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S WADC TECHNICAL 1EPORT 56-:313

~ ART If\ASTIA DOCUMENT No. AD 110406

A STUDY OF PARACHUTE SEAM DESIGN CRITERIAPort II - Investigation of the Strength of Nylon Webbing Joints

CHARLES R. MILLER

PIONEER PARACHUTE COMPANY, INC.

JUNE 1956

This report is not to be announced or distributedautomaticully in occordance with AFR 05 .A'3A

paragraph 6d.

WRIGHT AIR DEVELOPMENT CENTER

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FOREWOR

This report, phase II of a study of seam characteristics, was prepared

by Pioneer Parachute Company, Inc., of Maxcheter. Connecticut, under AirForce Contract No. AF 33(616)-28(Y7. Thii contract was initiated underProject Number 6065, "Parachute Perforsuance and Design Studies," aro Tas'Number 61512, "Parachute Stresses and Airflows," and administered under the

direction of the Squipment Laboratory, Directorate of Development, WrightAir Development Center, with Mr. Alfons Hegele as project engineer.

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WAATR 56-313 rt !.I

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~ABSTRACT

The purpose of Phase I of this investigation was todeteiinine the iiost efficient :oint obtainable, using presentlyknoim fabrication teahniques ;o join the cords and webbingsspecified in the contract.

The investigation attempts tQ evaluate the most efficientjoint with respect to fabrication techniques, as well asstrength considerations.

The variables co-nzidered were:

1. Type of joint

! 2. Size of thr-ead and sewing needle

~3. Pattern of stitching

4. Number of stitches per Inch

The data shows that the most efficient joint in NylonCords of the MM-C-5040 type is one in which the and of onecord ts superimposed on the other and stitched with a two-stepzig-2.ag stitch pattern. Thread size and length of stitching~Iz a function of the cord strength.

The most efficient joint in Nylon Cords of the NIL-C-7515type (coreless) is one in which one of the free ende of theii cords to be joined is threaded into the other for a certaindistance.and then stitched with a two-step zig-zag stitch.-The thread size, length of stitching and distance which oneend is threaded into the other Is a function of the strengthand diameter cf the co.d.

The most efficient joint in the nylon webbings that weretested is one in which the stitching pattern is of two, three,four or six point configuration. The number of points in thestitchir pattern is a function of the width of the webbing.The size of the thread and the length of the stitching patternare functions of the strength of the webbing.

webbing joints, to determine. if the efficiency could be increasedby the addition of reinforcing webbings and tapes. Tedt resultsshow a definite increase in efficiency in the reinforced joints.

WADC TR 56-313 Pt Ii ii.

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As a result of the tsts, it can be itated that *f.4 rostefficient non-reinforced webbir- Jolnt ic .- the t-., three,four or six point cnnfiguration, with the numuer of pointsdepending upon the width of the webbing. The overallofficlency of this type of Jol. can be raised substantiallyby the addition of reinforcing webbings, but this ma-keefabrication more difficult arnd is more costly.

PUBLICATION REVIEW

This report has been reviewed and is approved.

* FOR THE COMMANDER:

ROBERT A. BARREREColonel, USAFChief, Equipment Laboratory

WADC TR 56-313 Pt 1i iv

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TABLE OF CONTENTS

Section Page

I Introduction . .. . . . . . . . . . .. . . . . . . 1

II Specimen Fabrication .... ..........

Iii Test Methods . .. ...... .. .... .. ... . 6H IV Order of Joint Efficiencies ............. 7

V Analysis of Joint Efficiencies ........... 12

VI Analysis of Joints for General Usage ..... ........ 15

1. Basis of Evaluation .... ............... ... 15

2. Breaking Strength vs. Stitches per Inch ..... ... 15

3. Comparison of Stitch Patterns . .. .. .. . .. 15

4. Burned Ends vs. Plain Ends ............ 17

5. Effect of Thread Size .... ............ . 18

VII Conclusions .. .. .. .. .. . . .. . . .. . . . 18

1. Nylon Cord, MIL-C-5040. .... .............. ... 18

2. Nylon Cord, MIL-C-7515 .... ............. .... 18

3. Nylon Webbing . ... r................... 18

WADO TR 56-313 Pt IIV

LIST OF ILLUSThiTIONS

i Comparison of OverlaT: Strength - I

--- pSide by Side vs. Superimposed 5....... ...

2 Test Arrangement - Tinius Olsen ............... 6

3 Test Arrangement - Baldwin Southwark ......... 6

4 Cord Joint Comparison . . 13

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WADC TR 56-313 Pt II I

LIST OF T! .RS

Table Page

jmparisors, of Brek S gth and Stitches per Inch . 16

IA Thread Size vs. Breaking Strength ... ........... ... 19

II Crd J .oint Test - Phase II - Series I .... ......... 21

III Cord Joint Tests - Phase II - Series II .......... .. 22

IV Cord Joint Tests - Phase II -Series II ............ 23

V Four Point, Split Four Point andThree Point Stitch Patterns ....... .............. 24

VI Crossed Box, Four Point andThree Point Stitch Patterns ... ............. 25

VTI Four Point, Split Four Point andThree Point Stitch Patterns ..... .............. ... 26

VIII Four Point, Split Fou r Point andThree Point Stitch Patterns ..... .............. ... 27

IX Four Point, Split Four Point andThree Point Stitch Patterns ........ ... ..... 28

X Four Point, Split Four Point andThree Point Stitch Pattern ..... .............. 29

XI Cross Box Stitch Pattern ....... ............. .. 30

XII Single and Double Row w.o-Step Zig-Zag Stitch Pattern . 31

XIII Single and Double Row Two-Step Zig-Zagand Diamond Stitch Patterns ..... .............. ... 32

XIV Four Point Stitch Pattern with Reinforcing Wrap . ... 33

XV Four Point Stitch Pattern with Reinforcing Webbing 34

XVI Cross Box, Four Point and Three Point Stitch Pattern 35

XVII Reinforced Four Point and Three Row Two-Step ,Zig-Zag Pattern ....... ............ ....... ...

