Fabric Strength
• Strength of a fabric is the resistance to Tearing, Breaking or Bursting when various types of forces are acting on it.
• The strength of the fabric is important for their durability, as there are subjected to various types of stresses during their use.
• The strength or resistance of a fabric can be of different nature depending on the type of force/stress acting on the fabric.
• There are three very widly used strength measurements for fabrics.
Strength Measurements for Fabrics.
• Tensile Strength - Resistance to tensile force.
• Tearing Strength - Resistance to tearing force.
• Bursting Strength - Resistance to bursting force.
❖ Apart from these fabric strength properties, resistance to tensile force at the seam is an important property of garments and it is defined as Seam Strength.
Tensile Strength
• Tensile Strength is a resistance of a materiel to stretching in one direction. tensile test is the method employed to measure tensile Strength. the direction which the load is applied depends on the purpose of the test. mostly both warp and weft directions are tested.
• There are three methods depending on the shape and preparation of fabric specimens.
⮚ Raveled strip method
⮚ Cut-strip method
⮚ Grab method
Tearing Strength
• Tearing strength of the fabric is the measure of resistance to a tearing force of the fabric. tearing test is the method employed to measure tearing strength. mostly both warp and weft directions are tested.
• Following test methods are available for measure tearing strength. they differ from each in the shape of the test sample or tearing art. ⮚ Ballistic Tear Test
⮚ Tongue Tear Test
⮚ Tongue Double rip Tear Test
⮚ Wing-rip Tear test
Bursting Strength
• Bursting strength is the resistance to a bursting force. This measures the strength of warp and weft yarns simultaneously. bursting test is the method employed to measure bursting strength. this test is mainly done for knitted fabrics.
Objectives of Strength Testing
The fabric strength is depends on many factors such as,
❖ Characteristics of raw materials
❖ Yarn specifications such as, count, irregularity, strength,twist,.....etc.
❖ Fabric structure, designs,crimp,....etc.
❖ fabric finish.
Fabric strength testing can be used to,
• Cheek for conformation to lay down specifications.
• Find out the effects of any structural details. Ex:- same fabric made out of different types of warp and weft yarns.
• Obtain knowledge as to the effect after exposure to weather, laundering,...etc.
• Determine suitability for a particular end use.
• Find out the reasons for a customer complaint.
• Research purpose.
Determination of maximum Force Using the Strip Method
ISO 13934-1
Scope and Application
• Application for the determination of maximum force and elongation at maximum force of textile fabrics using the strip method.
• Mainly applicable to woven fabrics. can be used for fabrics produced by other techniques as well.
•Non applicable to woven elastic fabrics, coated fabrics, textile- glass woven fabrics and fabrics to made from carbon fibers or polyolefin tape yarns.
Apparatus
• Template
• Tensile testing machine
Conditioning
Stranded Atmospheric Conditions in 24 hrs
• Relative Humidity - 65% ± 4%
• Temperature - 200C ± 20C
Tensile testing machine
Preparation of Test Specimens
• From the Laboratory Sample cut two sets of test specimens, warp direction and weft direction.
• Each set consist of 5 specimens.
• Don't cut test specimens within 150mm of eighter edge of the laboratory sample.
• Cut test specimens diagonally due to avoid using the same ends and same picks.
Width
• Threads shall be removed in approximately equal numbers from each of the long edges of cut specimen until the width of the test specimen is 50mm.
Length
• The length should be sufficient to provide a nominal gauge length. Mark the gauge length on the specimen drawing a line across the width of the specimen.
Test Procedure
• Mount the specimen between clamps.
• Clamp the test specimen centrally.
• Start the machine and put the clamps in motion.
• Record the maximum force at rupture from N.
• Perform test for 5 specimen warp and 5 specimen for weft.
• Disregard results when the test specimen slips of by greater than 2mm along the clamping line.
• The breaks occurs within 5mm of the clamping line, record the results as “jaw breaks”. at the end of five readings examine the results. if any “jaw breaks” fall above the “normal” result then those can be included. if “jaw break” occurs below the “normal” result, then those should be excluded and further test performed to obtain five normal breaks.
