Test Summary
The test can be used to compare the propagation resistance of various plastic films and sheeting of comparable thickness. Standard sized samples are cut with two “legs” which are torn apart at a constant speed while the tensile force is measured. Films are arbitrarily defined as having a thickness of less than 0.025 mm, and sheeting less than 1 mm.
Test Procedure
Samples may be pre-conditioned if required, and are cut to a defined shape with two “trouser legs” of 12.5 mm each. The legs are held in opposed grips on the tensile testing stand, and separated at a constant speed of 250 mm/min. As the sample is torn, the tensile force is recorded. The nature of the sample –non-extensible or highly extensible - may be determined by inspecting the force/distance curve once produced. For low extensible films, the average load is calculated, disregarding the first and last part of the force/distance curve. For highly extensible materials, report the initial force to continue propagation of the slit and the maximum force .and extension at maximum load.
Test Apparatus
- Die cutter
- Micrometer reading to 0.0025 mm
- Force testing stand
- Suitable range loadcell compatible with the force testing stand
Preparation
Where conditioning is required, test specimens are stored at 23 ± 2° C, 50 ± 5 % RH for 40 hours.
Method
- If required, pre-condition the samples at 23 ± 2° C, 50 ± 5 % RH for 40 hours.
- At least five samples are required.
- Specimens are cut, ideally using a die cutter, which is kept in good condition to ensure the cut specimens are cut reproducibly, not varying by more than 0.5% from the given dimensions. Sample may be cut in the longitudinal or transverse direction of the sample.
- The thickness of the specimen is accurately measured in several points in the below the slit, and an average value calculated.
- Specimens are clamped with one “leg” in each of the grips of the force testing stand.
- The test stand is set in motion at a fixed crosshead speed of 250 mm/min.
- Continue the test until the tear has propagated through the entire length of the entire unslit length of the sample.
- For non- extensible materials calculate the mean load over a 25 mm interval of the tear disregarding the first and final portions of the force/distance curve.
- For highly extensible materials, determine the initial force to continue propagation of the slit, the maximum force .and extension at maximum load.
Report
The test report shall contain:
- All the information necessary for the complete identification of the sample
- The average thickness of each specimen, and the average thickness of all test specimens
- For non-extensible materials report the average value of tear resistance over the designated 25 mm of the tear calculated in newtons, plus the standard deviation of the averaged value of at least five samples
- For highly extensible samples, report the mean of the initial tear propagation force in newtons, the mean of the maximum tear propagation force in newtons, and the mean of the extension to maximum force in mm, Calculate the standard deviations of these averages of at least five samples
Mecmesin Test Equipment Required for ASTM D 1938
Please refer to the latest official ASTM D 1983 standard for more detailed information. This overview is intended to provide a basic understanding of the test procedure and suitable equipment to meet the standard.
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