1. Aerospace Materials Aerospace Engineering
© 2011 Project Lead The Way, Inc.

2. Commonly Used Aerospace Materials
Wood Steel Aluminum alloys Titanium alloys Magnesium alloys Nickel alloys Fiber-reinforced composites

3. Factors for Selecting Materials
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Course Name
Unit # – Lesson #.# – Lesson Name
Function
What is the component used for?
Material Properties
Strength to weight ratio
Stiffness
Toughness
Resistance to corrosion
Fatigue and effects of environmental heating
Production
Machinability
Availability and consistency of material
Stiffness is the ability of a material to resist deflection or stretching.
Toughness is the work per unit volume required to fracture a material.
Fatigue is the reduction of strength by repeated cyclic or random stress.
Machinability is the way a material responds to specific machining techniques.
Availability of both raw and processed material is affected by many factors, including:
Cost of materials
Quality control processes by the material producers
Geopolitics (international relationships between trading partner countries)

4. Cyclic Stresses
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Average commercial aircraft 30 year life cycle 60,000 Hours 2,500 Days – 357 weeks – 6.85 Years 20,000 Flights 667 flights per year 100,000 miles of taxiing 4 times around the Earth’s circumference
Total average maintenance and service cost are double the original purchase price

5. Flight Stresses
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Pressure differential fuselage to outside 0 kPa to 60 kPa (8.6 psi) Temperature differential ground to cruise Ground temp to -56 oC (-69 oF) Impact load of landing Landing gear now supports aircraft Wings flex from upward lift force to downward force of their own weight Tires accelerate from 0 kph to 400 kmph (this creates a puff of smoke)
Each flight subjects the aircraft to stresses similar to the ones listed below.
The fuselage endures cyclic pressure cycles from ground level to inflight conditions which stress the aircraft from a pressure differential of 0 kPa to 60 kPa (8.6 psi). On the ground inside and outside of the aircraft are equal to atmospheric pressure (~101.3 kPa or 14.7 psi). Inflight there is pressure differential between the outside pressure 18.7 kPa (2.8 psi) at a typical cruise altitude of 12,200 m (~40,000 ft) and the pressure inside the fuselage of 78.5 kPa (11.4 psi). The pressure inside the cabin is approximately that of 2,100 m (~6,900 ft), which is determined through the FAA aircraft certification process. Note that the fuselage is not maintained to be the same as ground level to reduce the fuselage pressure differential. The interior of the fuselage must be maintained at a pressure associated with an altitude below 10,000 ft (3,048 m); otherwise, the FAA requires supplemental oxygen to be supplied.
The aircraft is subjected to a thermal cycle of ground level (temperature at takeoff) to -56 oC (-69 oF) at a typical cruise altitude of 12,200 m (~40,000 ft).
Impact load of landing when landing gear cycles from no weight to supporting full weight of aircraft. Wings support the weight of the aircraft during flight through lift (upward force) to downward force of supporting their own weight.
Landing gear tires accelerate from 0 kmph to 400 kmph (250 mph). This creates a puff of smoke as tires scrub the runway and accelerate to the landing speed.

6. Keep in Mind
Reducing material density reduces airframe weight and improves performance Fuel efficiency Climb rate G-force loading Material density reductions are 3 to 5 times more effective than increasing tensile strength, modulus, or impact resistance

7. Early Aircraft Built of Wood
Wright Brothers used Spruce Widely available Uniform piece to piece Good strength to weight ratio Different properties in different directions Easy fabrication and repair

8. Aerospace Materials – Wood
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Unit # – Lesson #.# – Lesson Name
Sensitivity to moisture Rot and insect damage Natural product lower consistency than man-made
Spruce was an excellent product during the early days of aircraft manufacturing. Since then the progress made in material engineering has provided more consistent and superior properties.

9. Aerospace Materials – Wood
Rarely used today in production aircraft Used today in homebuilt and specialty, low-volume production Chinese have selected oak for the heat shield of a reentry vehicle

10. Aerospace Materials – Metal Alloy
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Unit # – Lesson #.# – Lesson Name
Material Forms
Sheet ˂ 0.250in.
Skin of fuselage, wings, control surfaces, etc.
Optional resource available: L2_1_Stamping Dies (Length = 6:08). If you choose to display the video, pause the presentation and play the video.
Optional stamping dies video

11. Aerospace Materials – Metal Alloy
Material Forms
Plate ˃ 0.250in.
Machined into varying shapes and parts
Forging – Material is plastically deformed by large compressive forces in closed dies
Produces high strength non-uniform cross sectional parts

12. Aerospace Materials – Metal Alloy
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Unit # – Lesson #.# – Lesson Name
Material Forms
Extrusion – Material is forced through dies to create a uniform cross section
Uses include stiffeners and ribs
Optional resource available: 1_Metal Extrusion Video (Length = 1:19). If you choose to display the video, pause the presentation and play the video.
Optional metal extrusion video

13. Aerospace Materials – Metal Alloy
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Course Name
Unit # – Lesson #.# – Lesson Name
Material Forms Casting – Liquid material is solidified in a mold
Optional resource available: L2_1_Casting (Length = 1:08). If you choose to display the video, pause the presentation and play the video.
Optional casting video

14. Aerospace Materials – Aluminum Alloy
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Unit # – Lesson #.# – Lesson Name
Cutting-edge (1920s-60s)
Most abundant metal in the earth’s crust
Pure aluminum is relatively soft
The P-12 fighter, built for the U.S. Army in 1928, could hold a 500-pound bomb. It used bolted aluminum tubing for the fuselage's inside structure rather than the typical welded steel tubing.

