REPORT NO. NADC-8/52d-66 EE 7~

TRAXIAUJY WOVEN FABRICS OF JVA, DACRONJZOLYESTER AND

S. 'YRIDS OF KEVIAR AND DACRON POLYESTER

LEANOR TH.=VADAA

S,• ýD .

Aircraft and Crew Systems Technology DirectorateNAVAL AIR DEVELOPMNT CENTER

Warminster, Pennsylvania 18974 D"ELECTE

J)UL 181980.

AIRTASK NO. AO3P-03PA/OM~B/k14F411P60ll~~

WORK UNIT i.D2 4

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

S>3 Prepared forV, • NAVAL AIR SYSTEMS ý.OiMANDDepartment of the Navy

C-> Washington, DC 20361

S'A Ol

N OT ICES

REPORT NUMBERING SYSTEM - The numbering of technical project reports issued by the Naval Air DevelopmentCenter is arranged for specific identification purposes. Each number consists of the Center acronym, the calendaryear in which the number was assigned, the sequence number of the report within the specific calendar year, andthe official 2-digit correspondence code of the Command Office or the Functional Directorate responsible for thereport. For example: Report No. NADC-78015-20 inmcates the fifteeth Cantor report for the year 1978, and preparedby the Systems, Dirertcrate. The numerical codes are as follows:

CODE OFFICE OR DIRECTORATE

no Commander, Naval Air Development Center01 Techr.ical Director, Naval Air Development Center02 Comptroller10 Directorate Command Projects20 Systems Directorate30 Sensors & Avionics Technology Directorate40 Communication & Navigation Technology Directorate50 Software Computer Directorate6a1 Aircraft & Crew Systems Technology Directorate70 Planning Assessment Resources80 Engineering Support Group

PRODUCT ENDORSEMENT - The discussion or instructions concerning commrcial products herein do not constilutean endorsement by the Government nor do they convey or imply the license or right to use such products.

APPROVED BY:.__________________ DATE:-

E. J. UCDR USN

UNCLASSIFIEDSECUMITY CLASSIFICATION OF THIS PAGE (When Date Entered)

REPOR DOCMENTTIONPAGEREAD INSTRUJCTIONSBEFORE COMPLETING FORM

I.:'REPORT NUMBER 12. GOVT A•CCESSION "1. 3. RECIPIEN'T'S CATALOG NUMBER

4. TITLE (.w.d Subtitle) S. TYPE OF REPORT & PERIOD COVERED

TR'IAXiALLY WOVEN FABRICS OF KEM.I-R, DACRON

POLYESTER AND HYBRIDS OF KEVLAR AND DACRON FINAL REPORTPOLYESTER 6. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(s) 5. CONTRACT OR GRANT NUMBER(e)

ELEANOR TH. VADALA AIRTASK.NO. A03P/03PA/001B/6WF41-411-0001WORK UNIT NO. DH 814

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASKAREA & WORK UNIT NUMBERS

Aircraft and Crew Systems Technology Directorate

Naval Air Development Center (60)Warminster, Pennsylvania 18974

11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

Naval Air Systems Command 3 APRIL 1980Department of the Navy 13. NUMBER OF PAGES

Washington, DC 20361 1514, MONITORING AGENCY NAME & ADDRESS(Il diferent from Controlling Ot1C6) IS. SECURITY CLASS. (of this report)

UNCLASSIFIEDIS&, DECLASSI FICATION/ DOWNGRADING

SCHEDULE

16. DISTRIBUTION STATEMCNT (of this Report)

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

17. DISTRIBUTION STATEMENT (of toe abetrac entered In Block 20, It different from Report)

IS. SUPPLEMENTARY NOTES

J19. KEY WORDS (Continue on reverse old* I1 neceesary and Identify by block number)a LTA applications, hybrid material,

flexible material, urethane coating,triaxial weave, mechanical and physical properties,Dacron polyester, environmnental exposure,Kevlar ,aramid, creasing

20. _it A'CT (Continue on revere, sIde It necessary and Identity by block n•mber)

ITo provide data for possible LTA (Lighter Than Air) application,four triaxially woven fabrics were made using yarns of: (1) Kevlar aramid,(2) Dacron polyester and (3) hybrids of aramid and polyester. The woventriaxial fabrics were coated with urethane. The material samples werecharacterized by removal and test of specimens. The test matrix includedcreasing and environmental conditioning tests.

DD FjORM7 1473 EDITION OF I NOV b• IS OBSOLETES/N 0102.LF.01444601 UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGE ("hon Date Entered)

UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS PAGE (U2csi Data Entered)

The results of this evaluation indicate that sow.m damage is done tothe Kevlar aramid yarns during processing thro'ugh the triaxial weavingprocess. The all aramid sample yielded the highest oreaking strengthwhen normalized on the bases of the uncoated fabric. Creasing, however,had a deleterious effect on the strength of the -,'-mid warp samples.