XVIII Four Point, Split Four Point andThree Point Stitch Pattern ..... .............. ... 37

XIX Reinforced Four Point and Three Row[ Zig-Zag Stitch Pattern ...... ............... .. 38

XX Six Point Stitch Pattern with Reinforcing Wrap . . . . 39

XXI Four Point and Six Poli-t Stitch Patterns .. ...... . 40

WADC TR 56-313 Pt II vii

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1. INTlRODUCT ION

Phase II covers the investigation of the fabricationmetLIods and the strength of Joints made with nylon cords andwebbings, presently used or suspension lines and risers ofparachutes. The investigation attempts to determine the highestjoint efficiency obtain=Die, with low-st amount of r -itching,compatible with the presertly known fabricaticn techniques.

In some cases, the most efficient Joint is not themost desired joint from the standpoint of efficient and economicalproduction. Where such conflict arises, the joints are evaluatedin relation to theiv• ease of manufacture as well. as their strength

I efficiency.

The manufacturing equipment, necessary for the fabrlca-tion of the required test samples, was selected from regularproduction machinery and set aside for use on this program.

£ The equipment included the following machinery:

1. Single needle sewing machine (III W 151)capable of stitching with Size "E", "F","FW" and 3 cord thread.

2. Single needle sewing machine (97-10)capable of stitching with 5, 6 and 8 cordthread.

3. Zig-zag stitch sewing machine (17 W 15)capable of stitching with Size "E", "F","FF" and 3 cord thread.

4. Miscellaneous equipment, such as, hotwire cutters, rotary blade cutters,waxing equipment and small tools.3.1. The testing equipment, necessary to the completion of

the program, included the following:

Pioneer Parachute Co., Inc.

1. Tinius Olsen testing M nhine -=a^ah oftesting webbings up to 20,000 lbs.[! tensile strength.

2. Scott Tester - Model J-2 capable of testingtapes, webbings and cords up to 500 lhs.tensile strength.

3. Scott Tester - Model X-5 capable of testingthreads up to 20 lbs. tensile strength.

WADC TR 56-313 Pt i 1I.

Cheney Brothers Laboratories

1. Scott Tester - Model Q c,,Lable of bestingtapes, webbings and cords3 d 2000 lbs.tensile strength.

Massachusetts Institut- of Technology

1. Baldwin South.4ark Testing Machine capab!of testir materials up to 300,000 lbs.tensile strength.

In addition to t'he strength testing machinery, various

other laboratory equipmF-t is available at Cheney BvothersTextile Laborator-y. A partial list would include conditioningovens, twist testers, abrasion tester and various small tools.

The general test procedure conforms to SpecificationCC(3-T-191b, as outllred in the contract. Wherever possible

t- tests were varformed under standard conditions. Anexception proved necessary in the testing of the 20,000 lbs.and. webbings It was necessary to test thesewebbings at the Physical Testing Laboratories of the Mass-achusetts Institute of Technology. These laboratories arenot conditioned, hence, the webbings were necessarily testedunder prevailing conditions at the laboratory.

The variables encountered in the manufacture of thetest specimens were:

1. Varying stitches per inch.

2. Varying thread tension.

3. Inability .f oterator to maintainprecise stitch patterns on theheavier webbings.

i. Tight and loose stitching, due tothe webbings becoming hard andinflexible during stitching.

The variables encountered in testing were:

1. 'Variation in strength, between test

inherent variance in webbing strength.

2. Strength difference due to a variationin stitches per inch between samples.

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1i, SPECIMN FABRICATION

Njlon -*cnrC, MIL-C-5040, Type iI and III

The first joint spe;imens to be fabricated and tested-are nylon cords, !IL-C-504G, Type Ii and III. These testsare tabulated undel Series 1. Page 21.

Prior experience with this type of cord (core yarnsencased in a braided sleeve) had shown that the highest basicefficiency was obtained by superimposing the cord ends, one onthe other, and stitching with a two step ztg-zago Further testswere conducted to de ermine the optimum length f overlap,stitches per inch and thread size.

Figure 1, Page 5, shows the comparison of the side by

side vs. superimposed construction. All stitching was done withNylon Thread, MI-L-T-7807, Type I, Class I, Size "E", 8-11 stitchesper inch counting on side row. Stitching was 1/8 : 1/32 wide.

The "side by side" construction ("A") yielded an averagestrength of 302 lbs. and the stitching failed in all casps.

The "superimposed" construction ('B") yielded an averagestrength of 328 lbs. and the cord failed in all cases.

2. Nylon Cord, Coreless, NIL-C-7515, Type II and VI

This cord is of "coreless" braided construction. Thesuperimposition method of joining, as outlined for the MIL-C-5040type cords, proved less efficient for the "coreless" cord.

Prior experience had proved that the higaest basicefficiency obtained with this type of cord was obtained bythreading the cord into itself and then stitching with a two stepz Lg-zag stitch for an optimum distance. The tests of the:oreless" type cords are tabulated under Series I!, Pages 22 & 23.

