Thermomechanical Analysis (TMA) is a thermal analysis technique used to measure changes in the physical dimensions (length or volume) of a sample as a function of temperature and/or time. TMA is commonly used to determine thermal expansion coefficients and the glass transition temperature of polymer or composite materials.

A simplified explanation of the TMA technique may be described as follows. A specimen is placed onto the base of a quartz sample holder and a suspended quartz probe is lowered down and positioned so that it just touches the top surface of the sample. Different probe types of varying tip geometry may be used and, typically, the probe is loaded with some finite weight. The TMA sample holder assembly is then placed into a furnace unit and the vertical movement of the quartz probe is continuously monitored. Typically, TMA tests are run in a heating mode at some controlled heating rate. Probe displacement profiles are subsequently analyzed in terms of thermal expansion coefficients, softening temperatures, and/or the glass transition temperature.

Examples

• Composite materials are increasingly being introduced as replacement materials for parts previously manufactured from metals. As such, the thermal expansion behavior of a composite part becomes a critical design parameter. The TMA technique is useful, here, because it provides direct information about a material's thermal expansion characteristics. TMA thermal expansion data can be analyzed over a specified temperature range or at some particular temperature.
• Determining the glass transition temperature of a composite material using nonmechanical tests is often problematic. The thermal response of highly crosslinked material can be negligible and the presence of a thermally inert, inorganic filler further serves to attenuate the detection of subtle thermal transitions. The TMA technique can readily be used to determine the glass transition temperature of a composite material. Distinct slope changes in the thermal expansion profiles below and above the glass transition temperature range are readily analyzed for Tg.