The analys of Test Methods of Tear Strength

Breaking strength is also known as tearing strength. The testing methods includes trapezoidal method, tongue method (there is a single tongue and double tongue of the points), hammer fall method. Strictly speaking, hammer fall method also belongs to the tongue method, but the ways of determination are different.

 

Trapezoidal method:

Draw two diagonal lines at the ends of the strip to form an isosceles triangle in the middle and then cut at the bottom. Try to clamp and follow the two diagonal lines and add tensile loading. The first yarn that is close to the incision will bear more external force, while the other yarns will endure less force. When the first yarn experience cracks, it will split. Then the line below will become the first yarn. It will endure strong tension until tears apart. At last, the maximum force in the process is the tearing strength of the fabric. It is directly related to the tearing force, and is used to evaluate the tenacity of the fabric. The comparability and stability of the results are good, easy to measure and can be carried out in normal machine with general strength.

 

Tongue method:

Cut it into two pieces along the length of the strip. Apply tensile load in the two clamps of the machine respectively. The yarn in longitudinal direction experiences tension; the lateral yarn slides. The tension of the sliding yarn and the elongation increases dramatically and will form a stressed triangle. The first yarn of the bottom incision of the triangle withstands the greatest force. When it tears, it will have the highest tear value. The yarn breaks one by one until the fabric is torn. Factors affecting the triangle will also affect the fabric tearing strength. So, that is why  the strength of tongue tear does not only reflect the tenacity of the fabric, it can also evaluate the effect of dyeing and finishing process and other factors caused by the friction effect of tear on the impact.

 

The result of a single tongue tear is generally expressed as the maximum value during tearing. When a more accurate result is needed, it is available as the mean value of the five peaks. However, at this point, the five zone markings must be made starting at 5 mm from the incision (12.5 mm length for each zone) within the tear length on the specimen. During testing, when it is torn to a marking, put a marking to a corresponding point in the recording curve. Afterwards, read the highest value in each of the region, and take the average. Note: the zone division must be made on the sample otherwise it cannot be determined in the curve because the displacement of the curve includes the length of tearing, as well as the slip of yarn and elongation.

 

Hammer fall method:

The testing method uses the principle of conversation of energy, which measures the energy consumed to test the tearing of a specific length of fabric. (Fall of Fan-shaped pendulum and potential energy consumed). The energy will be converted into the strength of tearing, which is the average tearing  strength of the process of tearing. The feature of Hammer fall method and tongue method are similar. They quickly complete thetearing process. It is easy to use. The result is stable and is popular nationally.

 

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