3. Nylon Webbing, MIL-W-5622 1000 Lbs. and 3W10 Lbs. t.#.

The MIL-W-5625 webbings were used to test the many joint1stitch patterns, thread sizes and stitches per inch to determineI the most efficient joint to be used on other webbings. The

various configurations and their respective series numbers arediscussed in detail, in another section of the report.

4. Nylon Webbing MIGL-W4-088- &"ae X

The MIL-W-4088, Type X webbing specimens were curnstructedin the varicus joints which exhibited superior ,ualities in thetests of the MIL-W-5625 webbings.

It was on the MIL-W-4088, Type X webbing thaL the firstof the reinforced end joints were tested. (Se, Series XI and XII,

Pages 33 & 34.)

WALC TR 56-313 Pt II 3* FaIA

5. Nylon Webbing, MIL-W- 088, Type XVIII

The various loints of ,uperior qti.ites we c duplicatedin the MIL-W-4088, Type XVIII webbing. The .-- .;cimrens of thelongitudially reinficed Joints were constructed with theType XVIII webbing.

6. Nylon Webbing. MIL-W-78Z, Type I aid II

The MIL-W-5787, Tyjpe I and ii (20,000 lbs. and40,000 lbs.) webbing joints were fabricated in accordance withSeries XXIII and XXIV, as shown on Pages 39 and 40; Thereinforced type joints were not used because reinforced webbingsof suitable width were not available.

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36 32''i

IL

_IIB

Side By Side Superimposed

Comparison of Overlap Strength - Side by Side vs. Superimposed

Figure 1


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Ill. TEST MbETHODS

i. Cord Tests

The nylon cords o1 550 "-s. tensile strength andlower were tested on a Scott Mode] Q Tester of 2000 Ibs.capacity. The cord specimens of he MIL-C-7515, Type VI,2OO lbs. tensile strength were tested on a Tinius Olsentesting machine.

2. WebbinZ Tests

The webbing specrinens below a rated strengtl- of

20,000 lbs. were tested on a Tinius Olsen testing machine.The testing machine had dual ranges of 5000 lbs. and 20,000 lbs.capacity, and a Jaw separation speed of 4 inches per minute.IThe webbing specimens above a rated strength of20,000 lbs. were tested at the Physical Testing Laboratory ofthe Massachusetts Institute of Technology at Cambridge, Massachu-setts. The testing machine was a Baldwin Southwark Tester of300,000 !bs. capacity and the Jaw separation speed was 3 inchesI!• pe.- minute. I

The webbings tested on the Tinius Olsen machine were

held on webbing holding fixtures in the manner shown in Figure 2

The webbings tested on the Baldwin Southwark machinewere of loop form and tested over pins as Ehown in Figure 3.

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Test Arrangement-Tinius Olsen Test Arrangement-Bald:lr. Southwark

Figure 2 Figure 3

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IV. ORDER OF JOIT EFFIC!-2C!ES

The various Joints are presented here with reference

to the most efficient Joints for individual materials. Noattempt is made, at this poiaz, to establish a universallyefficient joint. In Sectio-ii V, Analysis of Joint Effic!encies,the various types of Joints are evaluated with respect toestablishment of the most efficient Joint for universal usage.

1. Nylon Cord, MIL-C-5040, Type II, 375 lbs. t.s.

The strongest joint obtained with the MIL-C-5040,Type Ii cord yielded an average breaking strength of 355 lbs.The low was 350 lbs. and the high was 360 lbs. The averageefficiency was 77.7%, based on an average control strength of457 Ibs.

This joint was fabricated in accordance with theSeries I type overlap, as shown on Page 21. The length ofoverlap ("L ) was 6 inches and the thread was Size "F". Thestitch was a two step zig-zag, 6 to 7 stitches per inch,1/8 4 1/32 inches wide.

0Although this proved to be the strongest joint, it

is not the most efficient from the standpoint of the amountof stitching used. The next strongest joint, using the sameslizc thread, but only a three inch overlap in lieu of sixinches, yielded an average breaking strength of 353.3 lbs.It is evident that the three inch overlap, yielding a strengtho 353.3 lbs., is more efficient than the six inch overlapyielding 355 lbs., all other factors being equal.

2. Nylon Cord, MIL-C-5040, Type 111, 550 lbs. t.s.

The most efficient Joint obtained with the MIL-C-5040,Type III cord yielded an average breaking strength of 555 lbs.,or an average efficiency of 90.2%, based on an average controlstrength of 615 lbs.

This Joint was fabricated in accordance with theSeries I type overlap, as shown on Page 2.-. The length ofoverlap ("L) was two inches and the thre .d was Size "FF". Thestitch was a two stop zig-zag, 6 to 7 stitches per inch,1/8 _1/32 inches wide,,

The Joint of next highest efficiency yielded &naverage breaking strength of 481.6 lbs., or an average efficiencyof 78.4%.

This joint was fabricated in accordance with theSeries I type overlap. The length of overlap was three incheeand the thread was Size "F". The stitch was a two step zig-zag,6 to 7 stitches per inch, 1/8 '1/32 inches wide.

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WADC TR 56-313 Pt YI 7

| NinCord, MIL-C-7515, 'e II 5' lbs. t~s.

The most efficient Joint obtained with wie MIL-C-7515,550 lbs. t.s. cord yielded an averagc breaking strength of, 11 l-s., or an average efiul-en. )f 99 ., based on anaverage control strength of 593 1*s.

This Joint was fabricaied in accordance with theSeries Ii type overlap, as shown on Page 23. The length oioverlan ("Li) was 6 inches and the length of stitching was2 inch-es, The stitch was a two step zig-zag with Size "F"thread, 6 to 7 stitches per inch counting on the side row,3/16 + 1/16 wide.

