Three Types of Tear Strength Test

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In actual wear and application, some parts of fabrics usually undertake sudden tear strength, such as fabrics are hook by something sharp, some parts of pants of hips are affected by external force when squatting down, etc., so that fabrics internal yarn will break or crack, due to bear maximum loading, which is called breakage or tear. Tear strength test is widely used in international trade of textiles for the reason that it reflects objectively the characteristics of sudden tear of fabrics in actual wear and the degree of fabrics influenced in finishing process. The following explains the detail of three methods related to test tear strength.

1. Pants-Shaped Tearing Method

a. Principle
The two legs clamping pants-shaped samples make sample notch line a straight line between up and down clamps. Power on the tester, push tension toward notching, record the tear strength until it is torn to the specified length, and calculate tear strength in accordance with the peak on curve run by automatic drawing device, or through electronic device.

b. Test Procedure
Start the tester, and tested sample is torn to sample end mark at tear speed of 100mm/min. Record tear strength, and if you want to get the tear track of the specimen, you can record the tear strength and tear curve of each specimen in the direction of each fabric using a recording instrument or an electronic recording device. If the peak derives from high density fabrics, it should record manually. The ratio of the walking rate to the tear rate on recording paper should be set to 2: 1, in order to observe whether the tear is carried out in the direction of the applied force and whether yarns slide from fabrics instead of being teared. Tests meeting the following conditions are valid:

 Yarns never slide from fabrics.
 Specimen never slides from clamping device.
 Tear completely and tear is carried out in the direction of the applied force.
Test results that do not meet above conditions should be removed. If 3 or more in 5 test results are removed, the test is proved to unfit the specimen. If increase specimens according to the agreement, it’s better to double the specimens, meanwhile, the test result should be reported according to the agreement.


2. Trapezoidal Tear Method

a. Principle
Draw a trapezoid on the specimen; hold the two non-parallel sides of the trapezoid with strength tester's clamp. A continuous increasing force is applied to the specimen, so that tear is spreading in the direction of specimen’s width, to test average maximum tear strength.

b. Test Procedure
The distance of two clamps is set to (25±1) mm, and tensile speed is 100 mm/min. Choosing appropriate load range make tear strength fall on the full range of 10%~90%. The specimen is mounted, and clamped along non-parallel sides of trapezoid to let notch lying between two clamps, with short side kept tight and long side creasing. Start the tester, record tear strength using automatic recording device if you have enough capital. Tear strength should not be recorded if tear is not carried out along notch line.


3. Impact Pendulum Tear Method

a. Principle
The specimen is fixed on the clamp, cutting a notch. Releasing pendulum in the maximum potential position; when removable clamp leaves the fixture, the specimen is torn in the direction of notch. Work that fabrics is torn to a certain length coverts to tear strength.

b. Test Procedure
Push the stop of pendulum, release pendulum. When pendulum swings back, holding it to avoid destroying pointer position. Tear strength can be read from scale value of measure device or digital screen, whose unit is Newton. Depending on the types of instrument used, the data read may need to be multiplied by the corresponding coefficient specified by the manufacturers to transform the representation in Newton. The inspection results shall fall within the range of 15% -85% of the scale used, and the test shall be repeated at least 5 times in each direction.

To observe whether the tear is carried out in the direction of the applied force and whether yarns slide from fabrics instead of being teared. Tests meeting the following conditions are valid:
 Yarns never slide from fabrics.
 Specimen never slides from clamping device.
 Tear completely and tearing range is within the width of 15mm all the time


Related machines:
Elmendorf tear tester
http://www.testextextile.com/product/elmendorf-tear-tester-tf140c/

[Srijoni Roy]

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