What is the Bursting Strength Test of Fabric?

As we can see, the bursting strength is crucial to help the consumers learn about the product’s breakage performance. Also, the bursting strength test is a very intuitive test method to test the bursting strength effectively by initiating the deformation of the knitted products which is caused by the directional push force applied on the elbow, knee, toe, and other parts. In this post, we will explore test principles, standards, and other aspects of the bursting strength test.

The definition and mechanism

Bursting refers to the phenomenon in which the fabric expands and ruptures under the load applied to the fabric in a perpendicular way. And the bursting strength points to the maximum force measured during the process of pressing the specimen in the direction of the spherical top bar perpendicular to the plane of the specimen until it is broken. It is a significant mechanical index of the fabric, directly reflecting the durability index of knitted fabric when the specimen is deformed and ruptured by the external pressure from the top. Plain tissue will develop a crack parallel to the longitudinal direction of the fabric. Moreover, there is more coil dispersion along the lateral direction of the fabric. However, if the bead tissue is damaged, there will be the breakage of the yarn almost without the coil dispersion.

The test principle and the test methods

The specimen is held on the extendable diaphragm by a circular gripper, and gas pressure is delivered under the diaphragm to expand the diaphragm and the specimen. Throughout this process, the pressure is increased at a constant rate until the specimen ruptures. Finally, we can measure the bursting strength of the fabric. There are three commonly used methods for determining the bursting strength, respectively the hydraulic method, the pneumatic method, and the steel ball method. If you want to find out more about the test methods, you’d better read another page about the details.

Related variables that affect the test result

Test area
In the bursting strength test, the larger the test area, the larger the test area of the specimen subjected to stress and the more yarns will be stressed on the fabric. The following table displays the bursting strength at different test areas when the specimen is tested for 18 to 25 s.

As indicated in the table, with the increase in the test area, the bursting strength of each type of specimen is noticeably reduced. We can analyze the reasons for this by taking the woven fabric as an example. When the stress area of the woven fabric increases by 4 times, the diameter of the stressed area grows up to 2 times. The number of stress warp and weft yarns changes at the same time. As less stressed yarns lead to less relatively stressed areas, the single yarn strength stays constant, resulting in a relatively small bursting strength. In fact, the bursting strength value is equal to the multiply of the product of bursting strength and stress area. It can be estimated from the data in the following table that the bursting strength value rises with the growth of the test area. As a result, we can conclude that the strength decreases but the bursting strength value increases.

The bursting strength of various fabrics when the specimen has different test areas  kPa
Test area(cm²）	Woven plain weave fabric		Woolen knitted plain fabric		Knitted plain weave fabric		Knitted double-sided fabric
7.3	460.0	453.3	548.2	634.8	589.1	286.1	638.0	659.6
10.0	354.2	338.2	462.4	454.8	489.7	225.2	507.3	477.7
50.0	171.8	173.3	178.2	193.2	175.8	87.9	212.5	218.1

The theoretical relationship between the bursting strength and the test area should be inversely proportional. However, in reality, there is considerable friction at the yarn nodes and the test area is not equal to the stressed area. Therefore, it can be concluded that the inverse relationship is somewhat weaker.
From the table, it can be observed that the bursting strength of the specimen whose test area is 7. 3 cm² is three times more than that of 50. 0 cm². Besides, from the outcome of one test area, the tester can generate a rough estimation of the outcomes of other test areas.

Time to burst
The bursting time refers to the time required for the bursting process, which is clearly defined in GB/T7742.1-2005. However, we can not set the time to burst. So we need to control the bursting speed for reaching the time to burst. It can be seen that the relationship between bursting time and bursting speed is not linear, which is caused by the nonlinear stress-strain relationship within the fabric. In general, we can see that the time to burst decreases when the bursting speed becomes higher. Besides, the bursting speed and bursting time have a certain linear relationship in a small scope.

Bursting speed
Bursting speed points to the increasing rate of the volume of pressurized liquid in the bursting test. According to the GB / T 7742. 1-2005, the bursting time should be kept from 15s to 25s. The following table shows the data getting from the test of six kinds of specimens with a test area of 7.3 cm². It indicates that with mounting bursting speed, the bursting strength will go up. But the change in strength is significantly smaller than the change in speed and different specimens react differently to the diverse speeds. It can be inferred that the little change in bursting speed has little impact on the test result. But we should take the change of bursting speed into account when the results are within the limit of conformity assessment.

