Methods of Tensile Testing of Textiles
Tensile testing is a common method used to evaluate the mechanical properties of textiles. This type of testing measures the response of a textile material to an applied force, typically in the form of a pulling or stretching force. The results of a tensile test can provide important information about the strength, elasticity, and durability of a textile material.
Methods of Tensile Testing of Textiles
I. Constant Rate of Elongation (CRE)
Constant rate of elongation tests are tests used to determine the strength of textile materials. In constant rate of elongation tests, the specimen is extended at a constant rate and the force is a dependent quantity.
It is possible in constant rate of elongation tests for load to decrease while elongation increases.
II. Constant Rate of Loading (CRL)
Constant rate of loading tests are tests used to determine the strength of textile materials. In constant rate of loading (CRL) tests, the specimen is loaded at a constant rate and the elongation is a dependent quantity.
It is not possible in constant rate of loading tests for load to decrease. Load must increase all the time.
Fiber Testing Instruments
I. Ballistic Tester
Tensile Strength of a single fiber can be determined by Ballistic Tester and the test carried out by Ballistic Tester is called Ballistic Test.
Ballistic Tester contains a pendulum. A specimen of fiber is placed in the way of pendulum of Ballistic Tester. Pendulum is released from a given angle to the vertical and on its swing, it engages with one of the specimen jaws and break one of the jaws. Tensile strength of specimen is determined by the energy lost by pendulum when it contacted with specimen jaw and this energy is the one which was, in actual, needed by the pendulum to break the fiber.
Ballistic Test is more rapid than a normal Load-Elongation Test.
II. Instron Tensile Tester
Instron Tensile Tester acts on the principle of Constant Rate of Elongation. In Constant Rate of Elongation, the specimen is extended at a constant rate and the force is a dependent quantity.
In Instron Tensile Tester, one end of the specimen is clamped in jaws, which are mounted on a cross-head that is traversed at a constant rate by mechanical drive. The drive comes from a computer-controlled stepper motor. The other end is clamped in jaws which are mounted on a stiff load cell containing a strain-gauge.
The drive is connected to the recorder drive, and the electronic circuits of the load cell lead to deflection of the recorder pen. The load and elongation are digitally transferred to a computer. And data is plotted in graphs and analysis are done on the basis of plotted graphs to know whether tensile strength of specimen under observation is either low or high.
A finite, but small, deflection is, of course, necessary in order to measure load. Medium and large Instron-type testers cater for a wide range of specimens, from single fibres and yarns to large cords, but smaller instruments have been introduced for specialist investigations of single fibres or fine yarns.
III. Lea Strength Tester (C.S.P)
Lea strength tester is used for determining the Tensile Strength and Elongation of Cotton, Wool, Jute and other textile materials in form of skein.
The machine consists of a sturdy metal plate base with load measuring unit fixed at the top and the driving assembly fitted at the bottom. An electric motor transmits power to the lead screw through gear box. The pendulum rod is connected with the upper lea holder through main boss.
The strength is determined in such a manner that the test specimen is gripped by two lea holders vertically arranged one below the other and continuously tensile stressed until it breaks. Elongation is also determined at the same time in the form of extension of the specimen held between the grips during the tensile test. The machine comes in four different capacities which are 100 lbs., 200 lbs., 300 lbs. and 500 lbs. A suitable capacity of Lea Strength Tester may be selected prior to order. If the count is known and the strength is determined with the help of "HIROSHIMA" Lea Strength Tester, by multiplying both the values i.e. COUNT x strength in LBS determines CSP (Count Strength Product).
Below mentioned would be required to carry out the test which are not included with Lea Strength Tester and can be procured separately.
- Wrap-reel for making Lea.
- Direct Yarn Count Balance for determining the Count.
IV. High Volume Fibre tester (HVF)
High volume fiber tester is used to determine fiber properties like length, strength, micronaire, maturity & colour.
High volume fiber tester has following features:
- HVT Expert 1201: Measuring the important fiber properties like length, strength, micronaire, maturity, moisture & colour.
- Less space occupation, less weight and comfortable Stainless Steel top workspace.
- Combined and independent module testing.
- Parallel as well as simultaneous operations ensures faster testing.
- Flexible report options like date wise, lot wise, cotton type wise as well as consolidated reports.
- Spin-ability estimation of predicted CSP and Process proficiency (PP) in addition to SFI, FQI calculations.
- Length & Strength: Strength can be measured in ICC and HVI mode.
- Fineness & Maturity: Fineness range: 2.0 to 8.0 microgram / inch and true maturity properties like maturity ratio, percentage maturity and maturity co-efficient measurements through double compression.
- Fully automatic model embedded with microcomputer controlled technology for rapid measurement.
V. Uster HVI 1000
HVI uses the constant rate of elongation principle while testing the fibre sample. The available conventional methods of strength measurement are slow and are not compatible to be used with the HVI. The main hindering factor is the measurement of weight of the test specimen, which is necessary to estimate the tenacity of the sample. Expression of the breaking strength in terms of tenacity is important to make easy comparison between specimens of varying fineness.
The fibres are selected, combed and carefully prepared to align them in the jaw clamps. Each and every fibre spans the entire distance across the jaw surfaces and the space between the jaws.
Strength is measured physically by clamping a fibre bundle between 2 pairs of clamps at known distance. The second pair of clamps pulls away from the first pair at a constant speed until the fibre bundle breaks. The distance it travels, extending the fibre bundle before breakage, is reported as elongation.
In the HVI instruments the fibres are randomly selected and automatically prepared for testing. They are combed to remove loose fibres and to straighten the clamped fibres, also brushed to remove crimp before testing.
