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Materials and Processes Engineering
Polytechnique
Supplement to Case Study Course
Daniel Menard
19 October 2004
2
Aeropace materials 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:
• 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?• 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
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
Bending
23
BENDING TERMSBENDING TERMSBENDING TERMSBENDING TERMS
SPRINGBACKSPRINGBACKSPRINGBACKSPRINGBACK
Bending
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 FORMINGTOOLING AND SETUP FOR HYDRO FORMING
26
SINGLY CURVEDSINGLY CURVEDSINGLY CURVEDSINGLY CURVED
SHRINK FLANGESHRINK FLANGESHRINK FLANGESHRINK FLANGE
STRETCH FLANGESTRETCH FLANGESTRETCH FLANGESTRETCH FLANGE
CURVED SECTIONSCURVED SECTIONSCURVED SECTIONSCURVED SECTIONS
TYPICAL HYDRO-FORMED SHAPESTYPICAL HYDRO-FORMED SHAPESTYPICAL HYDRO-FORMED SHAPESTYPICAL HYDRO-FORMED SHAPES
Hydro Forming
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 TECHNIQUESTRETCH 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
29CLOSED-DIE FORGINGCLOSED-DIE FORGING
CLOSED-DIE FORGINGCLOSED-DIE FORGING
Relation of Materials Selection to Manufacturing-Forging
30
Metal Removal techniques, Other techniques
Metal removal:• 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 mechanicalproperties 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• Bolting, Riveting
Metallurgical• Welding, Brazing
• Friction Stir Welding
38
Mechanical Joining
What is mechanical joining?• 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 partielleCouverture partielle Couverture complèteCouverture 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 CoatingAnodizing 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
ProcessCorrosion Protection
Coating Thickness
Chromic Acid Anodizing (CAA) Good 0.0001"Sulfuric Acid Anodizing (SAA) Better
0.0003 to 0.0005"
Hard Anodizing Excellent 0.002"
46
Corrosion Prevention Processes - Inorganic CoatingChemical 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 CoatingPlating 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:• Applied on Steel to avoid dissimilar contact with aluminum
• 0.0005 inch thick
• used as a sacrificial coating due to it being anodic to steel
Chromium:• 0.002 to 0.004 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 CoatingsPaints
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 resistance to chemicals, weathering, impact
• 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
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 Five Harness Satin (5HS)
Plain Weave (PW)
54
Composite Materials
Graphite• 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
55
Te
ns
ile S
tre
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th
Co
mp
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siv
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tre
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th
Imp
ac
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tre
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th
Inte
rla
min
ar
Sh
ea
r
De
ns
ity
Te
ns
ion
Fa
tig
ue
Co
st
Fiberglass
Graphite (carbon)
Aramid (Kevlar)
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…..
60
61
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 advancementsResin 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
100
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• 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• Epoxies
• Cyanoacrylates (Crazy Glues)
• Contact cements
• Silicones
Rubbers• Silicones
• 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 DouglasDC 9-32
Initial Lavatory fire
78
Flammability Requirements
Interior flammability to FAR 25.853, FAR 25.855, FAR 25.856
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
• 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
• 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
Ch
ord
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
Exterior: Aerodynamic and conductive surface
Ext. Door
Int. Door
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?• 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???