Factors affecting the tearing strength

Tearing 

Tearing is defined as the force required to start to tear a fabric, in terms of warp or weft under certain conditions. A tear in a fabric or garment usually occurs progressively along a line and a moving fabric can be started to get caught in a sharp object. Several methods are used to measure tear strength, such as the double tongue rip (tear) test, a trapezoidal tear test, (ASTM D5587), and a single tongue tear test (ASTM D2661, BS 4303).

Ingredients for tearing vary in their sensitivity. Some materials can be quite resistant to tearing when they are in full form, but when a small cut or tear is made, the material becomes compromised and the effort to tear along that line is reduced.

Tearing strength

The process of forcibly tearing the material, without the aid of a cutting tool. The strength that is used to tear the material is called tearing strength. A tear in a piece of paper, fabric, or some other similar object may be the result of intentional effort on its own empty hand or may be accidental. Unlike cutting, which is usually in straight or patterned lines controlled by tools like scissors, a tear is usually uneven and for the most part unplanned. An exception is found in a tear along a perforated line, such as a roll of toilet paper or paper towels, which were previously partially cut, so attempts to tear will probably create a straight line. The specific tearing strength is defined as the sum of warp and weft tearing strength divided by the fabric mass per unit area.

When a fabric is torn by a sharp object and immediately the small prick is transformed into a long slit by a very small extra effort. This is the most common type of fabric energy failure in end-use. For garment items, such as outdoor clothing, overalls, and uniforms, tear strength is very important. The fabric tear property measured is the strength required to propagate an existing tear and not the force required to start the tear, as this usually requires thread cutting. In the test, the sample is first cut and the strength required to increase the cut is measured. It grips the two halves of the cut in a standard tensile tester and is conveniently carried through the tear test force-extension curve. The different tear tests performed in this method, called tongue tear tests, differ greatly in the geometry of the sample. ASTM D2261 describes a single rip tear test method, and BS 4303 also describes a wing rip tear test method. Results can be expressed as maximum, moderate, or average tear resistance.

Another method of measuring tear strength is the ballistic tear test, which measures energy loss during tearing. ASTM 1424 describes a tear strength test using the Elmendorf tear tester. The relationship between tearing force and energy loss has the following equations:

Energy loss = Tearing force x Distance

Tearing strength testing different standards

Items                                                               The main standards

i. Pendulum method                        ISO 9290, ASTM D 1424, DIN 53862, DIN EN ISO 13937.1. KS-K 0535, EN ISO 13937.1, etc.

ii. Tongue method                             ASTM D 2261.DIN 53859.1.DIN EN 13937.4.NF G 07-146, NFG 07-148, NFG 07-149, KS K 0536.EN ISO 13937.4, etc.

iii. Trapezoidal method                     ASTM D 5587.DIN 53859.5.KSK 0537, etc.

iv. Another Methods                     BS 4303(Wing Method). DIN 53859.2(Rectangular method). DIN EN ISO 13937.2(Trouser method). DIN EN ISO 13937.3(Wing Method). NFG 07-145(Nail method).NF G 07-147 (Nail method).NF ISO 13937.3(Wing Method). EN ISO 13937.2(Trouser method) etc.

Now, due to the different test methods available to measure the strength of the fabric from different angles, we had to calculate the following factors considering the compression, extension, and weak areas of the fabric which affect the tensile / tear test result-

i. Grab or strip test method related: a number of tests, gauge length, extension rate, jaw or grip, jaw fracture within 5 millimeters of the jaw mouth, etc.

ii. Regarding tear test method: Geometry of test piece, nature of separation, yarn properties, fabric structure, yarn sliding, jamming, density, test speed, fiber used in yarn construction, etc.

iii. Bursting test method related: to stretch, yarn alignment, fabric making, etc.

Kothari V. K clarified that the mechanical and comfort-related properties of the fabric are related to the linear density, twist level, thread density, crimp levels of warp and weft, cover factor, fabric thickness, and structural properties of fabric skew and bow. It is no doubt that the strength of the fabric depends directly on the strength of the yarn. Other issues related to the variation in the properties of yarns, especially those made with natural fibers, are stapled length, fiber fineness, fiber strength, twist quantity, evenness, fiber length variation, fiber finishing, drafting, and doubling in spun yarn spinning,  chemical treatment like sizing, thick and thin places, slubs, neps, and so on. It is easy to calculate yarn strength using both a single yarn strength tester and a Lea tester. However, since the Lea strength tester is affected by the frictional force present during the test and is not sensitive to the weak point of the individual yarn, and does not represent multiple strengths of a single thread, it does not serve any purpose from the next point processing result. We only need to consider the results of the single-thread test here.

Factors affecting the tearing strength

The factors affecting the tearing strength are as follows:

a. The GSM of the fabric indicates the tear strength. Higher GSM means more tearing power.

b. The strength of the yarn is directly related to the tearing strength of the fabric. More yarn strength means more tear strength.

c. Weave designs mean plain weave may have the lowest tear strength. Similarly, spun yarn has less tear strength than the filament yarn.

d. The knitted fabric is less strong than the woven fabric.

e. A tearing strength tester is a suitable tool for measuring the tear resistance of various materials including textiles and fabrics.

How to improve tearing strength

a. Since the fabric has a core problem, there is no specific remedy to improve it.

b. Marginal improvements may be possible through washing or some treatment.

c. Tear strength is a property that cannot be improved once a fabric is made. Longer fiber lengths and higher twisted yarns may result in higher tear strength characteristics for future production.

d. By reducing the number of threads on the opposite side of a test, the strength of the tear can be increased.

e. Use yarn with a high breaking load in the direction of the test to increase the strength of the tear.

f. Reduce friction between yarns to increase the strength of the tear test.

g. Use a good quality fabric softener.

Elmendorf tear tester method

Sample preparation

i. At first, we take a sample of 100 × 75.

ii. The template is placed on the sample and cut according to the template.

iii. A slit was made in the middle of the sample, with a range of 20 mm.

iv. In the experiment, Elmendorf continuously tore the fabric to a distance of 43 mm from the end of the slit to the opposite end.

v. The pendulum lever principle is used here.

Test procedure:

i. The instrument has a sector-shaped pendulum that carries a running sample clamp and a fixed clamp on the frame.

ii. When the pendulum is raised to the starting position, the sample is transferred between the two clamps.

iii. A tear begins by cutting a slit in the sample between the clamps.

iv. The pendant is then released and the specimen is torn off as a moving clamp, moving away from the stationary clamp.

v. The pointer is attached to the pendulum, which graduates directly to the tearing force reading.

Conclusion

Substances vary in their sensitivity to tearing. Some elements can be quite resistant to tearing when they are in full form but when a small cut or tear is made the material becomes compromised and the effort required to tear that line is reduced.

Video Credit:

http://en.labthink.com/en-us/products/test-property/tearing-resistance-tester.html?