Structures and Materials- Section 5 Major Structural Materials for Aeronautic and Automotive Structures

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An overview of the major materials used in aeronautical and automotive structures will be given in this section. The mechanical and physical properties of the materials will be highlighted, with an emphasis placed on the stiffness versus density and strength versus density of various materials.

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Structures and Materials- Section 5 Major Structural Materials for Aeronautic and Automotive Structures

  1. 1. Section 5 Major Structural Materials for Aeronautical and Automotive Structures An overview of the major materials used in aeronautical and automotive structures will be given in this section. The mechanical and physical properties of the materials will be highlighted, with an emphasis placed on the stiffness versus density and strength versus density of various materials. © Loughborough University 2010. This work is licensed under a Creative Commons Attribution 2.0 Licence .
  2. 2. Contents <ul><li>Structural Materials </li></ul><ul><li>Steels </li></ul><ul><li>Aluminium Alloys </li></ul><ul><li>Advanced Fibre-Reinforced Polymeric Composites </li></ul><ul><li>Summary of Major Mechanical Properties </li></ul><ul><li>Stiffness – Density Chart </li></ul><ul><li>Strength – Density Chart </li></ul><ul><li>Failure Modes of Structural Materials </li></ul><ul><li>Ductile Fracture </li></ul><ul><li>Brittle Fracture </li></ul><ul><li>Temperature Dependent Ductile-Brittle Fracture Transition </li></ul><ul><li>Allowable Stress and Factor of Safety </li></ul><ul><li>How to Obtain Data on Material Properties? </li></ul><ul><li>Credits & Notices </li></ul>
  3. 3. Structural Materials <ul><li>Key factors to be considered for load bearing aeronautical or automotive structures: </li></ul><ul><ul><li>Strength-to-density ratio </li></ul></ul><ul><ul><li>Stiffness-to-density ratio </li></ul></ul><ul><ul><li>Fracture toughness and impact toughness </li></ul></ul><ul><ul><li>Suitability for manufacturing technique </li></ul></ul><ul><li>Aeronautical structural materials </li></ul><ul><ul><li>Aluminium alloys </li></ul></ul><ul><ul><li>Advanced composites </li></ul></ul><ul><ul><li>Titanium alloys </li></ul></ul><ul><ul><li>Steels </li></ul></ul><ul><li>Automotive structural materials </li></ul><ul><ul><li>Steels </li></ul></ul><ul><ul><li>Aluminium alloys </li></ul></ul><ul><ul><li>Magnesium alloys </li></ul></ul><ul><ul><li>Plastics </li></ul></ul><ul><ul><li>Advanced composites </li></ul></ul>
  4. 4. Steels <ul><li>Major steel alloying elements </li></ul><ul><ul><li>Carbon </li></ul></ul><ul><ul><li>Chromium </li></ul></ul><ul><ul><li>Nickel </li></ul></ul><ul><ul><li>Manganese </li></ul></ul><ul><ul><li>Molybdenum </li></ul></ul><ul><li>Steel categories </li></ul><ul><ul><li>Carbon steels </li></ul></ul><ul><ul><li>Alloy steels </li></ul></ul><ul><ul><li>Stainless steels </li></ul></ul><ul><li>Carbon steels according to carbon content: </li></ul><ul><ul><li>Low-carbon steels (<0.3%) – inc. mild steel </li></ul></ul><ul><ul><li>Medium-carbon steels (0.3% - 0.7%) </li></ul></ul><ul><ul><li>High-carbon steels (0.7% - 1.4%) </li></ul></ul><ul><li>Maraging steels: alloy steels without carbon </li></ul><ul><li>Mechanical properties of steels are controlled primarily by two means: </li></ul><ul><ul><li>Alloying </li></ul></ul><ul><ul><li>Heat treatment </li></ul></ul>
  5. 5. Aluminium Alloys <ul><li>Major aluminium alloying elements: </li></ul><ul><ul><li>Copper (Cu) </li></ul></ul><ul><ul><li>Magnesium (Mg) </li></ul></ul><ul><ul><li>Zinc (Zn) </li></ul></ul><ul><ul><li>Lithium (Li) </li></ul></ul><ul><li>Aluminium alloy catagories: </li></ul><ul><ul><li>2xxx (with Cu as major alloying element) </li></ul></ul><ul><ul><li>5xxx (with Mg as major alloying element) </li></ul></ul><ul><ul><li>7xxx (with Zn as major alloying element) </li></ul></ul><ul><li>Common grades: </li></ul><ul><ul><li>2024-T3 </li></ul></ul><ul><ul><li>5052 </li></ul></ul><ul><ul><li>7075-T3 </li></ul></ul><ul><li>Al-Li alloys : higher strength , lower density and improved weldability , but are less tough </li></ul><ul><li>Heat treatment condition code for aluminium alloys: </li></ul><ul><ul><li>F: as fabricated </li></ul></ul><ul><ul><li>H: strain hardened or cold worked </li></ul></ul><ul><ul><li>O: annealed (i.e. softened) </li></ul></ul><ul><ul><li>T: heat treated </li></ul></ul>
