1. Materials and Processes Engineering
Polytechnique
Supplement to Case Study Course
Daniel Menard
19 October 2004

2. Aeropace materials Aerospace Processes
Aluminum, Steel, Titanium, Stainless steel alloys
Hardware, castings, Al honeycomb, bearings
Kevlar, fiberglass, graphite, plastics
Adhesive films, adhesive pastes, Nomex, tapes
Sealants, fillers, paints, protective films, lacquers
Acids, bases, oxidants, reducers, wiping solvents, alkaline cleaners
Electrical components, flammability, documentation
Hydraulic fluids, cutting fluids, machining lubricants, jet fuel, engine oil
Aerospace Processes
Machining, forming, bending, drilling, riveting, fastening, metal bonding, heat treatment, shot peening, polishing, swaging, NDT techniques, corrosion resistance, fatigue, welding, plumbing, rolling, torquing,
Curing, bonding, assembling, painting, surface preparation, trimming, repairing, protecting, cutting, baking, cold working
Masking, anodizing, plating, conversion coatings, chemical milling, inspection, passivation
electrical bonding, material testing, design, identification, storage

3. Introduction Objectives: You will learn about:
Provide awareness of the main aerospace materials,their manufacturing processes and their subsequent conversion into useful parts
You will learn about:
Factors affecting selection of the correct material for the job
Techniques used to alter shapes of metals
Techniques to change material properties
Techniques for joining materials
Corrosion protection
Composite construction
Flammability compliance
Short introduction to wing design (M&P point of view)

4. Relation of Materials Selection to Design
Selection of the best material for a part involves the identification of the interrelationship between:
DESIGN
Service conditions
Function
Cost
MATERIALS
Properties
Availability
Cost
PROCESSING
Equipment selection
Influence on properties
Cost

5. Engineering design is less than 5% of the cost of an airplane but influences more than 80% of the final cost

6. Performance Characteristics of Materials
Physical properties
Viscosity, Density
Mechanical properties
Fatigue resistance, Strength
Chemical properties
Corrosion resistance,
Thermal properties
Thermal expansion, fire resistance
Electrical properties
Transmittivity, conductivity

7. Performance Characteristics of Materials

8. Standards and Specifications
Material & Process properties are usually formalized through standards and specifications
Standards intended to be used by as large a body as possible
ASTM or ANSI
SAE
Aerospace manufacturers such as Bombardier write their own intended for more limited group
Company specifications
BAMS: Bombardier Aerospace Material Specification
BAPS: Bombardier Aerospace Process Specification

9. Metals and their processes
Major metal and alloy groups used in aircraft industry:
Aluminum alloys
Carbon and alloy steels
Stainless steels
Heat-resistant alloys
Titanium alloys

10. Aluminum alloys Low density (~1/3 density of steel)
Low melting temperature ~1180 °F
Low hardness
Adequate strength, further strengthening achieved through:
Alloying
Cold working
Heat treatment
Very good fracture toughness
Very good corrosion resistance

11. Aluminum alloys

12. Carbon and alloy steels
High density
High melting temperature ~2760 °F
High hardness
High strength and fracture toughness
Strength -toughness combinations achieved through heat treatment
Excellent wear resistance
Poor corrosion resistance

13. Performance Characteristics of Materials

14. Stainless Steels High density High melting point ~2750 °F
High hardness
High strength and fracture toughness
Strength-toughness combinations achieved through heat treatment
Excellent wear resistance
Very good corrosion resistance
More expensive than steels

15. Heat-resistant alloys
Reduced density
High melting point ~2500 °F
High static strength
Excellent high-temperature behavior
Very good corrosion resistance
Adequate oxidation resistance at elevated temperatures
No special surface protection required
Expensive

16. Performance Characteristics of Materials

17. Titanium alloys Low density (~1/2 density of steel)
High melting point ~3000 °F
Good strength
Further strengthening achieved through heat treatment
High fatigue strength
High fracture toughness
Very good high-temperature behavior
Excellent corrosion and oxidation resistance
Expensive

18. Performance Characteristics of Materials

19. Process Selection
The selection of a material must be closely coupled with the selection of a manufacturing process.
The goal in selecting a manufacturing process is to choose one that will satisfy Engineering requirements and Production capabilities
This will translate in: Adequate material and process properties, low cost and low cycle time manufacturing, acceptable quality; a good enough part
Main metal manufacturing processes broken down in a few broad classes:
Casting
Deformation
Material removal
Heat treatment
Joining
Finishing

