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ASTM D638-measuring the strength of unreinforced and reinforced plastics

This testing standard covers the tensile properties of plastics in the form of dumbbell-shaped test specimens. Specimens up to 14 mm, or 0.55 in, in thickness will be tested under conditions of pretreatment, temperature, humidity, and testing machine speed.

Testing Procedure:

place your dumbbell-shaped specimen into the grips of the test machine, taking care to align the long axis of the specimen and the grips with an imaginary line joining the points of attachment of the grips to the machine. Tighten the grips evenly and firmly to the degree necessary to prevent slippage of the specimen during the test, but not to the point where the specimen would be crushed. Attach the extension indicator. The change in jaw separation is never to be used for calculating modulus or elongation. Set the speed of testing and start the machine. Record the load-extension curve of the specimen. Record the load and extension at the yield point (if one exists) and the load and extension at the breaking point.

Equipment Required:

Universal Test Machines feature constant rate of extension (constant crosshead speed) and constant load rate control (e.g. lb/min). ASTM D638 requires a testing machine of the constant rate- of-crosshead-movement or Constant Rate of extension (CRE) type.

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