The document provides information on aircraft materials and structures. It discusses the different types of aircraft structures including frame, monocoque, and semimonocoque structures. It also describes various materials used in aircraft construction such as metals, non-metallic materials, composites, and carbon fiber. Specific metal alloys discussed include aluminum alloys, magnesium alloys, and titanium alloys. The key properties and applications of these alloys are summarized.

1. Subject Name: Aircraft Design
Subject Code: BAE-DS-601
Prepared By: Mr. Vishnu Raj
Unit 4 :Structural Layout
Topic: Aircraft Materials and Structures
Date : 08/03/2022

3.  Forms main bodyof aircrafttowhichwings, tail plane,
engines and gears areattached
 In modernaircraft formsa tubestructure housing
flight deck, paxcabin, hold and equipment
 Alsoactsasa pressure hull in pressurized aircraft
Introduction

5.  Framestructure:
 A box frame madeupof aseriesof vertical,
horizontal, diagonal and
longitudinal tubular steelpipes
 Design producesasquareprofiled fuselage
 Used in old aircraftand light modern aircraft
 Frame takes up all theloads
 Heavier if shape altered
 Covered with fabric, fiberglass, aluminum, Kevlare.t.c.
Types

6.  Monocoque structure:
 Skin takesupall flight and ground loads
and shape gives structure itsrigidity
 Anydamage toskin directseffects its load
carrying capacity
 Complications indesigning doors
windowsand hatches
 Inherently heavyand fragile by
design, notused in airliners.

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 Loads shared byskin, frames, stringers and
formers
 Tolerant todamage
 Good strengthto
weightratio
 More redundancy then monocoqueconstruction

8.  Reinforces shellstructure:
 Best redundancy in shellstructure
 Reinforced windows, doors and
hatchattachment points
 Longeronsadded forfurther load
distribution, prevent crack propagation

9. Contd.
Joining methods
Riveting:
 Old process, time
consuming, moredrag
Bonding:
 Using an adhesive toattach metallicparts

10. Joining methods
Milling:
 Toremove unnecessary
material
 Material retention adds
rigidity

11. Etching:
 Using chemicalstoremove material orcreatedesignor shapes in billets
Joining methods
 Pressurecabin terminatesat the
frontand rear bulkheads
 Usuallydomeshaped for betterpressure
distribution
 In somedesigns floorpartof
pressure hull, un- pressurised
hold in thiscase

13.  In moderndesignsare notused as bulkheads
 Seriesof panelsattached tosupporting beamsof aircraft
 Honeycombpanels used for best
weight to strength ratio
Cabin floors

14.  Flightdeck:
 Heated forde-icing
 JAR approved for birdstrikes
 Laminated like carwindscreens
 Stepped nose profile used in most subsonicairliners
 Helps in:
 Aerodynamic profiling
Windows
 Better ground and forwardvisibility
 Reduction in size of screenwindows
 Sheds waterbetter
 Reduces impactforce
 Reduces pressureloads
Windows (flight deck)

15. Thestrongestpartof fuselagewherewingsare attached
All flight loadsconvergeat thispoint
Spar attachment

16. AIRCRAFT MATERIALS
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17. Monolithic
Materials
Hybrids
Ceramics and ceramic alloys
& Glasses
Metals
(& Metallic Alloys)
Polymers (& Elastomers)
Sandwich
Composite
Lattice
Segment
Composites: have two (or more) solid
components; usually one is a matrix and
other is a reinforcement
Sandwich structures: have a
material on the surface (one or
more sides) of a core material
Lattice* Structures: typically a combination
of material and space
(e.g. metallic or ceramic forms)
Segmented Structures: are divided in 1D, 2D or 3D
(may consist of one or more materials).
Hybrids are designed
to improve certain
properties of
monolithic materials
Classification of composites.
 Based on the matrix: metal matrix, ceramic matrix, polymer
matrix.
 Based on the morphology of the reinforcement: particle reinforced
(0D), fiber reinforced (1D), laminated (2D).
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18. Metallic Materials
• Metallic Materials are materials that are like
metal, having the properties of metal,
containing or consisting of metal.

19. Non-metallic materials
• In addition to metals, various types of plastic materials are found in aircraft
construction. Some of these plastics include transparent plastic, reinforced
plastic, composite, and carbon-fiber materials.
• Plastic:
• Plastics are used in many applications throughout modern aircraft. These
applications range from structural components of the thermosetting plastics
reinforced with fibre glass to decorative trim of thermoplastic material.
Transparent plastic:
• Transparent plastic is used in canopies, windshields, and other transparent
enclosures. You need to handle transparent plastic surfaces carefully because
they are relatively soft and scratch easily. At approximately 225°F, transparent
plastic becomes soft and pliable.