20. Casting What is casting? Casting:
Metal is molded into the required shape by pouring liquid metal into an expendable pattern that is surrounded by a refractory slurry coating
Casting:
Can produce large or complex finished shape
Avoids extensive machining and associated costs
High dimensional accuracy
Weight savings

21. Deformation processes
Main deformation processing methods used in aircraft industry are:
Bending
Hydro forming
Stretch forming
Forging

22. Bending What is bending?
The straining of flat sheet (or strip metal), by moving it around a straight axis.
Metal flow takes place within the plastic range of the metal, so that the bent part retains a permanent set.
Minimum bend radius is a function of metal type, condition, and thickness
Metal cracks on tensile surface if bend radius smaller than a certain value
Springback; dimensional change of the formed part after forming

23. Bending
BENDING TERMS
SPRINGBACK

24. Hydro Forming What is hydro forming?
A sheet metal forming operation in which a pliable rubber pad attached to a ram is forced by hydraulic pressure to become a mating die for a punch on a press bed.
Developed in the aircraft industry for the limited production of a large number of diversified parts.
Can readily produce contoured flanged parts

25. Hydro Forming
TOOLING AND SETUP FOR HYDRO FORMING

26. TYPICAL HYDRO-FORMED SHAPES
Hydro Forming
SINGLY CURVED
SHRINK FLANGE
STRETCH FLANGE
CURVED SECTIONS
TYPICAL HYDRO-FORMED SHAPES

27. Stretch Forming What is stretch forming?
The shaping of a metal sheet or part by first applying suitable tension or stretch and then wrapping it around a die of the desired shape.
Produces parts with of large radius of curvature
Springback is reduced because stress gradient is relatively uniform
STRETCH FORMING TECHNIQUE

28. Forging What is forging?
Metal is worked into the desired shape by impact via hammering.
Outstanding grain structures
Best combination of mechanical properties

29. Relation of Materials Selection to Manufacturing-Forging
CLOSED-DIE FORGING

30. Metal Removal techniques, Other techniques
Machining
Chemical Milling
Other Processes
Heat Treatment
Joining
Shot peening (grenaillage)

31. Machining
Main mechanical metal removal method used in aircraft industry
What is machining?
Removing material from a metal part, usually using a cutting tool, and usually using a power-driven machine.
Machining advantages include:
High dimensional tolerance
Good surface finish
Complex geometry capabilities
Precautions include:
Economics of machining
Programming (NC)
Machining labor
Tooling

32. Machining

33. Chemical milling
Main chemical metal removal method used in aircraft industry
What is chemical milling?
Chemical milling is a metal removal method in which metal is shaped into intricate shapes by masking certain portions and then etching away unwanted material.
Advantages include:
Allows reduced web thickness’ below practical limit of other processes
Thickness of 0.010” as opposed to 0.040” for machining
Can accommodate curved parts
Precautions include:
Reduction in service fatigue performance of parts
Environment

34. Heat Treating Main heat treatment methods used in aircraft industry
Quenching and tempering of steels
Age hardening of nonferrous alloys
What is heat treatment?
Heat treatment is defined as a controlled heating and cooling of a solid metal or alloy by methods designed to obtain specific properties by changing the microstructure

35. Heat Treating for steels
Annealing
Softens material and yields lowest mechanical properties
Changes properties such as machinability by achieving desired microstructure
Normalizing
To refine grain structure subjected to high temperatures during hot work operations that increase grain size
Quenching and tempering
Achieved by reheating a steel that has been previously hardened
Used to manipulate properties such that optimum mechanical properties are achieved while providing high toughness
Surface hardening
Achieved through both heating and controlled cooling to put a hard, wear-resistant surface layer on a part
The area below the surface (core) is softer or tougher by comparison
Commonly used surface hardening treatments include:
Carburizing, Nitriding, Carbonitriding

36. Heat Treating for non-ferrous alloys
Annealing
Achieved by heating to a select temperature & holding for a period of time. After heating, aluminum is cooled at a rapid rate through quenching
Purpose is to soften metal to prepare it for a hardening treatment
Precipitation hardening (a.k.a. Aging)
Strengthening of metals by extremely small uniform particles that precipitate from a supersaturated solid solution

