What is the principle of burst (burst) strength tester? The fabric bursting (bursting) strength tester is mainly used to determine the bursting strength of fabrics. We have mastered the bursting principle and rupture characteristics of the fabric burst strength tester through experiments, and are familiar with the use of the device. The following is an introduction to the relevant principles.
【testing method】
There are three main methods for testing burst strength or burst strength: burst method, marble burst method and steel ball method.
Foreign countries such as the United States, Japan, South Korea, Canada, Australia, etc. use the burst method for testing.
China GB/T7742.1-2005 "Textile Fabric Bursting Performance Part 1: Determination of Bursting Strength and Bursting Expansion Degree Hydraulic Method" standard quotes the burst test method in the international standard ISO13938-1:1999.
The test principle is: clamp the sample on the extensible diaphragm, apply liquid pressure under the diaphragm, and increase the liquid volume at a constant speed, so that the diaphragm and the sample are expanded until the sample ruptures, and the bursting force is measured [ 2], this method can also test the burst expansion of the sample.
Before the national standard "Cotton Knitted Underwear" was revised, the burst strength was tested by the marble burst method, that is, a 25mm round marble was used to press the knitted fabric to test.
The test methods listed in the GB/T19976-2005 "Determination of Bursting Strength of Textiles by Steel Ball Method" standard formulated in 2005 have two differences compared with the previous ones: First, the diameter of the bursting marble (steel ball) is changed to 38mm, the second is to stipulate that the strength tester is the internationally used CRE (constant velocity extension type) strength meter.
【working principle】
Billiard burst method: The billiard burst strength tester uses a pair of brackets to replace the upper and lower holders of the electronic fabric strength tester. The upper and lower brackets can move relative to each other to fix the sample in the cloth clamping ring. When the lower support is lowered at a certain speed, the marble on the ejector rod vertically pushes against the sample until the sample bursts, and the instrument automatically displays the bursting strength and the bursting elongation value.
Elastic diaphragm method: liquid is used to break the fabric. A fabric sample of a certain area is placed between the pressure hood and the pressure box, and a rubber gasket (elastic diaphragm) of appropriate thickness and good toughness is placed under the sample and clamped with a ring clamp of a specified size. Turn on the liquid inlet switch and gently increase the fluid pressure under the diaphragm until the sample ruptures. Read the burst strength value from the hydraulic gauge, and read the burst elongation of the sample when it bursts on the extensometer.
Test procedure and operation
1. Billiard-style bursting method
①, preheating for 30min after power-on, under reset state, select the burst function. Set the margin and positioning shift (the margin is the distance from the outer circle of the ejector rod to the inner circle of the holder, and the positioning shift is to collect the strength value at the set elongation, used for geotextile).
②. Press the "Experiment" button, put the sample into the cloth clamping ring and screw it tightly, and then place it flat on the cloth chuck (push the cloth chuck to the end).
③. Press the "stretch" button to start the test. After the sample is completely burst, the lower holder automatically returns to the initial position, and the display shows various data.
④ Repeat the above steps to test 5 samples.
If the sample is not clamped tightly, it will slip out of the ring, or the bursting deformation of the sample is too large, the phenomenon of the sample will not break. At this time, the test result is invalid, and the test should be repeated with another sample.
⑤ After the test is completed, the instrument automatically records and counts all the data.
⑥. Clear the data and prepare for the next test.
2. Elastic diaphragm method
① Check and calibrate the instrument: check whether the various parts of the instrument are normal; if necessary, the comprehensive performance of the instrument can be verified with a standard diaphragm; the elastic diaphragm must be replaced when it is obviously deformed (in the absence of a sample, the diaphragm will expand To a certain height, observe the shape of the diaphragm, if there is a significant difference from the normal spherical crown shape, the diaphragm should be replaced).
② Clamp the sample: Cover the sample on the diaphragm in a flat and tension-free state, and then clamp the sample with a ring clamp. When pressurizing, prevent the specimen from being damaged by the clamp.
③ Pre-test: Before the test, two additional pre-samples should be used for pre-test, to observe whether the rupture is completed within the specified time range under the gradually increasing hydraulic pressure (generally 30s ± 10s for fabrics; wool) Type fabric is specified as 15s±10s). If it does not match, the pressurization rate can be adjusted to make the average burst time within the specified range.
④ Formal test: Use the adjusted pressure rate to test the samples one by one, and record the bursting strength and bursting expansion. If the sample breaks at the edge of the clamp ring, another sample should be taken and redone.
⑤ Diaphragm correction number: use the same liquid velocity as the above test, clamp the diaphragm with a clamp without a sample, and make the diaphragm expand to the average burst expansion degree of the above-mentioned sample. The required pressure is the diaphragm Correction number.
【Burst mechanism】
The plain weave will form gaps parallel to the longitudinal direction of the fabric, and there are more loops scattered along the transverse direction of the fabric;
The breakage of the piqué structure is in the shape of a hole, and the damage is mainly manifested as the break of the yarn, and it is almost impossible to form a loop.
The three methods have similar failure mechanisms: weak ring theory
From the theory of weak loops, it can be known that when knitted fabrics are subjected to bursting or bursting, they will be damaged at a certain weakest point first, and then stress concentration will be generated at this damaged point. As the test site goes on, the plain weave fabric will be damaged. There will be a large number of loops scattered along the transverse direction, and the slits will continue to expand in the longitudinal direction; the piqué fabric will have more yarns to break, and the slits will expand along the circumference.
【Test Results】
The comparison of the results of different test methods is as follows:
1) The diameter of the steel ball is larger than that of the marble, and the bursting force obtained by the steel ball method is also greater than that of the marble burst method.
2) The three test methods have similar failure mechanisms, and the shape of the cracks after the fabric is destroyed is basically the same.
3) The results of the three test methods have a good linear relationship with each other, and there is a good correlation between the three.
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