It has been found experimentally that within the elastic limit, the shear stress is directly proportional to shear strain. Mathematically,
τ ∝ φ or τ = C . φ or τ / φ = C
where, τ = Shear stress,
φ = Shear strain, and
C = Constant of proportionality, known as shear modulus or modulus of rigidity. It is also denoted by N or G.
The following table shows the values of modulus of rigidity (C) for the materials in every day use: