Heat Deflection Temperature (HDT) - ISO 75
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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.
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