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How to Test Plastic Properties

Deflection Temperature

Deflection Temperature shows the temperature at which an arbitrary amount of deflection occurs under established loads. It is not intended to be a direct guide to high temperature limits for specific applications. It may be useful in comparing the relative behavior of various materials in these test conditions, but it is primarily useful for control and development purposes.

A specimen is placed on supports 4 inches apart and a load of 66 or 264 psi is placed on the center. The temperature in the chamber is raised at the rate of 2 + 0.2 °C per minute. The temperature at which the bar has deflected 0.010 inch is reported as "deflection temperature at 66 (or 264) psi fiber stress." ASTM D-648.