15. Aerospace Materials – Aluminum Alloy
Currently most widely used material Readily formed Moderate cost Excellent resistance to chemical corrosion Excellent strength to weight ratio

16. Aerospace Materials – Aluminum Alloy
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Unit # – Lesson #.# – Lesson Name
Strength and stiffness are affected by: Form Sheet Plate Bar Extrusion Forging Heat treating and tempering
Ductility is the amount of plasticity that precedes failure.
Brittleness is a lack of ductility. This is often confused with lack of strength.
Stronger aluminum more brittle

17. Aerospace Materials – Aluminum Alloy
Alloy Series
Principle Alloying Element
1xxx
99.000% minimum Aluminum
2xxx
Copper
3xxx
Silicon Plus Copper and/or Magnesium
4xxx
Silicon
5xxx
Magnesium
6xxx
Unused Series
7xxx
Zinc
8xxx
Tin
9xxx
Other Elements
Most common alloy is 2024 (24ST) 93.5% aluminum, 4.4% copper, 1.5% manganese, and 0.6% magnesium

18. Aerospace Materials – Aluminum Alloy
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Course Name
Unit # – Lesson #.# – Lesson Name
High-strength applications – 7075 – 7050 – 7010
Zinc, magnesium, and copper
Sheet aluminum is clad with a thin layer of pure aluminum for corrosion protection
Aluminum lithium
Same weight savings as composites but can be formed by standard techniques
Eurofighter Typhoon uses aluminum lithium in the wing and tail leading edge.

19. Aerospace Materials – Steel Alloy
Steel is very cheap and easy to fabricate First utilized in fuselage construction Steel tubing replaced wire-braced wood construction Today’s applications: High strength and fatigue resistance Wing attachment fittings High temperatures Firewalls and engine mounts

20. Aerospace Materials – Steel Alloy
Alloy of iron and carbon Carbon adds strength to soft iron As carbon content increases, strength and brittleness increase Typical steel alloys are1% carbon Other common alloy materials – Chromium, molybdenum, nickel, and cobalt

21. Aerospace Materials – Steel Alloy
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Properties of steel are influenced by heat treating and tempering
Same alloy can have moderate strength and good ductility or high strength and brittleness, depending on heat treatment
Ductility is the amount of plasticity that precedes failure.
Brittleness is a lack of ductility. This is often confused with lack of strength.
Materials temperature is raised to °F - The point at which carbon goes into solid solution with the iron

22. Aerospace Materials – Titanium
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Greater strength to weight ratio and stiffness than aluminum Capable of sustaining temperatures almost as high as steel Corrosion-resistant
Titanium parts manufactured complete with Wire EDM and Matsurra CNC mill. These parts are now on the planet Mars as part of JPL's Mars Rovers.

23. Aerospace Materials – Titanium
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Difficult to form
High forming temperatures and stresses
Seriously affected by any impurities
Most impurity elements – Hydrogen, oxygen, and nitrogen
Higher fabrication cost
Expensive – 5 to 10 times as much as aluminum
Most titanium alloys must be formed at temps over 1000F and at very high forming stresses. Mechanical properties are seriously affected by any impurities that may be accidentally introduced during forming.

24. Aerospace Materials – Titanium
Extensively used in jet-engine components Lower-speed aircraft, high-stress airframe components Uses include landing gear beams and spindles for all moving tails

25. Aerospace Materials – Titanium
Super Plastic Forming/Diffusion Bonding (SPF/DB) Extreme temperature and pressure causes titanium to flow into the shape of the mold. Separate pieces of titanium are diffusion-bonded at the same time, forming a joint that is indistinguishable from the original metal

26. Aerospace Materials – Magnesium
Good strength to weight ratio Tolerates high temperatures Easily formed – Casting, forging, and machining Uses include engine mounts, wheels, control hinges, brackets, stiffeners, fuel tanks, and wings

27. Aerospace Materials – Magnesium
Prone to corrosion – must have a protective finish Flammable Should not be used in areas that are difficult to inspect or where the protective finish could erode away

28. Aerospace Materials – High Temperature Nickel Alloys
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Unit # – Lesson #.# – Lesson Name
Inconel, Rene 41, and Hastelloy Suitable for hypersonic aircraft and reentry vehicles
Nickel alloy honeycomb sandwich is used for the stealth nozzles of the F-117
Hastelloy is used primarily in engine parts

29. Aerospace Materials – High Temperature Nickel Alloys
Heavier than aluminum and titanium Difficult to form

30. Aerospace Materials – Composites
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Unit # – Lesson #.# – Lesson Name
Mid 1960s and early 1970s Empennages of the F-14 and F-15
Optional resource available: L2_1_Composites (Length = 1:19). If you choose to display the video, pause the presentation and play the video.
In the mid 1960s and early 1970s, composites began being used. Their first production usage was on the empennages of the F-14 and F-15.
Optional composites video

31. Aerospace Materials – Composites
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Boron/epoxy – horizontal stabilizers, rudders, and vertical fins Mid-1970s carbon fibers Carbon/epoxy speed brake 1980s composite use expanded from 2% on the F15 to 27% on the AV-8B Harrier
Uses included wing (skins and substructure), forward fuselage, and horizontal stabilizer

32. Aerospace Materials – Composites
Modern fighters consist of 20% composite material 15-25% weight savings depending on structure Boeing 787 uses upward of 50% composites and includes composite wing and fuselage

33. Aerospace Materials – Ceramic
High temperature resistance Uses include engine exhaust nozzles Space shuttle uses aluminum structure with heat-protective tiles

34. Resources
Black, T., & Kohser, R. (2008). Degarmo’s materials & processes in manufacturing. Danvers, MA: John Wiley & Sons, Inc. Hunt, E., Reid, D.,Space, D., & Titlon, F. (2011). Commercial airliner environmental control system. The Boeing Company. Retrieved from