How is Fabric Bursting Strength Measured?

 Why do the Fabric Bursting Strength Test?

In our clothes, part of the package elbows, knees, and other locations, over time these parts of the textile will be deformed, and knitted pants’ knee location is easy to wear out, About our socks, over time, from time to time there are toes out to observe the world. This is because these parts of the textile, in the use of the process, are constantly subjected to a concentrated load of the top, the role of pressure and expansion until destruction, this destructive effect is called a bursting. Since only testing the tensile strength of knitted fabric does not reflect this top breaking strength, so we need to use specific equipment to test the force that the knitted fabric is subjected to when it expands to rupture, this special test fabric top breaking strength or bursting strength of the instrument called the Bursting Strength Tester.

In addition, before producing final products, such as truck covers, tarpaulins, trampoline fabrics, swimming pool covers, and compactor curtains, We should test the above textiles using a burst strength tester to ensure that the burst strength meets the specified requirements.

Burst strength or bursting strength is an important physical indicator of the quality or durability of a knitted fabric.

Fabric Bursting Strength Test Method

1 Hydraulic Method

The testing principle of the hydraulic method is, a certain area of the specimen is clamped on the extendable diaphragm, and liquid pressure is applied under the diaphragm. Then increase the volume of liquid at a constant rate, so that the diaphragm and specimen expand, until the specimen rupture, and the expansion strength and expansion degree is measured. The commonly used hydraulic bursting strength machines are Mullen C type/ Mullen A type bursting strength machines, both of which use the liquid pressure of glycerin to produce the top-up effect through the elastic membrane to complete the test. The main difference is that the range of Mullen C and Mullen A are different, the range of Mullen C is 2 to 200PSI, while the range of Mullen A is 10 to 500PSI, but when using, only 15%- 75% of the full range is allowed to be tested, otherwise, the elastic membrane will be easily burst.

For some high-elasticity fabrics, the customer requires to break the fabric, if the fabric cannot be broken on the Mullen C, it needs to be broken on the Mullen A. The standard methods commonly used for the Mullen-type hydraulic bursting testing machine are American standards and European standards. The American standard is ASTMD 3786, the unit is PSI; the European standard is ISO13938-1, and the unit is KPa.

2 Pneumatic Method

The testing principle of the pneumatic method is that the specimen is clamped on an extendable diaphragm and gas pressure is applied under the diaphragm. Then, the volume of gas is increased at a constant rate to expand the diaphragm and specimen until the specimen ruptures, and the bursting strength and bursting distension are measured. It uses an air pump to provide the pressure of gas to expand the fabric by bulging the elastic membrane. It consists of an air pump, tester, and testing software, and the tester contains the test cup, elastic membrane safety cover, etc. Usually, applicable standards are GB/T 7742.1 ISO 13938-1 ASTMD3786, etc.

3 Steel Ball Method

The testing principle of the steel ball method is, the specimen of a certain area is clamped in the circle of a fixed base, and the round spherical top rod is vertically pushed to the specimen with a constant moving speed so that the specimen is deformed until it breaks and the bursting strength is measured.

The commonly used steel ball method fabric strength instrument is the bullet-type electronic fabric strength machine or tensile tester equipped with a steel ball fixture. It is the use of steel spherical surfaces to break the fabric. In this test, we commonly use American standards. Such as for ASTMD 3787 and ASTMD 6797, both standards are in pounds (LBF), the top breaking speed is 12 inches/min, and the diameter of the steel ball top bar is 25 mm. In the Chinese standard, we use the top breaking speed is 100mm/min, the unit is Newton (N), and the diameter of the steel ball top bar is 20mm. According to the sampling requirements of the multi-functional bullet-type electronic fabric strength machine, five circular specimens with an area greater than or equal to 100 square centimeters are taken on the sampling machine, the specimens should be representative, the test area should avoid folding, pleating and avoid the edge of the fabric. It is best to extend the diagonal sample.

The Testing Procedure of the Pneumatic Method Bursting Strength Test

Take TESTEX Fabric Digital Bursting Strength Tester TF142 as an example.

First, let’s have a look at the basic structure of the instrument.

1 Machine Construction & Control Panel

 

1. Controller and Display
2. Oil Level
3. Acrylic Safety Cover
4. Sample Holder
5. FootScrew
6. Air pressure gauge
7. Pressure Adjusting Valve

2 Digital Bursting Strength Tester TF142 has four test modes

 CRB: Constant Speed Burst Method

On this page, preset the test area and expansion rate, and then touch Enter to enter the testing page.

CE: Constant Expansion Burst Method

On this page, preset the test area, expansion rate, and end expansion height, then touch Enter to enter the testing page.

CP: Constant Pressure Burst Method

On this page, preset the test area, expansion rate, and end pressure, and then touch Enter to enter the testing page.

CTB: Constant Time Burst Method

On this page, preset the test area, expansion rate, and bursting time, and then touch Enter to save and enter the testing page.

Definition of several terms related to this test

Test Area   The area of the specimen in the circular gripper.

Bursting Pressure The maximum pressure is applied to the lower gasket diaphragm and the specimen until the specimen ruptures.

Diaphragm Pressure In the absence of a specimen, the pressure that is applied to the diaphragm, which

required to achieve the average expansion of the specimen.

Bursting Strength The pressure is obtained by subtracting the diaphragm pressure from the average bursting pressure.

Bursting Distension The degree of expansion of the specimen under the bursting pressure is expressed as the bursting height.