On the basis of all around performance, znh6 a.-d aramid sample andthe hybrid of polyester warp and aramid fill co:.nn:truction would be thebest choices for use in LTA applications. Kevlaz aramid fabrics, however,must avoid critical compressive loading which i, accentuated at anysmall radius of curvature or point of concentr.-:;d pressure.

0a

UNCLASSIFIEDSECURITY C.LASSI FICATION OF THIS PAGE'(When Date Entered)

NADC-80020-60

SUMMARY

To provide data for possible LTA (Lighter Than Air) application,four triaxially woven fabrics were made using yarns of (1) Kevlar aramid,(2) Dacron polyester and (3) hybrids of aramid and polyester. The woventriaxial fabrics were coated with urethane. The material samples werecharacterized by removal and test of specimens. The test matrix includedcreasing and environmental conditioning tests.

The results of this evaluation indicate that some damage is done tothe Kevlar aramid yarns during processing through the triaxial weaving process.The all aramid sample yielded the highest breaking strength when normalizedon the bases of the uncoated fabric. Creasing, however, had a deleterious effecton the strength of the aramid warp samples.

On the basis of all around performance, the all aramid sample and thehybrid of polyester warp and aramid fill construction would be the bestchoices !or use in LTA applications. Kevlar aramid fabrics, however, mustavoid critical compressive loading which is accentuated at any small radiusof curvature or point of concentrated pressure.

Accession For

NTIS GMA&IDDC TABUnannouncedjustification_.___--

e-t Co e.. ,

oAvail and/or

Dist special

NADC-80020-60

TABLE OF CONTENTS

Page No.

S UMMiARY .. . . . . . . . . .. . . . . i

LIST OF TABLE. . . . . . . . . . . . . . . . . . . . . . . . . . 3

LIST OF FIGURES. .. . . . . . . . . . . . . . . . . . . .. . 3

INTRODUCTION . . . . . . . . . . . . . . . . . ... . . . . . . 4

Yarn Usage... . . . . .................. 4

Fabric Geometry .......... .... . . . , 5

Bias Ply Construction ......... .... .. . 5

High Modulus Film With Single Ply ........... 5

Triaxial Construction. o . # * .***..... 5

DEVELOPMENT WORK . . . . . . . . . . .... . . .. . . . 5- 6

Triaxial Basic Weave. ..... .............. 6

Triaxial Biplain Weave ........ . . ......... 6

Candidate Materials .................. . 6

Coating of Candidate Materials...... . .. .. . . . . 6

Test Methods ........... .e • • .. . .. .. 7

Tensile Strength . . . # 0 eg... .. . . . . . . 7

Crease Test. . .. . . .0. . . . . . . . . . . . . . . 7

Environmental Z qsure .... . .. ... . . . . . 7

Tear Strength .o. .. . . . . . . . . . . . . . . . . 7

TEST RESULTS AND DISCUSSION . . . o . . . . . . . .o . . 8

Tensile Strength. . . .. .. . ... . . ....... 8

Tear Strength . . . . . .. . . . . ... .. . . . .. 8- 9

CONCLUSIONS . . . ...... . . . .. . . . . .o o o . . o 9

REFERENCES . . . .................. .. . 10

t 2

NADC-80020-60

LIST OF TABLES

Table No, Title Page No.

I Description 'of Triaxial Basic and Biplain U1

Fabric Samples

II Breaking Strength of Triaxial Fabric Samples 12

ill Tear Strength of Triaxial Fabric Samples 13

LIST OF FIGURES

Figure No.

1 Yarn Stress Strain, Curves of Dacron, Nylon 14and Kevlar

Basic and Diplain Triaxial Weave 15

3

,IFI

NADC-80020-60

I N T R O D U C T I 0 N

Recent interest in the Navy has developed concerning new uses for LTAvehicles such as reconnaissance, transportation, heavy lift operations, etc.Historically, the Navy abolished its LTA Program in 1961. No rigid airshiphas been built in the United States since 1934. The last non-rigid builtfor the Navy was constructed in 1959 - 1960.

Airships are pressure sensitive vehicles. Consequently, there isusually a need for at least part of the airship, whether rigid or non-rigid,to be capable of volume change and to be constructed of flexible material,reference (a). The classical rigid airship consisted of a framework structure,an external cover, interior gas cells and auxiliary structures. The externalcovers were cotton and acetate doped fabric to provide a smooth aerodynamicshape and to prevent environmental degradation tx the airship system, reference(b). The non-rigid airship incorporates the load carrying structure and theexternal cover in a single flexiLle unit, stabilized by interior pressure andusing air filled ballonets for pressure control. The following is a briefsummary of yarn and fabric geometry isage for LTA applications.

