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# Designer Materials 2

## by PhysicsJackson on Jan 31, 2008

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## Designer Materials 2Presentation Transcript

• Testing Materials How do materials behave under different conditions? May 29, 2009
• 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...
• 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).
•
• 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
• 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
• 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).
• 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