Method A of this standard adopts the international standard ISO 9073-4-1989 “Textiles – Test methods for nonwoven fabrics – Part 4: Determination of tear resistance”.
1Theme content and scope of application
This standard specifies two methods for measuring the tearing strength of nonwoven fabrics, method A – trapezoidal method and method B – falling weight method.
Method A – the trapezoidal method is suitable for all types of nonwoven fabrics.
Method B – the falling weight method is only applicable to the determination of the tearing strength of thin non-woven fabrics with a mass below 120g/m2.
2Quotation standards
GB 6529 Standard atmosphere for humidity conditioning and testing of textiles
GB 8170 Numerical Rounding Rules
3 A method–trapezoidal method
3.1 Principle
Take a trapezoidal strip sample and cut a cut of a certain length at the midpoint of the short side of the trapezoid as the starting point of tearing. Then clamp the trapezoidal sample along the clamping line into the upper and lower jaws of the strength testing machine. A continuously increasing load is applied to the specimen, causing the specimen to tear along the incision and gradually expand until the specimen is completely torn.
3.2 Instruments
3.2.1 A constant velocity traction type (CRT) strength testing machine or a constant velocity elongation type (CRE) strength testing machine can be used. For arbitration tests or in the event of a dispute, the CRE type shall prevail.
3.2.2 The clamps used to clamp the specimen should be wide enough to clamp the entire width of the specimen, and there should be no slippage of the specimen in the jaws during testing.
3.3 Sampling
There should be no obvious creases or defects on the sample that would affect the quality of the test. The sample should be taken at a distance of more than 1m from the end of the cloth, and a 1m long sample should be cut for each variety.
3.4 Preparation of samples
3.4.1 On the sample, 100mm away from the edge of the fabric, cut 10 longitudinal and 10 transverse samples in parallel arrangement. Generally, you can cut a few more strips than the specified number for backup.
3.4.2 Size of the sample: First cut it into strips with a width of 50mm and a length of not less than 200mm.
3.4.3 Use a trapezoid template (its dimensions are shown in Figure 1) to mark the hypotenuse of the trapezoid, that is, the clamping line, and cut a 10mm length perpendicular to the short side in the middle of the short side of the trapezoid. of incision.
3.5 Humidity adjustment of the sample and standard atmosphere for testing
The samples were subjected to pre-humidification and humidity conditioning treatment according to the provisions of GB 6529.
The test is conducted in the standard atmosphere specified in GB 6529, and the arbitration test uses the secondary standard atmosphere.
3.6 Test steps
3.6.1 Before testing, calibrate the distance between the upper and lower clamps to 100±1mm.
3.6.2 Adjust the traction speed of the lower clamp to 100mm/min.
3.6.3 Pre-test: Select the tensile force range of the strength testing machine so that the maximum tearing strength falls between 20% and 80% of the full scale (the constant velocity elongation CRE testing machine is not subject to this limitation).
3.6.4 Formal test: Place the sample in the upper and lower clamps, make the clamping line flush with the jaw line of the clamp, and then tighten the screws of the upper and lower clamps. At the same time, pay attention to the fact that the sample is in the middle of the upper and lower clamps. The symmetrical position is so that the short side of the trapezoidal sample remains vertical, and then the strength testing machine is started. After all the samples are torn, the maximum tearing strength value is recorded.
3.6.5 During the test, if the clamp screws are not tightened and the specimen slips in the jaws, the test data should be discarded. Due to differences in manufacturing processes, the longitudinal and transverse tearing directions may sometimes appear irregular in one direction during testing. Any such abnormality should be noted in the test report
3.7 Result expression
Calculate the average value of the maximum tearing strength in the longitudinal and transverse directions. The unit is Newton (N). Calculate to two decimal places and round to one decimal place after rounding according to GB 8170.
3.8 Test report
a. Test methods and instruments;
b. Sample name, code, raw materials and mixing ratio;
c. Test results: The tearing strength is expressed in Newton (N), and the coefficient of variation is expressed in percentage;
d. Atmospheric conditions for testing;
e. Any deviations from the provisions of this standard and abnormalities must be noted.
4 B method–dropping weight method
4.1 Principle
An approximately semicircular sample is clamped on the movable clamp and fixed clamp of the drop weight tearing instrument. An incision is made between the two clamps, that is, in the middle of the sample, and a sector-shaped pendulum is used to drop from the vertical position to The momentum in the horizontal position causes the specimens in the movable and fixed clamps to tear rapidly.
4.2 Instruments
Falling weight fabric tear strength tester.
4.3 Sampling
There should be no obvious creases or defects on the sample that would affect the quality of the test. The sample should be taken more than 1m away from the end of the cloth. Cut a 0.5m long sample for each variety.
4.4 Preparation of samples
4.4.1 Cut out 10 longitudinal and 10 transverse specimens each from the sample within 100mm from the edge of the fabric in a parallel arrangement using a template of the specified size. Generally, you can cut more than the specified number for backup. .
4.4.2 Sample size
The width is 92mm, the height is 63mm, the incision line length is 20mm, the specified tear length is 43mm, and the arc curvature radius R is 43mm. Its specific dimensions and drawing are shown in Figure 2. In addition to using templates to cut and cut, they can also be made into dies to prepare specimens.
4.5 The humidity control of the sample and the standard atmosphere used for testing are the same as 3.5.
4.6 Test steps
4.6.1 Before the test, check the level of the instrument and the zero pointer state of the pointer when no load is applied, and make necessary adjustments. Check the height of the knife edge and the length of the incision line must meet 20mmrequirements.
4.6.2 Pre-test: Select an appropriate range according to the actual strength, so that the test value falls within the range of 20% to 80% of the full scale value.
4.6.3 Lift the sector-shaped pendulum to the vertical position, which is the starting position of the test, and push the pointer to the baffle. Place the bottom edge of the semicircular sample at the center bottom position of the two clamps, and then Tighten the two clamps and press the cutter handle to make a 20mm long incision in the center of the sample from bottom to top.
4.6.4 Press the pendulum baffle, the sector-shaped pendulum falls quickly and swings to the right. Since the movable clamp and the pendulum are integrated into one, the sample is torn and broken. When the pendulum swings back, Hold it gently with your hand. At this time, pay special attention to the position of the pointer that your hand cannot touch, and then record the reading.
4.6.5 During the test, if the clamps are not tightened and the sample is found to have slipped in the clamps or the tearing trajectory deviates more than 45° from the vertical centerline of the sample, the test data should be discarded and retested. Do it again. Due to the differences in web forming, reinforcement, bonding and other processes, when doing longitudinal and transverse tearing strength, the tearing direction may be irregular in a certain direction, and some tearing directions may even be perpendicular to the incision line. Such abnormal conditions should be noted in the test report.
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