SThe joint of next highest efficiency yielded an

average breaking strength of 580 lbs., or an average efficiencyof 97.8%.

SThis Joint was fabricated in accordance with theSeries II type overlap and was identical with the Joint ofhighest efficiency except that Size "FF" thread was used inlieu of Size "F".

. Nvion Cord, MIL-C-751.5, Type v. 200 lb. -. s.

The strongest joint obtained with the MIL-C-7515,2000 lbs. t.s. cord yielded an average breaking strengthof 2346 lbs., or an average efficiency of 97.5%, based on anaverage control strength of 2405 lbs.

This Joint was fabricated in accordance with theSeries II type overlap, as shown on Page 23. The length ofthe overlap was 6 inches and the leng*'l of the stitching was2 inches. The stitching was a two step zig-zag with Size "FF"thread, 6 to 7 stitches per inch, 1/4 + 1/32 wide.II -0

The joint exhibiting the next highest strength yieldedan average breaklin strength of 2340 lbs., or- an averageefficiency of 97.35.

This Joint was constructed the same as the joint ofhighest strength except that Size "F" thread was used in lieuof Size "FF".

0. the jointL .... Atic..3 Wita ta-e 161'e 61e

Size "F", yielded an average strength of 2340 Ibs., as against2346 Ibs. for the heavier thread, Size "FF"1,, it is evident thatthe joint stitched with the lighter thread, Size "F", is themost efficient.

WADC TR 56-313 Pt 11 8

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.N. lon Webbing, ?MIL-W-'5625, 1000 lbs. t.s.

jThe mostu efficient joint obtained with the KIL-W-5625,1000 lbs. t.s. webbing yielded .. average bra "Ing strength of1490 lbs., or an average efficiency of 100.9%, based on anaverage control strength of 1476 lbs.

This joint was fabricated in accordance with theSeries XXVII, Overlap T>T "A", as shown on Page 42. The lengthof the overlap was 6 inches and the stitch pattern was a threepoint cross stitch. The thread was Size "FF", 8 stitches perinch, The joint was re.rforced between rhe webbings by Nylon Webbing,MIL-W-4088, Type I, 500 lbs. t.s.

The joint of next highest efficiency yielded an averagebreaking strength of 1488 lbs., or an average efficiency of 100.8%.

This joint was constructed in accordance with SeriesXXVII, Overlap Type "B", as shown on Page 42. The length ofoverlap was 6 inches and the stitch, pattern was a three pointcross stitch. The thread was Size "FF", 8 stitches per inch. Thejoint was reinforced on both sides by Nylon Webbing, MIL-W-4088,Type I, 500 lbs. t.s.

6. Nylon Webbing, MIL-W-56e5, 3000 lbs. t.s.

The most efficient joint obtained with the MIL-W-5625:Id 3000 lbs. t.s. webbing yielded an average breaking strength of3833 lbs., or an average efficiency of 94.9%, based on anaverage control strength of 4040 lbs.

This joint was fabricated in accordance with theSeries IV, Overlap T1ype "C", as shown on Page 27. The lengthof the overlap was 6 inches and the stitch pattern was a threepoint cross stitch. The thread was Size 3 cord, 11 stitches perinch.

The joint of next highest efficiency yielded an averagebreaking strength of 3746 lbs., or an average efficiency of 93%.

This joint was fabricated in accordance with theSeries IV, Overlap Type "C', as shown on Page 27. The lengthof the overlap was 6 inches and the stitch pattern was a threeDoint cross stitch, ThA thread WM -54 meL^%,inch.


This joint was fabricated in accordance wit theSeries XXII, Overlap Type 'A", as shown on Page 38. The lengthof overlap was 6 inches and the stitch pattern was a four pointcross stitch. The overlap was reinforced between the webbings by1000 lb. Nylon Tape, MIL-T-5038, Type .V. The thread wasSize 3 ,ord, 8 stitches per inch.


1 7. Ny.loi, Webbina, _MIL-W-4088, :ype X, 87'0 1bs. ts.

The most efficient Joint obtained wlth t,....: -w-4o88,S 6,700 lb. nylon webbing, yielded an average breaking strength of

9100 lbs., or an average effilenoy X b . , u nu ii ave.agcontrol strength of 9800 lbs.

This Joint was fabricated i a accordance with Series X ,VI,Overlap Type "B". as shown cn Page 41. The thread size was6 cord, 6 stitches per inch, and the length of overlap was 8 inches.The stitch pattern was a 4 point cross stitch and the overlap wasreinforced on both sides by Nylon Webbing, MIL-W-4088, Type XII,1200 lbs. t.s.


This joint was fabricated in accordance with Series XXVI,Overlap Tye " as shown on Page 41. The thread size was6 cord, 6 stitches per inch, and the length of overlap was 8 inches.The stitch pattern was a 4 point cross stitch and the overlap wasreinforced between the webbings by Nylon Webbing, MIL-W-4088,Type XII, 1200 lbs. t.s,

8. Nylon Webbing, MIL-W-4088, Type XVIII, 6000 lbs. t.s.iI1 iThe most efficient joint obtained with the MIL-W-4088,

6000 lb. nylon webbing, yielded an average breaking strength of640 lbs., or an average efficiency of 100.1%, based on anaverage control strength of 6433 lbs.

This joint was fabricated in accordance with Series XVII,Overlap Type "B", as shown on Page 36. The thread size was 3 cord,8 stitches per inch, and the length of overlap was 6 inches.The stitch pattern was a 4 point cross stitch with the overlapreinforced on both sides with 1000 lb. Nylon Tape, MIL-T-5038,Type IV.


