Physics & Maths

Physics & Maths

What the spec says:

"You should be familiar with typical stress-strain and load-extension graphs for low carbon steel. You should understand how to calculate stress, strain and Young’s modulus of elasticity in a material."

Material Calculations


The stress applied to a material is the force per unit area applied to the material. The maximum stress a material can stand before it breaks is called the breaking stress or ultimate tensile stress.

Tensile means the material is under tension. The forces acting on it are trying to stretch the material. Compression is when the forces acting on an object are trying to squash it.

The equation below is used to calculate the stress.

stress = stress measured in Nm-2 or pascals (Pa)
F = force in newtons (N)
A = cross-sectional area in m2


The ratio of extension to original length is called strain, and it has no units as it is a ratio of two lengths measured in metres.

strain = strain it has no units
DL =extension measured in metres
L = original length measured in metres

The Young Modulus

The Young Modulus is the modulus of elasticity. This means it is a number which represents how easy it is to deform (stretch) a material.

The equation for the young modulus is as follows:

The two parts from the equation are worked out from the formulas above (stress and strain).

Graphs of materials

Load / extension graph

Load extension graph

Stress / strain graph

ss graph stress strain graph stress strain graph