Uses of materials

The properties of a material determine whether they are suitable for given uses. A certain property will be required for any given use. There may be more than one suitable material to choose from, and the advantages and disadvantages of each one must be evaluated.

Example

The table shows some properties of samples of aluminium alloy, mild steel and timber.

Aluminium alloyMild steelTimber
Density (g/cm3)2.87.70.7
Tensile strength (MPa)38024020
Compressive strength (MPa)38024015
Resistance to moistureGood - does not need paintingRusts unless protectedAbsorbs water unless protected
  1. Identify the weakest metal shown in the table, and explain your answer:
    • The mild steel is the weakest metal, although timber is the weakest material of the three.
    • Mild steel has a lower tensile strength than aluminium, so it stretches more easily when forces are applied. It has a lower compressive strength, so it is crushed more easily when forces are applied.
  2. All three materials could be used to make the frame for a train carriage. Evaluate these materials for this use:
    • Timber has the lowest density, so a wooden frame could be the most lightweight. However, timber is the weakest material, so the frame will need to be thicker or use more pieces. This might make the wooden frame heavier than a metal frame.
    • Mild steel is almost as strong as the aluminium alloy. However, it is 2.75 times denser than aluminium, so a steel frame is likely to be much heavier. A heavier carriage may reduce the number of carriages the train can pull or reduce its acceleration so that journey times increase.
    • The aluminium alloy is four times denser than timber, but at least 19 times stronger. An aluminium frame is likely to be the most lightweight of the three materials. Aluminium alloy has a good resistance to moisture. Unlike mild steel and timber, it does not need protecting. Overall, aluminium alloy would be the best choice.
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