Thermal strains

Temperature change can also cause strain. In an isotropic material the thermally induced extensional strains are equal in all directions, and there are no shear strains. In the simplest cases, these thermal strains can be treated as being linear in the temperature change θ − θ₀ (where θ₀ is the temperature of the reference state), writing ε_ij^thermal = δ_ijα(θ − θ₀) for the strain produced by temperature change in the absence of stress. Here α is called the coefficient of thermal expansion. Thus, in cases of temperature change, ε_ij is replaced in the stress-strain relations above with ε_ij − ε_ij^thermal, with the thermal part given as a function of temperature. Typically, when temperature changes are modest, the small dependence of E and ν on temperature can be neglected.