IIndian Journal of Textile Research

Vol. 9,iJune 1984, pp. 46-54

Comparison of Different Tearing Test Methods

I C SHARMA & D ADHIKARY

The Technological Institute of Textiles, Bhiwani 125022

Received 24 March 1983; accepted 4 February 1984

A comprehensive comparison of the major tear test methods in use (single rip test, tongue double rip test, wing rip test,trapezoid test, impact tear test and wound bursting strength test) has been made with the objective of assessing their relative

Inerits and establishing correlations among them. The fabrics used for the purpose were polyester-viscose blends. Single rip testhas been found to be the most suitable one for carrying out a tearing test. Single rip, double rip and impact tear tests showsimilar performance and provide almost identical values of fabric characteristics, while the wing rip test differs onlymarginally. The trapezoid test shows a relatively poor correlation with these test methods, and the wound bursting methoddiffers widely from them.

A number of methods are employed for determiningthe te~r slnmgth of fabrics, but no attempt seems tohave been made to establish definite correlations

among these methods. The reason is that the tearfailure of materials depends mainly on the conditionsof usb or testing, the stress pattern being largelydetermined by the variables, which are characteristicof the 'm~thod used, or more precisely, of the specimengeometry at disposition of the operator rather than ofthe m~terial under test. In the present investigation, acomparison of most of the established tear testmethods has been attempted with the objective of

workibg out correlations among them. In doing so,however, it was apprehended that a possible difficultycould 'arise while comparing the test results obtainedusing different test procedures due to the widevariation in specimen dimensions used in thesemethods, especially the tear length, tail length and tailwidth.

ThJ different test methods included in the study are:singlel rip test, tongue double rip test, wing rip test,trapezoid test, impact tear test (performed usingElmendorf tester) and wound bursting strength test

(burst~ng tear test). The rip test has been taken as thestand~rd method and the results of the other test

methods have been compared with those obtained bythis method.

An,attempt has also been made to study the tearbeha~iour of fabrics with changes in blendcomposition and fabric density. In .the first case,polyester and viscose were chosen as the componentfibres .of yarn and their mutual proportions changed.In the second case, the pick level was changed.

46

Materials and Methods

Nine fabric samplt:s wen: prepan:u from yarns ofthree different polyester-viscose blends, viz. 48/5f, 60/40 and 80/20, using them in both warp and weft ways.This was done to observe the effect of blend

composition on the tear strength of the fabric. Theexperimental conditions employed were as follows:ends/in, 64; picks/in, 56; yarn count. 2/365 (for bothwarp and weft); and TPI, 20 for single and 16 for all thesamples. Two more samples were prepared with twomore pick levels, namely 48 and 52, keeping the yarnblend composition the same (60/40: PIV) for both warpand weft and other variables unchanged. In thenomenclature of the sample codes (Table 1), the firstdigit denotes the warp blend composition(polyester: viscose), i.e. A-60/40, B-80/20 and C-48/52,the second digit the picks/in, i.e. P-48, Q-52 and R-56,and the third digit the weft blend composition, i.e. X­60/40, Y -80/20 and Z-48/52.

Prior to testing, all the samples were conditioned in astandard_atmosphere (RH, 65% and temperature, 27± 2°C) for 48 hr. Standard test methods as per theIndian standard specifications 1 were used todetermine the yarn and fabric characteristics. For yarntesting, skeins of 120 yd weft yarn were prepared andthe average count was tested on Knowle's balance. The

average warp yarn count was tested on a quadrantbalance. Yarn crimp for both warp and weft wasmeasured on Eureka crimp tester (Type FT-07) taking109 tension and 20 cm test length. The single yarnstrength and elongation at break were measured on

Instron tensile tester. The cross-head speed was soadjusted that rupture of the specimen occurred in 20

SHARMA & ADHIKARY: COMPARISON OF DIFFERENT TEARING TEST METHODS

± 2 see; the speeds were 250, 300 and 350 mm/min for48/52, 60/40 and 80/20 polyester-viscose blendsrespectively.

Wound bursting strength was measured on Eurekabursting strength tester. The average strength of eachsample was found from 10 observations. Elmendorftester (range 0-6400 g) was used for the impact tear test.

