Physical Measurements On Fabric_textile Testing_by_abubakkar Marwat

Abu Bakkar Marwat (05-NTU-05)

6th semester

Physical Measurements on Fabrics

Fabric Strength: • Fabric tensile strength • Fabric seam strength • Fabric bursting strength • Fabric tear strength • Fabric stretch and recovery 1- Fabric tensile strength depends upon:
Raw material
Yarn strength (twist: more twist for more strength)
Fabric construction (weave: plane weave is stronger than floats-satin, sateen which are weaker, Density: low density cause weave slippage which result in seam slippage)
Finish applied (resin finish improves weave slippage)
Adverse of “finishing” process 1.1- Measurement of fabric tensile strength: 1.1.1- Strip Test: (British) BS 2576 In this method a fabric strip is extended to its breaking point by a suitable mechanical means which can record the breaking load and extension. Five fabric samples both in warp and weft direction are prepared with each not containing the same longitudinal threads. Samples are prepared 60mm x 300mm and then frayed to get 50mm wide specimen. The rate of extension is set to 50mm/min & gauge length is 200mm. pretension is 1% of the probable breaking load. Any breaks that occur within 5mm of the jaws or at loads substantially less Load cell than the average should be rejected. The mean breaking force Constant and mean extension %age of initial length are reported. Weft-samples

Warp-samples

60mm

rate of elongation

50mm

300mm

300mm

Warp

clamps

Fixed jaw

Strip tester

25 mm

75mm

150mm

1.1.2- Grab Test: (U.S) ASTM D 1682 The grab test uses jaw faces which are considerably narrower tan the fabric, so avoiding the need to fray the fabric to width and hence making it a simpler and quicker test to carry out. The sample used is 100mm x 150mm. jaws are 25mm square which stress only the central 25mm of the fabric. A line is drawn 37.5mm from the edge of fabric to assist it in clamping so the same set of threads are clamped in both jaws. The gauge length is 75mm and speed is adjusted so that the sample is broken in 20±3s. In this test, there is a certain amount of assistance from yarns adjacent to the central stressed area so that the strength measured is higher than for a 25mm frayed strip test.

2- Fabric Seam strength: Grab test Seam failure occurs due to a number of causes: • Sewing thread either wears out or fails before the fabric does. • Yarns making up the fabric are broken or damaged by the sewing needle. • Seam slippage occurs. These problems depends the sewing machine used, sewing thread, sewing speed, size of sewing needle and stitch length.

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Abu Bakkar Marwat (05-NTU-05)

Physical Measurements on Fabrics

6th semester

2.1- Seam slippage: Seam slippage is the condition where a seam sewn in the fabric opens under load. Some of this gap may close on removal of the load but some of it may be a permanent deformation. 2.2- Causes of seam slippage: • Fabric made from slippery yarns (filament yarns-round cross section & smooth surface) • Low density- warp & weft interlacing is low • Seam details: (seam allowance, seam type, stitch type, stitch rate & stitch length allowance is more-more seam slippage, seam slippage is more in case of chin stitch than in lock stitch, normal stitch length-5 stitches per cm) • Type of sewing machine • Sewing needle number & sewing needle adjustment/height • Sewing thread used-thread having smooth surface cause seam slippage • High tension of sewing thread causes seam puckering 200

2.3- Seam slippage tests:

0

5

Force N 100

2.3.1- Seam strength test-BS 3320 Five warp and five weft specimens each 100mm x 350mm are used. Each sample is folded 100mm from Without seam one end and a seam is sewed 20 mm from the fold Measured line (using a special sewing thread and sewing A+6mm force machine settings), the folded part is then cut away 12mm from the folded edge and leaving the seam With seam 8mm from the cut edge. From this sample 150mm length without seam is cut (having same warp or weft A threads) and is stretched in tensile tester up to a load of 200N and a force elongation curve is drawn. The remaining sample with seam is then tested in 0 25 50 75 Elongation mm the same way making sure that the force elongation curve starts from the same zero position. Horizontal separation between the curves as shown in Fig. is then due to opening of the seam. A standard strength tester with 25mm grab test jaws and 75mm gauge length is used. In order to find the force required to open the seam, separation (A) of the curves at 5 N is measured and this distance (A) is added to the “seam opening” (6mm usually. Next a point is found where separation between the curves is “A+6mm”. The value of load at this point is the seam strength. If the curves do not reach the specified separation (A+6mm) below 200 N then the result is recorded as “more than 200 N”. The US Standards ASTM D 434 and ASTM D 4034 are very similar to the above method except that a load of 1 lbf (4.4N) is used for correcting for slack in the system instead of 5N. The required result is the load to produce a seam opening of 6mm (0.25in.).

100

2.3.2- Fix load method (seam slippage-grab test): Principle: A strip of fabric is folded and stitched across its width. A force is then applied to the strip at right angles to the seam using grab-test jaws and the extent to which the seam opens for a given force is measured. The force applied depends upon the end use of the fabric under test. Test force for ladies dresses, cushions and tickings-80N; for greater stresses such as in overcoats, suits and overalls-120N and for considerable seam strength as in upholstery-175N is used.

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Abu Bakkar Marwat (05-NTU-05)

6th semester

Physical Measurements on Fabrics

Method: Five samples each for warp and weft of 200mm x 100mm are used. Each sample is folded in a half and a seam is machined 20mm from the fold, using the special sewing thread and a stitch rate of 5 stitches per cm. The folded edge is then cut off 12mm from the fold line. 25mm wide jaws with a gauge length of 75mm and at a speed of 50mm/min are used. Load is increased to either 80, 120 or 175 N depending on the end use of the fabric and held at that value for 2min. The load is then reduced to 2.5 N and held at that value for 2min. The width of the seam opening at its widest place is then measured to the nearest 0.5 mm. The mean value for the war-wise and for weft-wise specimens is reported. With this method it is not always obvious where the opening starts and finishes. It also produces the problem of tests with no numerical results due to the seam or fabric failing or the test being stopped before reaching the required seam opening. 2.3.3- Upholstery seam slippage: (BS 2543) Five samples each for warp and weft of 200mm x 100mm are used. Each sample is folded in a half and a seam is machined 20mm from the fold, using the special sewing thread and a stitch rate of 5 stitches per cm. The folded edge is then cut off 12mm from the fold line. 25mm wide jaws with a gauge length of 75mm and at a speed of 50mm/min are used. Load the specimen in the jaws so that only the centre of the specimen is clamped as shown. Increase the load to 175N and hold at that for 2 min. reduce the load to 2.5N and hold for a further 2 min. measure the width of the seam opening at its widest place to the nearest 0.5 mm. give the mean value for warp and weft wise specimens.

25 mm

gap 100mm

Upholstery seam slippage

3- Fabric Tear strength: 3.1- Introduction: A fabric tears when it is snagged by a sharp object and the immediate small puncture is converted into a long rip. It is probably the most common type of strength failure of fabrics in use. It is particularly important in industrial fabrics that are exposed to rough handling in use such as tents, sacks and parachutes. Out door clothing, overalls and uniforms are types of clothing where tearing strength is of importance. 3.2- Measuring tearing strength: This property requires to measures the force to propagate an existing tear and not the force required to initiate a tear. A cut is made in the specimen and then the force required to extend the cut is measured. This is conventionally carried out by gripping the two halves of the cut in a standard tensile tester. 3.2.1- Single rip tear test: (ASTM D2261) The test is sometimes referred to as the single rip test, the trouser tear or in the US as the tongue tear test. 10 specimens are tested from both fabric directions each measuring 75mm x 200mm (3x8in.) with an 80mm (3.5in.) slit part way down the centre of each strip as shown in Fig. a. one of the ‘tails’ is clamped in the lower jaw of a tensile tester and the other side is clamped in the upper jaw. The separation of the jaws causes the tear to proceed through the uncut part of the fabric. The extension speed is set to 50mm/min (2in./min) or an optional speed of 300mm/min can be used. There are three ways of expressing the result: 1. The average of the five highest peaks 2. The median peak height 3. The average force by use of an integrator If the direction to be torn is much stronger than the other direction, failure will occur by tearing across the tail so that it is not always possible to obtain both warp and weft results. [email protected]

