SOUTHEAST UNIVERSITYDepartment of textile Engineering

Course Title: Textile Testing & Quality Control-I

Course Code: TEX-2031

Assignment on Tensile Strength

Submitted To:

S.M. Masum AlamLecturer

Department of Textile

Submitted By:

Md. Mazadul Islam Ripon ID: 2013000400016Batch: 22 Sections: A

Submission Date: 20-12-2014

Contents:

Introduction Tensile Strength according to material Tensile Strength Test of Fiber Latest fiber testing instruments

Advanced Fiber Information System (AFIS) Fiber contamination tester (FCT) Stelometer Pressly Fiber Strength Tester

Yarn Strength Test Uster Tester Lea Strength Tester

Tensile Strength Test of Fabric Strip Test (British Standard) Grab Test (US standard)

Conclusion Reference

Tensile Strength : Tensile strength is the ability of a material to withstand a pulling (tensile) force. It is customarily measured in units of force per cross-sectional area. This is an important concept in engineering, especially in the fields of material science, mechanical engineering and structural engineering.

The ability to resist breaking under tensile stress is one of the most important and widely measured properties of materials used in structural applications. Tensile strength is important in the use of brittle materials more than ductile materials.

Corrosionpedia explains Tensile Strength:The tensile strength of a material is the maximum amount of tensile stress that it can take before failure, such as breaking or permanent deformation. Tensile strength specifies the point when a material goes from elastic to plastic deformation. It is expressed as the minimum tensile stress (force per unit area) needed to split the material apart.

For example, if a metal rod one square inch in cross section can withstand a pulling force of 1,000 pounds but breaks if more force is applied, the metal has a tensile strength of 1,000 pounds per square inch. The tensile strength for structural steel is 400 megapascals (MPa) and for carbon steel is 841MPa. Tensile strength is different for different densities of steel.

There are three types of tensile strength:

1) Yield strength  - The stress a material can withstand without permanent deformation2) Ultimate strength  - The maximum stress a material can withstand3) Breaking strength  - The stress coordinate on the stress-strain curve at the point of rupture.

Tensile Strength according to material:

1. Fibera) Single fiber strength testb) Bundle fiber strength test

2. Yarn

a) Single yarn strength testb) Lea yarn strength test

3. Fabric

Tensile Strength Test of Fiber:In this, HVI, AFIS & FCT play an important role, so their principle working method, working time and sample requirements are given. It gives various new technologies employed in printing, which will give an idea about the new testing methods and procedures.

Machine speeds and settings need to be matched to the properties of the fiber in process. With the annual production of cotton lint approaching 100 million bales, with spinner's demands & for increasingly high quality, and with the testing of every bale becoming almost universal in export mills, cotton testing has never been more important.

The following observations have made the cotton testing an important one.

Raw material typically accounts for half of the cost of making cotton yarn. Competitive man-made fibers can be made to more precise specifications. Scientific blending, based on knowledge of each bale, leads to cost & quality effective

processing. Machine speeds and settings need to be matched to the properties of the fiber in process. Demands on the yarn quality are increasing.

Latest fiber testing instruments

Latest trend in the fiber testing was the developments of a single instrument in which all the major testing parameters can be tested. The instruments we discuss in this category are:

High volume instrument (HVI) Advanced fiber information system (AFIS) Fiber contamination tester (FCT) Stelometer Pressly Fiber Strength Tester

High volume instrument:

High volume instrument systems are based on the fiber bundle strength testing, i.e., many fibers are checked at the same time and their average values determined. Traditional testing using micronaire, pressley, stelometre, and fibro graph are designed to determine average value for a large number of fibers, the so called fiber bundle tests. In HVI, the bundle testing method is automated. Here, the time for testing is less and so the number of samples that could be processed is increased, quite considerably. The influence of operator is reduced.

The HVI testing is attractive due to the classing of cotton and the laying down of a mix in the spinning mill. This HVI testing is suitable for the extensive quality control of all the bales processed in a spinning mill. The mill is in a position to determine its own quality level within a certain operating range. The time for testing per sample is 0.3 minutes. It is best applied to instituting optimum condition for raw material. About 180 samples per hour can be tested and that too with only 2 operators.

Principles of fiber testing using HVI

Sample preparation

The fibro gram method is preferred while preparing the sample for fiber length estimation. The sample has to be presented to the measuring zone by clamping the fibers at a random catch point. Here the fibro sampler is used.

The test specimen obtained using the fibro sampler/comb combination is a beard of fibers with individual fibers projecting to different length from the clamping point. In HVI, the strength testing is also done on the same beard of fibers with individual fibers projecting to different lengths from the clamping point.