Instron tensile tester was used for single rip, tonguedouble rip, wing rip and trapezoid tear tests. The cross­head speed and the ratio between the cross-head speedand the chart speed were kept as 100 mm/min and 2: 1

respectively. Clamping lengths were 100, 180, 1150 and25 mm for single rip, double tongue rip, wing rip andtrapezoid tear tests respectively. The full scale load was10 kg for single rip and wing rip tests, 20 kg for tonguedouble rip test and 50 kg for trapezoid tear test. Theaverage tear strength of each sample was found from 5observations in both warp and weft ways.

Measurement of yarn withdrawal force-Keepingparity with Taylor's experiment, a strip of fabric (5 inlong and 3 in wide) was taken. Leaving 2 in from oneend of the longer sides to allow the specimen to begripped by the fabric jaws, and another 0.5 in for aclearance from the jaw line, a transverse cut was madeacross the width of the specimen. The specimen wasthen marked across its width at a distance of 1 in from

the transverse cut and all the crossing threads in theremaining portion of the specimen were unravelled, sothat the length of each of the freed longitudinal yarnsfrom the marked line was 1.5 in, the rear end of the

specimen in the fabric form being already gripped by apair of fabric jaws. The yarn clamp, .initially beingseparated from the jaws by a distance of 2 in, was thenmoved apart until the said yarn was completelywithdrawn from the strip; the force required to remove

the yarn was recorded in the autographic device. Threesuch specimens from fabric samples BRX, BR Y andBRZ were tested in the filling direction.

Effect of dimensional changes on tear strength­Specimens were prepared from the sample CQY withchanges in tail width, tail length and tear length tostudy the effect of these variables on the tear strength.This experiment was carried out to facilitate

comparison of different tear test methods, taking riptest as the standard, because the specimen dimensions

in other tests varied widely .• \. ;.; .Selection of methodfor interpretation of clii:lrts- The

average method is tedious and time-consuming, aseach peak load in the chart is required to be measured.This is not very logical too, because it does not ensure

the propagation of tear through the fabric.The use of average method becomes further

undesirable when pendulum type machines are usedfor testing, as the charts obtained from such machinesdo not show the details of fluctuations and show only a

single maximum where inertia error is too high. In fact,the records obtained in many cases in pendulum typetesters do not allow the treatment of data to be carriedout as referred to in the standard handbooks. In the

present study, Instron tester has been used where sucherrors are not encountered and so the argument putforward in the last paragraph does not hold muchground. Yet, the reason mentioned earlier is sufficientto warrant the acceptance of the average method. Thesame reason applies to the energy method. In addition,this method involves some other complications arisingfrom the extensibility of the fabric.

Median method loses its ground the same way as theaverage method. Besides, it involves some error in thedetermination of the sin~le rip strength using Instrontester in that some minor maxima always occur in thechart, which do not essentially indicate yarn rupture.The test results from Instron tester show lower values

than those from pendulum type testers. The relationhas been given by Tur12 as:

Tearing strength (pendulum type) = 1.10 x Tearingstrength (Instron type)

In such cases, the single highest peak value will bedesirable, because it ensures tear propagation. Butthen, the particular single value in question may besaid to have occurred merely due to chance, which doesnot provide sufficient accuracy. Hence, considering allpros and cons, it seems that the average of five highestsingle values will be best fitted for the purpose and itwill ensure tear propagation as well as a high level ofaccuracy. The average often single highest peak valuesmay provide better accuracy, but then the differencewill be marginal. Turl's experimental result2 showsthat the ratio often single highest peak values to five ofthe same is 0.978. Hence, use of five instead of ten

values is justified.In fact, the method accepted in the present study

tallies with the US Federal specification for the

trapezoid test. TurP suggested picking up of fivehighest peak values at five equal intervals. But this alsodoes not seem to be logical in that some of the peakvalues taken at five equal intervals may be lower thanthe average of five highest peak values taken from theentire load diagram (keeping no bar on the interval),because a single interval may be comprising five ormore values, which are higher than those in the rest ofthe diagram. In that case, the average value worked outby his procedure will in no way ensure tearpropagation through the fabric.

