ASTM D648 for Deflection Temperature of Plastics
The heat deflection temperature (HDT) describes the temperature at which a plastic material starts to deform under a predetermined load. This value is used in materials testing to evaluate the thermal resistance of a material. It is measured by subjecting a defined specimen to an increasing temperature under constant load in a 3-point bending process until a defined deflection is reached. Both ASTM D648 and ISO 75 standards describe the test procedure and regulate the requirements for the test equipment and test conditions, such as load, specimen geometry and heating rate to achieve internationally comparable results.
Приложение
Material selection & comparison
Rank plastics, composites, and thermosets by their ability to resist bending under heat & load.
Guide choices for parts exposed to elevated temperatures (automotive, electronics, appliances).
Product design & engineering
Set upper temperature limits for structural components under service loads.
Predict dimensional stability in hot environments (engine covers, circuit boards, kitchenware).
Manufacturing optimization
Determine safe ejection temperatures for injection molded parts (cool to near/ below HDT to avoid post mold warping).
Optimize cooling cycles and mold design for production efficiency.
Quality control & R&D
Verify material consistency and formulation performance.
Evaluate effects of fillers, reinforcements, and additives on heat resistance.
In short, HDT is essential for designing durable, heat resistant plastic components and ensuring they perform safely in real world thermal mechanical conditions.
Test methods
ASTM D648 contains the standard test method for the heat deflection temperature of plastics under flexural load in the edgewise position of the specimen. Two test methods are determined based on the support span (separation of the lines of contact between specimen and supports):
Method A: 101.6 ± 0.5 mm
Method B: 100.0 ± 0.5 mm
Regardless of the method, constant flexural stress of 0.455MPa or 1.82MPa must be applied.
Specimens to ASTM D648
Alignment | Edgewise position |
Injection-molded | Min. length: support span +12.7 mm Width: 3~13 mm Thickness: 12.7 ± 0.5 mm |
Components | Thickness: ≥3mm |
QTY | ≥2pcs |
Test requirements to ASTM D648
Test fixture | Support radius: l 3 ± 0.2 mm; Support span: l Method A: 101.6 ± 0.5 mm Flexural stress: l 1.82MPa l 0.455MPa |
Temperature | Starting temperature: l Room temperature; Rate of temperature increase: l 2 ± 0.2 °C/min Thermometer position: l No further than 10 mm from the specimen, without touching it |
Results | Standard deflection: 0.25mm |
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