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How to Test Plastic Properties

Flexural

Flexural properties of plastics are obtained by placing a specimen on two supports spaced 4 in. apart. A load is applied in the center at a specified rate and the loading at failure (psi) is the flexural strength. For materials which do not break, the flexural property usually given is Flexural Stress at 5% strain.

In bending, a beam is subject to both tensile and compressive stresses.

Because most thermoplastics do not break in this test even after being greatly deflected, the flexural strength cannot be calculated. Instead, stress at 5% is calculated, i.e., the loading in psi necessary to stretch the outer surface 5%. ASTM D-790.