ASTM D1922 guides the Elmendorf Tear Test of plastics where the Propagation Tear Resistance of Plastic Film and Thin Sheets is evaluated by Pendulum Method. The results are used in preparing specifications of the material thickness of the plastics used in packaging.
All plastic films and sheets are prone to tear with increased force. The ASTM D1922 test method is widely used to rank the relative tear resistance of thin plastic films and sheets. The pendulum impact tester determines the minimum force required for an existing slit to propagate through a specified distance to the edge of the specimen. The test is result-oriented and is used in the specification of thickness and material of the plastics used in packaging. It depends upon the application whether a low propagation impact or a high propagation impact is required.
Ten samples are incised from the plastic sheet in the direction of the machine, and ten samples are cut from the sheet in the transverse direction. A sample is placed in the tester and mounted in place. A knife is used to create a slit in the sample, which ceases 43 mm from the distant edge of the sample. The pendulum is allowed to propagate the slit more through the remaining length of 43 mm. Energy loss of the pendulum through the procedure is used to calculate an average tearing force.
For Elmendorf Tear testing, three types of standard samples are considered. Constant radius samples are the most widely used test samples for testing plastic films. The constant radius sample is beneficial for materials where the rupture may not propagate up the sample as desired. A rectangular sample of dimension 63 mm × 76 mm can also be used. A modified rectangle increases the height on the specimen edges to help lower the unscrambling of the external edges.
The test results are recorded as tearing force in milli-newtons (or grams-force). Sample thickness is recorded, although thickness and tearing force do not have a direct relationship. Hence, only results for samples having equal thickness can be compared.