Yarn Usage

Cotton and Fortisan yarns dominated early LTA applications for flexibleunits. These ya4ns became obsolete with the introduction of high strengthnylon and Dacron polyester yarns. In addition to higher strength to weight,nylon and Dacron showed improved resistance to abrasion, heat and mildew.,

A more recent development in yarits for high strength to weight applica-tions are the aramids. Kevlar 29, one of the aramids, has been the mostadvanced structural yarn being used in aerostat applications. Typicalmechanical properties of twisted Kevlar 29 are shown compared with otherorganic yarns in Figure 1. Kevlar has twice the strength of most organics.

Stress strain curves for most organic fibers show a linear portion atlower stresses, and non-linear at higher stresses. Kevlar is an exceptionin that it's stvess strain curve is linear regardless of stress.

Materials which show no linearity on their stress-strain curve are notacceptable for use in the construction of airship envelores. Uncontrolledstretch results in distortion of che envelope shape which affects theaerodynamic performance of the airship. It also produce3 severe problemswith the rigid components which are attached to the envelope such as nosestiffening, suspension systems, cars, fins, etc.. This is the reason whyDacron polyester yarns are usually preferred to the use of nylon; nylonhas bettor tensile strength but greater stretch. The polyester fabrics,such as Vacron, demonstrate satisfactory elongation and are standard foruse in (Goodyear) airships and tethered balloons today.

4

/1

NADC-80020-60

Fabric Geometry

Bias Ply Construction

Most woven fabrics are biaxial structures wherein two systems of yarnsintersect and interlace at right angles to one another. These orthogonallywoven fabrics are effective in transmitting stress in their respective direc-tions, warp and fill, but not in any diagonal or bias direction. Such weavesare considered to be dimensionally unstable. The usual solution to providingthe dimensional stability required for LTA applications was to bond two ormore plies of fabric together such that one is oriented 450 to the other.This places a major axis in all directions and dimensional stability isachieved.

High Modulus Film With Single Ply

Another material construction which can be used to increase the dimen-sional stability of an orthogonal base fabric involves the lamination ofan unsupported high modulus film to a base substrate. In this construction,the high modulus film is analog~as to the bias ply previously described and mustlock the fabrics rectangular weave geometry and prevent yarn slippage anddistortion. The film provides a tensile member in the bias direction. Todate however, only the higher efficiencies obtained from closely spacedfilamentary materials, such as textiles appear to be satisfactory for non-rigid airships.

Triaxial Construction

A recently patented development, triaxial weave, provides for transferof stresses in the bias direction with use of three systems of yarn. Thethree yarns intersect and interlace at 600 angles with one another andprovide for a more uniform distribution of load during deformation, reference(c). The three systems of yarn are intermeshed in a single fabric to providequasisotropic properties. Theoretically, this should make possible the con-struction of a single ply envelope.

DEVELOPMENT WORK

Potentially, Kevlar 29 and triaxial weave are very promising candidatesfor LTA applications. On this basis, they were selected for development work.

A series of candidate fabrics were fabricated for use in aerostats andpartially tested under contract to N. F. Doweave, Inc. Doweave Inc., is nolonger in business. Currently, Gentex Corp., using similar equipment iscapable of weaving triaxial fabrics.

V5

,~1

NADC-80020-60

With a view toward the simplification of fabric design, it was decidedto include two current production fabrics in the study; an all polyester(Dacron 52) sample in the basic weave pattern and an all aramid (Kevlar 29)sample in the biplain weave, reference (d). Two new constructions, bothhybrids of polyester and aramid yarns, were made, one each of the basicweave and the biplain weave. Mechanical and physical testr were ccnductedby personnel from this Center and the Philadelphia College of Textilesand Science.

Triaxial Basic Weave

The basic weave, the simplest triaxial configuration, consists of twowarp yarns in the machine direction. These are not interwoven but one liesover the other, Figure 2. The fill yarn (transverse direction) passes ove:"one set of warp and under the other set thereby locking the yarnso togetherin triangular intersections. The hexagonal holes in this open weave areabout twice the yarn diameter.

Triaxial Biplain Weave

In the biplain weave construction, less porosity is achieved by weavingthe horizontal or fill yarns over and under the two sets of warp yarns, Figure 2.The biplain weave may be considered one of the triaxial counterparts of thetraditional plain weave, in which tl'e fill yarn is woven over and under eachwarp yarn, one by one, reference (c). The biplain construction achieves closedstructural fabric with exceptional dimensional stability.

