2. Materials for Automobiles CEEN0903 Summer 2011

3. Classes of Materials Metals Made of metallic elements: Sn, Cu, Fe Ceramics Compounds between metallic and nonmetallic elements: Sodium Carbonate (Na 2 CO 3 ), Quartz Includes both clay and glass Polymers Most are organic compounds: PVC, Isoprene Includes plastic and rubber

4. Frame: Metallic Windows: Ceramic Tires: Polymeric

5. Stress and Strain Three types of loads Tensile Compressive Shear

6. Stress and Strain Tension Tests Specimen with a round cross-section is deformed until fracture Record force versus elongation Elongation is dependent on cross-sectional area Engineering Stress: F is the load applied perpendicular to the cross section in units of newtons (N) or pounds force (lb f ) A 0 is the original cross-sectional area of the specimen Stress units are megapascals (MPa), 1 MPa=10 6 N/m 2

7. Example High Heeled Shoes One shoe has a heal with a diameter of 2cm One shoe has a heal with a diameter of 6cm Calculate the stress on a womens heal for each shoe Given: Woman weighs 120lb (54 kg) g=9.8 m/s 2 Assume the weight is equally distributed between the two feet, and ignore the presence of the toe part of the shoe

8. Stress and Strain Engineering Strain: l 0 is the original length of the specimen l i is the instantaneous length of the specimen Δl is the change in length Strain is unitless but sometimes expressed as a percentage, in which case it is multiplied by 100

9. Tension Test

10. Elastic Deformation Hookes Law: σ=Eε True for most metals in tension at low levels of stress and strain E is the modulus of elasticity or Youngs modulus Stiffness of a material Metals: 45 GPa<E<407 GPa Ceramics: 70 GPa<E<500 GPa Polymers: 0.007 GPa<E<4 GPa Deformation in which stress and strain are proportional is called elastic deformation Deformation can be recovered upon removing the force

11. Example A piece of copper originally 305 mm (12 in.) long is pulled in tension with a stress of 276 Mpa (40,000 psi). If the deformation is entirely elastic, what will be the resulting elongation? Equations: σ=Eε

12. Plastic Deformation Beyond a certain strain, stress and strain are no longer proportional and deformation cannot be recovered Hookes law is no longer valid Stress level at which deformation becomes plastic is called the yield strength, σ y Yield strength is a measure of resistance to plastic deformation and ranges from 35 MPa to 1400 MPa for metals

13. Stress-Strain Behavior Toughness: ability of a material to absorb energy up to fracture

14. Ductility Ductility measures the degree of plastic deformation at fracture A material with little or no plastic deformation prior to fracture is termed brittle A material with a large amount of deformation prior to fracture is ductile Ductile materials undergo necking prior to fracture Necking occurs after the maximum stress is reached and all further deformation only occurs at the neck

15. Material Properties CeramicsPolymersMetals Elastic Modulus 70-500 GPa0.007-4 GPa45-407 GPa Yield Strength HighLowVaries Toughness Small Large DuctilityBrittleDuctile Car PartWindowsSeats, Tires Frame, Body, Engine

17. Metallic Car Parts Frame and Body Soft/Formable Light weight Ex: Steel (Fe, C) look up type Considerations: Quick acceleration Fuel economy Stability Crash-worthiness Current research: Al and Mg instead of steel Engine and Axels Hard Strong at high temperatures Corrosion resistant Ex: Cast Iron (Fe) Axel- cyclic loading (different from constant loading) Considerations: Vibration dampening both to prevent fracture and for passenger comfort

18. Car Windows Side Windows Tempering Glass heated Cooled rapidly to room temperature Properties Compressive surface stress on outside Tensile stress inside Higher fracture strength Windshield Tempered glass sandwich Polymer layer in the middle Cracks run sideways and not through the middle EU versus US standards

19. Car Tires Rubber Vulcanization: Polymer chains cross-linked by heating the material up and adding sulfur

20. Car Tires

21. Steel Tempered Glass Rubber Tempered Glass Sandwich Cast Iron

22. Key Equations Questions? σ=Eε