The bursting strength of fabrics when the sample is tested at various speeds  kPa
Bursting speed(cm³min-1）	Woven plain weave fabric		Woolen knitted plain fabric		Knitted plain weave fabric		Knitted double-sided fabric
50	438.4	442.4	564.6	626.7	245.2	573.8	621.9	640.2
120	452.1	453.3	564.6	628.2	261.0	581.2	628.2	714.1
180	467.0	464.2	548.2	634.8	286.1	589.1	638.0	726.1

Coefficient of Variation
The CV value indicates the degree of dispersion of the test results and represents the percentage of the standard deviation of the test results from the average value. The CV value of uniform specimens is also a good indicator of the accuracy of the test method. The following result is reached on the basis of ten repeatable tests of three uniform specimens.

The CV value of the bursting strength test kPa
Serial number	9# woven plain weave fabric	10# knitted plain weave fabric	11# woolen knitted plain fabric
1	474.6	488.7	632.8
2	475.3	485.6	634.2
3	462.3	493.2	636.5
4	468.5	484.5	640.5
5	472.4	492.0	637.2
6	465.6	497.1	639.0
7	474.3	489.2	648.5
8	471.5	488.2	635.4
9	468.7	495.5	633.5
10	475.5	491.2	647.4
average value	470.9	490.5	638.5
standard deviation	4.5	4.1	5.5
The CV value\%	1.0	0.8	0.9

If you intend to do the bursting strength test and obtain the test result accurately, you’re supposed to carefully analyze all of the variables that could affect the test’s outcome.

The problems and corresponding solutions

1 The specimen should be representative. And the test area should avoid folding and creasing, and should not be the cloth’s edge.

2 Sometimes, the specimen is unable to be broken by the bursting strength equipment. It demonstrates that there is an insufficient amount of glycerin in the hydraulic cylinder, pressurization stroke and the seal ring of the piston rod has been destroyed. Thus, you need to replenish glycerin, replace the seal ring, adjust the pressurizing screw in the gearbox and reinstall the rubber membrane and lock it tight.

3 We should distinguish the front and back of the specimen in accordance with the standard. In general, the reverse side of the sample is facing the diaphragm and the front side is facing upward, which is consistent with the actual wearing state. The reason is that the front of the specimen is facing outward to simulate the normal state of wearing clothes when the bursting comes from the bottom of the specimen. In addition, the specimen should also be adjusted to be in the proper wet condition in accordance with the standard.

4 We should usually do the pre-test to control the time to burst and the flow rate. In the subsequent test, the instrument will automatically adjust the flow rate according to the pre-test, to ensure that the time to burst keeps between 15s and 25s. If not, the test result should be rounded off and retested. If the time to burst of the specimen is not within the range after testing it three times, we should check the bursting strength testing machine promptly for malfunction, oil leakage, or loosening of the test cover.

5 The personnel who implement the standard should have a thorough understanding of the method parameters and details of the bursting. Some standards have specified the requirement of the bullet diameter, the inner diameter of the circle (test area), the number of specimens, and so on while others do not. For example, the different test areas and bullet diameters for bursting and breaking have a significant impact on the result. Besides, the standard FZ/T 73037-2019 for the sock specifies that the diameter of a steel ball is 20mm, while the standard FZ/T 73060-2017 for a monolithic knitted upper requires to use of a steel ball of 25mm. That is because both standards are about footwear items, and the use of small-diameter steel balls is more in line with the actual state of use. Therefore, on the one hand, when applying the testing parameters, special attention should be paid to the key one. On the other hand, the testing report should also represent the key parameters for better readability.

6 Obviously, sealing must be taken into account as there is high bursting pressure of the bursting strength tester. If the specimen is not sealed in an effective way, there will be side leakage and slippage. There are two main reasons for this. On the one hand, it may be the fact that the test area is too large to be easily sealed. On the other hand, too much pressure leads to poor clamping, which used to work in the form of a lever. In other words, the pressure will be so large that the specimen can not balance on a surface, resulting in a gap between surfaces, and side leakage as well. If the pressure is too high, the specimen will have slipped. Then you will get incorrect test results. Therefore, you must increase the finishing size of the clamping mechanism parts to increase the bending strength of the workpiece.

