Commonly used indicators of fiber strength
1. The new cracking strength is the force required when a fiber material is directly stretched by the outside world until it breaks. It is an index that expresses the absolute value of the tensile force. The basic unit is Newton (N), and the derived units include cN (centinewton), mN ( millinewton), kN (kilonewton), etc. The readings measured on various strength machines are strength. For example, the strength of a single fiber and a bundle of fibers are the force required to stretch a fiber and a bundle of fibers until they break, respectively. 2. Relative strength: The strength required to break fibers of unit fineness is called relative strength, which is an indicator used to compare the tensile breaking properties of fibers of different thicknesses. When fibers have different thicknesses, their breaking strengths are also different. Therefore, the breaking strengths of fibers of different thicknesses are not comparable. In order to facilitate comparison, the breaking strength can be converted into the force at a specified thickness, that is, the relative strength. Due to the different provisions of the standard thickness, there are many kinds of relative strengths of fiber materials, and the following three are commonly used. (3) Breaking length: Breaking length can be understood as assuming that the fibers are connected end to end to become a continuous long fiber, and one end of it is naturally suspended. When the gravity of the suspended fiber causes the fiber to break, the suspended fiber is The fiber length is the breaking length (that is, the length of the fiber when its own gravity and its strength are equal). Generally, the fracture length is represented by L, and the unit is kilometers (km). In production practice, the breaking length of fibers or yarns is not measured using the hanging method, but is calculated using strength. The calculation formula is: According to these conversion formulas, it can be seen that for the same breaking strength and breaking length, the breaking stress also varies with the density of the fiber. Only when the fiber density is the same, the breaking strength and breaking length are comparable. 3. New crack elongation The percentage of the elongation produced when the fiber is stretched to the original length is called elongation. The elongation of a fiber when it is stretched to break is called elongation at break, which represents the ability of the fiber to withstand tensile deformation. The calculation formula is: 4. Wet-to-dry strength ratio The percentage of the strength of the fiber when it is completely wetted to the strength in the dry state (under standard atmosphere) is called the wet-to-dry strength ratio. Understanding the change in strength of the material after wetting can help us understand the water and moisture resistance of the material during wet processing or cleaning. The wet-to-dry strength ratio of most fibers is 100%. 5. 10% constant stretch load is the load (force) required when the fiber is stretched by 10%. It is specially used for cotton-type chemical fibers and is an indicator used when matching the performance of blended chemical fiber fabrics. The measurement of cotton fiber strength should be carried out under standard temperature and humidity conditions. (1) Bundle fiber: Y162 type bundle fiber strength machine or Stello strength tester, namely YG011N type bundle fiber strength tester, is often used. The five finished small cotton bundles (each bundle is about 3 mg) are broken separately on the Y162 bundle fiber strength machine. After the bundle fiber breaking strength is measured, it is converted into single fiber strength and other indicators. (2) Single fiber: Use a single fiber strength machine (such as YG001N electronic single fiber strength meter). Extract several fibers from the cotton sample, break them one by one on a single fiber strength machine, and measure indicators such as strength and elongation. Current single fiber strength machines are computer-controlled and have comprehensive test information. When using this method, in order to make the measurement results representative, a large number of tests must be performed, which is time-consuming and labor-intensive.
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