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Fabric testing
- 1. PREPARED BY RASMIN THAHANI Z, ASSISTANT PROFESSOR, SYED AMMAL ARTS AND SCIENCE COLLEGE, RAMANATHAPURAM. FABRIC TESTING TEXTILE TESTING
- 3. INTRODUCTION: Bursting strength is the strength of a fabric against a multi directional flow of pressure. The bursting test measures a composite strength of both warp and weft yarns simultaneously and indicate the extent to which a fabric can withstand a bursting type of force with the pressure being applied perpendicular to the surface of the fabric.
- 4. The reason for this method of testing may be due to the material in use is stressed in many directions simultaneously. Filter cloths, sacks, nets and parachute cloths are examples for fabrics stressed in all directions. Also, knitted fabrics can not be easily tested in strip form and fabrics without well defined direction like felted cloth or bonded fabrics may be conveniently tested on a bursting strength tester.
- 5. METHODS OF MEASURING BURSTING STRENGTH Bursting strength of a fabric can be determined using either: • Mechanical type bursting strength or • Hydraulic pressure type bursting strength tester.
- 7. PRINCIPLE: The pressure in a liquid is exerted in all directions and this phenomenon of a liquid is used for testing bursting strength in Hydraulic bursting strength tester.
- 8. SAMPLE SIZE: The specimen for this test should be cut so that the sample is ½ inch greater in diameter than the outside diameter of the clamp ring. The specimen are chosen avoiding inclusion of the same ends in the different specimen.
- 9. The instrument used for testing bursting strength should have a constant rate of speed and must be capable of giving a uniform displacement of 6 ± 0.25 cubic inches per minute. The clamp should have an internal diameter of 1. 20 inches. For proper operation, the machine must be stopped at the instant of rupture in order to avoid additional application of pressure and load on the specimen.
- 10. PROCEDURE The specimen is clamped by a ring over a thin flexible rubber diaphragm which itself is clamped by over a circular hole in the upper face of the reservoir. The liquid used may be water or glycerin.
- 11. The pressure in the liquid is increased, by valves or screw driven piston. Due to increase in pressure, the diaphragm bulges, taking with it the specimen. At some point the fabric bursts, and the pressure at that point is indicated by the pressure gauge.
- 13. Since the rubber diaphragm requires a certain pressure to stretch it, corrections are made by doing a blank test. i.e. noting the pressure required to distend the diaphragm the same amount without the presence of fabric. In the test specimen, it cuts by chisel for ½ inch is made (either in warp or in weft direction or in both) or if a ¼ inch hole is punched and then the same test is a carried out, then it is called as wounded bursting
- 15. INTRODUCTION The tearing strength is a measure to tearing of either the warp or weft series of yarns in a fabric. A fabric which tears easily is regarded as an inferior product. The amount of resistance of a fabric to tearing is often important ad particularly in fabrics like bandage cloth, adhesive tapes, military fabrics, etc.
- 16. General Conclusions Thread break singly or in very small groups during tearing. Therefore, the single thread strength of the yarns an important. If the fabric construction allows, the threads group together due to tearing force, instead of the successive breakage of individual threads. This grouping tendency will be more prominent if the yarns are smooth and can slip over one another.
- 17. The grouping phenomenon is also influenced by the weave. Thus in a twill or a 2/2 Matt weave, thread grouping is prominent and they provide better resistance for tearing than plain weave. High set fabrics do not allow easy group of the threads. Special fabric finishes like drip dry and crease resist treatments reduce the tearing strength.
- 19. INTRODUCTION The Elmendorf tearing tester was designed for tearing test on paper and can be used for fabric testing. The test is a single rip ballistic test which has the advantage of rapidity and simplicity. The specimens are relatively small in area and thus require less fabric.
- 20. This method is applicable to treated and untreated woven fabrics, including those heavily sized, coated or resin treated, provided the fabric does not tear during the test in the direction crosswise to the direction of the force applied.
- 21. PRINCIPLE The average force required to continue a tongue type tear in a fabric is determined by measuring the work done in tearing it through a fixed distance.
- 22. PREPARATION OF TEST SPECIMENS From the fabric sample, warp way and weft way test specimens of the required size and are prepared with the help of the template. The length wise direction shall be parallel to the warp or weft direction for which the tearing strength is required. The specimens are put so that no two warp specimen contains the same set of warp yarns and no two weft specimen contain the same set of weft yarns.
- 24. While cutting the specimens, care should be taken to align the yarns running in the width direction parallel with the die so that when the slit is cut, the specimen tear will take place between these yarns and not across them. A cutting knife can also be used to cut the specimens of length 100 mm and width 75 mm. Ten warp way and ten weft way specimens are prepared. The specimens are then conditioned and tested in the standard testing atmosphere.
- 25. DESCRIPTION The elmendorf tester provides means for holding the specimen with two clamps, stationary and moveable, and for tearing it by the fall of the pendulum due to the force of gravity. The tester is provided with the augmenting weights – the NBS augmenting weight which increases the capacity from 1600 to 3200 g and the Textile Augmenting Weight which further increases the capacity to 6400 g.
- 26. Without the augmenting weights, the capacity is 1600 g. it is also provided with three scales graduated in hectograms (100 g. units) corresponding to the three capacities.
- 27. PROCEDURE The instrument is levelled and adjusted for zero point. The capacity of the instrument is selected so that the specimen tears between 20 and 60 percent of the scale value. The pendulum is raised to the starting position and the pointer is set against its stop. The conditioned test specimen is fixed in the clamps so that it is well centered, with bottom edge set against the marks and the upper edge parallel to the top of the clamps.
- 28. Then the clamps are tightened using approximately the same force on both the clamps. If the slit has not been cut by the die, using the knife, a 20 mm slit is cut in the specimen. The pendulum is then released by depressing the pendulum stop. The stop is held down until after the tear is completed and the pendulum is caught on the return swing by the hand without disturbing the position of the pointer. The reading opposite to the pointer is noted directly.
- 29. The readings are rejected if the specimen slips in the jaw or if the tear deviates more than 6mm away from the projection of the original slit. The above procedure is repeated for all the test specimens and the average tearing force is calculated for the warp and weft way test specimens.
- 30. When a tester is used in which the scale is graduated to indicate the percentage of the original potential energy of the pendulum consumed in tearing the specimen, the following formula is used to calculate the tearing strength: Tearing strength Capacity of x Pointer in grams = Instrument Reading 100
- 31. Thank You