Three different test methods of fabric tearing strength tester_Gellowen

Three different test methods of fabric tearing strength tester

Fabric tearing strength tester is a commonly used test instrument for testing the tearing strength of fabrics. There are three standard test methods: trouser method (GB/T3917.2-2009), trapezoidal method (GB/T3917.3-2009), and impact pendulum method (GB/T3917.1-2009). The tearing principles of the three methods are similar, and there is a certain correlation between the results. Shanghai Qianshi R&D engineers made the following analysis of the results of the three different test methods.

1. Trouser method

When the trouser method is torn, a yarn stress triangle is formed at the tear. When the stressed yarn gradually separates up and down, the yarn that is not directly stressed has some relative movement and gradually moves closer to form an approximate stress triangle area. Due to the friction resistance between the yarns, sliding is limited. During sliding, the tension of the yarn increases rapidly, and the deformation elongation also increases sharply. When the yarn constituting the bottom of the stress triangle is deformed to the breaking elongation, the yarn breaks immediately. When other conditions are the same, the larger the force triangle is, the more yarns are stressed at the same time, and the tear strength increases. Tearing is the breaking of yarns in the fabric one by one, so the tear strength is approximately proportional to the yarn strength. In addition, the greater the breaking elongation of the yarn, the larger the force triangle is, the more yarns are stressed at the same time, and therefore the greater the tear strength; when the friction resistance between the longitudinal and transverse yarns is large, the yarns of the two systems are not easy to slide, the force triangle becomes smaller, the number of yarns stressed is small, and thus the breaking strength becomes smaller, so the friction resistance between the warp and weft yarns plays a negative role in the breaking strength. The yarns that break in the trouser method sample are the yarns that are not directly stressed.

2. Trapezoidal method

There is also a force triangle in the tearing of the trapezoidal method, but because the transverse yarn of the sample is not perpendicular to the horizontal line of the clamp when the trapezoidal method sample is clamped, but at a certain angle, the yarn that breaks during the stretching process is at a certain angle to the force direction, and the breaking mode is mainly caused by the straightening and deformation of the directly stressed yarn. When other conditions are the same, the tear strength measured by this method mainly depends on the breaking work of the yarn.

3. Impact pendulum method

When the impact pendulum method is torn, a yarn approximate force triangle is formed at the crack. When the stressed yarn gradually separates, the yarn that is not directly stressed has some relative movement and gradually moves closer to form an approximate force triangle area. The factors affecting the tear strength are mainly the strength of the yarn itself and the mutual friction between the yarns.

The common feature of the three test methods is that the tearing of fabric is achieved by breaking the yarns one by one. According to whether the tearing is to tear the warp yarn or the weft yarn, it is called warp tearing or weft tearing respectively. During the tearing process, the fabric around the broken yarn increases the breaking strength that a single yarn can withstand due to the skewness and slippage of the yarn. Except for the drop hammer method, the other test methods all use a fabric strength machine to stretch a certain distance at a constant speed of 100mm/min, and the peak value or peak average value of the force value during the stretching process is the tearing strength. The tearing strength measured by the constant speed stretching method is generally greater than the value measured by the drop hammer method. The reason is that the tearing speed of the drop hammer method is faster. During the high-speed impact process, the yarns in the fabric do not have more time to slide against each other, making the tearing force triangle area smaller and the number of force-bearing yarns reduced, so the tearing strength is lower. Since the drop hammer method test is closer to the simulated wearing state, it can better reflect the durability and toughness of the fabric after finishing, and this method is often used for finished product inspection. The single-slit method is generally used for fabrics with roughly equal tear strength in the warp and weft directions, while the trapezoidal method is suitable for testing fabrics with large differences in tear strength in the warp and weft directions.