Test methods constant-deflection-rate tests

The test is conducted in a bath of oil, with the temperature increased at a constant rate of 2°C per minute. The DTUL is the temperature at which the sample attains a deflection of 0.0254 cm (0.010 in.). This test is only a guide. It represents a method that could be correlated to product designs, but as with most other tests conducted on test specimens and not on a finished product, it is just a guide (Fig. 5-7). 

DIN EN ISO 75-1,-2 (successor to DIN 53461) sets out a method of determining heat deflection temperature (HDT), which is in widespread use, so it is outlined below. The standard test specimens are rectangular in section and should preferably be laid flat and subjected to three-point flexion at constant load. A force F that can vary depending on the thickness of the specimen is applied hy weights and/or springs to achieve an outer fiber elongation of 1.80 (method A), 0.45 (methods), or 8.00 N/mm (method C). The specimens loaded in this way are then heated at a constant rate of 120 K/h (or 50 K/h). When deflection of the specimen reaches an outer fiber elongation of 0.2%, the temperature at which this occurs is the heat deflection temperature (also known as heat distortion temperature). 

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