Trapezoidal Tear Test
ASTM D5587 covers a very specific tear propagation procedure for textiles. This test is often used for acceptance testing when large shipments of fabric or garments are imported from abroad. Tensile testing machines which can achieve a Constant-Rate-of-Travel (CRT) are used to perform this test.
Sample specimens are cut into rectangles and lines are usually drawn onto the samples to create the trapezoid shape. The lines are used to align the sample into the grips on the machine.
Vise grips with jaw inserts measuring 50mm x 75mm (Height x Width) are needed to perform the trapezoidal tear test. Pneumatic vise grips are commonly used in order to make the test more repeatable and exact. Serrated jaw faces usually work best, however other grip faces such as rubber or smooth metal can be used.
As the tear propagates, the individual woven fibers will pull and break. These individual breaks will appear as peaks on the load curve. Peaks can be analyzed individually, or averaged together to create a model for the entire fabric. Common tabulations include the minimum tearing force, and the peak tearing force as well as an average of the five peaks.