  6. 6. Advanced Fibre-Reinforced Polymeric Composites <ul><li>One-dimensional fibrous reinforcement and three-dimensional matrix </li></ul><ul><li>Typically long continuous fibre reinforcement (15 micron diameter) and matrix can be any material </li></ul><ul><li>Typical fibres: </li></ul><ul><ul><li>Carbon </li></ul></ul><ul><ul><li>Glass </li></ul></ul><ul><ul><li>Aramid (such as Kevlar) </li></ul></ul><ul><li>Typical matrix: </li></ul><ul><ul><li>Epoxy </li></ul></ul><ul><ul><li>Polyester </li></ul></ul><ul><ul><li>Phenolic </li></ul></ul><ul><ul><li>Polyetheretherketone (PEEK) </li></ul></ul><ul><ul><li>Bismaleimide (BMI) </li></ul></ul><ul><ul><li>Polyimide </li></ul></ul>
  7. 7. Advanced Fibre-Reinforced Polymeric Composites (continued) <ul><li>Most useful: polymer-based fibre-reinforced composites </li></ul><ul><ul><li>Carbon Fibre-Reinforced Plastics (CFRP) </li></ul></ul><ul><ul><li>Glass Fibre-Reinforced Plastics (GRP) </li></ul></ul><ul><ul><li>Kevlar Fibre-Reinforced Plastics (KFRP) </li></ul></ul><ul><li>FRP’s are still considered brittle when compared with steel and aluminium alloys </li></ul><ul><li>Mechanical properties: significantly direction-dependent and dependent on amount of fibre-reinforcement (volume fraction) and fibre-orientation </li></ul><ul><li>In-plane mechanical properties better than properties in the through-the-thickness (for 2D layups) </li></ul>http://en.wikipedia.org/wiki/File:Rutan.variEze.g-veze.arp.jpg © Superleague formula: the beautifulrace 2007. Sourced from http://www.flickr.com/photos/7480659@N06/2090647287 available for download under a Creative Commons licence .
  8. 8. Summary of Major Mechanical Properties * Unidirectional (UD) with 60% fibre-volume fraction Density (kg/m 3 ) E (GPa)   y MPa  ult (MPa) K 1c (MPa.m ½ )  (  10 -6 1/  C) Metals and Alloys Aluminium Alloys 2024 7075 Cast Iron Steels mild steel high strength Nickel Alloy Titanium Alloy Magnesium Alloy Polymers or Plastics Epoxy and Polyester PVC Composites CFRP* GRP* Ceramics Alumina Silicon Carbide 2800 2800 7200 7850 7850 8800 4500 1800 1250 1400 1750 1950 3750 3000 72 72 83-170 210 210 190 110 45 2-4 2-4 140 35 390 450 0.33 0.33 0.2-0.3 0.29 0.29 0.3 0.33 0.35 0.3-0.4 0.4 0.3 0.3 0.1-0.2 0.1-0.2 410 480 120-290 220 340-1000 200-1600 760-1000 80-280 30-100 46 630 300 5000 10000 480 550 69-480 430 550-1200 400-2000 900-1200 140-340 30-120 - - - - - 45 23 6-20 100-200 50-154 - 55-115 - 0.4 - 32-45 20-60 4 3 23 23 10-12 12 14 12 10 27 55-90 80 -0.9 7 9 4
  9. 9. Stiffness versus Density Composites Density (kg/m 3 ) 100 300 1,000 3,000 10,000 30,000 0.01 0.1 1 10 100 1,000 Young’s Modulus (GPa) Woods and Wood Products Foams Metals and Alloys Polymers
  10. 10. Strength versus Density Metals and Alloys Composites Woods and Wood Products Polymers Foams Density (kg/m 3 ) 100 300 1,000 3,000 10,000 30,000 0.1 1 10 100 1,000 10,000 Strength (MPa)
  11. 11. Failure Modes of Structural Materials <ul><li>Investigation of failure of load-bearing structures is essential to design and understanding of service conditions </li></ul><ul><li>Two characteristic modes of fracture </li></ul><ul><ul><li>Ductile </li></ul></ul><ul><ul><li>Brittle </li></ul></ul><ul><li>Factors that affect how a structure will fail are: </li></ul><ul><ul><li>Manufacturing process </li></ul></ul><ul><ul><li>Loading characteristics </li></ul></ul><ul><ul><li>Structural configuration </li></ul></ul><ul><ul><li>Environmental or service effects </li></ul></ul><ul><li>Fracture mode could change if some of these factors change </li></ul><ul><li>Most mechanical failures involve both, with one being dominant </li></ul>
  12. 12. Ductile Fracture <ul><li>Ductile fracture is a gradual process of nucleation, growth and coalescence of micro-cracks in the structure + local stress concentration </li></ul><ul><li>Extensive plastic deformation </li></ul><ul><ul><li>Distortion </li></ul></ul><ul><ul><li>Considerable dissipation of energy (heat, sound) </li></ul></ul><ul><li>Fracture surface is rough , fibrous and dull </li></ul><ul><ul><li>Characteristic ‘cup and cone’ shape </li></ul></ul><ul><li>Materials that often fail in this manner: </li></ul><ul><ul><li>Ductile metals </li></ul></ul><ul><ul><li>Plastics at room and moderate temperatures </li></ul></ul>© Sigmud 2008 sourced from http://tinyurl.com/yb9e5no available for download under a Creative Commons licence .
