce the cost per unit weight is the objective.
Cost required to lift 1 kg of weight to orbit by a spacecraft is
$20000. That much is not required for a aircraft. But we can save
up to $1000 per kg of weight in a aircraft.
Improve the property of the material thus we can loose on
weight.
Reduce the density, improve the strength.
Reduce the drag coefficient.
On Boeing777 a badly painted square foot area on each flight of
ten flights will increase the 21 gallons of fuel consumption in
each year.
Percentage of total take-off weight
Aircraft Structure
Wings
Fuselage
The landing gear
Flab's
Rudder
Elevators
Ailerons
Spoilers
Wings
While in static at ground and taxiing,
The wings will bending down. Upper side will be in tension and
lower portion will be in compression.
This contributes considerably to life of the aircraft.
While taking off the loads are quite fluctuating. The wings will
act like a cantilever beam.
While in air, the load on the wings were quite consistent.
The wing will pose towards the upper side. Upper side will be in
compression and lower portion will be in tension.
This situation of load is heavy, for this criteria wing design
made very strongly.
The upper portion is made up of compression resistant material
must be highly stiff and resisting the buckling, the lower portion
is made up of tension resistant material high fracture toughness is
required.
Fuselage
Carries the total payload.
Acts vertically downwards, supported by the wings exactly at the
mid length. Thus the lower portion in compression correspondingly
the upper portion in tension.
When the aircraft rolls, torsion is applied.
For a high altitude flight cabin must be pressurized, then it is
subjected to longitudinal and circumferential tension.
Due to pressurization and de-pressurization it must be designed
against low cycle fatigue. Due to the tension fracture toughness is
required.
Landing Gear
Stresses are high while taking of when the full load of fuel is
applied.
Fatigue is applied while taxiing.
While landing vertical descending is 1m/s (>2mph). So landing
load cant be considered as shock load.
But the full aircraft load is applied on landing gear in touch
down. Stresses were high.
The landing gear must be retracted back to the fuselage, for the
aerodynamic performance. It should occupy minimum space. So the
density reduction will not applied for this part. It must be
designed for the low cycle fatigue.
Must posses high fracture toughness. Critical components were
heat treated.
Control surfaces
The control surfaces consist of the rudder, elevators, ailerons
and flaps.
These are lightly loaded components.
Flab must be robust against the flying debris in the runway.
These are thin components, must have adequate stiffness for
their functional requirements.
Acoustics also considered for the components located near by the
engine.
Thank you for the opportunity
Questions Please??
