Consider the case of simple stress due to an axial load P which is supported by a column

of cross-sectional area A and original length L as shown in Figure 2.1. The applied force

induces an internal stress σ such that:

P = (σ × A) and hence σ = P/A (i.e. load/unit area)

Figure 2.1

The deformation induced by the stress is quantified by relating the change in length to the

original length and is known as the strain in the material normally given the symbol ε where:

ε = (change in length/original length) = (δ /L)

Note: the strain is dimensionless since the units of δ and L are the same.