  13. 13. Brittle Fracture <ul><li>Brittle fracture defined by a sudden complete disruption of the material with little or no plastic deformation </li></ul><ul><li>Initiates from interior flaws or stress risers with little warning </li></ul><ul><ul><li>Dissipates limited energy </li></ul></ul><ul><li>Fracture surface is clean , smooth and shiny </li></ul><ul><ul><li>Characteristic chevron marks usually perpendicular to loading direction </li></ul></ul><ul><li>Materials that often fail in this manner: </li></ul><ul><ul><li>Hard metals (cast irons and other cast metals) </li></ul></ul><ul><ul><li>Ductile metals and plastics at below-zero temperatures </li></ul></ul><ul><li>Tensile strengths significantly lower than compressive strengths </li></ul><ul><li>Flaw population has significant effect on fracture behaviour </li></ul><ul><ul><li>Brittle fracture is notch (surface finish) sensitive </li></ul></ul>© Sigmud 2009. Sourced from http://en.wikipedia.org/wiki/File:Cast_iron_tensile_test.JPG available for download under a Creative Commons licence .
  14. 14. Temperature Dependent Ductile-Brittle Fracture Transition FCC metals Low-strength alloys (BCC metals, low carbon steel and thermoplastics) High-strength alloys Temperature Absorbed Energy
  15. 15. Allowable Stress and Factor of Safety <ul><li>Limit load = maximum in service load </li></ul><ul><li>Factor of safety is applied to the limit load (value decided by design authority) </li></ul><ul><ul><li>Ultimate load = 1.5  limit load </li></ul></ul><ul><ul><li>Proof load = 1.15  limit load (military aircraft) </li></ul></ul><ul><li>The structure must be able to withstand ultimate loads without failure </li></ul><ul><li>The structure must be able to support limit loads without detrimental permanent deformation </li></ul><ul><li>Procedure is to design a structure to zero Margin of Safety </li></ul><ul><ul><li>Balance between safety and weight </li></ul></ul>F = Allowable stress (from material properties data) f = Applied ultimate stress (from calculations / analysis / test) xxx denotes tension, compression, shear, buckling, bearing etc.
  16. 16. How to Obtain Data on Material Properties? <ul><li>You can access an excellent resource for both metallic and composites material properties from the web via any computer connected to the Loughborough network at www.knovel.com or www.matweb.com </li></ul><ul><ul><li>MMPDS – Metallic Materials Properties Development and Standardisation – A U.S. DoT publication </li></ul></ul><ul><ul><li>MIL-HDBK-17 – Composite Materials Handbook (Vol. 2 contains material properties) </li></ul></ul>
  17. 17. This resource was created by Loughborough University and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme. © 2010 Loughborough University. Except where otherwise noted this work is licensed under a Creative Commons Attribution 2.0 Licence . The name of Loughborough University, and the Loughborough University logo are the name and registered marks of Loughborough University. To the fullest extent permitted by law Loughborough University reserves all its rights in its name and marks, which may not be used except with its written permission. The JISC logo is licensed under the terms of the Creative Commons Attribution-Non-Commercial-No Derivative Works 2.0 UK: England & Wales Licence.  All reproductions must comply with the terms of that licence. The HEA logo is owned by the Higher Education Academy Limited may be freely distributed and copied for educational purposes only, provided that appropriate acknowledgement is given to the Higher Education Academy as the copyright holder and original publisher. Credits

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