1. Material Selection for Aerospace Applications
Darren Pyfer, P.E.
Engineering Specialist Senior
October 16, 2001

2. Agenda Vought Aircraft Industries Corporate Overview
Material Selection Criteria
Material Types
Material Forms
Examples
10/16/01

3. Vought Aircraft Industries Corporate Overview

4. Vought Company Overview
Largest Single Supplier of Aerostructures to Boeing:
Producing More of the 747 Structure Than Any Other Commercial Supplier for Boeing
Producing More of the C-17 Structure Than Any Other Military Supplier for Boeing
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5. Vought Company Overview (cont.)
Largest Single Supplier of Aerostructures to Gulfstream Aerospace
Designed and Build Integrated Wing System for the Gulfstream GV As a Risk-sharing Team Member
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6. Vought Company Overview (cont.)
Largest Single Supplier of Aerostructures to Northrop on the B-2 Stealth Bomber Program
Designed and Built the Intermediate Wing Section of the B-2 Bomber including the Engine and Landing Gear Bays
10/16/01

7. Vought Commercial Products
737
767
747 GV
757
777
CFM56
CF6
GIV
HAWKER 800
CF34
10/16/01

8. Vought Military Products
F/A-18E/F
E-8C/JSTARS
S-3
F-14
E-2C
P-3
EA-6B
T-38
V-22
Global Hawk
10/16/01

9. Vought Product Line Summary
Nacelle
Comp
Control
Surfaces
Empennage
Fuselage
Doors
Wings
737
747
757
767
777 GV
C-17
10/16/01

10. Material Selection Criteria

11. Static Strength
Material Must Support Ultimate Loads Without Failure. Material Must Support Limit Loads Without Permanent Deformation.
Initial Evaluation for Each Component
Usually Aluminum Is the Initial Material Selection
If Aluminum Cannot Support the Applied Load Within the Size Limitation of the Component, Higher Strength Materials Must Be Considered (Titanium or Steel)
If Aluminum Is Too Heavy to Meet the Performance Requirements, Graphite/Epoxy or Next Generation Materials Should Be Considered
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12. Stiffness
Deformation of Material at Limit Loads Must Not Interfere With Safe Operation
There Are Cases Where Meeting the Static Strength Requirement Results in a Component That Has Unacceptable Deflections
If That Is the Case, The Component Is Said to Be a ‘Stiffness’ Design
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13. Fatigue (Crack Initiation)
The Ability of a Material to Resist Cracking Under Cyclical Loading
Spectrum Dependant
Stress Concentration Factors
Component Is Limited to a Certain Stress Level Based on the Required Life of the Airframe
Further Processing May Improve Fatigue Properties Such As Shot Peening or Cold Working
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14. Damage Tolerance (Crack Growth)
The Ability of a Material to Resist Crack Propagation Under Cyclical Loading
Slow Crack Growth Design
Use of Alloys With Increased Fracture Toughness
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15. Weight Low Weight Is Critical to Meeting Aircraft Performance Goals
Materials Are Tailored for Specific Requirements to Minimize Weight
Materials With Higher Strength to Weight Ratios Typically Have Higher Acquisition Costs but Lower Life Cycle Costs (i.e. Lower Fuel Consumption)
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16. Corrosion Surface Corrosion
Galvanic Corrosion of Dissimilar Metals (see Chart)
Surface Treatments
Proper Drainage
Stress Corrosion Cracking
Certain Alloys Are More Susceptible to Stress Corrosion Cracking (see Chart)
Especially Severe in the Short Transverse Grain Direction
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17. Dissimilar Metal Chart
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18. Stress Corrosion Cracking (SCC) Chart
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19. Producibility Commercial Availability Lead Times
Fabrication Alternatives
Built Up
Machined From Plate
Machined From Forging
Casting
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20. Cost Raw Material Cost Comparisons Aluminum Plate = $2 - $3 / lb.
Steel Plate = $5 - $10 / lb.
Titanium Plate = $15 - $25 / lb.
Fiberglass/Epoxy Prepreg = $15 - $25 / lb.
Graphite/Epoxy Prepreg = $50 - $100 / lb.
Detail Fabrication Costs
Assembly Costs
Life Cycle Costs
Cost of Weight (Loss of Payload, Increased Fuel Consumption)
Cost of Maintenance
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21. Specialized Requirements
Temperature
Lightning and Static Electricity Dissipation
Erosion and Abrasion
Marine Environment
Impact Resistance
Fire Zones
Electrical Transparency
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22. Performance vs. Cost Dilemma
Highest Performance For The Lowest Cost Is the Goal of Every Airplane Material Selection.
Mutually Exclusive
Compromise Is Required
Define the Cost of Weight to the Aircraft
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23. Material Types

