Shear Strain:

When the deforming forces act tangentially (Figure) the shear strain is defined in terms of the angle θ (in radian) through which a line perpendicular to the fixed plane is turned after deformation. For small angle deformation, shear strain is given by:

θ = Δx/ y

Figure: Shear Strain

With this background knowledge about stress and strain, you are now in a position to understand elasticity of materials. Before doing that, it will be useful to study the experimentally observed variation of strain with the stress (applied deforming force) for a few solids.