Young Modulus

  • The value of a Stiffness Constant only applies to a certain sample. F_or example, a longer piece of the same material would have a lower stiffness constant._ The Young Modulus on the other hand is a material property, meaning it can be applied to all samples of the same material. It is calculated by the formula:
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Stress and Strain

  • Stress is a measure of the force applied per unit cross-sectional area of a material. It is measured in Pascals (Pa, or Nm-2, or Kgm-1s-2 if you want to be pedantic). It is hence calculated by the formula:
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  • Strain is the change in length relative to original length. It has no units since it is the ratio of two lengths. It is calculated by the formula:
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  • A stress on a material causes a strain.

  • For a material, a stress-strain graph can be drawn. The gradient of this graph is then the Young Modulus. The Young Modulus is also measured in Pascals. By finding the area under a stress-strain graph, it is possible to work out the energy stored per unit volume in a material.

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  • The Young Modulus, being a material property as it is, can be used to generalise the elastic properties of a material. This is very useful, for example, in working with seat belts, as it important to be able to calculate how far they will stretch for any length or thickness.
Written by Sam Adam-Day.