The Usefulness of HDT and a Better Alternative to Describe the Temperature Dependence of Modulus

The majority of the short-term properties that appear in a material data sheet are measured at room temperature. The heat deflection temperature (HDT) represents the only systematic attempt to characterize elevated temperature performance. The HDT test describes a particular response to temperature under a specific set of conditions, however it is often treated in the material selection process as a maximum use temperature. As the trend toward computerized property databases has progressed, the tendency to rank order properties for a large number of materials from different families has increased the separation between the property value and its significance to the design engineer.

This paper will briefly review the HDT test as defined by ASTM D 648 and the International Standards counterpart ISO 75. It will then discuss an alternative method for capturing a more complete picture of the effect of temperature on modulus. This technique, known as dynamic mechanical analysis (DMA), provides an excellent tool for evaluating materials and comparing their mechanical performance over a wide temperature range.