20. Reinforced plastic
• Reinforced plastic is used in the construction of radomes, wingtips,
stabilizer tips, antenna covers, and flight controls. Reinforced plastic has a
high strength to weight ratio and is resistant to mildew and rot. Because it is
easy to fabricate, it is equally suitable for other parts of the aircraft.
• Reinforced plastic is a sandwich type material (fig. 4-4). It is made up of
two outer facings and a center layer. The facings are made up of several
layers of glass cloth, bonded together with a liquid resin. The core material
(center layer) consists of a honeycomb structure made of glass cloth.
• Reinforced plastic is fabricated into a variety of cell sizes.

21. Rubber
• Rubber is used to prevent the entrance of dirt, water or air, and to prevent the loss of
fluids, gases, or air. It is also used to absorb vibration, reduce noise and cushion impact
loads. The term “Rubber” is as all inclusive as the term “metal”. It is used to include not
only natural rubber, but all synthetic and silicone rubbers.
• Natural rubber has better processing and physical properties than synthetic or silicon
rubber. These properties include :
• 1. Flexibility
• 2. Elasticity
• 3. Tensile strenght
• 4. Tear strenght
• 5. Low heat build up due to flexing (hysteresis)
Synthetic rubber is a available in several types, each of which is compounded
of different materials to give the desired properties
Synthetic Rubber

22. Composite & Carbon Fiber Materials
• High performance aircraft require an extra high strength to weight ratio material.
• Fabrication of composite materials satisfies this special requirement. Composite
materials are constructed by using several layers of bonding materials (graphite
epoxy or boron epoxy). These materials are mechanically fastened to conventional
substructures.
• Another type of composite construction consists of thin graphite epoxy skins
bonded to an aluminum honeycomb core. Carbon fiber is extremely strong, thin
fiber made by heating synthetic fibers, such as rayon, until charred, and then
layering in cross sections.

23. AIRCRAFT MATERIALS
1. Basic requirements
• High strength and stiffness
• Low density
=> high specific properties e.g. strength/density, yield
strength/density, E/density
• High corrossion resistance
• Fatigue resistance and damage tolerance
• Good technology properties (formability, machinability, weldability)
• Special aerospace standards and specifications
2. Basic aircraft materials for airframe structures
• Aluminium alloys
• Magnesium alloys
• Titanium alloys
• Composite materials

24. Development of aircraft materials for airframe structures
composites
Mg alloys
other Al alloys
pure AlZnMgCu
alloys
pure AlCuMg
alloys
new Al
alloys
steel
Year
AlCuMg alloys
wood
other materials
Relative share
of structural
materials Ti alloys
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25. Composite share in military aircraft structures in USA and
Europe
Structural materials on Eurofighter

26. Development of composite
aerospace applications over the last 40 years
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27. Structural materials on Eurocopter

28. Aluminium Alloys

29. Characteristics of aluminium alloys
Advantages
• Low density 2.47- 2.89 g/cm³
• Good specific properties – Rm/ρ, E/ ρ
• Generally very good corrosion
resistance (exception alloys with
Cu)
• Mostly good weldability – mainly
using pressure methods
• Good machinability
• Good formability
• Great range of semifinished
products
(sheet, rods, tubes etc.)
• Long-lasting experience
• Acceptable price
Shortcomings
• Low hardness, susceptibility to
surface damage
• High strength alloys (containing Cu)
need additional anti-corrosion
protection:
– Cladding – surface protection using
a thin layer of pure aluminium or
alloy with the good corrosion
resistance
– Anodizing – forming of surface oxide
layer (Al2O3)
• It is difficult to weld high strength
alloys by fusion welding
• Danger of electrochemical corrosion
due to contact with metals:
– Al-Cu, Al-Ni alloys, Al-Mg alloys, Al-steel

30. Reference aluminium alloys in airframe structure
Structure Part Control parametr Reference alloys
Wing Upper panels
Upper stringers
Lower panels
Lower stringers
Beams, ribs
compression
compression
damage tolerance (DT)
tension + DT
static properties
7150-T6/T77
7050-T74
2024-T3, 2324-T39
2024-T3
7050-T74, 7010-T76
Fuselage Upper panels
Lower panels
Stiffeners
Main frame
compression, DT, formability
tension + DT
tension/compression
complex
2024 clad-T3
2024 clad-T3
7175-T73
7010+7050-T74
Other
parts
All types 7010/7050/7075

