Thermomechanical Analysis (TMA) is used to characterize physical properties of materials when force is applied at specified temperatures and time periods. TMA is useful for investigating properties of viscoelastic materials, such as organic polymers. These materials exhibit both viscous and elastic properties that affect their response to mechanical stresses. For example, under conditions of ramping temperature under a fixed load, the viscoelastic material can exhibit changes in volume that correlate with changes in properties such as shrinkage, expansion, swelling and softening.

Measurements are performed by a probe that applies force to the sample. Before the test conditions are applied, the sample length is measured under a light force, which is used as the initial length (l₀). As linear displacement occurs as a function of changing the applied force or temperature. The change in sample length (dl) is measured by an electrical transformer called an LVDT (linear variable displacement transducer). An example application is monitoring length change as the sample is slowly heated. In this case, the observance of a dramatic change in sample length can indicate a phase change, such as a glass transition (Tg), and the temperature at which Tg occurs can be calculated from the plot of length change versus temperature.