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How to Test Plastic Properties

Stiffness In Flexure

Stiffness In Flexure is determined by clamping a specimen into the apparatus shown here and a 1% load applied manually. The deflection scale is set at zero. The motor is engaged and the loading increased, with deflection and loading figures recorded at intervals. A curve is drawn of deflection versus load, and from this is calculated stiffness in flexure in pounds per square inch.

This test does not distinguish the plastic and elastic elements involved in the measurement and therefore a true elastic modulus is not calculable. Instead, an apparent value is obtained and called "stiffness in flexure." It is a measure of the relative stiffness of various plastics and taken with other pertinent property data; is useful in material selection. ASTM D-747.