Results and Discussion

The tear mechanisms of single rip, double rip, wing

rip and impact tear tests show that the number of yarnsin the ladder of a del at the tear locus depends upon the

extent of yarn slippage and yarn extension. With a

47

INDIAN J. TEXT. RES., VOL. 9, JUNE 1984

·~

!

highel!polyester content in the yarn, the extensibility ofthe yarn increases. Consequently, the number of activethreads in the del increases and hence contributes moreto th~ system in supporting a higher load. The tearmechanism in the trapezoid tear test too is governedmostly by the ultimate elongation of the yarns or inother words by the unextended initial length andexten~bility of the yarns. However, its effect on tearingstrength could be better judged from the equationgiven by Teixeira et al.4 for single rip test and from the

equatifns given by SteeleS and Hager et at.6 fortrapezoid tear test. Though Taylor's equation 7 takes agood account of yarn strength, it ignores the role of

yarn ~tensibility.In t;e case of wound bursting test, the role of yarn

extensibility induces some complicacy and does notlend itself easily to critical analysis, primarily becausethe threads in one direction tend to prevent the fullapplication of load in the other. Hence, the ratio ofyarn extensibilities along and across the direction oftear, or in other words, the elongation balance betweenthe tW<i>sets of threads right angled to each other is an

impor~ant factor in determining the bursting tearstreng1lh(Table 1). To better understand the matter, wefocus attention on Table I to mark out three values of

warp tfaring strength for three different warp blend

compositions, viz. 48/52, 60/40 and 80/20, when theweft blend compositions are the same, i.e. 60/40. Thevalues are 5.60, 5.93 and 6.43 respectively. In the firstcase, where the warp blend is 48/52 and the weft blend60/40, i.e. the warp yarn has got a lower extensibilitythan the weft yarn4, application of force causes thewound warp to rupture before the maximum extensionof weft yarns has occurred. So, the contribution of theweft yarns in offering resistance to the applied load ispoor. In the second case, where the extensibility ofwarp yarns is elevated to the level of that of the weftyarns (the blend compositions being 60/40 for both),the warp yarn distends more than that in the first casebefore it fails and hence utilizes more weft services,leading to increase in tearing strength. In the thirdcase, where the warp yarn extensibility has beenincreased further, exceeding that of the weft yarn (theblend compositions being 80/20 and 60/40 for warpand weft respectively), the warp yarn, before itruptures causes the weft yarn to distend further thanthat in the earlier two cases. Eventually, it earns furthercontribution from weft yarn and thus yields a fabric ofhigher strength. This is quite evident from our results,the strength increasing from 5.93 to 6.43.

The warp tear values, when the weft blendcompositions are changed and the warp blends are the

Iii'

;1

';... ;..~,'.'".