In HVI, strength testing is also done on the same beard of fibers prepared for length measurement. While using the low volume instrument -fibro stelo for strength measurement, the sampling is done on the separate fiber bundles, of which 15 mm long is prepared after remounting the short fibers by combing. For micronaire testing, a sample of cotton weighing approximately 10 grams is used. For color testing, random mass of fibers sufficient to cover the test window is used for measurement.

Measurement of different parameters using HVI & LVI

Length

Both the high volume instrument and the low volume instrument use an optical principle of determination of fiber length. A narrow rectangular beam of light is allowed to fall on the specimen beard. The attenuation of Light through the specimen at different areas of the beard is measured and used to obtain the different span length values. In the HVI, the tip of the beard is scanned first and scanning gradually proceeds towards the clamp while in the LVI, the beard is scanned in the opposite direction. In both the instruments, the span length values are obtained by actual measurement.

Strength

In the LVI, the fibrostelo is used. This module uses the pendulum lever principle of loading the specimen to estimate the fiber strength characteristics. A random sample of cotton fibers is prepared, short fibers being removed by combing so that all the fibers in the test specimen extend all the way through the jaws.

Breaking tenacity in g/tax = (breaking load in kg/ sample weight in mg) x 15 mm.

HVI Strength Measurement

HVI uses the "Constant rate of elongation" principle while testing the fiber 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 problem is overcome in the HVI by positioning the jaws and breaking the fibers at a constant "Amount" location across the beard. By breaking the fibers at a constant amount location, it is made sure that the samples are broken with a constant number of fibers between the jaws.

Therefore, raw data strength is directly proportional to the force to break the fibers. The raw data so obtained are then adjusted to desired Levels by testing samples of designated values. In order to make the estimation of the specimen linear density accurate enough, a micronaire correction factor is normally introduced so that the strength values are not affected by variations in micronaire.

Advanced Fiber Information System (AFIS):

Advanced Fiber Information System is based on the single fiber testing. There are two modules here, one for testing the number of naps and the size of naps, while the other one is used for testing the length and the diameter. Both modules can be applied separately or together.

With the introduction of AFIS, it is possible to determine the average properties for a sample, and also the variation from the fiber to fiber. The information content in the AFIS is more. The spinning mill is dependent on the AFIS testing method, to achieve the optimum conditions with the available raw material and processing machinery. The AFIS-N module is dealt here and it is basically used for counting the number of naps and the size of naps. The testing time per sample is 3 minutes in AFIS-.N module.

This system is quick, purpose oriented and reproducible counting of naps in raw material and at all process stages of short staple spinning mill. It is thus possible, based on forecasts supervisory measures and early warning information to practically eliminate subsequent complaints with respect to finished product. The lab personnel is freed from the time consuming, delicate and unpopular, proceeding of nep counting. Personnel turnover and job rotation no more affects the results of the nep counting. The personnel responsible for quality can now at least deal with the unpopular naps in a more purpose-oriented manner than ever before

Figure:

AFIS -Working principle

Advanced Fiber Information System (AFIS)

Source: International Textile Centre

A fiber sample of approximately 500 mg is inserted between the feed roller and the feed plate of the AFIS-N instrument Opening rollers open the fiber assembly and separate off the fibers, naps, trash and dust. The trash particles and dust are suctioned off to extraction. On their way through the transportation and acceleration channels, the fibers and naps pass through the optical sensor, which determines the number and size of the naps.

The corresponding impulses are converted into electrical signals, which are then transmitted to a microcomputer for evaluation purposes. According to these analyses, a distinction is made between the single fibers and the naps. The statistical data are calculated and printed out through a printer. The measuring process can be controlled through a PC-keyboard and a screen.

Time requirement:

It can be evidenced that the rest Its are provided very quickly using the AFIS measurement method and this with reference to approximately the same weight of sample material. This to be particularly the case when one compares the AFIS-N method with the frequently- used manual/ visual ASTM method. The savings are 150 with raw cotton and 1:25 with draw frame sliver.

  Fiber Contamination System (FCT):

The FCT system is used for testing stickiness, naps, trash and seed coat fragments. The sample in the form of bundle is fed into a self-cleaning, micro carding device integrated in the FCT, to produce about 10m of transparent web in order to expose the impurities and contaminants in the best way possible. An area of 1 sq. m per sample is tested.

Firstly, the web is analyzed by a machine vision system for the presence of trash, naps and seed coat fragments and then they are pressed between the 2 stickiness crush rollers in the same manner as with the crush rolls of the commercial cards. The cotton web removed by the vacuum is then deposited on the stickiness crush rollers. They are examined by a laser signal analysis system for determining the stickiness content. Time taken for one sample is 40 seconds.

The advantages are:

1)    Major contaminants like stickiness, seed coat naps and fiber naps are also considered as parameters for trading cotton.

2)    Evaluation of performance of the preleasing systems such as cards, comber etc., for determination of their optimum operational setting and efficiency are done.