24. Aluminum
Aluminum Accounts for ~80% of the Structural Material of Most Commercial and Military Transport Aircraft
Inexpensive and Easy to Form and Machine
Alloys Are Tailored to Specific Needs
2000 Series Alloys (Aluminum-copper-magnesium) Are Medium to High Strength With Good Fatigue Resistance but Low Stress Corrosion Cracking Resistance.
2024-T3 Is the Yardstick for Fatigue Properties
5000 and 6000 Series Alloys Are Low to Medium Strength but Easily Welded
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25. Aluminum (cont.)
7000 Series Alloys (Aluminum-zinc-magnesium-copper) Are High Strength With Improved Stress Corrosion Cracking Resistance but Most Have No Better Fatigue Properties Than 2000 Series
7050 and 7075 Alloys Are Widely Used
7475 Alloy Provides Higher Fatigue Resistance Similar to 2024-T3
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26. Aluminum Tempers
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27. Aluminum Tempers (cont.)
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28. Aluminum Tempers (cont.)
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29. Aluminum Comparison Chart
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30. Titanium Better Strength To Weight Ratio Than Aluminum or Steel
Typically Comprises ~5% By Weight in Commercial Aircraft and Up To ~25% By Weight For High Performance Military Aircraft
Good Corrosion Resistance
Good Temperature Resistance
Good Fatigue And Damage Tolerance Properties In The Annealed Form
Typical Alloy Is Ti 6Al-4V Either Annealed or Solution Treated and Aged
High Cost For Metals
10/16/01

31. Steel
Steel May Be Selected When Tensile Strengths Greater Than Titanium Are Necessary
Steel Is Usually Limited to a Few Highly Loaded Components Such As Landing Gear
There Are Many Steel Alloys to Choose From (See Chart); Select the One That Is Tailored for Your Application.
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32. Steel (cont.)
Mil-Hdbk-5 List of Aerospace Steel Alloys:
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33. Composite
The Embedding of Small Diameter High Strength High Modulus Fibers in a Homogeneous Matrix Material
Material Is Orthotropic (Much Stronger in the Fiber Oriented Directions)
Fibers
Graphite (High Strength, Stiffness)
Fiberglass (Fair Strength, Low Cost, Secondary Structure)
Kevlar (Damage Tolerant)
Matrix
Epoxy (Primary Matrix Material) to 250° F
Bismaleimide (High Temp Applications) to 350° F
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34. Material Properties Comparison
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35. Next Generation Materials
Aluminum Lithium
GLARE (Fiberglass Reinforced Aluminum)
TiGr (Graphite Reinforced Titanium)
Thermoplastics
Resin Transfer Molding (RTM)
Stitched Resin Fusion Injected (Stitched RFI)
10/16/01

36. Mil-Hnbk-5 Overview
Document Contains Design Information On The Strength Properties of Metallic Materials and Elements for Aerospace Vehicle Structures. All Information and Data Contained in This Handbook Have Been Coordinated With the Air Force, Army, Navy, Federal Aviation Administration and Industry Prior to Publication and Are Being Maintained As a Joint Effort of the Department of Defense and the Federal Aviation Administration.
10/16/01

