ASTM D648, ISO 75 Heat Deflection Temperature

ASTM D648, ISO 75 Heat Deflection Temperature

Scope:

Heat Deflection Temperature (HDT) test by ASTM D648 is performed to determine the short-term heat resistance of polymeric materials. To find a suitable material for design application, it is necessary to identify materials that lose rigidity over a narrow temperature range and materials that can sustain light loads at high temperatures. Therefore, The heat deflection temperature is the temperature value at which a standard test bar of that material deflects a specified distance under a load.

Test Procedure:

A deflection measuring device is employed for deflection temperature under load test by ASTM D648. Specimen bars of the test material are placed under the measuring device. Each bar is applied with a load of 0.45 MPa or 1.80 MPa. The specimen bars are then let down into a silicone oil bath, where the temperature is raised at 2° C per minute. The specimens are lowered down until they deflect 0.25 mm for ASTM. The deflection value is 0.32 mm for ISO flatwise and 0.34 mm for ISO edgewise.

There may be a specification for numerous materials that calls for the usage of this test procedure, but with some procedural changes that come first when conforming to the specification. So, before applying this test method, it is advised to consult that material specification. 

Except in applications where the parameters of duration, temperature, loading method, and fiber stress are identical to those described in this test method, data produced by this test method shall not be utilized to forecast the behavior of plastic materials at high temperatures. 

The temperature at which a typical test bar deflects a predetermined distance when subjected to a load is known as the heat deflection temperature. It is applied to assess momentary heat resistance. It makes a distinction between materials that retain their stiffness throughout a narrow temperature range and those that lose it at higher temperatures while supporting low loads.

Specimen size:

Specimen bar size for ASTM is 5 inches × ½ inch × ¼ inch. As per ISO, edgewise testing is done using a bar having measurements of 120 mm × 10 mm × 4 mm. For ISO flatwise testing, a bar measuring 80 mm × 10 mm × 4 mm is required.

Data:

The temperature value is recorded at the specified load and deflection.

Conclusion:

ASTM D648 plays a role in the detection of heat resistance of polymeric materials and specifies their use. The deflection of the material in response to the load is noted and heat deflection temperature is recorded.