This joint was fabricated in accordance with Series XVIII,Overlap Type 'C", as shown on Page 36. The thread size was3 cord, 8 stitches per inch, and the length of overlap was 8 inches.The stlcn pattern wa a iz4ple rci of zig-zag .....t., /4 nh

wide.

The Joint of next highest efficiency yielded an averagebreaking strength of 6200 lbs., or an average efficiency of 96.4%.

This joint was fabricated in accordance with Series XVII,Overlap Type "B", as shou on Page 36. The thread size was3 cord, 8 stitches per inchj and the length of overlap was 8 inches.The stitch pattern was a four point cross stitch with the overlapreinforced on both sides with 1000 lb. Nylon Tape, WIL-T-5038,Type IV.

WAX TA ,o-31'R Pt II 10

o. 2__ylon Webbing, - I, 20,000 . t.s.

The most eificient Joint obtainea wiun the MIL-W-5787,20,000 lbs. webbing. yielded an average breaking strength of 21,000

This joint was fa'ricated in accordance with Series XXIV,as shown on Page 39. The thread size was 8 cord, 6 st:A.chesper inch, and the length of overlap was 10 inches. The patternwas a six point cross stitch reinforced at both ends by NylonWebbing, ?kIL-W-4088. Type XII.

10. Nylon Webbing, MIL-W-5787, Type Ii, 40,100 lbs. t.s.

The most efficient joint obtained with the MIL-W-5787,40,000 lbs. webbing, yielded an average breaking strength of 35,500lbs.

This Joint was fabricated in accordance with Series XXIII,Reinforced End Overlap, as showm on Page 39. The thread sizewas 8 cord, 6 stitches per inch, and the length of overlap was14 inches. 'The pattern was a six point cross stitch.

11. Nylon Webbing- MT-W-41088, -ype XIII, 60n lbs. t.s.

The MIL-W-4088, 6000 lb. webbing was introduced into thetest program to determine if the results obtained in the testsof the MIL-W-4088, Type X webbing joints would hold true for theType XIII, which is of a similar weave, The results indicatethat the most efficient joints obtained in the Type X weobingjoints were, in general, the most efficient joints in theType XIII webbing tests. The most efficient joint obtained withthe MIL-W-4088, Type XIII, 6000 lb. webbing, yielded an averagebreaking strength of 6353 lbs., or an average efficiency of86.9%, based on an average control strength of 7313 lbs. Thisjoint was fabricated in accordance with Series XII, Page 34.

WADC TR 56-313, Pt II 11

V. ANALYS±S OF JO!IT EFFICIENCIES

1. Nylon Cords, MIL-C-504O. Types IT aj.1 III.

The MIL-C-5040 type cords, core yarns encased in a^ ol ccv,,-... derive ti-e inajo.L portion of" tneir strength fromthe core yarns. An increase in ...... il stenth -':tsc od,is realized by the add4'cion of core yarns. The function oP thesleeve is not primarily one of strength, but rather, to ho-dthe core yarns in place.

fence, it would appear that the most efficient Jointin this type of cord would be one in which the stitching patternencompassed and bound to;ather the maximum number of core yarnsin the overlap ends, one to the other.

To illustrate this point, a typical sectional view ofthe cord is shown in Figure 4 along with two methods of stitch-ing the overlapped ends. It is evident from Figure "' that themost efficient type of overlap would be one constructed with atwo step zig-zag stitch, in which the ends of the cords weresuperimposed, one on the other.

After the general construction of the joint wasdetermined, the optimum le-nth - of overla thread --

stitches per inch was established by test.

For the Nylon Cord, MIL-C-5040, Type II, the test dataindicates that the most efficient joint, on the basis of lengthof overlap, thread size and stitches per inch, was the jointyielding an average breaking strength of 353.3 lbs. (77.3%efficient) for three inches of overlap, stitched with Size "F"thread as shown in Series I, Page 21.

For the MIL-C-5040, Type III, cord, the most efficientJoint was the one yielding an average breaking strength of555 lbs. The length of overlap was two inches and the threadwas Size "FF". (See Series I, Page 21.)

2. Nylon Cords, MIL-C--7515, Types II and VI.

As explained in Section II, Specimen Fabrioation, theplain overlapping of the "coreless" cord proved less efficientthan the method of threading one end of the cord into the otherand then stitching for an optimum length.

The joint formed by superimposing one end of the Type IIcord on the other and zig-zag stitching, yielded an average break-ing strength of 555 lbs. for a two inch overlap in which thecord failed. The Joint formed by threading the cord ends, oneinto the other for 6 inches and then zig-zag stitching for twoinches, yielded an aveoage breaking strength of 590 lDb.


The test data on the "coreless" tpe cords show Themost efficient joint constructiun to be on-, in whir, an endof the cord to be joined is threaded into au>. 4 nd thenstitched rith a t-vc, step zig-zag stitch for an optimum length.The length of stitching, the st e of thread, and the lengthof insertion of one cord into te other, would be a functionof the strength of the specific cord.

Braided Sleeve

Core/0 0 Yarns

0 '0 i0

O Core Yarns

Side by Side Superimposed

Cord Joint Comparison

Figure 4

3. Nylon Webbing, MIL-W-5625, 1/2 Inch Wide, 1000 lbs. t.s.

The results of the joint tests on the MIL-W-5625,1000 lbs. t.s, webbing, showed the most efficient constructionto be the reinforced type joint, stitched with a 3 point crossstitch pattern. This joint utilizes a reinforcing webbinginserted between the overlapped ends of the 1000 lb. webb'Dfirand extending for a distance of 1 inch beyond the ends of theoverlap. (See Series XXVII on the Overlap Type "A", Page 42.)

