This double tear method determines the fabric tear force, known as the tongue test, using a test specimen in the form of a tongue. The tear force measured is the force required to propagate a previously started double tears when the force is applied parallel to the cut and the fabric tears in the direction of the applied force.
This method is mainly applicable to woven textiles fabrics, but it may also be applicable to some nonwovens fabrics (with the same under-mentioned restrictions as for the woven fabrics). However, the method is not applicable to knitted fabrics and woven elastic fabrics. The force to continue both tears over a specified distance is at a constant rate of displacement. The tear force is calculated from the force peaks.
In principle two parallel slits, connected by a slit at right angles to form a tongue, are cut in a rectangular test specimen. The tongue is inserted into the upper grip and the remaining two parts of the test specimen are clamped symmetrically in the lower grip to ensure both cuts each form straight parallel lines. A force is applied in the direction of the cuts to simulate two parallel tears. To record the test, we suggesting using a high-speed intelligent test data logging rate. This is the transfer rate to the PC of 100 Hz or more to capture and record all the peaks and troughs.
We suggest using pneumatic action grips with rubber coated jaw faces for clamping of the material fitted to a tensile testing machine. While manual action grips will work, many of our users prefer the pneumatic action grips for ease of use, productivity, and better repeatability. Pneumatic action grips allow you to set a clamping pressure, while the manually operated grips depend on the operator's strength (which may not be so repeatable). We find that gripping pressure and specimen alignment are very important in these tests. Too much gripping pressure can produce premature breaks, while not enough gripping pressure can lead to specimen slippage or breaks at or near the jaws. These grips are usually fitted to single-column or dual-column table-top design. The use of testing software, such as Bluehill® 2, test method is used to input specimen details, set the desired test control, automatically calculate the desired results and statistics, and produce a test report all in accordance with the standard.
We suggest reviewing ISO13937-4 to fully understand the test fixture and results requirements.