Monthly Archives: December 2014

TMA Penetration Probe

One of the probes for the thermomechanical analyzer (TMA) is the penetration probe.  Penetration probe is sometimes called the micro-indentation probe or micro-indenter.  The penetration probe is useful in determining softening temperature (aka softening point) and hardness of a bulk material.  For example, ASTM E2347 details test procedures and calculations to determine the indentation softening temperature that is very similar to Vicat softening temperature.  With this probe, the indentation hardness can also be measured and Young’s modulus calculated successfully provided the Poisson’s ratio is known.

The penetration probe is also useful for coatings and films.  It can be used to compare the same organic coating of various thicknesses or to compare various organic coating formulations.  By carefully designing experiment and testing samples side by side it is possible to compare and choose the most suitable material combinations for an application. There are things to consider when designing your experiment.  For example, it is known that hardness is dependent on coating thickness and substrate material when the coating is less than ~100 microns.  Another thing to consider is that penetration experiment requires a load and therefore it may be a creep experiment over time at a constant temperature.