Information on the most widely used ASTM standards within the materials testing industry
HDT/VICAT Testing
Heat deflection temperature (HDT) (ISO 75, ASTM D648) indicates the relative behavior of different types of material under load at elevated temperatures. It is determined for materials such as thermoplastics, hard rubber and duroplastic laminates.
Vicat softening temperature (VST) (ISO 306, ASTM D1525) provides a value for the temperature at which a thermoplastic material begins to soften rapidly. This temperature is determined using a needle-shaped indenter with a round cross-sectional area of 1 mm.
UnitedTest HDT/VICAT Testing Machine
Heat Distortion Temperature Tester/VST softening temperature apparatus
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What's HDT/VICAT Testing?
Heat deflection temperature (HDT) (ISO 75, ASTM D648) indicates the relative behavior of different types of material under load at elevated temperatures. It is determined for materials such as thermoplastics, hard rubber and duroplastic laminates.
Vicat softening temperature (VST) (ISO 306, ASTM D1525) provides a value for the temperature at which a thermoplastic material begins to soften rapidly. This temperature is determined using a needle-shaped indenter with a round cross-sectional area of 1 mm.
Test Procedure:
HDT Heat deflection temperature test:
The bars are placed under the deflection measuring device. A load of 0.45 MPa or 1.80 MPa is placed on each specimen. The specimens are then lowered into a silicone oil bath where the temperature is raised at 2° C per minute until they deflect 0.25 mm for ASTM, 0.32 mm for ISO flatwise, and 0.34 mm for ISO edgewise.
VST VICAT softening point test:
A test specimen is placed in the testing apparatus so that the penetrating needle rests on its surface at least 1 mm from the edge. A load of 10N or 50N is applied to the specimen. The specimen is then lowered into an oil bath at 23 degrees C. The bath is raised at a rate of 50° or 120° C per hour until the needle penetrates 1 mm.
Principle of HDT/VICAT test
The measurement principle is simple: to determine the temperature at which a sample under a given load is softened to allow a decrease in 3-point bending (HDT) or depressed (Vicat) of a needle.
The samples are placed in a thermostatic bath equipped to impose a temperature ramp. An electronic system continuously measures the descent of the load placed on the specimen, and stores the temperature corresponding to the criterion used.
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| HDT – test in flat position | HDT – test on edge |
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| HDT - Sample dimensions ISO 75 | Vicat - Sample dimensions ISO 306 |
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| VICAT Test |
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