A Comparative Analysis of Basic Mechanical Properties Testing Methods for Textiles

In the course of daily use, textiles are subject to a variety of forms of damage, such as breaking, tearing, and bursting caused by mechanical external forces such as tensile, compression, bending and friction, etc. Therefore, the basic mechanical properties of textiles influence the durability of textiles and are the main element of quality assessment.

The article describes the damage mechanism of the basic mechanical properties of textiles such as breaking strength, tearing strength, bursting strength and seam properties, and introduces the testing methods for the mechanical properties of fabrics and the matters that should be noted during the testing process, which can play a certain reference role in improving the testing accuracy and product quality.

★ Maximum Force

The maximum force of the fabric record when a test specimen is taken to rupture during a tensile test under the specified conditions.

1 Principle of damage

When the fabric is stretched by an external force, the yarn in the fabric is gradually straightened by the bend, the yarn stretched becomes thinner, the non-stretched yarn in the lateral direction under the action of tangential sliding resistance, both sides of the yarn gradually concave inwards, the fabric becomes “bundle waist-shape”, and eventually the yarn breaks off one by one and the fabric disintegrates. A diagram of the fabric stretching and fracture process is shown below.

2 Testing standards

ISO 13934-1: Textiles – Tensile properties of fabrics – Part 1: Determination of maximum force and elongation at maximum force using the strip method
ISO 13934-2: Textiles – Tensile properties of fabrics – Part 1: Determination of maximum force using the grab method

Both test methods are suitable for woven fabrics and can be applied to other fabrics, but not usually to elastic fabrics, geotextiles, glass fibre fabrics and carbon fibre and polyolefin flat filament fabrics. Both test methods use an constant-rate-of-extension (CRE) to test the maximum force of fabrics in the wet and dry state.

The principle of strip method: stretch a fabric specimen of a defined size at a constant rate until it ruptures. The principle of gripping method: hold the central part of the specimen in a specified size gripper and stretching the specimen at a constant rate until it ruptures.

In the strip method, the entire width of the sample is held and stretched by the gripper, while in the grip method, the central part of the sample is held and stretched by the gripper in the width direction. Compared to the gripping method, the strip method gives less uneven results and saves on test material, but the fabric specimen is easier to prepare for the gripping method and the test procedure more closely resembles the actual use. The gauge length, specimen size and extension rate of the two standards are shown in the table below.

Standard	ISO 13934-1 strip method	ISO 13934-2 grip method
Gauge length / mm	elongation at maximum force≤75%: 200±1 elongation at maximum force＞75%: 100±1	100±1 or 75±1 With the consent of the parties concerned
Specimen size / mm	length >200 effective width: 50±0.5 (excluding raw edges)	width: 100±2 length＞100
Extension rate	20mm/min or 100mm/min	50mm/min

★ Tearing Strength

When the fabric is actually worn, certain parts of the fabric are suddenly subjected to a concentrated load, for example, if certain parts of the fabric are suddenly hooked by sharp objects or if the body is squatting and the hip or crotch of the trousers are suddenly subjected to an external force, the yarn will be subjected to a maximum load and will then break or crack.

1 Principle of damage

A stress triangle is formed during the tearing of a fabric, the tear strength of a fabric is positively correlated with the individual yarn strength and the greater the elongation at maximum force of the yarn, the greater the stress triangle and the greater the number of stressed yarns, and therefore the greater the tear strength.

2 Testing standards

There are various forms of tearing in the use of various fabrics in different scenarios. The following methods are currently available for testing the tearing strength of fabrics.

ISO 13937-1: Textiles – Tear properties of fabrics – Part 1: Determination of tear force using ballistic pendulum method (Elmendorf)
ISO 13934-2: Textiles – Tear properties of fabrics – Part 2: Determination of tear force of trouser-shaped test specimens (Single tear method)
ISO 13937-3: Textiles – Tear properties of fabrics – Part 3: Determination of tear force of wing-shaped test specimens (Single tear method)
ISO 13937-4: Textiles – Tear properties of fabrics – Part 4: Determination of tear force of tongue-shaped test specimens (Double tear test)
ISO 9073-4: Textiles – Test methods for nonwovens – Part 4: Determination of tear resistance

The above-mentioned test methods are based on different principles and the triangles formed are significantly different and the results obtained are not comparable. For example, the ballistic pendulum method is generally more suitable for twill fabrics with a higher tear strength, such as denim fabrics; the trouser-shaped specimen (single tear method) is generally more suitable for various woven fabrics (cotton printed and dyed fabrics, combed woollens) and non-woven fabrics with a regular tear direction.

★ Bursting Strength

Under the action of the load perpendicular to the plane, the fabric appears the phenomenon of bursting expansion and rupture, and the force at this time is called the bursting strength. The bursting test is similar to the force applied to a garment at the elbow, knee, etc. and simulates the real situation when worn. It is particularly suitable for knitted fabrics, triaxial fabrics, non-wovens and parachute fabrics, and is an important indicator for assessing the intrinsic quality of some knitted fabrics.

1 Principle of damage

Under the action of the bursting force, the fabric elongates and first starts to deform along the warp and weft directions, and at the point of weakest strength, the yarn breaks and then tears along the warp or weft direction, presenting a right-angle or linear break.

2 Test standards

ISO 3303-1: Rubber or plastics-coated fabrics – Determination of bursting strength – Part 1: Steel-ball method.
Test principle: clamp a test specimen between rigid coaxial apertures , a polished steel ball traversing at a fixed speed is pressed against the test piece until failure occurs. The force required to cause failure and the displacement of the polished steel ball at failure are recorded.