Stelometer (CRL) :

1. Capable of measuring strength as well as elongation of fiber bundle.2. Works with Pendulum lever principle.3. The loading of the specimen is carried out by a pendulum system, which is mounted in

such a way that it rotates about its C.G.4. It eliminates the inertia effects associated with normal pendulum principle.5. The beam and pendulum start in a vertical position but the C.G. of beam is such that

when it is released the whole assembly rotates.6. The speed of rotation is controlled by adjusting the dashpot.

Figure:

Pressley Fiber strength tester :

1. The beam AB is pivoted at O.2. When B rises, the clamp C1 moves upwards.3. Initially the beam have a slight inclination of a few degree to the

horizontal.4. The heavy rolling weight (W) when released from the catch, it

rolls down the beam.5. A 'O increases until the fibers break.6. As soon as the break occurs, the arm AO drops

and the brake arrangement stops the carriage instantly.

7. The distance A'O is the measure of breaking force. The scale is directly graduated on the beam AB.

8.

The load on specimen (p) ∞ A’O, so the rate of loading is government by the speed of rolling of wt. In normal condition the velocity gradually increase as it roll down and thus the rate of loading

increases throughout the test. If we can control the velocity of rolling wt. by a specially made device, we can achieve CRL test condition. In HVI, this principle is used.

Integrated indices of fiber quality :

If a versatile measure of cotton quality can be quantified and universally accepted, it would be enormously valuable in both technical and commercial applications. Numbers of different cottons, such as bales in a warehouse, are much easier to compare if each has one descriptive number rather than several. A single-figure index should meet the following criteria:

It is based on common HVI results, and should not require purchase of additional instruments. It reflects a balance between market forces and technical considerations.

Is, as often happens, more or fewer properties than usual are tested, the estimate is unbiased, i.e. for average cottons the premium or discount (p/d) is unchanged

Yarn strength test:

(i) Single yarn strength:Intron, Uster etc. 500mm gauge length and speed adjusted so that the time to break is 20 ± 3sec.(ii) Skein Method (Lea Strength):Advantages:

It tests a long length of yarn in one test.

Yarn is expected to break at its weak spots, so give more realistic strength values.

Same hank can be used to measure yarn count.

Disadvantages:

Result depends on friction between yarn and also between yarn and hook.

No measure of strength variability.

Uster Tester:

Uster Technologies, in its industry often called Uster, is a Swiss manufacturer of analytical instruments and on-line monitoring systems for the textile industry, based in Uster, Switzerland. It emerged as a management buy-out form of the Zellweger Luwa Group in 2003 and is a now a publicly owned company with international subsidiaries.

Uster Technologies is traded on the SIX Swiss Exchange in Zurich.

Products and services:

Uster Technologies mainly produces laboratory and on-line systems used to measure and control the quality of fibers and yarns.

For cotton ginning, classing and trading:

Modern, industrial cotton gins often operate with sensors by Uster, to control their process and to the resulting fiber quality.

Cotton classing is required to measure and classify each cotton bale according to its specific physical attributes. Measurement information produced by Uster's HVI (High Volume Instrument) covers following parameters: fiber length, length uniformity, fiber strength, fiber maturity, short fiber content, micronaire (fiber fineness), color grade, leaf and extraneous matter.

When cotton is traded, its value is determined by the above-mentioned quality parameters, as measured by the HVI in the classing agencies. Hence Uster’s HVI has defined a set of standards for a large part of all cotton trades worldwide.

For yarn production:

Uster products are used in the spinning mill for measuring and analyzing the quality of the raw materials (i.e., fibers of different materials), intermediate products (i.e., sliver, roving) and final product (i.e., yarn) along their entire manufacturing process.

Most important process parameters a spinning mill has to control are: quality of the incoming fibers, yarn evenness, hairiness, tensile strength and elongation, contamination with disturbing materials, twist, friction, etc. By measuring these parameters, the instruments can be used as tools for a mill-wide quality assurance process.

An overview of Uster products applied in the spinning mills:

The “Uster Tester”, a laboratory system for the measurement of evenness, thick places, thin places, neps, hairiness, diameter, dust, trash, fineness of yarns

Yarn tensile testers - at conventional (5m/min) and high speeds (400m/min) Yarn fineness tester Yarn twist tester Yarn friction tester Single fiber measuring system (AFIS = Advanced Fibre Investigation System) Fiber bundle measuring system (HVI) Yarn clearer (Uster Quantum), which is mounted in the automatic winding machine, i.e., “on-line”

While developing these different testing instruments, often the first of their kind, Uster often also had to invent either the measuring method or the suitable measurement parameters.

