For measuring both the thermal and the mechanical properties, a thermomechanical analyzer (TMA) is used. Temperature-dependent dimensional changes in solids, liquids and pastes determine the suitability of an application for a given material or provide information about the composition, structure and conditions of processing.
TMA measures these dimensional changes while allowing the sample to be subjected to an additional mechanical load (DIN 51005, ASTM E 831, ASTM D 696, and ASTM D 3386). This makes it possible to determine the thermal length change (with negligible mechanical load: dilatometry, DIN 51045) as well as the thermomechanical characteristics.
Besides the linear thermal expansion and the coefficient of thermal expansion, TMA can also be used to study phase transition temperatures, sintering temperatures, shrinkage steps, glass transition temperatures, dilatometric softening points, volumetric expansion, density changes, delamination and sintering kinetics.
Instruments for thermomechanical analysis are applied in all areas from research and development to quality control. Typical domains include plastics and elastomers, thermosets, composite materials, adhesives, films and fibers, ceramics, glass and metals.
The linear thermal expansion is an important variable for assessing the dimensional behavior of a material in response to a change in temperature.
This plot shows the thermal expansion (dL/L0 in %) of an epoxy resin between -70°C and 270°C. In the first heating (blue curve), the onset of the glass transition (Tg) occurs at 123°C. In the second heating (red curve), the onset of Tg is slightly shifted, to 125°C. This shift could be due to relaxation effects or post-curing.