31. Typical mechanical properties of alloy 2024
4.4Cu-1.5Mg-0.6Mn, E = 72.4 GPa , ρ = 2 .77 g/ccm
Temper Tensile strength
MPa
Yield strength
MPa
Elongation
%
Fatigue strength
MPa
At 500 mil. cycles
Bare 2024
0 185 75 20 90
T3 485 345 18 140
T4, T351 470 325 20 140
Alclad 2024
0 180 75 20 -
T3 450 310 18 -
T4, T351 440 290 19 -

32. Use of aluminum-lithium alloys in commercial aircraft

33. • Typical castings in aircraft structures
Al – front body of engine
32 kg - D=700 mm
Al- steering part - 1,1 kg
390 x 180 x 100 mm
Al – pedal - 0,4 kg
180 x 150 x 100 mm
Al – casing - 1,3 kg
470 x 190 x 170 mm
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34. Magnesium Alloys

35. Basic wrought Mg alloys
• Mg-Al-Zn (AZ)alloys
– The most common alloys in aircraft industry, applicable up to 150 °C
– Composition – 3 to 9 % Al, 0.2 to 1.5 % Zn, 0.15 to 0.5 % Mn
– Increasing Al content → strength improvement , but growth of susceptibility
to stress corrosion
– Zn → ductility improvement
– (Cd + Ag) as Zn replacement → high strength up to 430 MPa
– Precipitation hardening → strength improvement + decrease of ductility
– The most common alloy for sheet and plates – AZ31B (applicable to 100 °C)
Alloy Composition Semi-product Rm, MPa Rp0.2, MPa Ductility,%
AZ31B-F 3.0Al-1.0Zn bars, shapes 260 200 15
AZ61A-F 6.5Al-1.0Zn bars, shapes 310 230 16
AZ80A-T5 8.5Al-0.5Zn bars, shapes 380 240 7
AZ82A-T5 8.5Al-0.5Zn bars, shapes 380 275 7
AZ31B-H24 3.0Al-1.0Zn sheet, plates 290 220 15

36. • Mg-Zn-Zr alloys (ZK)
– Zn(Zinc) → strength improvement
– Zr(zirconium) → fine grain → improvement of strength, formability and corrosion
resistance
– Better plasticity after heat treatment
– Alloying with RE a Cd → tensile strength up to 390 MPa
– Application up to 150 °C
• Mg-Mn alloys (M)
– Good corrosion resistance, hot formability, weldability
– Not hardenable → lower strength
Alloy Composition Semi-product Rm, MPa Rp0.2, MPa Ductility, %
ZK60A-T5 5.5Zn-0.45Zr bars, shapes 365 305 11
M1A-F 1.2Mn bars, shapes 255 180 12

37. • Mg-Th-Zr (HK)
– Th(Throium)
– High temperature alloys
– Example: alloy HK31A - service temperature 315 to 345 °C
• Mg-Th-Mn (HM)
– Medium strength
– Creep resistance → service temperature up to 400 °C
• Mg-Y-RE (WE)
– RE-Rhenium
– Y-yttrium
– Hardenability, formability, good weldability
– Y → strength after hardening, Nd → heat resistance, Zr → grain refinement
– Application to 250 °C
alloy composition semi-product Rm, MPa Rp0.2, MPa ductility, %
HM21A-T8 2.0Th-0.6Mn sheet, plates 235 130 11
HK31A-H24 3.0Th-0.6Zr sheet, plates 255 160 9
Mg-RE (WE) 8.4Y-0.5Mn-
0.1Ce-0.35Cd
bars, shapes 410 360 4

38. • Typical properties of several cast magnesium alloys
alloy composition product Rm
MPa
Rp0.2
MPa
ductility
%
AM60A-F 6.0Al-0.13Mn pressure die
casting
205 115 6
AZ91A-F 9.0Al-0.13Mn-
0.7Zn
pressure die
casting
230 150 3
AZ63A-T6 6.0Al-3.0Zn-
0.15Mn
sand casting 275 130 5
AZ91C-T6 8.7Al-0.13Mn-
07Zn
sand casting 275 145 6
AZ92A-T6 9Al-2Zn-0.1Mn sand casting 275 150 3
AM100A-
T61
10.0Al-0.1Mn sand casting 275 150 1
QE22A-T6 2.5Ag-2.1RE-0.7Zr sand casting 260 195 3
WE43A-T6 4.0Y-3.4RE-0.7Zr sand casting 250 165 2
ZK61A-T6 6.0Zn-0.7Zr sand casting 310 195 10
EZ33A-T5 3.3RE-2.7Zn-0.6Zr sand casting 160 110 2