• If all results are “jaw breaks” of it five “normal breaks” can not be obtained, then individual results shall be reported. “jaw breaks” result shall be indicates as such in test report.
Calculation and Expression of Results
Express the breaking strength in Newton “breaks” results shall be indicates as for each set of warp and weft direction readings, calculate arithmetic mean of the breaking strength and round off as follows,
Strength,
• < 100N to the nearest 1N • ≥ 100N to < 1000N to the nearest 10N • ≥ 1000N to the nearest 100N
Test Report
Test Report should be include the followings.
• Test stranded and year.
• Gauge length used in mm.
• Whether pre tension applied in newtons.
• Specimen condition, weather dry or wet.
• No of test specimens including no of test rejected and reasons.
• Width of strip if not 50mm and number of threads in strip.
• Any divination from procedure.
• Arithmetic mean of readings of max force and if required of the force or rupture in Newtons.
Determination of Tearing Strength in Ballistic Pendulum Method
ISO 13937-1
• The test is mainly applicable to woven and non woven textile fabrics.
• Test is not applicable to knitted and woven elastic fabrics.
•It is not suitable for highly loose fabrics.
Principle
• The force required to continue a tear of previous started in a fabric is determined.
• The specimen is fastened in the clamps and tear is started by cutting a slit in the specimen between the clamps.
• After released pendulum and the specimen is torn completely as the moving jaw moves away from the fixed one.
• Then tear force is measured.
Apparatus
• Pendulum tearing testing machine.
• Template for tearing test
Conditioning
• Stranded Atmospheric Conditions at least 24 hours. Relative Humidity - 65% ± 4% Temperature - 200C ± 20C
Unit : Kgf / gf / N / Lbf
Tearing testing machine
Procedure
• Check that the apparatus is Zero.
• Position the test specimen in the jaws so that the long side of the test specimens is parellel to the upper edge of the jaws. • Clamp the test specimen centrally.
• Using the knife, cut the slit of 20 mm.
• Realese the pendulum by depressing the pendulum stop. • Read the tear force by mean of digital display.
• Test all 5 warp and 5 weft specimens average the warp and weft results individually.
Test Report
Test Report should be include the followings.
• Test standerd and year
• Test performed date.
• Specimen condition time accoriding to standerd atmosperic conditions.
• No of test specimens including no of test rejected and resons. • Any diviation from procedure when tearing.
• Arethmetic mean of readings of tear force in Newtons.
Determination of Bursting Strength
ISO 13938 - 1
Definition
• Pressure at burst
Pressure applied to test specimen which clamp over an underlying diaphragm until the test specimen rupture.
• Bursting distension
Extension of a test specimen at the bursting pressure.
Scope
• Force of pressure required to rupture a textile fabric by distending it with a force applied right angle to the plane of the fabric under specified condition.
Principle
A test specimen is clamped over an diaphragm by mean of a circular clamping ring. increasing fluid pressure is applied to the under side of the diaphragm, causing distention of the diaphgram and the fabric. the volume of fluid is increased at a constanat rate per unite time untill the test specimen bursts. the bursting strength and bursting distention are determine.
Apparatus
• Bursting testing machine.
Conditioning
• Stranded Atmospheric Conditions at least 24 hours. Relative Humidity - 65% ± 4% Temperature - 200C ± 20C
Selection of Testing Area
Auto Bursting Strength T150mm 150mm
Fabric width
Mullen Bursting strength tester
Rubber diaphragmTest Specimen
Hydraulic Liquid
(Glycerin)
Procedure
• Condition The test sample in the slandered atmospheric conditions at least 24 hrs.
• Insert the specimen between the top and bottom clamps ensuring that specimen is free from creases and folds. • Clamp the specimen by following the manufactures instructions appropriate the machine.
• Applied pressure to the specimen until the burst. • Repeat test for 5 specimens.
• Calculate the bursting strength as follows.
Calculations
Bursting Strength = Reading of the Pressure required pressure gauge distend the rubber diaphragm
Unit : Kpa
kgf / cm2
P.S.I.