37. Joining Mechanical Metallurgical Bolting, Riveting Welding, Brazing
Friction Stir Welding

38. Mechanical Joining What is mechanical joining? Advantages include:
Joint formed by inserting a fastener into two or more bodies to hold them together.
Advantages include:
No dimensional distortion
No alterations in grain structure or heat treat properties
Permits the joining of dissimilar materials
Disassembly of joined components with relative ease
Precautions:
Interrupted stress flow; weaker structure

39. Metallurgical Joining
What is metallurgical joining?
Joint formed by heat to produce the coalescence of metals.
Advantages include:
No interrupted stress flow; very strong structure
Precautions:
Inability to weld dissimilar metals
Alterations in grain structure
High risk of welding defects (due to melting)
Cracks, porosity, inclusions, shrinkage, segregation, etc.
Cycle time, cost

40. Metallurgical Joining (new technique)
Friction Stir Welding
Joint formed by using the heat created by a tool on the surface of the two mating surfaces (not reaching the fusion transition).
Advantages include:
Ability to join dissimilar metals
Allow for manufacturing savings
Smaller details
Can be automated
Precautions:
Fairly new technology to be proven
Alterations in grain structure to be determined

41. Shot peening (grenaillage)
What is shot peening?
Shot peening is process in which the surface of a part is bombarded with small spherical media called shot.
Objective is to induce a layer of compressively-stressed material that will improve service properties.
Shot peen, under specific conditions can also be used for forming operations (such as wing planks)
Advantages include:
Substantial improvement in service performance of parts
Stress corrosion cracking resistance
Fatigue resistance
Precautions:
Strict control required to avoid excessive work hardening
Exhausts ductility of the surface material
Leads to micro-crack formation
Reduction in service performance

42. Couverture partielle
Couverture complète

43. Corrosion
Aircrafts are designed for high intensity & high cycle life for service over many years
Appropriate corrosion protection is vital
Four elements are required to get corrosion:
Anode
Cathode
Contact
Electrolyte
If in any way we can eliminate one of the elements, we can
prevent corrosion

44. Corrosion Cell

45. Corrosion Prevention Processes - Inorganic Coating Anodizing of Aluminum
Electrolytic process which produces an oxide layer at the surface of a metal. It is a controlled corrosion process
Advantages include:
Improve corrosion resistance
Increased abrasion resistance
Increased paint adhesion
Improved adhesive bonding
Precautions:
Anodizing may affect fatigue life of parts
Expensive

46. Corrosion Prevention Processes - Inorganic Coating Chemical conversion coating of aluminum
Reaction of the metal surface with a solution which causes the formation of a protective molecular film
Also known as Alodine or Iridite (commercial products)
Advantages include:
Corrosion protection
Slightly conductive, does not affect fatigue properties
Excellent base for painting
Can be done by immersiion or manual application
Precautions:
No abrasion resistance
Limited corrosion protection vs Anodizing

47. Corrosion Prevention Processes - Inorganic Coating Plating of steel
The electro deposition of an adherent metallic coating upon an electrode for the purpose of obtaining a surface with properties or dimensions different from those of the basis metal.
Advantages
Improved corrosion resistance over steels
Precautions
Environment: use of cyanides, heavy metals

48. Plating Cadmium: Chromium: Nickel:
Applied on Steel to avoid dissimilar contact with aluminum
inch thick
used as a sacrificial coating due to it being anodic to steel
Chromium:
0.002 to inch thick
Used where exceptional wear resistance and low friction properties are required
Detrimental effect on fatigue properties
Nickel:
Used as an alternate to Cadmium plating, where resistance to over 400 degree F, or abrasion resistance are required.
Nickel plating is not a sacrificial coating like Cadmium plating

49. Corrosion Prevention Processes - Organic Coatings Paints
Primers
Solvent or waterbased
Epoxy base, Acrylic base
Applied to treated surfaces, add extra corrosion film
High resistance to chemicals, weathering, impact
Top Coat
Mainly Polyurethane
Appearance, exteriors, cockpit, visible parts
Extra corrosion barrier, sub floor line
High Temperature Coatings
Teflon Filled Coating

50. Non metallic materials
Composites
Sealants
Paints (seen in corrosion protection)
Other materials
Flammability

51. Composite materials
Definition: A combination of two or more materials, differing in form or composition on a macro-scale. The constituents retain their identity.

