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Designer Materials 2

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  • 1. Testing Materials How do materials behave under different conditions? May 29, 2009
  • 2. Which to Use..?
    • In pairs, summarise the key characteristics of the 4 main material classes:
      • Metals Ceramics Polymers Composite
      • Think about the properties that we discussed last lesson…
      • List some examples...
  • 3. Which to Use..?
    • In pairs, summarise the key characteristics of the 4 main material classes:
      • Metals - Tough. Strong in tension . Can have plastic properties. E.g. Iron, Steel, Copper.
      • Ceramics - Stiff. Strong in compression . Week in tension. Brittle. E.g. Cement, Diamond, Porcelain.
      • Polymers - Long chain molecules. Some are brittle. Some are very elastic. Some are tough. E.g polythene. Cotton, leather.
      • Composite - More than 1 material. Has properties of each material e.g. reinforced concrete with steel bars).
  • 4.  
  • 5. Testing Materials Materials behave differently when we put them under stress. This is due to the object and the material.
    • Example:
    • If you sit on a match it will snap
    • But a chair made of the same material holds your weight
  • 6.
    • How will a spring behave under tension?
    • Measure the extension for different masses (0g to 300g) and record results into a table. DO NOT DAMAGE SPRING!!!
    • Plot the results onto a graph - Mass vs. Extension
    • What happens if you add another sprint next to the first? Next to it or attached to it…?
    x m
  • 7. Hooke’s Law
    • Robert Hooke, who in 1676 stated,
    • The power ( sic .) of any springy body is in the same proportion with the extension.
    • announced the birth of elasticity. Hooke's statement expressed mathematically is,
    • F = k . x
    • where F is the applied force (and not the power, as Hooke mistakenly suggested), x is the deformation of the elastic body subjected to the force F , and k is the spring constant (i.e. the ratio of previous two parameters).
  • 8. Hooke’s Law
    • But what happened when you added more springs?
    • Does it change the shape of the graph?
    • Does it change the spring constant?
    • How can we get around this..?
    • For homework - work out if we could work out a consistent constant