39. Titanium Alloys

40. Characteristics of titanium and titanium alloys
• Pure titanium - 2 modifications
– αTi – to 882 °C, hexagonal lattice
– βTi – 882 to 1668°C, cubic body centered lattice
– With alloying elements, titanium forms substitution solid solutions α and β
• Commercially pure titanium can be used as structural material in many applications, but Ti
alloys have better performance.
• Basic advantages of Ti
– Lower density comparing steel ( ρ = 4.55 g/cm³)
– High specific strength at temperatures 250 – 500 °C, when alloys Al, Mg already cannot be used
– High strength also at temperatures deep below freezing point
– Good fatigue resistance (if the surface is smooth, without grooves or notches)
– Excellent corrosion resistance due to stabile layer of Ti oxide
– Good cold formability, some alloys show superplasticity
– Low thermal expansion => low thermal stresses

41. Properties of important wrought titanium alloys
Alloy Temper Rm, MPa Rp0.2, MPa Elongation,
%
E, GPa
α and pseudo α
Ti-5Al-2,5Sn annealed 790 - 860 760 - 807 16 110
Ti-5,6Al annealed 875 750 8 -
Ti-11Sn-1Mo-2,2Al-
5Zr-0,2Si
annealed 1000 - 1100 900 - 990 15 114
α + β
Ti-3Al-2,5V annealed 620 - 690 520 - 585 20 107
Ti-6Al-4V hardened
annealed
1170
900 - 990
1100
830 - 920
10
14
114
Ti-6Al-2Sn-2Zr-2Cr-
2Mo-0,25Si
hardened 1275 1140 11 122
pseudo β and β
Ti-10V-2Fe-3Al hardened 1170 - 1275 1100 - 1200 10 112
Ti-15V-3Cr-3Al-3Sn hardened 1095 - 1335 985 - 1245 6 - 12 -

42. Cast titanium alloys
• Comparison with wrought alloys
– Similar chemical composition
– Higher content of impurities, specific casting structure and defects (e.g. porosity)
– Lower ductility and fatigue life
– Often better fracture toughness
• Manufacture of shape castings
– Good casting properties (fluidity, mold filling)
– Hydrogen absorption, porosity
– Vacuum melting, special molds, hot izostatic pressing of castings (HIP)
• HIP – heating close to solidus + pressure of inert gas (elimination and welding of voids due to plastic deformation) – conditions
910 to 965 °C/100 MPa/2 h.
Alloy Heat Treatment Rm, MPa Rp0.2, MPa A5 , %
Ti-6Al-4V stress relief annealing 880 815 5
Ti-6Al-2Sn-4Zr-2Mo 970°C/2h + 590°C/8h 860 760 4
Ti-15V-3Cr-3Al-Sn 955°C/1h + 525°C/12h 1120 1050 6
Examples of cast alloys

43. Composite Materials

44. Most composites consist of a bulk material (the ‘matrix’), and a
reinforcement, added primarily to increase the strength and stiffness of the
matrix. This reinforcement is usually in fibre form.
Today, the most common man-made composites can be divided into three main
groups:
Polymer Matrix Composites (PMC’s) – These are the most
common and will be discussed here. Also known as FRP - Fibre Reinforced
Polymers (or Plastics) – these materials use a polymer-based resin as the matrix,
and a variety of fibres such as glass, carbon and aramid as the reinforcement.
Metal Matrix Composites (MMC’s) - Increasingly found in the
automotive industry, these materials use a metal such as aluminium as the matrix, and
reinforce it with fibres such as silicon carbide (SiC).
Ceramic Matrix Composites (CMC’s) - Used in very high
temperature environments, these materials use a ceramic as the matrix and reinforce it with
short fibres, or whiskers such as those made from silicon carbide and boron nitride (BN).

45. Polymer fibre reinforced composites
Common fiber reinforced composites are composed of
fibers and a matrix.
Fibers are the reinforcement and the main source of strength
while the matrix 'glues' all the fibres together in shape
and transfers stresses between the reinforcing fibres.
Sometimes, fillers or modifiers might be added
to smooth manufacturing process, impart special properties,
and/or reduce product cost.

