Deflection Temperature Under Load (HDT)
Heat Deflection Temperature: Understanding Short-Term Heat Resistance of Materials
Heat deflection temperature (HDT) is a critical measure of a material's ability to withstand high temperatures while maintaining its structural integrity. HDT is defined as the temperature at which a standard test bar deflects a specified distance under a load. This test is used to determine a material's short-term heat resistance, helping to distinguish between those that can sustain light loads at high temperatures and those that quickly lose rigidity over a narrow temperature range.
Test Procedure
To measure HDT, the test specimens are first placed under a deflection measuring device. Then, a load of either 0.45 MPa or 1.80 MPa is applied to each specimen, depending on the standard being used. The specimens are then lowered into a silicone oil bath where the temperature is raised at a controlled rate of 2° C per minute. The test is stopped when the specimen deflects the specified distance, which is typically 0.25 mm for ASTM, 0.32 mm for ISO flatwise, and 0.34 mm for ISO edgewise testing.
Specimen Size
The size of the test specimen can vary depending on the standard being used. For ASTM testing, a standard bar size of 5" x ½" x ¼" is typically used. ISO edgewise testing uses a bar size of 120mm x 10mm x 4mm, while ISO flatwise testing uses a bar size of 80mm x 10mm x 4mm.
Data
The results of the test provide data on the temperature at which the specified load and deflection occur. This information is critical for understanding a material's short-term heat resistance and helps engineers make informed decisions about material selection in high-temperature applications.
Applications
HDT is a critical factor to consider when selecting materials for use in high-temperature environments. It is often used in the aerospace, automotive, and electronics industries, among others. For example, in the aerospace industry, materials used in the engine must be able to withstand extreme temperatures, making HDT a critical factor in material selection. In the automotive industry, materials used in engine components, such as intake manifolds, must be able to withstand high temperatures to ensure reliable performance. In the electronics industry, HDT is used to select materials for use in components that generate heat, such as circuit boards and power supplies.
Conclusion
Heat deflection temperature is a critical factor in determining a material's ability to withstand high temperatures while maintaining structural integrity. The test provides valuable data for engineers when selecting materials for use in high-temperature applications. HDT testing is used in various industries, including aerospace, automotive, and electronics, among others. By considering HDT when selecting materials, engineers can ensure the reliable performance of components in high-temperature environments.