TUTORIAL

What can we conclude?

• The values of Young's modulus for polymers are low, so most polymers are unlikely to be useful for stiffness-limited designs.
  
• Some metals, ceramics and woods could be considered - but composites appear best of all.

This still leaves quite a lot of choices, so what might be considered next to narrow the choice further?

What can we conclude?

• The strength of ceramics is only sufficient for loading in compression - they would not be strong enough in tension, including loading in bending.
• Woods may not be strong enough, and composites might be too expensive.
• Metals appear to give good overall performance

Once we have identified a promising class of materials, we need to decide which members of this class are the best - for instance which metals?

What can we conclude?

• Some metals look very good for light, stiff components - e.g. magnesium, aluminium, titanium, while others are clearly eliminated - e.g. lead.
  
• Steels have rather a high density, but are also very stiff. Given their high strength and relatively low cost, they are likely to compete with the other metals.

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Let's summarise what we've learnt about materials selection.