52. Composite Materials
A composite, as used in the aerospace world, is a non-homogenous mixture of fibers and a matrix, designed to procure oriented strength to a part.
Advantages include:
High strength and stiffness to weight ratio
Good fatigue properties
Fewer details, less assembly required
Precautions:
Material cost
Processing cost
Repair Cost

53. Five Harness Satin (5HS)
Composite Materials
Matrix
Thermoset resins are used, such as Epoxy (mainly) and Phenolic.
Cured at 250oF or 350oF. Also can be cured at room temperature for repair.
Fibers
Graphite
Kevlar
Glass
Fiber’s style
Woven (plain, 5HS, 8HS, etc.)
Unidirectional
Plain Weave (PW)
Five Harness Satin (5HS)

54. Composite Materials Graphite Kevlar Glass
Most widely used for primary structural applications
Best balance of properties
Kevlar
Uses limited by low compressive strength
Light weight
Glass
Lower stiffness, uses in secondary structures

56. Composite Processing - Autoclave (Temperature, Pressure and Vacuum)

57. Composite materials - Preparation for Curing

58. Composite Typical Cure Cycle

59. Autoclave Curing…Controlled process?
The Truth…..

62. Lightning Protection on Composites
Because of their low electrical conductivity (compared to metals) outside composites parts need to be protected against lightning.
A metal foil, or a wire mesh, is included in the lay-up of the the part to conduct the electrical charge in case the part is hit by a lightning.
If not…..see next slide….

63. Lightning Strike Test - Graphite Laminates, not protected with a metallic foil

64. Composite Materials - RTM advancements Resin transfer Molding
Process of manufacturing composite parts using matched metal tools
Dry fabric is placed in a mold.
The mold is closed tightly
Resin is injected at high pressure in the mold
Advantages include:
Manufacturing cost (less details for same assembly)
Complex parts can be manufactured rapidly
Precautions:
Initial set-up cost
Properties vs metallic structures

65. RTM Flap

66. Fiber Metal Laminates (Glare)
New technology trying to use the best of both worlds
Fuselage panels using composite bonded with traditional aluminum
Used on Airbus 380
Advantages include:
Light weight
Reasonable structural properties loss
Precautions:
Strength
Cost (royalties)

67. Composite Sandwich Panel Construction

68. Types of Honeycomb Used at Bombardier
HEXAGONAL
FLEX-CORE
OVEREXPANDED

69. Bonded Structure Comparison
Relative stiffness
Relative strength
Relative weight
100
700
350
103
3700
925
105 t 2t 4t

70. Sealants
The main purpose of sealants is to prevent contamination from entering or to prevent fluids from leaking
Polysulfide Sealants:
95% of the sealants used
Great fluid resistance
Used for
Aerodynamic sealing
Fuel tank sealing
Pressure and environmental sealing

71. Sealant types Silicone Sealants Firewall Sealants
Used where a high temperature resistance is required (400 to 500 degrees F).
Firewall Sealants
Silicone sealant specifically formulated to meet the fireproof requirements (2000 degrees F flame for 15 minutes)

72. Sealing Philosophy - 3 levels of sealing
1st level - Environmental Sealing
Faying surface sealing
Wet installation of fasteners
2nd level - Pressure Sealing
1st level sealing
Fillet sealing
3rd level - Fuel Tank Sealing (liquid tight sealing)
2nd level sealing
Brush Coat of Fasteners

73. Fuel Tank Sealing
WET SIDE
DRY SIDE
OUTSIDE SURFACE

74. Other Materials … Adhesives Rubbers
Epoxies
Cyanoacrylates (Crazy Glues)
Contact cements
Silicones
Rubbers
Ethylene Propylene (Skydrol resistant)
Oils, Hydraulic fluids, Grease, Jet fuel, Plastics

75. Flammability Regulations- United Airlines, McDonnell Douglas MD-90
Rotorblast – Engine disk hit on fuel line

76. Flammability - Air France Airbus 340-211
Hydraulic pump fire

77. Flammability - Air Canada McDonnell Douglas DC 9-32
Initial Lavatory fire

78. Flammability Requirements
Interior flammability to FAR , FAR , FAR
All materials/assemblies within the aircraft passenger, cargo and crew areas must meet some of the following flammability requirements, depending on their location, size and function:
Vertical burn
Horizontal burn
45/60 degrees burn
Smoke density
Heat release
Burn through

