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How to Test Plastic Properties

Izod Impact

Izod Impact testing is done by clamping a specimen in the base of a pendulum testing machine so that it is cantilevered upward with the notch facing the direction of impact. The pendulum is released, and the force consumed in breaking the sample is calculated from the height the pendulum reaches on the follow-through.

The Izod impact test indicates the energy required to break notched specimens under standard conditions. It is calculated as ft. lb. per inch of notch and is usually calculated on the basis of a one inch specimen although the specimen used may be thinner in the lateral direction.

The Izod value is useful in comparing various types of grades of a plastic. In comparing one plastic with another, however, the Izod impact test should not be considered a reliable indicator of overall toughness or impact strength. Some materials are notch-sensitive and derive greater concentrations of stress from the notching operation. The Izod impact test may indicate the need for avoiding sharp corners in parts made of such materials. For example, nylon and acetal-type plastics, which in molded parts are among the toughest materials, are notch sensitive and register relatively low values on the Izod impact test. ASTM D-256.