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Abu Bakkar Marwat (05-NTU-05)

Physical Measurements on Fabrics

6th semester

3.2.2- Wing rip tear test: (BS 4303) The wing rip test is capable of testing most types of fabric without causing a transfer of tear. During the test the point of tearing remains substantially in line with the centre of the grips. The design of the sample is also less susceptible to the withdrawal of threads from the specimen during tearing than is the case with the ordinary rip test. Five specimens across the warp and weft are tested using a constant rate of extension testing machine with the speed set at 100mm/min. the tearing resistance is specified as either across warp or weft according to which set of yarns are broken. The British standard (BS 4303) uses a sample shaped as in Fig. which is clamped in the tensile tester. The centre line of the specimen has a cut 150mm long and a mark is made 25mm from the end of the specimen to show the end of the tear. It is not suitable for loosely constructed fabrics which would fail by slippage of the yarns rather than by the rupture of threads. The results can be expressed as either the maximum tearing resistance or the median tearing resistance. The median value is determined from a force elongation curve such as that shown in Fig. and it is the value such that exactly half of the peaks have higher values and half of them have lower values than it. 3.2.3- Elmendorf tear tester: (ASTM D-1424) It is a pendulum type ballistic tester which measures energy loss during tearing. The tearing force is related to the energy loss by the following equation: Energy loss = tearing force x distance Loss in potential energy = work done The apparatus shown consists of a sector-shaped pendulum carrying a clamp which is in alignment with a fixed clamp when the pendulum is in the raised starting position, where it has maximum potential energy. The specimen is fastened between the two clamps and the tear is started by a slit cut in the specimen between the clamps. The pendulum is then released and the specimen is torn as the moving jaw moves away from the fixed one. The pendulum possesses potential energy because of its starting height. Some of the energy is lost in tearing through the fabric so that as the pendulum swings through its lowest position it is not able to swing to the same height as it started from. The difference between the starting and finishing height is proportional to the energy lost in tearing the fabric. The scale attached to the pendulum can be graduated to read the tearing force directly or it may give percentage of the original potential energy. The accuracy of the instrument depends on very carefully cutting of the specimen which is normally done with a dia. The range of the instrument is from 320gf to 3840gf in 3 separate ranges obtained by using supplementary weights to increase the mass of pendulum. When a fabric is being torn all the force is concentrated on a few threads at the point of propagation of the tear. This is why the force is involved in tearing are so much lower than those needed to cause tensile failure. Depending on the fabric construction threads can group together by lateral movement during tearing, so improving the tearing resistance as more than one thread has to be broken at a time. The peaks that are same on the load extension curve fig. are more often from the breaking of a group of threads than from the individual ones. The bunching of threads is also helped by the ease with which yarns can pull out length wise from the fabric. The ability to group is a function of looseness of yarns in the fabric. Weave has an important effect on this: twill or a 2/2 matt weave allows the threads to group better thus giving better tearing resistance than a plane weave. High sett fabric inhibit thread movement and so reduce the assistance effect resin treatment such as crease resistance finishes which cause the yarns to adhere to one another also have the same effect. The tensile properties of the constituent fibres have an influence on tearing resistance as those the high extension allow the load to be shared where as fibres with low extension such as cotton tear easily. [email protected]

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Abu Bakkar Marwat (05-NTU-05)