,,~~m

~~~i

•

,

Table I-Mean Strength (X) Values Obtained by Different Tear Test Methods

Sample Warp/ Tear testcode Weft

SingleDoubleWingTrapezoidElmendorfWoundrip

ripriptearkgburstingkg

kgkgkg kgf/cm2I

d

ARXW6.4439.9904.21315.5264.0995.930F

6.0679.6403.95414.8323.8277.1003 ARYW6.27110.2474.13216.0004.1056.080

~F8.15811.5594.90417.5894.7617.830 YARZ W6.26410.0764.37915.7084.1695.860~ F

4.8507.9763.37910.1223.1716.1207,

BRXW8.35912.1865.29421.2515.0436.4308 F5.8349.8844.02914.7673.8946.8409 BRYW8.26212.2745.18020.7864.8846.74010 F8.05011.7904.93217.8284.7687.650II,

BRZW8.26512.6035.32522.7005.0816.43012!

F4.9488.4463.38311.2833.2546.34013!

CRXW4.9738.0243.20012.4803.5235.60014! F5.98210.2044.09614.7683.8946.76015! CRYW5.0777.6183.22812.0603.5455.69016 F7.92611.3964.95617.0724.5087.54017 CRZW4.8528.1483.18212.9603.4045.31018 F4.7657.9013.0749.6643.1045.85019 APXW8.84512.5965.14918.7835.1396.25020 F7.22811.8634.83813.1294.7416.09021 AQXW7.2]011.l774.726]6.6454.6916.140

221

F6.77010.7194.43713.9654.3126.560

W, warp; F, weft

I48

111l1P'1IU

SHARMA & ADHIKARY: COMPARISON OF DIFFERENT TEARING TEST METHODS

same (60/40), are 5.86, 5.93 and 6.80 for the weft blends48/52, 60/40 and 80/20 respectively (Table 1). As thewarp has the same blend and hence the sameextensibility in all the cases, the weft yarn distendsequally in each case. Hence, when the extensibility ofweft yarn increases, its contribution towards the warptear tends to decrease. But since the strength of weftyarn also increases, the ultimate contribution goes infavour of warp, causing increase in the warp tearstrength. An interesting point here is that the weft yarnhas never failed, even though it has got lowerextensibility, apparently contradicting the contentionthat failure in a wound bursting strength test alwaysoccurs in the less extensible direction. In fact, theresults show that in all the above cases, the weftextension has never reached its maximum value beforethe tear headed its way across the warp threads. Apossible explanation for this is that while the weft yarnpossesses a lower extensibility than the warp yarn dueto the lower polyester content, it has a higher crimplevel. This is due to the difference in bending rigidityand threads/in of the two sets. Hence, with theapplication ofload, when the crimp is totally removed,the weft provides a greater unextended length thanthat provided by warp; this reduces the ultimateelongation imbalance between the two sets.

A close inspection of the fabric specimen during thebursting tear test shows that the force applied to thespecimen tends to extend it in all possible directions.But as the fabric comprises only two sets of threads,viz. warp and weft, the total load on the sample isultimately distributed in these two directions. Now,when some of the threads in one of the directions are

severed, the resultant load in that direction isshared bythe unsevered threads. So, the magnitudes of loadsupported by each yarn in these two directionsobviously differ, depending upon the relativeextensibilities and the population of the two sets (or ontheir respective thread spacing and length of cut).

Again, it is well known from the geometry of thebursting tear tests that the distension is alwaysmaximum at the central zone of the specimen and itfalls progressively towards its periphery. Now, weconsider a single thread belonging to any set beingplaced centrally in the specimen, which is interlaced atequal distance along its length with the crossingthreads belonging to the other set. When the specimenis distended, the mutual pressure between the two setsincreases and each of the two intersections acts as a

clamp for the length of yarn being held between them.Thus, a single yarn can very well be supposed to becomprising a number of such clamped lengths. As thedistension is maximum at the centre and minimum atthe periphery, the clamped lengths, originally beingequal, differ in extensions from each other. The

extension of the yarn is maximum at the centre andminimum at its either end. The more frequent theinterlacement, or in other words the more the numberof crossing threads/in interlacing with the said yarn,the shorter is the intersected length and greater is theelongation difference. Consequently, the yarn yields toa lower strength.

It is clear from above that the central threads are theones which are subjected to the maximum stressconcentration at their centres, and when the centralthreads are severed, the threads immediately adjacentto the cut share the maximum load. Besides, the rubberdiaphragm bulging out from the slit pulls theunsevered set of threads apart, causing further stressconcentration on the severed set at the tear locus.

