Temperature of deflection under load

The temperature of deflection under load (often abbreviated as HDT, Heat Deflection Temperature) is a measure of the ability of a material to maintain its shape under load at elevated temperatures. Here’s a breakdown of the concept:

• Test Specimen: A standardized specimen of the material being tested, usually in the form of a bar or plaque, is used for the test.
• Loading: The test specimen is supported at both ends and subjected to a specified load, typically applied at the center of the specimen.
• Heating: The specimen is heated uniformly at a controlled rate while under the specified load. The temperature at which the test is conducted depends on the standard being followed and the application requirements.
• Deformation: As the temperature increases, the material softens and begins to deform under the applied load. The deformation is measured at specific intervals or at the point where a predetermined deflection or sag is reached.
• Characterization: The HDT is determined as the temperature at which the specimen deflects by a specified amount (often 0.010 inches or 0.25 millimeters) under the applied load. This temperature provides an indication of the material’s resistance to deformation at elevated temperatures.

The HDT is an important parameter for materials used in applications where elevated temperatures and mechanical loads are present, such as automotive components, electronic enclosures, and structural elements in buildings. It helps designers and engineers select materials that can withstand the operating conditions without excessive deformation or failure.