The relationship between the stress and strain that a particular material displays is known as that particular material's Stress-Strain curve. It is unique for each material and is found by recording the amount of deformation (strain) at distinct intervals of tensile or compressive loading (stress). These curves reveal many of the properties of a material (including data to establish the Modules of Elasticity E)

Stress–strain curves of various materials vary widely, and different tensile tests conducted on the same material yield different results, depending upon the temperature of the specimen and the speed of the loading. It is possible, however, to distinguish some common characteristics among the stress-strain curves of various groups of materials and, on this basis, to divide materials into two broad categories; namely, the ductile materials and the brittle materials


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
Strain The ratio of extension to original length is called strain 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