If the breaking strength and extensibilities of the twosets are such that the load shared by threads lyingacross and nearest to the cut reach their maximumcapacity (it may be higher or lower than that of theother set at right angle), before their counterparts do,they will rupture at the point of maximum stressconcentration, i.e. at their centres. With the rupture ofthe first threads on either end of the cut, the load will beredistributed among the rest of the threads and thesecond set of yarns will fail in a similar fashion.However, the rupture of yarns occurs in quicksuccession and the tear proceeds rapidly along the lineof the cut. However, in reverse situation, the tear willbe transferred to the other direction and will proceedcentrally across the cut on its either side. In the presentcase, it is evident that the warp threads, despite theirhigher breaking strength and extensibility, must havereached the point of their maximum capacity beforethe weft threads did.

Thus, the tearing strength of a fabric in a burstingtear test is dependent on several factors, viz. therelative extensibilities and the ultimate and relativebreaking strengths of the two sets of threads, thenumber of threads/in in either direction of the length ofthe cut, and the extent of thread slippage.

Effect of yarn withdrawal force-Increase inpolyester content with simultaneous decrease inviscose content results in a higher coefficient of yarnfriction and a lower yarn crimp level. The former is dueto the higher static coefficient of friction of polyesterfibre and the latter to the higher bending rigidity ofpolyester fibre. A higher value of static coefficient offriction always tends to increase the resistance to yarnwithdrawal from a fabric and conversely a lower crimptends to minimize it, but the effect of the former has agreater impact on the yarn withdrawal force andcauses an increase in its value (Fig. 1)..

With ultimate increase in yarn withdrawal force, thedel limits itself within a smaller area and depth,bringing fewer yarns into action. Obviously, the

49

INDIAN J. TEXT. RES., VOL. 9, JUNE 1984

Fig. If-Dependence of yarn withdrawal force on cut length

suppor~ng capacity of the del system is reduced and alower tearing strength is recorded. The above findingssuggest Ithat with increase in the polyester content ofyarn, aU the above-mentioned comp~nent variableschange and contribute differently to the tearingbehaviour of a fabric. While the yarn withdrawal forcetends tq minimize the tear strength, the other two tendto increflse it. The gross effect of the latter two is morethan that of the former and this causes increase instrength. However, the effect of blend compositionseems tIPbe more pronounced in the trapezoid tear test,which shows a steeper change in strength compared toany other test procedure (Table 1).The trapezoid teartest also yields the highest value in tearing any sample

and it if followed in both respects by the double rip,single np, bursting tear, wing rip and impact tear tests.

The tearing strength in any of the methods depends onthe nulmber of yarns sharing the applied load

simultapeously. Again, the population of the activethread~ in the del, in the case of trapezoid tear test,

depend~ markedly on the yarn extensibility, crimp,fabric density in either direction and the initial jaw

separa~on, or in other words, on the initial unextendedlength of yarn being placed immediately across the cut.In the double rip test, the yarn withdrawal force plays amajor ~ole, with contribution from yarn extensibilityand fabric density in either direction, in determiningthe yarh population in the del. But the yarn withdrawalforce, ih turn, is governed by the number of threads/in

y

at right angles, coefficient of friction, mutual pressurebetween the two sets of yarns, and percentage crimp. Itis clear that the factors influencing the tearing strengthin the trapezoid and double rip tests are different andcan be manipulated to get the opposite result. Forexample, the yarn withdrawal force in any sample canbe reduced by altering the surface finish of yarnwithout affecting the other variables, and in that case,the disagreement between the two test results will bediminished. Or, if the fabric density along the teardirection is decreased, the double rip will give rise to itsrecorded strength, while the trapezoid will react

. conversely (Table 1).The possibility of double rip test giving a higher

value than the trapezoid test for a very open fabric isevident from the data given in Table 1. The trapezoidvalues appear to cross the double rip values at a lowerpick level.

It is observed from Table 1 that the trend lines ofsingle rip and bursting tear tests and those of wing ripand impact tear tests have crossed each other. Thisshows that their relative positions are dependent moreon the characteristics peculiar to the sample than onthe methods themselves. However, for the presentstudy, the number of active threads in the tear region ofthe samples must have been more in the case oftr~pezoid test than in the case of double rip test(though double rip comprises two sets of yarns actingsimultaneously in two separate del structures) thatresulted in a higher value in the former test.