The next most efficient construction, as indicated bythe test results, utilizes reinforcing webbings on either sideof the overlap and extending beyond the exposed ends, for adistance of 1 inch. This joint also uses a 3 point cross stitch pattern.On both Joints the thread used was Size "F?". 8 stitches per inch.

The average brealcing strengths realized were, 1490 lbs.for the most efficient joint and 1488 lbs. for the jointf ne- t•g Wcot . iffieaxicy. Tne negligible difference in strengthrealized would make both joints equally efficient, on the basisof strength alone. A more complete analysis of these types ofoverlaps, will be made when considering the most efficient jointfor universal application.


4. ylon Webbing, MIL-W-5625, 1 inch U.de, 3000 lbs. t

The test data obtained from the webb-ng joint ,ests onthe MIL-W-5625, 3000 Its. webbing, shows the mu. vficient jointto be a plain overiap loint stitched with 3 cord thread, 11Stitches oer inch, in a 3 point -ross tvitch pattern. Thelength of overlap was 6 inches.

The joint of next highest efficiency was preciselythe same construction, with the exception that 8 stitches perinch were used in lieu of 11 stitches per inch,

The joint of next highest efficiency was the reinforcedtypejoint, utilizing a reinforcing webbing between the overlappedends of the 3000 lb. webbing. A comparison of the va.ious over-laps, here mentioned, will be found in Section VI, Analysis ofWebb Joints for Universal Usage.

5. Nlon Webbing, M_L-W-4,88, Type X, 8700 lbs. t.s.

The reinforced type joint, utilizing a reinforcingwebbing on both sides of the overlap, proved to be the mostefficient joint tested with the MIL-W-4088, 8700 lb. webbing.

The reinforced joint, utilizing the reinforcing webbingbetween the overlap webbs, proved to be the next highest ineff c-ency.

The most efficient Joint yielded an average breakingstrength of 9100 lbs., whereas, the joint of next highest effi-ciency in strength realized is sufficient to favor the doublyreinforced overlap (Series XXVI, Overlap Type "B", Page 41) overthe joint with the single reinforcing webbing between the overlap.(See Series XXVI, Overlap Type "A", as shown on Page 41.

6. Nylon Webbing, MIL-W-4088, Type XVIII, 6000 lbs. t.s.

The reinforced type Joint again proved to be the mostefficient in the case of the MIL-W-4o88, Type XViII, 6000 lb.webbing. This 4oint was the Series XMII, Overlap Type "B", asshown on Page 36, and utilized reinforcing webbings on bothsides of the overlapped webbs.

7. Nylon Webbing, MIL-W-5787, Type I, 20,000 lbs. t.s.

The Joints fabricated and tested with this webbing didnot include longitudinal reinforced Joints. No webbing ofsufficient width was immediately available for usp in these tests.As a Pvuult, the wenbings were tested with the wrapped end typeof reinfcrcement as described in Series XXIV, Page 39. Thesewere also made with the plain type overlap, utilizing 4 pointand 6 point cross stitch patterns.

8. Nylon Webbing, MIL-W-5787, ,ype I, 20,000 lbs. t.s.

These Joints were fabricated in accordance with theconfiguration shown in Table XX.

WADC TR 56-313 Pt II ll

VI. ANALYSIS OF JOINTS FOR CENERAL US.AGE

1. Basis of Evaluation

Manv different typ- of Joint construCtions werefabricated and tested. Some of the initial co;figurations wereeliminated quite readily because of obviously inferior qualities,which would be present for any type of webbing or cord ased. Theothers were not so easily analyzed. It was necessary, in somecases, to rate a joint of lower strength above one of higherstrength on the basis of some factor, such as, a lesser amount ofstitching used, a shorter overlap or a smaller size thread.

Other criteria for evaluation were facility of fabri-cation, necessity for additional meterials (reinforcing webbingsand necessity for non-standard materials or machinery.

2. Breaking Strength vs. Stitches per inch

In general, it was found that the breaking strength of aparticular joint was at its lowest, for a given length of overlap,if 5 stitches per inch were used. This was not due entirely tostitch failure. Webbing failures occurred in a substantial num-ber of cases where the 5 stitches per inch pattern was used. Adefinite increase in strength invariably resulted as the stitchesper inch were increased to 8. It was found that in the majorityof cases, as the stitches per inch were increased to 11, thestrength of the joint was reduced. The data presented in Table I,Page 16, illustrates the variations in breaking strength due tovariation in stitches per inch.

3. Comparison of Stitch Patterns

The following types of stitch patterns were tested:

1. Six Point Cross Stitch

2. Four Point Cross Stitch

3. Three Point Cross Stitch

4. Split Four Point Cross Stitch

5. Box Stitch

6. Zig-Zag Stitch - Single, double and triple row

7. Dimond Stitch

The highest joint efficiencies for the webbings wererealized in overlaps using the three, four and six point crogsstitch patterns. Where reinforcing webbs were used in conjunc-tion with the three, four and six point cross stitch patterns,increases in efficiency as high as 10% were realized.