Physical Measurements on Fabrics

6th semester

4- Fabric Bursting strength: Bursting strength is a method of measuring strength in which the material is stressed in all directions at the same time and is therefore more suitable for materials such as knitted fabrics, lace or non-woven. Fabrics used in parachute, filters, sacks and nets are simultaneously stressed in all directions during service. In service, a fabric is more likely to fail by bursting than by a straight tensile fracture; one example is the stress present at elbows and knees of clothing. During a test a fabric fails across the direction which has the lowest breaking extension. 4.1- Diaphragm Bursting test: (BS 4768) In this test the fabric to be tested is clamped over a rubber diaphragm by means of an annular clamping ring and an increasing fluid pressure is applied to the underside of the diaphragm until the specimen bursts. The operating fluid may be a liquid or a gas. Specimens of two sizes are used; 30mm & 113mm. the specimen with the larger diameter fail at lower pressure (approximately 1/5 of the 30mm diameter value). The standard requires 10 specimens to be tested. Procedure: The fabric sample is clamped over the rubber diaphragm and the pressure in the fluid increased at such a rate that the specimen bursts within 20±3 s. the extension of the diaphragm is recorded and another test is carried out without a specimen present. The pressure to do this is noted and then deducted from the earlier reading. Mean bursting strength “kN/m2” Mean bursting distance “mm” The US standard “ASTM D 3786” uses an aperture of 1.22± 0.3in. (31±0.75mm). Disadvantage: The disadvantage is the limit to the extension that can be given to the sample because the rubber diaphragm has to stretch to the same amount. Knitted fabrics, for which the method is intended, often have a very high extension. 4.2- Ball Bursting Test: In this test a 25 mm diameter steel ball is pushed through the stretched fabric and the force required to do so is recorded. The advantage of the test is that it can be carried out on a standard universal strength tester with a suitable attachment. There is also no limit to the amount a sample can be extended as there is with the diaphragm test. The US standard ASTM D 3787 specifies a 1.0000 in. diameter ball (25.4mm) with a clamp diameter of 1.75 in. (44.45mm) and a speed of 12 in/min (305mm/min). The British Standard for coated fabrics BS 3424 specifies a very similar dimension with a ball diameter of 25.2mm, a clamp diameter of 45mm and a testing speed of 5mm/s. an example of a compression fixture to carry out this test is shown. 5- Fabric Stretch and Recovery Properties: Certain types of clothings, particularly sports wear, are made to be a close fit to the body and does not appear baggy and this stretch has to be followed by the complete recovery of the original dimensions. Typical values of stretch that are encountered during the actions of sitting, bending, or flexing of knees and elbows are:    

Back flex = 13-16 % Elbow flexes, lengthwise 35-40 %, circumferentially 15-22 % Seat flex 25-30, across 6 % Knee flexes lengthwise 35-45 %, circumferentially 12-14 % [email protected]

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Abu Bakkar Marwat (05-NTU-05)

Physical Measurements on Fabrics

6th semester

Standing at rest is taken as the zero value for the purpose of calculating these increases. A stretched fabric is expected to recover to within 3% of its original dimensions.

5.1-ASTM D 3107 (for woven fabrics) This method is used to determine the amount of fabric stretch and fabric growth after a specified extension of fabrics woven in whole or in part from stretch yarns. 5.1.1-Lot Sample: A fabric roll at random is selected from the whole consignment, called lot sample. 5.1.2-Laboratory sample: Cut one meter laboratory sample after discarding first 1-2 meter fabric. 5.1.3-Test specimen:  Cut six test specimens (3 pairs) 64x560mm along the width of fabric so that there is no repetition of lengthwise yarns.  Each piece is then frayed to 50 mm.  So specimen dimensions = 50 x 560 mm, with one edge folded 32 mm and stitched at 25mm from the folded line and having 2 lines at centre 500mm apart (A = 500mm). A 10mm slit is made at the centre of folded line. 5.1.4-Conditioning: Condition the sample in standard conditions: 65±4% RH, 20±2°C 5.1.5-Procedure: 1. Clamp one end of the specimen in the top clamp of the stretch tester such that folded sewn loop hang freely. 2. Insert dowel pin through the loop and hang a weight of 4 lb for 5s and then remove. Repeat this for 3 times. 3. At the 4th stretch, the load is held for 10s and distance between the lines is measured to nearest 1mm. this length is ‘B’. 4. Then remove the weight and bottom clamp to relax the fabric. After 30±1s, measure the distance between two lines. This length is ‘C’. (or C30s. similarly growth for 30min-C30min and 1 hr-C1hr is calculated) 5. All the procedure is repeated for other 2 specimens. 6. Calculate for each specimen the percentage fabric stretch and the percentage immediate fabric growth by the formulas:

Fabric growth % =

B−A A C−A

A

× 100

____ (1)

500mm

Fabric stretch % =

× 100 ____ (2)

Where 64x56

50x560

0 A = original distance-500mm B = distance between lines when specimen is under 4-lb load C = distance between the lines measured after release of the load as directed in ‘4’.

4 lb/1.8Kg

Fabric growth after stretching to specified extension: 1. The second specimen of each pair is stretched to a fixed extension which is taken to be 85% of the stretch measured in ‘3’ (length ‘B’) 2. Hold the specimen in the extended position for 30±1 min after which the load is removed and growth is measured when specimen is relaxed for 30±1s and also after 30±1 min. 3. Equation ‘2’ is used to calculate the growth.

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Abu Bakkar Marwat (05-NTU-05)

6th semester

Physical Measurements on Fabrics

5.2-ASTM D 2594 (for knitted fabrics) This test is carried out for knitted fabrics havinmg low power. The fabrics are stretched to a fixed extensions for 2h and the growth measured. The amount of extension is governed by the end use of fabric as shwn in the table.

Loose fitting (comfort stretch) Form fitting (semi-support)

Stretch % Course ways 30 60

Stretch % Wales ways 15 35

5.2.1-Laboratory sample: 2 m length in lengthwise is taken after removing first 1m length. 5.2.2-Test specimen:  From each laboratory sample, 5 wale-wise (length wise) and 5 course wise (widthwise) test specimens 125±3 x 500±10 mm are taken. These specimens are cut from the laboratory sample by starting 25mm from the edge.  Fold each specimen in half lengthwise forming a loop and sew the edges opposite the fold together 6-13mm from the cut edges.  Two lines are drawn 125±3 mm apart on the central section of one face of the looped specimen. This length is taken as ‘A’. 5.2.3-Conditioning: These specimens are then conditioned under standard conditions at 65±4 %RH and 20±2°C. 5.2.4-Procedure: 1. The specimen is mounted on the tester such that sewn end is on the upper hanger. 2. Extend the specimen loop to the amount specified in Table. E.g., for loose fitting course wise, 30% of ‘A’ stretch is given i.e. 162.5 mm 3. Allow the loop to remain in the extended position for 2h. 4. After this the specimen is relaxed and growth is measured after 60s (B) and 1h (C). 5. In the same way 3 specimens for each the wale and course directions are tested. 5.2.5-Fabric Stretch: Fabric stretch can be measured at a fixed load. 1. Place a new specimen in the stretch testing equipment. 2. The specimen is four times stretched between 0-5 (0N-22.2N) lbf for loose fitting and 0-10 lbf (0N-44.5N) for form fitting. 3. Continue a 5th cycle by holding the specimen at their specific load for 10s then measure the distance between the lines. This is ‘D’ 4. In the same way two specimens are tested each for wales and course wise. Fabric stretch and growth are calculated as:

Fabric Stretch % =

A C−A

A D− A A

× 100 × 100

125±3 mm

125±3 mm

Fabric Growth1 h % =

B−A

500±10 mm

Fabric Growth60s % =

× 100

Where A- original length between the lines, i.e. 125±3 mm B- distance between the lines after removing the load and relaxing for 60s C- distance between the lines after removing the load and relaxing for 1 h D- distance between the lines when the specimen is under tension

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