Again, as the initial unextended lengths of thethreads are more in the case of trapezoid tear test thanin the case of double rip test in the tear zone because ofthe specimen geometry, any increase in yarnextensibility leads to a greater enhancement in yarnextension and hence in the number of active threads inthe former. The effect is accentuated by thesimultaneous effect of increased yarn strength andcreates a larger gap between the two test values, as isshown by the present results. In this respect too,double rip may assume the position of trapezoid ifother yarn and cloth constructional parameters aremanipulated in the sample, i.e. the trend lines shownhere may not be reproducible in other samples withaltered variables. This is also established by the data inTable 1,where the trapezoid test shows a change in thedirection of its trend. Besides, the trend lines of wingrip and impact tear tests, having crossed each other inand without crossing in, reflect that either one or bothof them must have changed their directions in thesecond case. These changes in the behaviour of thetrend lines have been caused by changes in fabricdensity along and across the tear directions. While inthe first case they are 64 and 56, in the second case theyare 56 and 64 respectively.

BRY

BRX

~RZ1

COUNT ,2/365X 2/365] FOR ALLRE E D X PICK, 64X 56 SAMPLES

WARP BLEND 'I. ,80/20

WEFT BLEND ",,48/52 BRZ

60/40 BRX80/20 BRY

STRIP WIDTH THROUGH WHICH

YARN IS WITHDRAWN, lin

YARN WITHDRAWN t FILLING

1/2 3f4CUT LENGTH,in

100

~ 1250:ou..

~ 120<l:0:oi= 115j~ 110>

95

135

140

145

150

130

105

50

SHARMA & ADHIKARY: COMPARISON OF DIFFERENT TEARING TEST METHODS

So, the observations that the trapezoid tear testresults assume the highest ranking and are affectedmore distinctly by changes in yarn blend compositionmay not be reproducible if the other parameters arealtered. This shows that the various test methods donot reflect and/or involve the same fabric and yarncharacteristics in the tearing action, at least not in anidentical fashion. The mechanisms of tear in tlte singlerip, double rip and impact tear tests are basically thesame and hence show similar trends in an identicalfashion. Double rip, of course, always records thehighest value, impact tear the lowest, and the single ripan intermediate position. The obvious reason for thisis that double rip consists of a couple of del structuresduring tear and hence always provides nearly doublethe number of threads than those provided by the othertwo in supporting the load in the entire specimen. Inimpact tear, which is basically a single rip test, a largefrictional force is developed among the slippingthreads due to the rapid pace at which this test iscarried out. Thus, the del collapses earlier at a muchlower load before it can increase considerably in area.

The wing rip, however, distinguishes itself from theabove three methods in respect of the geometry of tearlocus and the manner in which the load is applied to thespecimen. Due to the changed geometry of the tearlocus in the wing rip test, there is less scope for threadslippage and the load is applied to the specimen moredirectly, ultimately yielding a lower tear strength.However, there are instances when the wing rip showstear strength even lower than that shown by the impacttear tes~ (Table 1). Again, a critical inspection of thetrends, showing the effect of weft blend composition onthe warp tear strength for the two tear methods, revealsthat their relative positions have changed and evenreversed with change in warp blend composition(Table 1). This shows that the impact of yarn blendcomposition on the tearing strength in these twomethods is different and provides sufficient ground tosupport the dissimilarity of the two test.procedures, thedifference being not very marked, of course. The effectof warp and weft blend compositions on the weft andwarp tear strengths (Table 1) respectively is negligibleand does not indicate any definite trend.

Effect of fabric density-Data presented in Table 1show that with increase in fabric density along the teardirection, the different test methods exhibit a mixedbehaviour. The tear value increases in the trapezoidand bursting tear tests and decreases in the rest of themethods. In the single rip test, increase in fabric densityalong the tear direction increases the number ofcrossing points or frictional points per unit area of thefabric. This effect causes a greater resistance to beoffered to the yarn translation, tending to induce adecrease in the del zone. Similarly, because of the

increased cloth cover, the fabric ahead of the del regionjams earlier in the direction of the tear and the extent ofyarn movement in that direction being lesser there isreduction in the depth of the del. Hence, the del now,with smaller area and depth, comprises fewer yarns.However, increase in fabric density itself tends toincrease the population of active threads, but this haslesser impact relative to the previous two, andeventually the tearing strength falls (Table 1).Similar isthe case with double rip, wing rip and impact tear tests.

In the trapezoid tear test, increase in the number ofthreads/in in the direction of tear increases thepopulation of active threads in the del zone. On thecontrary, due to the increased number of frictionalpoints and a higher shear deformation, the frictionalresistance developed against yarn movement in thefringe area is higher and increases the loadconcentration. But this effect has been quite subduedunder the dominance of the former and ultimately ahigher tear strength results.

