Measuring the tear strength of fabrics by trapezoidal method

Reference standard: ASTM D 5587-2003 Scope of application 1.1 This method adopts the trapezoidal method to measure the tear strength of the fabric, using the constant velocity elongation testing-equipment' target='_blank'>tester (CRE). 1.1.1 Constant velocity elongation strength tester (CRE) has become a common equipment for measuring trapezoidal tear strength. It has to be admitted that some Constant Traction Strength Testers (CREs) are still in use. Therefore, these test instruments may also be used by agreement between the purchaser and the supplier. 1.2 This test method is applicable to most fabrics, including woven fabrics, air bags, blankets, pile fabrics, knitted fabrics, laminated fabrics, and cut pile fabrics. The fabric may be unfinished, heavy sized, coated, resin treated, or otherwise treated. Instructions are provided for wet-treated or non-wet-treated test specimens. 1.3 The tearing strength tested by this method needs to be pre-teared before the test. The resulting test value is not directly related to the force required to pre-tear. 1.4 There are two methods for calculating the tearing strength of the trapezoidal method: the force value of a single peak value and the average force value of the highest five peak values. General Test Method 2.1 On a rectangular specimen, mark an isosceles trapezoid (see Figure 1). The sample is torn a cut in the middle of the short side of the trapezoid and pre-teared. The two non-parallel sides of the trapezoid are clamped on the parallel clamps of the power machine. The distance between the clamps increases continuously, and the force is applied to enlarge the notch on the specimen. Simultaneously, force values ​​are recorded, and all forces for continuous tearing are calculated from an automatic chart recorder or microprocessing data collection system. Equipment 3.1 Strength tester: constant velocity elongation type (CRE), in line with the requirements of ASTM D 76, with automatic recorder and automatic microprocessor data collection system. 3.2 Clamps: The surfaces are parallel and smooth to prevent the specimen from slipping during the test. The size is 50*75mm (2*3in), and the long side is perpendicular to the direction of force. 3.3 It is recommended to use a pneumatic chuck, the size of the clamping surface is not less than 50*75mm (2*3in), according to the tooth or rubber surface, the clamping force is 13kN∽14kN (2900lbf∽3111 lbf). Manual collets can also be used if the specimen does not slip. 3.4 For some fabrics, in order to prevent slippage when a non-serrated clamping surface is used, for example, the rubber clamping surface can be covered with a layer of No. 80 ∽ 120 medium grain size. The emery cloth is fixed on the rubber clamping surface with pressure-sensitive tape. 3.5 Cut-out template, shape and size are shown in Figure 1(a) 3.6 Trapezoid template, size is shown in Figure 1(b) Sampling and test sample 4.1 Bulk sample: For acceptable testing, from the material specified or The number of rolls or the number of fabrics is randomly selected from the fabric samples approved by the buyer and the supplier, and the batch number or the number of fabrics is considered to be the basic sampling unit. Table 1 Lot or number of fabrics in batch samples All sample rolls or pieces Batch sample rolls or pieces 1∽3 All 4∽24 4 25∽50 5 ＞50 10% of all sample rolls or pieces∽Max 10 rolls Or 4.2 Laboratory samples: For acceptance testing, select one sample from each batch of samples, the sample being the full width of the fabric and approximately 1 meter long. For rolled fabrics, the sample taken must not contain the outer or inner core of the roll. 4.3 Test Specimens: From each laboratory sample unit, select five specimens each along the machine direction (warp direction) and perpendicular to the machine direction (weft direction). 4.3.1 Test direction: the length direction is the test direction. 4.3.2 Cutting of the test sample: if the sample is used for the machine direction test, the long side of the sample is parallel to the machine direction; if the sample is used for the perpendicular machine direction test, the long side of the sample is perpendicular to the machine direction. If the specimen is to be tested in the wet state, cut the wet test specimen close to the dry specimen. Keep labels for identification. 4.3.2.1 When cutting woven fabrics, pay attention to make the yarns on the short side parallel to the template, so that when the tear is carried out in the direction of the incision, the tear occurs between these yarns, not the yarns crossing these yarns. This consideration is especially important when testing bow and weft fabrics. 4.3.2.2 Cut the sample in a representative length and width direction. It is preferable to cut the sample along the diagonal direction of the sample, and the distance from the edge of the fabric is not less than 1/10 of the width. Make sure that the sample has no folds, creases or wrinkles, and avoid oil, water, grease, etc. on the sample during operation. 4.3.2.3 Use the template (see Figure 1) to mark an isosceles trapezoid on the sample, at 25mm (1 ) cut a 15mm (0.625in) incision in the middle of the edge (see Figure 1 and Figure 2). Preparation and calibration of the instrument 5.1 Set the initial distance between the two clamps to 25±1mm(1±0.05in). 5.2 Select the force value range of the full scale so that the maximum force falls within the range of 15%∽85% of the full scale. 5.3 Set the test speed to 300±10mm (12±0.5in./min). 5.4 The strength machine is calibrated in accordance with the supplier's instructions and ASTM D 76. 5.5 When using a microprocessed automatic data collection system, follow the supplier's instructions to set the correct parameters. Conditioning 6.1 Conditioning 1 for Standard Tests 6.1.1 Conditioning the specimens under standard atmospheric conditions, see Standard D 1776. 6.2 Humidity 2, used for wet sample testing. 6.2.1 When desizing is specified prior to wet testing, select a desizing method in accordance with D 629 that does not affect the normal physical properties of the fabric. 6.2.2 Immerse the specimen in distilled or deionized water at room temperature until it is completely soaked. 6.2.2.1 The soaking time must be sufficient to wet the sample, because the tear strength of the sample will not change significantly after soaking for a longer time.

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