Figure:

Yarn strength and C.S.P. by lea strength tester : C.S.P is the product of English count and strength of yarn in pound.

i.e. C.S.P = Strength of yarn in pound x Count in English system. Again, English count is the no. of hanks in 840 yards length per 1 pound weight of yarn. i.e. Count =(L* w)/ (l*W).

Here, L = length of the sample l = unit length of the system W = wt. Of the sample w = unit wt. of the system. A lea strength tester measures the strength of one lea yarn. One lea means 120 yards. Strength is measure of the steady force necessary to break a material and is measured in pound . The M/C works in constant rate of extension. Assuming the specimen to be extensible and an absence of any dynamic effects, we get from the figure:Fr=Mgr +MgRsinq. As the value of MgR and rare constant, therefore according to the applied force the M/C dial gives us the strength in lb on the basis of this q.M/c specification:

1) The Lea Strength Tester 2) Goodbrand & Co. Ltd. 3) Capacity: 100lb

Sample: 1. Size - One lea cotton yarn (1 lea =120 yards). 2. No. of sample – 20

Figure:

Working procedure:

1. At first one lea cotton yarn is measured by wrap reel and in this way 20 samples are taken for testing.

2. Now, the first sample is fixed with the upper jaw J1 and the lower jaw J2.

3. The m/c is started and observed the dial until the sample is torn out.

4. When the sample is torn out the m/c is stopped and the reading is taken.

5. By this way the others’ reading are taken.

6. Then all the samples are weighted and counts are calculated.

7. C.S.P of the all samples are calculated.

8. At last average and CV% are calculated.

Tensile Strength Test of Fabric:Tensile strength of the sample was determined by using ASTM method. This test method covers the grab and modified grab test procedures for the determining the breakage strength and elongation of the most textile fabrics. The grab test procedure is applicable to woven, non-woven and felted fabrics. While the modified grab test is used primarily for woven fabrics. This test method is not recommended for glass fabrics or for knitted and other textile fabrics which have high stretch.

Test to determine the breaking strength and elongation of most textile fabrics. Not recommended for knit fabrics or fabrics with high stretch value. To determine tensile strength of fabric two type of test are done. They are:

1. Strip Test (British Standard)

2. Grab Test (US standard)

Working Procedure:

1. The specimen was mounted securely in the clamps of the testing machine. Take care that the specimen is centrally located and the long dimension is as nearly parallel as possible to the direction of force application. Be sure that the tension on the specimens is uniform across the clamped width.

2. Mark across the specimen at the front inner edge of each jaw to check for specimen slips. When slips occur, the mark will move away from the jaws edge.

3. The machine was operated and the specimen were broken one by one first warp wise and then weft wise.

4. The breaking force was recorded from the mechanism proved for such purpose.

5. If specimen slips in the jaws, or breaks, at the edge of or in the jaws, or if for any reason the result fall markedly below the average of the set of specimens, discard the results and take another specimen. Continue this until the required number of except able breaks has been obtained. In the absence of other criteria for rejection a jaw break, any break occurring within 5 mm of the jaws which results in the value below 50 % of the average of all other break should be discarded. No other break should be discarded unless it is known to be faulty.

Strip Test (British Standard):

Sample Preparation:

1) 5 samples for warp direction

2) 5 samples for weft direction

First taken a sample of (60mmx300)mm and then frayed down to (50mmx300)mm

Figure:

Test Procedure:

1. Sample is clamped in the jaws 2. CRE 500mm per minute loading 3. Gauge length 200mm

Test Result:

Mean breaking force Mean elongation at break

Grab Test (US Style):

Sampling Preparation:

Sample size: 100x1500mm Jaw width – 25mm Gauge length- 75mm

Figure:

Test Procedure:

1. Sample is clamped between the jaw 2. Speed is adjusted so then the sample is broken in 20±3 seconds.

Test Results:

Mean breaking force. Mean elongation at break. 

Conclusion:

The above discussion gives an idea about main latest fiber testing techniques using HVI, AFIS, FCT and this concludes that one can achieve higher accuracy with least time in this system. Fiber testing is an important part in the final product, so it is clear one can achieve great quality with accurate testing techniques, which were discussed in this paper. Apart from this, various methods are also included which will give proper results in fiber testing.

When considering from economical point, it advisable to u medium volume instruments (M\ & low volume instrument (LVI) to achieve the same quality with medium cost. With present depression in textile field, it is essential to achieve good quality raw material by good testing techniques and achieve good growth in textile field. It is essential in this competitive global market survival with this latest fiber testing techniques.

Reference:

1. www.Textilelearner.com 2. www.Wikipidea 3. www.Nptel.com 4. www.truetzschler.de/2.Produktprogramm/ 5. www.uster.com/applications/applica-tions/a_ descr _qp.htm 6. http://www.michas-Ievcot.com 7. www.mark-10.com/ 8. www.Encyclopedia