Fabric Testing Instruments
I. Computerized Fabric Tensile Tester
Fabric Tensile Tester is Floor mounted and has a rugged steel body. It has auto self-aligning jaws and double screw rod mechanism for accurate parallel movement and precise measurement of breaking load without any parallax errors.
Instrument works in constant rate of elongation principle. Fabric Tensile Tester is fully controlled by computer and window based software to obtain results in numerical and graphical form.
It has a feature of auto quick rerun of bottom jaw after testing which enables more number of tests per hour and is easy to operate. Instrument works on constant rate of Elongation. Its Traverse speed ranges from 3 mm/min to 1000mm/min, increment of 1mm/min. It is easy to select the Testing speed of breaking time with this instrument.
Testing range of this instrument is from 0 to 1100 lbs. with 0.1% accuracy of full scale. Instrument is fully controlled by microprocessor unit.
This instrument has facility to have multiple numbers of load cells thus giving wide range of coverage with better accuracy at higher and lower load ranges with minimum least count.
Special facility for mounting additional load cells as a result of which there is no need to change either load cells or grips on the machine.
Speed of the machine can be regulated through computerized systems.
Optional features of Fabric Tensile Tester includes:
- Clamp for Single yarn strength testing
- Clamp for Lea strength testing with 55% elongation.
- Clamp for Fabric strength testing
II. Twin Column Servo Fabric Tensile Tester
Twin column servo fabric tensile tester is used to determine the tensile properties of varieties of fabrics. This series of Tensile Tester is widely used in wires & cables, hardware, metal, rubber, footwear, leather, apparel, fabric, tape paper products, pharmacy and so on, for tensile strength, tear resistance, peel strength, bend strength and shear force with different fixtures according to national and international standards customer required.
This instrument uses the motor to make displacement of the fixture. It places the fixture with sample between the upper and lower fixture, and the upper load cell with sensor records the tensile strength, and converts the strength into voltage sign and displays it to the display screen in the format that cab be understood by humans and the strength value is displayed automatically.
Twin column servo fabric tensile tester has following features:
- Motor system: A Servo motor, Servo driver and high precise ball screw.
- Control system: A computer control with TM2101 software, ability to back to origin automatically after the test and the ability to store data automatically or by manual operation.
- Graph scale automatic optimization: It can make graph to display with best measurement and can implement graphics dynamic switching in the test and has force-elongation, force- time, elongation -time, stress – strain graphs.
- It can save results automatically after test finished, and it is manual filing. It can display maximum force, yield strength, compressive strength, tensile strength, elongation, peel interval maximum, minimum and average, etc.
- User can set parameters of product material such as length, width, thickness, radius, area and so on.
III. Universal Tensile Testing Machine
Universal tensile testing machine is applicable in testing the tensile property of non-woven fabric, textiles, plastic films, complex films, flexible packaging materials, adhesives, adhesive tapes, glue, rubber, Paper, plastic, aluminum plate, enameled wire, waterproof materials, triangle etc. It is named after the fact that it can perform many standard tensile and compression tests on materials, components, and structures.
The specimen is placed in the machine between the grips and an extensometer if required can automatically record the change in gauge length during the test. If an extensometer is not fitted, the machine itself can record the displacement between its cross heads on which the specimen is held. However, this method not only records the change in length of the specimen but also all other extending / elastic components of the testing machine and its drive systems including any slipping of the specimen in the grips.
Once the machine is started it begins to apply an increasing load on specimen. Throughout the tests the control system and its associated software record the load and extension or compression of the specimen.
Machines range from very small tabletop systems to ones with over 53 MN capacity.
Universal tensile testing machine has following features:
- Load frame: usually consisting of two strong supports for the machine. Some small machines have a single support.
- Load cell: A force transducer or other means of measuring the load is required. Periodic calibration is usually required by governing regulations or quality system.
- Cross head: A movable cross head is controlled to move up or down. Usually this is at a constant speed: sometimes called a constant rate of elongation (CRE) machine. Some machines can program the crosshead speed or conduct cyclical testing, testing at constant force, testing at constant deformation, etc. Electromechanical, servo-hydraulic, linear drive, and resonance drive are used.
- Means of measuring extension or deformation: Many tests require a measure of the response of the test specimen to the movement of the cross head. Extensometers are sometimes used.
- Output device: A means of providing the test result is needed. Some older machines have dial or digital displays and chart recorders. Many newer machines have a computer interface for analysis and printing.
- Conditioning: Many tests require controlled conditioning (temperature, humidity, pressure, etc.). The machine can be in a controlled room, or a special environmental chamber can be placed around the test specimen for the test.
To Compare the tensile strength of 100 % pure cotton and its blends, also calculating their CLSP values.
This experiment is done to see how same count of different types of yarns has different strength and CLSP. We will also see the factors on which tensile strength of a product depends upon and when to use which yarns for different applications.
Comparing the single yarn strength having different TPI and same count
This experiment was conducted to see how does twists per unit inch or TPI in a yarn effect its strength. For this purpose, other parameters like fiber type and count of yarn are kept constant.
Why do fabrics shrink? Shrinkage in Fabrics!
During the manufacturing process of fabric or we call it fabric processing, fabric comes in lot of tension and stretches when it moves from one machine to another which causes stretching in fabric structure and when this tension is removed, and fabric is relaxed it tends to get back in its original structure causing shrinkage.
Worsted Yarn Manufacturing Process
A fine smooth yarn spun from combed long staple wool. Worsted yarns are more tightly twisted than the bulkier woolen yarns. The soft, heavy yarn is strong and durable and is often used for sweaters. Worsted yarns are also used for fine dress fabrics and suit materials.