Materials: The Young Modulus

Young Modulus Basics

The Young Modulus is a measure of the stiffness of a material.
It is defined as the ratio of stress to strain in a material.
Since it is the ratio of two similar quantities, the Young Modulus has no units.
More scientifically, it is defined as the ratio of tensile (or compressive) stress to tensile (or compressive) strain.

Stress in this context is the force applied to a material per unit area.
It is expressed as a force (in Newtons) divided by an area (in square metres).
Tensile stress can cause a material to extend, while compressive stress can make it compact or shorter.

Strain is a measure of deformation representing the displacement between particles in the material body relative to a reference length.
It is a dimensionless measure, as it is ratio of two lengths - the change in length and the original length.
Strain shows how much a material changes shape under stress.

Young Modulus (E) can be calculated by the formula E = stress/strain.
As stress and strain are both calculated based on the material’s original dimensions, the Young Modulus stays constant for a material regardless of its size or shape.

The Young Modulus is used in engineering and physics to determine whether a material will return to its original shape (elastic behaviour) or deform permanently (plastic behaviour) when a force is applied and then removed.
A higher Young Modulus means the material is stiffer or more difficult to deform.
Materials like steel or diamond have high Young Modulus values, indicating they are very stiff, while rubbers and plastics have low values, indicating more flexibility.

The behaviour of a material under applied forces can be represented graphically with a stress-strain graph.
The slope of the initial, linear part of the graph represents the Young Modulus.
Real-world materials often show non-linear behaviour on these graphs, meaning their Young Modulus can change under high stress or strain.