3 Main steps of the test

Sampling

According to the provisions of the product standard, or according to the agreement of the parties concerned to take samples. The sample should avoid folding, wrinkling, cloth edge or can not represent the part of the fabric. The test area should be used at 50cm² (79.8mm diameter).

If the preferred test area in the existing equipment is not applicable, or because the fabric has larger or smaller extension properties or other requirements of the multiparty agreement, can also use 100cm² (diameter 112.8mm), 10cm² (diameter 35.7mm), 7.3cm² (diameter 30.5mm) and other test areas.

Place the specimen on the diaphragm so that it is in a flat and tension-free state to avoid deformation in its plane. Clamp the specimen with the clamping ring to avoid damage and prevent slippage during the test.

Connect with power supply and air supply

Set the test parameters as standard requirements

• Choose the bursting test methods; usually, the CTB (Constant Time Burst method) will be used.
• Set the bursting test areas.
• Set Expansion rate, end Expansion height, end pressure, and burst time.
• Touch Enter to confirm and enter the testing page.

Install the test heads according to the preset parameter

7.3cm² and 50cm² can be selected, and the spanner can be used when installing the test heads. The diaphragms should be replaced if it is damaged, the method is the same.

Install the sample under the bursting test heads

and clamping it, and make sure that the P (pressure) and EXP (Expansion height) are zeroed before testing, and then touch the START icon to start the Test, the burst testing machine will stop automatically once the bursting test is finished, and record the test result automatically.

The D.Test 

Immediately after the initial test (e.g., 5 times) is completed, the D.Test (diaphragm pressure test) without a sample is performed. The diaphragm pressure is determined using the same test area and the same air pressure setting conditions as the above test. In the absence of a sample, the diaphragm is expanded until it reaches the average burst height of the sample. The expansion pressure is used as the “diaphragm pressure”.

Calculates the final test data 

The burst testing machine automatically stops and records the bursting strength of the fabric. When the diaphragm pressure test is complete, the bursting strength machine automatically calculates the final test data and displays it on the screen. Touch the PRT (report) to observe and view the test results.

The Net Pressure is the final test result.

Net Pressure = Gross Pressure of Preliminary Test – The Pressure of Diaphragms.

No. 1 test: 192.6 – 26.0 = 166.6 kPa

No. 2 test: 214.8 – 26.0 = 188.8kPa

No. 3 test: 191.3 – 26.0 = 165.3kPa

No. 4 test: 220.5 – 26.0 = 194.5kPa

No. 5 test: 165.4 – 26.0 = 139.4kPa

The average pressure = 196.9 – 26.0 = 170.9kPa.

And then print the test report as below.

Factors Affecting the Bursting Strength of the fabric

1 The internal factors of the fabric itself

 Yarn bursting strength and elongation at break. When the fabric yarn bursting strength and elongation is large, the top bursting strength of the fabric is high.

The influence of the fabric thickness, in other conditions the same, when the fabric is thick, the top bursting strength is large.

The warp or weft density of the fabric. When other conditions are the same, the fabric warp and weft density are different at the same time, the fabric top crack must be torn along the direction of the density is small, the split is linear, and the fabric top bursting strength is low.

Yarn hooking strength. In the knitted fabric, the yarn hooking strength is large, the fabric top burst strength is high. Yarn fineness and coil density also affect the top-breaking strength of knitted fabrics. Increase yarn density and loop density, top breaking strength also increased. The fabric is affected by the treatment of boiling and bleaching, brushing, dyeing, enzyme washing, and resin qualitative finishing. Under the influence of these different processes, the top bursting strength of the fabric decreases, and with different processes and materials, the top bursting strength decreases to a different extent. Generally speaking, regarding the bursting strength, the fabric with a dark color is lower than the one with light color.

2 Influence of external factors

 Influence of test methods

Using different burst testing methods, the test results will also be affected. Generally speaking, the top bursting strength measured by the hydraulic method and pneumatic method is much more stable than the item bursting strength measured by the steel ball method. If there is no special requirement, use the hydraulic or pneumatic method. In the top bursting strength is less than 80KPa, the difference between the pneumatic and hydraulic methods is not much, but in the item bursting strength card is greater than 80KPa, the general use of the hydraulic method will be more stable. Using the same test method, the test range is not the same, the test results will also have deviations. The practice has proved that with the same hydraulic method, using different ranges, the test results also have a certain deviation, generally speaking, with the use of a small range, the test results will be more accurate. Therefore, the ability to use a small range, the burst testing equipment should use a small range.

The influence of the test environment

In the top bursting strength test, the test environment has a great influence on the top bursting strength of the fabric, so the tester needs to strictly follow the standard to choose the corresponding test environment.

 Influence of the operator

The influence of testers’ readings. Relative to the hydraulic burst testing equipment, because different people may not see the same value, or not on the positive side of the counter reading, the reading will also have deviations. The influence of the wrong standard method chosen by the tester. Especially relative to the pneumatic fabric bursting strength tester, if you choose the wrong standard method or choose the wrong test cup or calibration error, the test results will also be greatly affected. The influence of the testers’ operation irregularities. Especially in the hydraulic bursting strength machine testing process, if the tester can not move the valve handle back to the original position at the moment that fabric bursts instantly, the bursting strength will be large. The influence of testers’ sampling. If the tester takes samples at the edge of the fabric or at the stretched place, the bursting strength will usually be less.