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The advisability of ueing a thret, four or mo - pointcross stitch, appears to be governed by th. width n" che webbingin question. The results indicate that the u. or four pointstitching on the narrow webbing, causes crowding of the stitchingand results in a strength veduL -ion. *nis reduction in strengthhas two apparent causes; first, a crowdlng of the -titches intoa smaller area, thus, excessively restricting the elongatJ.-n of thefibers within the stitch pattern and secondly, bringing tih pointsof termination of the stitching closer together in the lateralplane. This results in more fibers being stressed at a givenlateral line than if the termination points were more widely spaced.Hence, for a narrow webbing, one would use a three point cross stitchrather than a four point cross stitch. This can readily be seenby comparison of the results of the Series XXV and Series aXVIItests on Pages 41 and 42.

4. Burned Ends vs. Plain Ends

Tests were made to determine the effect of overlappedwebbing ends which were cut with a hot wire on the strength of the

joint. Comparative tests were made of Joints in which the overlappedwebbing ends ifere cut with a rotary blade cutter, but were not burnedor seared. Nylon Webbing, MIL-W-4088, Type X, 8700 lbs. t.s., wasused to make the comparative tests. The joint construction was a4 point cross stitch pattern, using 6 cord thread, 6 stitches perinch and an 8 inch overlap. The stitching was carried beyond theends of the overlapped webbings for a distance of approximately 1/8inch. The average breaking strength of the burned end joints was8020 lbs. The average breaking strength of the plain end jointswas 8120 lbs. The low breaking strength on the burned end Jointswas 7900 lbs. The low breaking strength on the plain end jointswas 7940 lbs.

The results indicate that there is not an appreciablereduction in strength, due to the stitching passing over the burnedends of the overlapped webbings. However, it must be noted that theburning (searing) of the test webbings was controlled, whereas,webbings burned in production might not receive as careful attention.This might result in excessive burning and resulting shap edges atthe webbing ends to cause excessive thread breakage and resultantpropagation of thread failure throughout the stitch pattern. It istherefore recommended that, wherever possible, searing of thewebbing ends be eliminated or the stitching be stopped short of thewebbing ends.

If the stitching is stopped short of the webbing ends,this will result in a reduction of the stitch length amounting toapproximately 3/8 to 3/4 of an inch. This data indicates that astrength reduction of 200 to 300 lbs. may result on a webbing of1400 lba, control strength.


5. Effect of Thrread c

In general, the use of a larger size t. -.Il resultin an increase in strength if all other factors are equal. Table IAillustrates tnis trend for the smaller size threac_, Size "E" to

* Size "FF'i.

It is usually possible tc reduce the amount of stitc ing

necessary to obtain a given breaking strength when a larger sizet read is used.VII. CONCLUSIONS

1. Nlon Cord, MIL-C.-3040

The most efficient joint construction for general use onthe Nylon Cord, MIL-C-5040, and other cords of generally similarconstruction, is the superimposed overlap, stitched with a two stepzig-zag stitch. The length and width of the stitch would be afunction ofC the strength and diameter of the cord in queztion.

2. Nylon Cord; ML-C-7515

The most efficient Joint construction for general use onthe Nylon Cord, MIL-C-7515, and generally similar cords, is thetype in which one of the joint ends is threaded into the otherand then stitched with a two step zig-zag stitch for an optimumlength. The length for which one end is threaded into the other,and the optimum length and width of zig-zag stitching, would bea function of the strength and diameter of the cord in question.

3. Nylon Webbing

On the basis of the test data obtained, the most efficientjoint construction for general use on the webbings tested and thoseof generally similar construction, would be one using a three, fouror six point cross stitch pattern, depending upon the width andstrength of the webbing used. The reinforced type Joints exhibitS the highest efficiencies, except for the MIL-W-5625, 3000 Ibs.webbing; but require additional materials, (reinforcing webbings)

to attain the higher breaking strengths.

For a plain webbing Joint, with no reinforcing webbings,the most efficient construction is that using a three or more pointstitch pattern, based on the width and strength nf fl- e-Thc length or utitching and thread size would also be a function ofthe strength of the webbing.

For reinforced Joints, the most efficient Joint would bethat using the plain Joint construction, but having a reinforcingwebbing of suitable width and strength, between the overlappedwebbings.

TR 56-313 Pt II 18

I"*

TATITF IA

THREAD SIZE VS. BREAKING S17ENGT14

iiI '

I i ','n . , .. .REAKING

MATERIAL SIZE INL V STRENGTH COMMET

Nylon Cord, I Two step zig-zag stitch.MIL-C-5040, 375 lbs ."E" 6-7 328.3 Cord failed at splice,

Nylon Cord, l I Two step zig-zag stitch.IMI-C-040 '.7 F"I 11 3353'.CrMIL-C-5040. 375 bs 3 Cord failed at splice,

Nylon Cord, E _ _Two step zig-zag stitch.MIL-C-501O, 375 ibs__"E"_ 6-7 6 326.6 Cord failed at splice.

jNylor Cord, Two step zig-zag stitch.MIL-C-504O, 375 !bs,."F" 6-7 6 355 Cord failed at splice.

Nylon Cord,I Two step zig-zag stitch.

ILCord1, 550 lbalV'E"' 6'-7 3 565 'Cord tailed at splice

Nylon Cord, j Two step zig-zag stich.?'MIL-C-7515, 550 lbs."F" 6-7 3 571.6 Cord failed at splice.

Nylon Cord, Two step zig-zag stitch.MIL-C-7515, 550 Iba."E" 6-7 566.6 Cord failed at splice.

3, £ Nlon Cord, Two step zig-zag stitch.

MI -C_=7515, 550 los."?" 6-7 6 157. Cord failed at splice.I Three point cross stitch.MIL-W-5625, Webbing failed at end of1 w., 100 lbs. "F" 6 1,378 stitchinz.

