Measuring the tearing strength of fabrics with trapezoid method

Reference standard: ASTM D 5587-2003 Scope of application 1.1 This method uses the trapezoidal method to determine the tearing strength of the fabric, using a constant velocity elongation strength tester (CRE). 1.1.1 Constant velocity elongation strength tester (CRE) has become a common equipment for measuring the strength of trapezoidal tearing. It must be admitted that certain constant velocity traction strength testers (CRE) are still in use. Therefore, these test instruments can also be used if the purchaser and the supplier reach an agreement. 1.2 This test method is applicable to most fabrics, including woven fabrics, inflatable bags, blankets, pile fabrics, knitted fabrics, laminated fabrics and cut pile fabrics. The fabric can be unfinished, resized, coated, resin treated or otherwise treated. Provide instructions for test samples that have been wet-processed or not. 1.3 The tear strength tested by this method must be pre-teared before the test. The obtained 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 trapezoid method: the force value of a single peak value and the average force value of the highest five peak values. Overview of the test method 2.1 On the 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 powerful machine. The distance between the clamps increases continuously, and the force is applied to increase the incision on the specimen. At the same time, the force value is recorded, and the continuous tearing force is calculated from the automatic chart recorder or the micro-processing data collection system. Equipment 3.1 Strength tester: Constant velocity extension 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 clamping surface size is not less than 50*75mm (2*3in), according to the tooth or rubber surface, the clamping force is 13kN∽14kN (2900lbf∽3111 lbf). If the sample does not slip, a manual chuck can also be used. 3.4 For some fabrics, in order to prevent the use of non-serrated clamping surfaces, for example, rubber clamping surface slippage phenomenon, a layer of No. 80 ∽ 120 medium grain size can be covered on the rubber clamping surface Use pressure-sensitive tape to fix the emery cloth on the rubber clamping surface. 3.5 Cut sample template, the shape and size are shown in Figure 1(a) 3.6 Trapezoidal template, and the size is shown in Figure 1(b) Sampling and test samples 4.1 Batch samples: For acceptable tests, specify or The number of rolls or the number of fabrics is randomly selected from the fabric samples approved by the buyer and the supplier. The batch number or the number of fabrics is considered as the basic sampling unit. If there is no agreement, the sampling will be carried out according to Table 1. Table 1 The number of batches or fabrics in a batch of samples The number of total sample rolls or pieces The number of rolls or pieces of batch samples 1∽3 All 4∽24 4　　25∽50 5　　＞50 10% of the total number of sample rolls or pieces∽Max 10 Or 4.2 Laboratory samples: For acceptance testing, select a sample from each batch of samples. The sample is the full width of the fabric and is about 1 meter long. For roll fabrics, the sample taken cannot contain the outer layer or inner core of the roll. 4.3 Test samples: From each laboratory sample unit, select five samples in the machine direction (warp direction) and perpendicular to the machine direction (latitude direction). 4.3.1 Test direction: The length direction is the test direction. 4.3.2 Cutting of the test specimen: If the specimen is used for machine direction testing, the long side of the specimen is parallel to the machine direction; if the specimen is used for vertical machine direction testing, the long side of the specimen is perpendicular to the machine direction. If the sample is subjected to a wet test, cut the wet test sample close to the dry sample. Keep the label for identification. 4.3.2.1 When cutting woven fabrics, pay attention to make the short-side yarns parallel to the template, so that when the tearing proceeds along the cutting direction, the tearing occurs between these yarns, not the yarns that cross these yarns. This precaution is particularly important when testing bow weft fabrics. 4.3.2.2 Cut the sample in a representative length and width direction. The more preferable method is to cut along the diagonal of the sample, and the distance from the edge of the cloth is not less than 1/10 of the width. Ensure that the sample has no folds, creases or wrinkles. During operation, avoid the sample being stained with oil, water, grease, etc. 4.3.2.3 Use the template (see Figure 1) to mark an isosceles trapezoid on the sample, at 25mm (1in) ) Cut a 15mm (0.625in) long cut in the middle of the side (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 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).

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