ISO 13938-1: Textiles – Bursting properties of fabrics – Part 1: Hydraulic method for determination of bursting strength and bursting distension.
Test principle: clamp the specimen onto an extendable diaphragm and apply liquid pressure underneath the diaphragm, forcing the diaphragm and specimen to expand, increasing the volume of liquid at a constant rate until the specimen expands and bursts and the bursting pressure is measured.

ISO 13938-2: Textiles – Bursting properties of fabric – Part 2: Pneumatic method for determination of bursting strength and bursting distension.
Test principle: it is essentially the same as the hydraulic method, except that a compressed gas is applied under the diaphragm, forcing the diaphragm and specimen to expand.

For the latter two methods, there is generally no significant difference between the results obtained using hydraulic and pneumatic breaking apparatus when the pressure does not exceed 800KPa, the pressure range that covers the performance level of most common garments. For special textiles with higher bursting pressures, the hydraulic method is more suitable.

★ Seam Performance

The garment is generally made up of several pieces of fabric, and the position where the pieces of fabric meet each other is called the seam. The quality of the seams has a direct impact on the quality of the fabric and its performance.

At the seam, the strength and slippage of the yarn can seriously affect the suitability of the textile and clothing fabric, so seam performance is an important indicator. Knitted fabrics are mainly assessed for seam strength, woven fabrics are assessed for seam strength and yarn slip resistance at the seam.

1 Seam strength

Knitted fabrics and woven fabrics due to different weaving methods, resulting in fabric in the tissue structure, taking performance and style vary greatly, their seam strength test methods are also different.

1.1 Knitted fabrics and elastic fabrics

Two methods are used for the seam strength of knitted and elastic fabrics:
FZ/T 01030: Knitted fabric and elastic woven fabrics – Determination of maximum force to seam rupture and burst distension – Bursting method
FZ/T 01031: Knitted fabric and elastic woven fabrics – Determination of maximum force to seam rupture and elongation – Grab method

1.2 Woven fabrics

The seam strength of woven fabrics is tested according to ISO 13935-1 (strip method) and ISO 13935-2 (grab method). These two test methods are applicable to the straight seams of woven fabrics, not applicable to elastic woven fabrics, geosynthetics, non-woven fabrics, coated fabrics, glass fibre fabrics as well as carbon fibres and polyolefin flat wire production of fabrics, the main test parameters of the two test methods are shown in the following table.

Main test parameters of ISO 13935-1 and ISO 13935-2

Standard	ISO 13935-1	ISO 13935-2
Gauge length / mm	200±1	100±1
Specimen size / mm	350 * 100	25 * 25
Extension rate	100mm/min	50mm/min

2 Slip resistance of the yarn at the seam

Slip occurs when the yarn at the seam is subjected to tension and friction, i.e. the warp (weft) yarn in the woven fabric moves on the weft (warp) yarn, and the slip is irreversible, the yarn slip is mainly used to measure the seam performance of the woven fabric.

The ability of the woven fabric to resist slip damage is called slip resistance and it has a direct impact on the fabric’s serviceability. The test method for slippage resistance at a seam of woven fabrics is the standard ISO 13936
Part 1: Fixed seam opening method
Part 2: Fixed load method
Part 3: Needle clamp method

★ Notes in Testing

1 Atmosphere of conditioning and testing

Fabric strength is mainly influenced by the strength of the fibres. The temperature and humidity of the test environment will affect the temperature and moisture regain of the fibres, which in turn affects the internal structure, state and tensile properties of the fibres.

When the moisture regain of the fibres is constant and the temperature increases, the thermal movement of the macromolecules within the fibre increases, the flexibility of the macromolecules increases and the intermolecular bond is weakened, resulting in a decrease in the strength of the individual fibres. Under the condition of constant temperature, the higher the relative humidity, the weaker the intermolecular bonding of the fibres and the looser the crystalline area, resulting in a reduction in the strength of the fibres. Therefore, the test should be carried out in strict accordance with the standard regulations, under the standard atmosphere conditions for conditioning and testing.

2 Test apparatus

The sensitivity and stability of the instrument will have a certain impact on the test results. When the sensitivity of the instrument is low, it will make the pre-tension inaccurate, and if the fabric strength is small, it will have an impact on the test results. When the fabric strength is large, the instability of the instrument will cause the CV value of the test results to be large, affecting the accuracy of the test. If the two clamps are not in the same plane, the clamp grip is slippery or the clamp surface is uneven, it will cause the specimen to break near the clamp, thus affecting the authenticity of the test results.

3 Pre-tension

Pre-tension is often required in the testing of fabric strength, the purpose of pre-tension is to make the fabric straight but not elongated. Too much pre-tension can cause fibre damage and thus affect the fabric strength; too little pre-tensioning can cause the fibre to not straighten sufficiently, thus affecting the final test results.

4 Sampling

Sampling should be taken in accordance with the standard and should be representative, avoiding creases, folds and edges, etc. and should not contain defects that would affect the test results.

5 The operator

The sample preparation process should be carried out in strict accordance with the requirements of the standard and hands should be kept dry and clean to avoid sweat on the hands affecting the test results.

★ Conclusion

This article identifies some of the factors that affect test results, the scope of application of the test methods, the test environment during testing, the apparatus, sampling, and standardised operation, which can be used to improve the accuracy of testing in the laboratory and guide manufacturers in effectively improving product quality.