79. Flammability - Testing
Cargo Liners-Oil Burner Test
Seat Cushions-Oil Burner Test

80. Information about Material Properties
A new material can’t be employed in a design unless the engineer has access to reliable material properties and costs.
The need for materials data evolve as a design proceeds from conceptual to detail design.
Conceptual design
Materials Selector
Database for range of metals
ASM Metals Reference Book
Detail design
At this stage, very precise data are required. Data are best found in:
Data sheets issued by materials producers
Actual tests performed on the material from which the part will be made

81. Costs vs material selection
Prices for materials are complex:
Nature
Transformation
Competition
Transportation
Many extra costs may be added:
Grades and tolerances
Inspection & testing
Size of order; cost of inventory vs just in time
Packing, marking, storage conditions

82. CRJ Wing

83. Wing Planks Integrally machined parts Surface treatment
Integrated stringers design drove material selection
Al 2000 series discarded because of poor damage tolerance
Al 7075 T6 discarded because of poor stress corrosion cracking
Upper planks 7150-T7751 for better Static and Compression
Lower planks 7475-T7351 for better damage tolerance
Surface treatment
Shot peen (Forming and Saturation)
Clean after shot peen, organic and iron residues (Acid or alkaline etch)
Chromic Acid Anodizing
Epoxy primer and Polyurethance topcoat (Exterior)
Fuel Tank Coating (Interior)

84. Wing Planks Shot peen forming Span Twist
Wing planks are formed to achieve right curvatures
Avoid machining of thick plates (material and process savings)
Span, Twist, Chord forming to desired shape
Manufacturing issues: Dimples, paint surface appearance
Span
Chord
Twist

85. Fuel access doors Composite door (internal) Aluminum door (external)
Conductivity with rest of structure critical
Avoid dissimilar material (corrosion)
Beware of in-flight flex leading to fretting leading to corrosion
Use of aluminized seal (flexible, conductive, compatible)
Interior: Fuel
Int. Door
Ext. Door
Exterior: Aerodynamic and conductive surface

86. Leading edges Al 6013 Formability, Corrosion resistance – No Clad
Formed
Machines pockets (Chemical milling)
No surface treatment

87. Inspection and Testing
To ensure material behavior and condition per specifications, inspection and testing must be performed
Testing can be divided into two categories:
Nondestructive
Destructive

88. Destructive Testing What is destructive testing? Chemical analysis
A test used for determining the constitutive properties of structural parts in which the test subject is at least partially destroyed
Chemical analysis
Tensile testing
Failure analysis
Metallurgical testing

89. Destructive Testing - SEM and Microscopic Surface Examination
Microscopic examination is the study of the surface of metals and alloys by scanning electron microscopy (SEM)

90. Failure Analysis Importance of failure analysis
Associated with economic losses
May also be associated with human losses
Failure analysis requires:
Understanding of analysis methods
Knowledge of aircraft components and systems
Knowledge of failure modes
A successful investigation may result in improvements in:
Design
Manufacturing
Inspection procedures

91. Modes of Failure Typical Modes of Failure
Failure associated with overload
Failure associated with fatigue
Failure associated with high temperature
Environmentally assisted fractures

92. Modes of Failure
Failure associated with fatigue

93. Modes of Failure
Environmentally assisted fractures

94. Destructive Testing - Tensile Testing
Main purpose to determine mechanical properties of material

95. Destructive Testing - Light Microscope & Metallographic Examination
Metallographic examination is the study of the structure of metals and alloys by light microscopy using prepared surfaces

96. Non Destructive Testing
A test used for determining the quality/characteristics of a material, part, or assembly, without permanently altering the subject or its properties.
VISUAL EXAMINATION
PENETRANT TESTING
RADIOGRAPHIC TESTING
ULTRASONIC EXAMINATION

97. Conclusions
The material and process selection methodology goes through a complex fight between multiple characteristics
The Design engineer must understand very well what are the true objectives and requirements in order to overweigh some of these characteristics
There are never perfect scenarios, at the end, the engineer must compromise between pros and cons
The objective is to have the best design possible with the functionality, acceptable quality, and a short manufacturing cycle time, all at the right cost.

98. Thank you - Merci
Questions???