Propagation Tear Resistance of Plastic Film and Thin Sheeting by Pendulum Method

Propagation Tear Resistance of Plastic Film and Thin Sheeting by Pendulum Method (Elmendorf Tear)
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Scope: A pendulum impact tester is used to measure the force required to propagate an existing slit a fixed distance to the edge of the test sample. One use of these results would be for the specification of material and thickness for plastic film used in packaging. Depending upon the application, a low propagation force or a high propagation force might be more desirable. Test Procedure: Ten samples each are cut from the plastic film in the machine direction and in the transverse direction. A sample is positioned in the tester and clamped in place. A cutting knife in the tester is used to create a slit in the sample which ends 43mm from the far edge of the sample. The pendulum is released to propagate the slit through the remaining 43mm. The energy loss by the pendulum is used to calculate an average tearing force. Specimen size: There are 3 standard samples for Elmendorf Tear testing. The preferred test sample for plastic films is the constant radius sample. This sample provides a constant radius from the start of the tear strength measurement - useful for materials where the tear may not propagate directly up the sample as intended. Another common sample is a 63mm x 76mm rectangle. For textiles, a modified rectangle adds height on the ends of the sample to help minimize unraveling of the outside edges. Data: Test results are presented as tearing force in milli-newtons (or grams-force). Sample thickness is also reported, although there is no direct relationship between thickness and the tearing force. Thus, only results for samples of the same thickness can be compared. Equipment Used: Thwing-Albert ProTear® Electronic Elmendorf Tearing Tester