Three point cross stitch.MIL-W-5625, Webbing tailed at end of1/2" w., 1000 lbs. "FF" 5 6 1,418 stitching.

Three point cross stitch.

_ ___-56 ",5 Webbint failed at end of

2Three point cross stitch.MIL-W-5625, Webbing failed at end of

11/2" w., 1000 lbs. 11 ,29, stitching.Three point cross stitch.

MIL-W-5625, Webbing failed at end of1/2" Ik~3w., 1000 lbs. "F" 8 6 1,432 stitching.Three point cross stitch.

L-W-5625, ~Ieb~gf 4 ~41/2" w., 1000 lbs. "FF"I 8 1 6 11,470 1stitching.


The reinforced joints, using a longitudinally reinf-'°cedwebbing, are of two types. One type uses tht reinforcing .ebbingbetween the overlapped webbings ana extends f&- a cert -,i distancebeyond the ends of the overlap. Se other type . 4ungitudinallyreinforced joint uses tnro reinforcing webbings, one on each sideof the overlap and ecxtending beyond the exposed ends for a certain

In general, these two types of reinforced Joints ar of

substantially the same efficiency. One exception would be theMIL-W-488, Type x, 8700 lbs. webbing, where the strength of thedoubly reinforced joint exceeded the strength of the singlyreinforced Joint by approximately 500 lbs.

The other type of reinforced joint (wrapped ends) are oftwo types. The fIrst type uses a reinforcing webbing wrappedlaterally around trae exposed ends of the overlap. The second typeuses a reinforcIng web h4 nr layed laterally on the top and bottomof the overlapped ends. Both of these reinforced joints are ofi substantially the same efficiency.

I i5

I,'

II

'WADO TR 56-313 Pt Ii 20

TABLE I

Cord Joint Test - ?ase II - Ser- T

II. _____

I 20 -7- 20 .% .

+ 1/32Two step zig-zag stitch, 1/8 - 0 wide, 6-'7 stitches per incn,coufting on side row.

My V Z .v V v-- IV.1MI

BREAKING

NYLON CORD THREAD STRENGTH F.MIL-C-5040 MIL-T-7807 "L" I LBS. [ COMMENT

S375 !bs. Size E"3 328.3 171.8snplice.

Type IICord failed at end of375 Ibs. Size "E" 6 326.6 71.51 splice.Type II, i Cord failed at end of

Type III Cord failed at end or

: e!siz "F" 3 5. 77.3 splice.

S37 lbs. Size ^F" 6 Cr355 77.7 splice.

I ,Cord failed at end ofjI±ype MiJ, splice on one specimen,H 550 lbs. 3 Size "E" 3 390 163.4 stitching failed on rest.

I Cord failed at end ofType III, splice on one specimen,550 lbs. Size "E" 6 415 67.5 stitching failed on rest.

Type III, Cord failed at end of.550 lbs. Size "Fl? 481.6 A78.4splice.±Type 11, Cord failed at end of

[ !150 lbs. Size "F" 6 1455 74.0 splice,

____~~______,Size IF, 6 2t'~ li Stitching failed on all75 lbs. Size ";E" _2_ _3 59.7___aples,

I Stitching failea in allIType II, "F"___ __ ........ al

375 Ibs. ISize "F" 250 154,y samp)les,

Cvrd failed at end ofType III, .?splice on all

1,550 lbs. Size "F" 2 555 90. m es.WADC TP 56-313 Pt I 21

TABLE 1..

CORD JOINT TESTS - PHASE II - SERIES 11

0I '-_ _ - -

S20 L ---

| I L -L, y.,,v vL vL - LN,,7;..

i [ SRENGTH .SNYLON CORD THPAR-,AD "L" EGTH EF.

MIL-C-75i51MIL-T-7807 "J(AVERAGE) %COMENT

Type II550 I bs. Size 'E" 3 5b5 95.3ord failed at end of splice.

Ty~~~e U ISI

.:550 ibs. Size 6 566.6 955pord failed at end of splice.Type IR ir-I 550 Ibs. Size IT" 3 571.6 196. Cord failed at end of splice.

S"1 ,I Type II* 550 lbs. Size "F" 6 573.3 96.7 Cord failed at end of splice.ITypel 56VI__ _ __ _ _ _ _ _

2000 lbs. Size "E" 3 1,345 155. d Stitching failed.

Type V6

2000 lbs. Size "F" -1,530 63.JStitching failed.

--Ii-._____I ___ _____ _

I MIL-C-7515, 550 lbs. t.s.Control u 593 lbs.II MIL-C-7515, 2000 lbs. t.s.Control = 2405 lbs.

22

I

TABtlE IV

CORD JOINT TESTS - PHAiaSE Ii - SERIES TI

I a"S

r A rIA

IBIIIz5~87SREKNGh 9E2 .od

NYLON CORD THREAD BRERAGEI r__S" COI _ _ _

MII ..t ! -- 7515 ,MI..L-T-7807 "L ST EN T...1 M N

.1 ~~Type VI, f±e t""i 2000 !bs. • 6 2340 2 .973 Cord filed at "All.

Ty pe VI,2000 lbs. "FF" 6 2346 2 97.5 Cord failed at "B".

Type II, Cord failed at end of550 lbs. "F" 6 590 2 199.5 stitching.

Type II, Cord failed at end of550 lbs. "FF" 6 580 2 97.8 stitching.

K____ __ 1-i1 7

r _ _ I._ _L-C-7515, 2000 lstsControl . 2405 lbs.

23

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a study of parachute seam design criteria · a study of parachute seam design criteria ... are...

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