37. Basis of Properties
Material Property Selection Is Dependant on the Criticality of the Structural Component
Critical Single Load Path Structure
A Basis (99% Probability of Exceeding)
S Basis (Agency Assured Minimum Value)
Other Primary Structure With Redundant Load Paths
B Basis (90% Probability of Exceeding)
Without a Test, A or S Basis May Be Required
Secondary Structure
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38. Grain Direction
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39. Material Properties (Mil-Hdbk-5) Example
Type
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40. Material Forms

41. Sheet Rolled Flat Metal Thickness Less Than .25” Fuselage Skin
Fuselage Frames
Rib and Spar Webs
Control Surfaces
Pressure Domes
Good Grain Orientation
Many Parts and Fasteners
Fit Problems
Straighten Operations
Shims
Warpage
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42. Plate Rolled Flat Metal Thickness Greater Than .25”
Wing and Tail Skins
Monolithic Spars and Ribs
Fittings
Unitized Structure; Fewer Fasteners
Grain Orientation Can Be a Problem
High Speed Machining Has Lowered Fab Costs
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43. Extrusion
Produced By Forcing Metal Through a Forming Die At Elevated Temperature To Achieve The Desired Shape
Stringers
Rib and Spar Caps
Stiffeners
Grain Is Aligned in The Lengthwise Direction
Additional Forming and Machining Required
Used In Conjunction With Sheet Metal Webs
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44. Forging
Produced by Impacting or Pressing The Material Into The Desired Shape
Large Fittings
Large Frames/Ribs
Odd Shapes
Control Grain Orientation
Residual Stresses Can Cause Warpage
Tooling Can Be Difficult
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45. Casting
Produced By Pouring Molten Metal Into A Die To Achieve The Desired Shape
Nacelle/Engine Components
Complex Geometry
Dramatically Lowers Part and Fastener Counts
Poor Fatigue And Damage Tolerance Properties
High Tooling Costs
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46. Composite
Produced By Laying Fabric, Laying Tape, Winding, Tow Placement and 3D Weaving or Stitching
Skins
Trailing Edge Surfaces
Interiors and Floors
Properties Can be Oriented To Load Direction
Excellent Strength To Weight Ratio
High Cost Of Material and Processes
Poor Bearing Strength
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47. Examples

48. Upper Wing Cover Skin - 7075-T651 Aluminum Plate
Stringers T6511 Aluminum Extrusion
After Machining; Age Creep Formed To -T7351/-T73511
Compression Dominated
Reduces Compressive Yield Strength
Greatly Increases Stress Corrosion Resistance
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49. Lower Wing Cover Skin - 2024-T351 Aluminum Plate Tension Dominated
Good Ultimate Tensile Strength
Very Good Fatigue and Damage Tolerance Properties
Stringers T73511 Aluminum Extrusion
High Ultimate Tensile Strength
Good Damage Tolerance Properties
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50. Spars 7050-T7451 Aluminum Plate
High Tensile and Compressive Strength in Thick Sections
Good Stress Corrosion Resistance
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51. Fixed Trailing Edge Surface
Graphite/Epoxy Fabric
Aramid/Phenolic Honeycomb
Fiberglass/Epoxy Fabric Corrosion Barrier
Secondary Structure
Stiffness Design
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52. Leading Edge 2024-0 Clad Aluminum
Heat Treated to -T62 After Stretch Forming to Shape
Clad For Corrosion Resistance
Polished For Appearance
De-icing by Hot Air/Bird Strike Resistance
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53. Landing Gear Support Beam
Titanium 6Al-4V Annealed Forging
High Strength and Stiffness
Critical Lug Design
Height is Limited By Wing Contours
Annealed Form Is Good For Fatigue And Damage Tolerance
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54. Wing to Body Attachments
PH13-8Mo Cres Steel Bar
Critical Lug Design
High Strength Requirement
Good Corrosion Resistance
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55. Flap Tracks PH13-8Mo Cres Steel Bar
Geometry Is Very Limited By Requirement To Be Internal To The Wing
Results In Very High Stress Levels
High Stiffness Is Required To Meet Flutter and Flap Geometry Criteria
Good Corrosion Resistance
10/16/01