46. Polymer matrix composites
• The properties of the composite are determined by:
- The properties of the fibre
- The properties of the resin
- The ratio of fibre to resin in the composite (Fibre Volume Fraction)
- The geometry and orientation of the fibres in the composite
Properties of unidirectional
composite material

47. Main resin systems
• Epoxy Resins
The large family of epoxy resins represent some of the highest performance resins of those
available at this time. Epoxies generally out-perform most other resin types in terms of
mechanical properties and resistance to environmental degradation, which leads to their
almost exclusive use in aircraft components
• Phenolics
Primarily used where high fire-resistance is required, phenolics also retain their properties
well at elevated temperatures.
• Bismaleimides (BMI)
Primarily used in aircraft composites where operation at higher temperatures (230 °C
wet/250 °C dry) is required. e.g. engine inlets, high speed aircraft flight surfaces.
• Polyimides
Used where operation at higher temperatures than bismaleimides can stand is required
(use up to 250 °C wet/300 °C dry). Typical applications include missile and aero-engine
components. Extremely expensive resin.

50. Properties of composites
• UD laminate
Properties directionally
dependent
• Quasi-isotropic laminate
Properties nearly equal in all
directions
Tensile
strength,
MPa
Angle between fibers and stress, °

51. Properties of epoxy UD prepreg laminates
Fibre fracture volume typical for aircraft structures
Prepreg
Fabrics and fibres are pre-impregnated by the materials manufacturer with a pre-
catalysed resin. The catalyst is largely latent at ambient temperatures giving the
materials several weeks, or sometimes months, of useful life. To prolong storage
life the materials are stored frozen (e.g. -20°C). High fibre contents can be
achieved, resulting in high mechanical properties.

52. Fiber metal laminates
• Consist of
alternating thin
metal layers and
uniaxial or biaxial
glass, aramid or
carbon fiber
prepregs

53. Fibre metal laminates
• Developed types
- ARALL - Aramid Reinforced ALuminium Laminates (TU-DELFT)
- GLARE - GLAss REinforced (TU-DELFT)
- CARE - CArbon REinforced (TU-DELFT)
- Titanium CARE (TU-DELFT)
- HTCL - Hybrid Titanium Composite Laminates (NASA)
- CAREST – CArbon REinforced Steel (BUT - IAE)
- - T iGr – Titanium Graphite Hybrid Laminate (The Boeing Company)
• Advantages
Fibre metal laminates produce remarkable improvements in
fatigue resistance and damage tolerance characteristics
due to bridging influence of fibres. They also offer weight
and cost reduction and improved safety, e.g. flame
resistance. They can be formed to limited grade.

54. Standard FML configurations
Type Configuration Metal alloy Prepreg
constituents
Prepreg
orientation
ARALL 2 2/1 – 6/5 2024-T3 Aramid-epoxy unidirectional
ARALL 3 2/1 – 6/5 7475-T76 Aramid-epoxy unidirectional
GLARE 1 2/1 – 6/5 7475-T76 Glass-epoxy unidirectional
GLARE 2 2/1 – 6/5 2024-T3 Glass-epoxy unidirectional
GLARE 3 2/1 – 6/5 2024-T3 Glass-epoxy Cross-ply
GLARE 4 2/1 – 6/5 2024-T3 Glass-epoxy Cross-ply
/unidirectional

55. Mechanical properties of FML
Laminate Metal
thickness
mm
Prepreg
thickness
mm
Tensile
strength
MPa
Yield
strength
MPa
E
GPa
Density
g/ccm
ARALL 1 0.3 0.22 897 535 67.5 2.16
ARALL 2 0.3 0.22 849 411 68.3 2.16
GLARE 1 0.3 0.25 1494 530 62.2 2.42
GLARE 2 0.2 0.25 1670 416 60.9 2.34
0.3 0.25 1449 406 63.0 2.42
0.4 0.25 1295 399 64.5 2.47
GLARE 3 0.3 0.25 849 382 51.3 2.42

56. Fatigue resistance of FML comparing to 2024 alloy

57. Fiber metal laminates - application
AIRBUS A 380
Panels of fuselage upper part – 470 m² , GLARE 4
Maximum panel dimensions 10.5 x 3.5 m
Weight saving - 620 kg
Adhesive bonded stringers from 7349 alloy

58. Sandwich materials
• Structure – consists of a lightweight core
material covered by face sheets on both
sides. Although these structures have a
low weight, they have high flexural
stiffness and high strength.
• Skin (face sheet)
– Metal (aluminium alloy)
– Composite material
• Core
– Honeycomb – metal or composite
(Nomex)
– Foam – polyurethan, phenolic,
cyanate resins, PVC
• Applications – aircraft flooring, interiors,
naccelles, winglets etc.
Sidewall panel for Airbus A320

59. Effectivness of sandwich materials
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60. Thank You