The warp tear strength decreases in all the testmethods with increase in pick level(Table 1).The effectis, however, less pronounced in the bursting tear test.

In the single rip test, increase in fabric density acrossthe tear direction increases the number of frictionalpoints per unit area of the fabric. Thus, the extent ofyarn translation being less now, the area of del isreduced and the strength eventually falls again.

The above arguments apply equally to the doublerip, wing rip and impact tear tests. In the bursting teartest, increase in fabric density across the direction oftear reduces the strength.

The trapezoid tear test exhibits a similar trend, butreacts in a different manner. With increase in fabricdensity across the tear direction, the crimp in the activeset of threads increases. As trapezoid tear is basically atensile strength test, being carried out with a woundspecimen having progressively changing length ofyarn, any application of force results in completetransfer of this increased crimp from the active to theidle set of threads. The idle set of threads, nowassuming a higher crimp level, tends to contract more inlength and exerts an increased load to active ones, thestress concentration being maximum along a line atpoints farthest from the jaws. Again, due to increase inthe density of idle threads, the number of frictionalpoints along any of the active threads is more. Hence,during the extension of the active threads, any singleone of them meets higher frictional resistance.Eventually the fabric gives way at a lower load.

Comparison of different tear test methods: Effect ofspecimen dimension on tear strength (single rip): It isseen from Fig. 2 that changes in specimen dimensionshave negligible effect on the tear strength of a fabric.The only exception is when the tail width is reduced to

51

INDIAN J. TEXT. RES., VOL. 9, JUNE 1984

Fig. 2-Effect of tail width, tail length and tear length .on tearI strength

TAIL WIDTH, in______ .L l J ..1 .1 .1 ..L J. .J__

1 2 3 4TAIL LENGTH, in

_._l __ ._ . ...L..._._.---1. ._ ...1..-.._._.--1._._._ ..L...._._._1 2 3

I TEAR LENGTH, in

..

y

affects not only the load capacity of the del, but alsothe amount of assistance rendered by the untornfabric. Hence, with increased tear length, the assistancerendered by the untorn fabric is higher and gives rise totearing strength.

However, within a limited scope, the results showthat the trapezoid has greatest sensitivity to anychange in variables and the bursting tear has the leastsenstivity. Double rip assumes the second position,being followed closely by single rip. But as far asreproducibility and reliability are concerned, single ripand bursting tear methods emerge to be the bestmethods followed by double rip, wing rip and impacttear tests, the trapezoid method coming last. However,double rip and trapezoid methods have the advantageof positional consistency compared to the othermethods.

Again, it is apparent from the earlier discussionsthat single rip and/or double rip involve more variablesin determining the tear behaviour of a fabric andreflect wider aspects of the yarn and clothcharacteristics. Their tear mechanism further revealsthat they are least dependent on specimen geometryand are governed more by the true merit of the cloth.Besides, they provide a much more stableresult compared to any other method, trapezoidmethod having the least merit in this respect. However,one point goes in favour of bursting tear test: itreplicates the true behaviour of the fabric in appareluse. In most of the cases, it has been experienced that awound fabric in use gives way to the pressure mountedby the flesh of the body, with both warp and weftplaying complementary roles.

The single rip method emerges as the second best inview of adaptability (i.e. its close simulation of thefabric behaviour in use), the double rip the last andothers taking intermediate positions. Double ripsatisfies the minimum number of field conditionsunder which the tear proceeds, because, in fact, thepossibility of a fabric running a double tearsimultaneously is remote. The trapezoid tear test haspractically been excluded from this consideration, as itis, in fact, a replica of the tensile strength test, beingcarried out in a modified form. Hence, it has littlerelevance to field performance.

It is clear from the above discussion that the singlerip tear test appears to be the best one, followed closelyby the double rip, impact tear and wing rip tests. Theranking of all the samples assessed by the different testmethods is shown in Table 2. It is observed that thewound bursting (bursting tear) results show themaximum deviation and its assessment seems to bemore disorderly in relation to those of the others.

The rest of the methods show almost identicalperformance, the trapezoid showing some exceptions.

6

0-- ---0- ----0--- --0----

EFFECT OF TAIL WIDTH ON TEAR STRENGTH

DEPENDENCE OF TEARING STRENGTH ON TAIL LENGTH

-----~.- EFFECTOFTEAR LENGTH ON TEARING STRENGTH

oo

SAMPLE CODE NO, cayWARP BLEND'!., 48/52

WEFT BLEND'!.. 80/20

EPI, 64

PPI, 52

COUNT, 2/365 x 2/365WEAVE, PLAIN

