Elmendorf Tear ASTM D1922
Plastic films and thin sheeting are widely used in the packaging industry for their flexibility, durability, and low cost. However, the quality of plastic film can vary greatly depending on its tear resistance, which is a critical factor in determining its suitability for specific applications. One way to measure tear resistance is through the Pendulum Method or Elmendorf Tear Test, as defined by ASTM D1922.
The Elmendorf Tear Test is a simple and reliable way to measure the force required to propagate a slit in a plastic film a fixed distance to the edge of the test sample. The test is performed using a pendulum impact tester, which measures the energy loss required to propagate the tear through the sample. The resulting data can be used to determine the material and thickness specifications for plastic film used in packaging.
To perform the test, 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.
The Elmendorf Tear Test uses three standard sample types, including the constant radius sample, the 63mm x 76mm rectangle, and a modified rectangle for textiles. The constant radius sample is the preferred test sample for plastic films, as it provides a constant radius from the start of the tear strength measurement. This is particularly useful for materials where the tear may not propagate directly up the sample as intended. The 63mm x 76mm rectangle is another common sample used in the test. For textiles, the modified rectangle adds height on the ends of the sample to help minimize unraveling of the outside edges.
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. Therefore, only results for samples of the same thickness can be compared.
In our opinion, the Elmendorf Tear Test is a valuable tool for measuring the tear resistance of plastic films and thin sheeting. The test procedure is straightforward, and the results can be used to determine the suitability of materials for specific packaging applications. Whether a low propagation force or a high propagation force is desired will depend on the application, and the data obtained from this test can help determine the optimal material specifications.