Test Report
Test Report should be include the followings.
• Test stranded and year
• Test performed date.
• Specimen condition time according to stranded atmospheric conditions.
• No of test specimens including no of test rejected and reasons. • Used hydrophilic liquid for generating fluid pressure.
• Any divination from procedure when bursting.
• Arithmetic mean of readings of busting strength in Kpa,P.S.I.,kgf / cm2
Determination of Maximum Force to seam Rupture Using The Grab Method
ISO 13935 - 2
Seam Slippage
• There are two major types of Seam slippage
1. When stress is applied to a seam, the yarns in the fabric slip out of the stitching causing an open seam; and,
2. When stress is applied to a seam, the yarns in the fabric shift of the slide in the weave construction causing seam and fabrication.
• We will refer to the first type as “seam slippage” and the second “yarn slippage”.
Yarn slippage-seam slippage
Scope
Applicable for determination of seam maximum force of sewn seams where the force is applied perpendicular to the seam.
Field of Application
Mainly used for woven textile fabrics. it may be applicable to fabrics produced by other techniques. it is not applicable to woven elastic fabrics, non-woven and coated fabrics. the sewn fabrics may be obtained from previously sewn articles or may be prepared from fabric samples as agreed to buy the parties interested in the results. this method is applicable to straight seams only and not curved seams.
Apparatus
• Constant Rate of Extension Tensile Testing Machine • Sewing machine suitable for seam type required
• Sewing thread
• Measuring ruler
Tensile testing machine
Sample Preparation
• If seams to be prepared for testing, the interested parties should agree on the following conditions of sewing.
• Type of sewing thread
• Type of needles
• Type of seam
• Seam allowance
• Number of stitches for inch
• If the client does not provide details, seam as per following details would be sewn. • Stitch density of 5 stitches per cm
• Seam allowance of 1.2 cm
• Sawing thread 100% polyester spun with continuous filament polyester and a staple polyester, ticket number 80.
• Sawing machine should adjust to give the correct conditions, using a spare piece of the fabric to be tested.
• Cut a sample of 250mm × 700mm.
• Fold the sample in half with the fold parallel to the longer dimensions make the seam in this direction and cut to give the agreed seam allowance.
• Seam may be sewn for testing parallel to the warp, weft directions, or both as agreed between the interested parties. • From each sample with seams cut a set of five test specimens of width 100mm.
• When using seams prepared as mentioned above, do not cut samples within 100mm of either end of the prepared seam. •On each test specimen draw a line at distance of 38mm from one edge running the full length of the test specimen.
Conditioning
The test specimen should be conditioned at 24 hrs in Stranded Atmospheric Conditions
• Relative Humidity - 65% ± 4%
• Temperature - 200C ± 20C
Procedure
•Gauge Length - Set thr gauge length in tensile machine 100±1 mm.
• Rate of Extension - set the rate of extension in the tensile machine 50mm/min
• Mounting the test specimen - clamp the test specimen centrally so that it's longitudinal center line passes through the center point of the front edges of the jaws. the line drawn on the test specimen should coincide with one edge if the jaws and the force is applied perpendicular to the seam in the middle of the gauge length.
• After closing the upper jaw, avoid pre tension, when adjusting the test specimen.
• Along the guide line in the lower jaw, so that the fabric hangs under its qwn weight when the lower clamp is closed. • Start the machine.
•If rupture occurs by,
⮚ Fabric tear
⮚ Fabric tear at jaws
⮚ Fabric tear at seam
⮚ Breakage of sewing thread
⮚ Thred pull out
• These readings should be recorded but not taken to account with other readings when averaging, Further test shouls performed to obtain five readings each directions. calculate the arithmetic mean of the seam maximum force in Newton.
Test Report
The test report shall include the following information;
• The test results and seam occurrences should include
• Reference to the stranded year.
•Identification of test sample and sampling procedure.
• Seam information
•Number of test specimens, including the number of tests rejected.
• Arithmetic mean of the seam maximum force in Newtons.
• Any deviations from the given procedure.
•In case of fabric tear or fabric tear at jaws, the individual results.