I in. However, the specimen has been marked to lenditself to the maximum yarn translation and hence thereis considerable doubt about the justification of theresults. So, with no significant effect of specimendimension on the tear strength, it has been consideredreasonable to assume that the tear values obtained bythe various test methods could fairly be comparedwithout much intervention from this factor.

The tear strength increases with decrease in taillength or increase in tear length or tail width (Fig. 2).This can be easily explained if we consider the totalsystem of the specimen and its components, viz. thetails, the del and the fabric in parallel with the del,analogous to springs. In fact, analysis of rip strengthby Teixeira ec al. 4 involves the· same approach. Theyassumed that the del and the fabric ahead of the del arein parallel connection and the combination of the twois in series connection with the tails, the resultantrepresenting the total system. Any increase in tailwidth increases the spring coefficient of the tail andsubsequently the spring constant increases. Again, ifthe tail length is reduced, the spring constant increases.Thus, both result in increase in the resultant springconstant of the total system or in other words increasein tearing strength.

'The fabric ahead of the del also plays an importantrole in determining the tearing strength, specially whenthe fabliic permits jamming' and trellis type distortion.IAccording to Teixeira et ai.4, the factor in fabricgeometry which influences the shape of the del and thenature of the fabric structure in parallel with the del

14

12C1

10.lC ibzWl>:Iii

Cl:

4:wt-

•

52

SHARMA & ADHIKARY: COMPARISON OF DIFFERENT TEARING TEST METHODS

Table 2-Ranking of Samples Assessed by Different Tear Test Methods

Rank Samplecode Single

Doublenp

rip

1

ARX19112

7193

ARY1194

975

ARZ 420

61010

7BRX164

82016

9BRY2121

102222

IIBRZI3

12314

13CRX55

142I

15CRY148

1682

17CRZ1512

181317

19APX12\3.

20176

21AQX618

221815

Frgures under each test column indicate the fabric samples No.

The first positions have been taken by samples 7, II, 19and 9 in all the test methods. The next six positions goto samples 4, 10, 16, 20, 21 and 22 in all, but thetrapezoid method excludes samples 20 and 22 from thiscategory and includes samples 3 and 5 instead. Again,for the next six positions, single rip and others pick upsamples 1, 2, 3, 5 and 14, but trapezoid replacessamples 3 and 5 by 20 and 22. The last six positionshave been assumed by the remaining samples in eachmethod.

From the ranking of the samples, a basic similarityamong the single rip, double rip, wing rip and impacttear tests is apparent. The coefficients of correlationfor these methods range from +0.9264 to +0.9310,which are indeed quite high (Table 3).The correlationshave been calculated taking the single rip as the basicmethod. While the trapezoid, due to its occasionaldeviations, shows a correlation value of + 0.8448 withsingle rip, the bursting tear shows a poor correlationvalue of + 0.3874.

It is, therefore, concluded that the single rip, doublerip, wing rip and impact tear tests have goodcorrelation and hence basic similarity with each other.Trapezoid shows a weaker relation and the burstingtear differs widely from them.

Tear test

Wing

TrapezoidElmendorfWoundrip

bursting

II

II1947

7II109

971619

199216

1010810

44144

1620920

21212221

3161122

522 75

I512

I2319

3

1412114

8868

2214202

202312

171516

1313518

151718

15

1212IS

136613

17181817

Table 3-Correlations among Different Tear Test Methods

Single

DoubleWingTrape- Elmen- Woundrip

npripzoiddorfburst-

ingWound burstingElmendorf

-0.4323

Trapezoid

- 0.90110.3990

Wing rip

0.94890.93230.5108

Double rip

0.94290.88720.92660.5147

Single rip

0.92640.93190.84480.93120.3874

Conclusions

(1) Increase in fabric density along the tear directionincreases the strength in the trapezoid and burstingtear tests and decreases it in the rest of the methods.

(2) Increase in fabric density across the teardirection decreases the tearing strength in all the testmethods, except the bursting tear test, which shows amarginal decrease.

(3) Single rip test method is the most suitablemethod for carrying out a tearing test.

(4) Single rip, double rip and impact tear tests showsimilar performance and provide almost identicalvalues of fabric characteristics, while the wing rip test

53

INDIAN J. TEXT. RES., VOL. 9, JUNE 1984

differs only marginally. The trapezoid method shows arelatively poor correlation with the above test methodsand the wound bursting method differs widely fromthem. I

AcknowledgementThe authors are thankful to Prof. R.C.D. Kaushik,

Director, TIT, Bhiwani, and Prof. S.K. Manuja forvaluable suggestions in designing and developing thisprojeot.

54

References

I Indian standard specifications IS: 6359 (Indian StandardsInstitution, New Delhi) 1971.

2 Turl L H, Text Res J, 26 (1956) 169.3 Turl L H, Text Res J, 28 (1958) 839.4 Teixeira NA, Platt M M & HamburgerW J, Text ResJ, 25(1955)

838.

5 Steele R & Gruntfest 1 J, Text Res J, 27 (1957) 307.6 Hager D B, Gagliardi D D & Walker H e, Text Res J, 17 (1947)

376.

7 Taylor H M, J Text Inst, 50 (1959) T-161.

(.