The conversion and related terminology

formula conversion
1 KPa = 1000 Pa
1 KPa = 7.5 mmHg = 10 mBar
1DaN = 10 N , DaN = Deca Newton
1Kg = 1000 g = 9.8 N = 2.2 Lbf(s)

Test area: the area of the test specimen within the circular clamping device

Bursting pressure: the highest pressure applied to a specimen clamped over an underlying diaphragm until the specimen ruptures
Bursting strength: the pressure obtained by subtracting the diaphragm pressure from the average bursting pressure
Diaphragm pressure: the pressure applied to the diaphragm to achieve the average bursting of the specimen without presenting it
Bursting distension: the degree of expansion of the specimen under the bursting pressure expressed as the height at burst or volume at burst
Height at burst: the distance between the upper surface of the specimen before bursting and the top of the specimen under the bursting pressure
Volume at burst: the volume of liquid required to reach the bursting pressure (for hydraulic testing)
Time to burst: the time required to expand the specimen until it breaks
Common units: kilopascal (KPa), millimeters of mercury (mmHg), millibar (mBar), Newton (N), kilogram (Kg), pounds (Lbf, LBS) ten times the Newton (DaN)

Applicable standards

GB/T19976-2005 Textiles-Determination of bursting strength-Steel ball method
GB/T 7742.1-2005 Textiles-Bursting properties of fabrics-Part 1: Hydraulic method for determination of bursting strength and bursting distension
ASTM D3786/D3786M-2018 Standard Test Method for Bursting Strength of Textile Fabrics-Diaphragm Bursting Strength Tester Method
ISO 13938-1:2019 Textiles-Bursting properties of fabrics- Hydraulic method for determination of bursting strength and bursting distension
ISO 13938-2:2019 Textiles-Bursting properties of fabrics-Part 2: Pneumatic method for determination of bursting strength and bursting distension
ISO3303-1:2012 Rubber-or plastic-coated fabrics-Determination of bursting strength-part 1: Steel-ball method

Purchase recommendations on the bursting strength tester

The pursuit of the brand
Every time when we want to purchase something, we are prone to look for the one enjoying a good brand, reputation, and market due to its excellent after-sale service and high quality. TESTEX is one of them, a professional manufacturer of textile testing instruments, whose products are sold to more than 60 countries and regions with a history of over ten years. If you are attempting to buy a suitable bursting strength tester, TESTEX may be your optimal choice.

Mode of clamping
Since clamping is one of the most dispensable parts of the bursting strength tester, we need to choose the proper one that can help you work efficiently. There are two modes of clamping in the market, manual clamping and pneumatic clamping. Actually, pneumatic clamping enjoys a wider market than manual one as pneumatic clamping can grip the test specimen firmly and also prevent it from slipping out of the machine. However, with manual clamping, you have to apply force on it without knowing what the exact value is. But if you have a limited budget, manual clamping is also a good choice.

The variety of instrument
As there are so many manufacturers, we have lots of choices to buy a bursting strength tester. Therefore, we must be careful about the variety so that we can find out the most suitable one. There are three models, the analog model, the digital model, and the computerized model. Among them, the digital mode is the preferred one which displays your test results in a digital way while the analog shows the data on an analog gauge. If you like using the computer, the computerized model is the suitable one that can connect the tester to the computer.
In conclusion, you can purchase a burst testing machine in terms of the elements mentioned above. And there is a kind of burst testing machine TF142A\B available on our website with reasonable price and high quality.

The daily maintenance of the bursting strength tester

A fabric bursting strength tester is used to test the bursting strength performance of woven, knitted, and non-woven fabric, paper, or sheet. Thus, we also require more skills and details in daily maintenance.

The main engine
1 The fixture equipped in the machine should be coated with anti-rust oil.
2 Due to frequent use of the jaws of the hydraulic universal testing machine, it will easily wear and oxide, damaging the small piston and causing oil leakage. So the jaws should be cleaned frequently.
3 Regularly check the screws in the jaw area. If you find it loose, please tighten it in time.
The oil source
1 Regularly check whether there are oil leaks at the host and oil source. If so, we should promptly replace the seal or combined gasket.
2 According to the use of the machine and the life span of oil, we should regularly replace the oil suction filter and filter element, and the hydraulic oil.
3 Don’t forget to turn off the host power when not using the bursting strength testing machine. If the machine works in standby mode, the transfer switch should be played to the “load” file. Otherwise, the electromagnetic reversing valve will have been in the energized state, shortening the service life of the device.
The control system
1 If we want to plug the interface on the controller, it is a must to turn off the controller power.
2 If the machine is not in the use for a long period of time after the test, we should turn off the controller and computer.
3 The interface on the controller should correspond one by one. And avoid inserting the wrong interface, which may cause damage to the equipment.
4 Regularly check whether the connection wire of the back panel of the controller is in good contact. And if it is loose, we should adjust it promptly.