Heat Distortion Temperature Testing of Plastics

Heat distortion Temperature Testing of Plastics

Heat distortion temperature testing of plastics (HDT) is a standard test (ASTM D648 and ISO 75) used to assess the temperature at which a polymer, plastic or plastic composite specimen deforms under a given flexural load (fiber stress).  The heat distortion temperature is also known as the ‘deflection temperature under load’ (DTUL) or ‘heat deflection temperature’ (HDT).

The properties of plastics, as of all materials, depend on temperature. This takes on special importance for mechanically stressed parts, which are exposed in use to high temperatures. As result the heat distortion temperature property of a plastic material is of paramount importance and has become necessary tool for product design, engineering, and product manufacturing, making the heat distortion temperature testing of plastics important.

During testing a plastic specimen with given dimensions is loaded into the Heat distortion temperature testing apparatus, in a three-point bend style test, aligned flat wise or edgewise direction.  The direction of the specimen, which depends on the standard used, ASTM or ISO, is a very crucial part of the overall test as it was found that it affects the result significantly.  Thus, special care should be taken in order to load the specimen in the correct position, according the relevant standard.

The fiber stress applied for the test is either 0.455 MPa or 1.82 MPa, and the temperature is increased at rate of 2 °C/min until the specimen deflects 0.25 mm (for ASTM). As a result the Heat deflection temperature of the tested plastic will be the temperature at which the specimen has deflected 0.25 mm.  Because of the quite different standards (ASTM and ISO) is it necessary to mention not only the HDT value and the stress applied but also the standard used as well.

Heat distortion temperature testing equipment at Impact


At Impact Solutions, we are equipped with a state-of-the-art Heat Distortion Temperature Testing of plastics machine (Figure 1) and we provide HDT testing solutions for both quality control and engineering projects.  At Impact we are also equipped with the latest technology for sample preparation, which enables us to obtain accurate and consistent results.  It is the combination of the advanced facilities and the expertise of our technology team which makes us number one choice for testing from the biggest “players” in the plastic/polymer industry.

For more information please contact us on +44 1324 489 182, or via email at info@impact-solutions.co.uk, where one of our plastic experts will be delighted to help you out.

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