fabric pendulum tear strength tester standards and principles

　　The testing method for fabric tearing strength requires a theoretical analysis of the force on the fabric during tearing. Different testing methods result in different characteristics and states of fabric tearing. As for the single seam method, when using the single seam method for tearing, a 10mm opening is cut in the longitudinal middle of the specimen, and the left and right sides are separated and clamped in the two clamps of the testing machine. When the yarn under force in the test strip gradually separates up and down, the yarn that is not directly under force in the horizontal direction begins to slide relative to the yarn under force and gradually approaches, forming an approximate triangular area, usually called a force triangle. The direction of the external force is almost perpendicular to the original axis of the broken yarn, and the broken yarn is the yarn that is not directly under force in the horizontal direction; When using the trapezoidal tearing method, a trapezoid with one side 10mm and one side 15mm is drawn longitudinally on the sample, and a 1mm small opening is cut in the middle of the 10mm side. The sample is clamped between the upper and lower clamps in a trapezoidal manner, with one side in a tense state and the other in a relaxed state. The direction of the external force is consistent with the axial direction of the broken yarn, or the direction of the external force is applied to the fabric at a certain angle. In the trapezoidal tearing process, the external force is borne by the straightening and deformation of the stressed yarn, while the transverse yarn acts as frictional resistance. The broken yarn is the stressed yarn system.

　　Testing standards:

　　The test method for tear strength of fabrics, GB/T 3917 specifies five methods for determining the tear strength of impact pendulum method, pants (single seam) sample, trapezoidal sample, tongue shaped sample, and wing shaped sample. This article mainly introduces the testing method of tear strength using the pendulum method.

　　For the testing method of fabric tear strength using the pendulum method, in addition to GB/T 3917.1, there are also ISO 13937-1 and ASTM D1424 testing standards. Among them, GB/T 3917.1 is equivalent to using the ISO 13937-1 standard. Except for ASTM D1424 which specifies two sample sizes, the other technical conditions are basically the same.

　　Testing principle:

　　The test of tear strength using the pendulum method involves cutting a section of the specimen in one direction to form two lobes, which are clamped onto the two jaws of the testing machine. When the pendulum swings and the movable fixture leaves the fixed fixture, the specimen is torn along the direction of the incision. The work done to tear a certain length of fabric is converted into tear force.

　　The characteristic of tearing is that the longitudinal yarn is pulled, and the transverse yarn slides. The frictional force generated by sliding is the transverse yarn being pulled. Therefore, the transverse yarn forms a force triangle area, where the deformation of the bottom edge of the yarn is greater and the external force is greater. As the distance from the * yarn increases, the force becomes smaller. When the yarn reaches the fracture elongation, fracture occurs and a peak fracture occurs, and the next yarn begins to form the bottom edge of the force triangle area. In this way, the transverse yarn gradually fractures until the fabric is torn.