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Heat Deflection Temperature (HDT) - ISO 75

The temperature at which a test specimen deflects a specified amount when loaded in 3-point bending at a specified maximum outer fiber stress. Deflection temperature is used to determine short-term heat resistance.

HDT Testing Methods
Method Outer Fiber Stress (MPa)
A 1.80
B 0.45
C 8.00

Testing is either performed using edgewise or flatwise specimen orientation. Testing parameters vary between the two configurations as shown below.

Specimen Orientation Parameters
Orientation Dimensions (mm) Span (mm) Standard Deflection Diagram
Edgewise 120x9.8-15x3-4.2 100 0.32
Flatwise 80x10x4 64 0.34

ISO 10350 Note

ISO 10350 requires testing in the flatwise orientation.

Similar Standards