C'ndidate Materials

Four candidate materials were woven on full scale production equipment.The fabric samples were identified as follows:

BP21P is a biplain triaxial fabric composed of 210 denier Dacron 52 yarns.

BP2!PK is a biplain triaxial fabric with 210 denier Dacron 52 warp yarnsand 200 denier Kevlar 29 filling yarn.

B20K is a basic triaxial fabric composed of 200 denier Kevlar 29 yarns.

B20KP is a basic triaxial fabric with 200 denier Kevlar 29 warp yarns anda 210 denier Dacron 52 filling yarn.

A description of the fabric samples is given in Table I.

coaning of Candidate Materials

Fabrics were coated with a ureriane transfer film by Reieves Brothers Inc.The weight of the urethane was approximately 3 ,. 4 oz./sq. yd&

6

RA-DC-80020-60

Test Methods

Tensile Strength

Fabric tensile strength was determined on uncreased, ana creased specimensin the three major axes: ma(.hine (900 to fill), transverse (filling) and inthe bias direction using the grab breaking strength method (Federal Specifica-tion CCC-T-191b, Method 5100). Grab test specimens measure four inches bysix inches and were tested with one inch jaws in an Instron Tensile Tester.Normally, textile tensile strength is tested with one inch by six inchspecimens. In directions other than true warp or fill however, tensiledeformation leads to anaznolous results. For e:cample, in the triaxial weave,very few yarns,if any,are gripped by both jaws during testing. Massiveslippage occurs in addition Lo the closing of the trellis configurationat yarn intersections.

Crease Test

The crease test consisted of placing a Z fold in a tensile specimen.The Z fold consisted of tw•o folds in an accordian fashion, with a one inchspacing between the folds. Each fold was a 1800 crease parallel to thefour inch width of the censile specimen. Each crease was individually "pressed,n'" by placing the test specimen on a flat surface and rolling the creasewith a ten pound rod. This was done a total of 100 times on each specimen.

Environmental Exposure

The environmental exposure test consisted of 30 days at 95% relativehumidity and 140°F temperature.

Tear Strength

Tear strength was measured in the machine and crosswise directions byboth the tongue (ASTM Standard D2261) and trapezoid methods. Tongue teartest specimens, six inches by eight inches, were cut so that the yarns to beruptured lie in the short direction. A cut three inches in length is madealong the longer centerline of the test specimen. This cut produces two-threeinch by three inch tongues which were placed in the upper and lower jaws of anInstron Tensile Tester.

Trapezoid tear specimens, 8-1/2 inches by 5-3/8 inches,were cut with aone inch slit placed midway along the longer direction. The sample is insertedon the bias betwee~n the jaws of the Instron Tensile Tester. This test isentirely of a tension type and has little meaning in terms of the practicaltearing characteristics of the fabric.

4. 7

NADC-80020-60

TEST RESULTS AND DISCUSSION

Tensile Strength

A comparison of breaking strength values for the triaxial fabric samplesis given in Table II. The breaking strength is stated in lbs./in. (breakingload in pounds divided by jaw: width). The breaking strength of the machineand transverse specimens of the all Kaviar sample (B20K) are about equal;206 lbs./in. rompared to 201 lbs./in. The bias strength is approximately50% of these values; a marked improvement over biaxial fabrics which havepractically no bias strength.

The replacemeont of the armnid fill yarn with a polyester yarn markedlyaffects the tensile strength in the transverse direction. The tensilestrength decreases from 201 to 81 lbs./in., 60%. deczease. The all polyestersample, BP21P, yielded the highest relative tensile strength of 333 lbs./in.in the machine (warp) direction.

Normalized breaking strength Table II, adjusts the data for differencesin the total fabric weight and is presented in lbs./in. divided by oz./yd. 2

Tensile properties depend primarily on fiber properties. Because thebase fabrics are not the same weight, the breaking strength is also normalizedto adjust for differences in the base fabric weight and is presented inTable II. The anticipated effect of the higher strength to weight ratio ofthe aramid yarns is here reflected in the higher tensile strength of thebasic triaxially woven fabrics (B20K and E20KP). The magnitude of thiseffect, however, is of a lesser degree than expected. The aramid Kevlarhas over twice the breaking strength of polyester. The all aramid samplehowever is only 47% stronger than the all polyester sample; 137 lbs./in.compared to 93 lbs./in.

It is theorized that damage occurs in the passage of t.,e aramid warpyarns through the triaxial weaving process. Little if any damage occurs inthe manipulation of the polyest-r warp yarns. As a result, the initialadvantage of the inherent high strength to weight ratio of che aramid yarnover the polyester yarn is partially lost during weaving.

The aramid warp samples show a greater loss in strength due to creasing.The strength of the polyester warp samples are unaffected by creasing butshow approximately a 30% reduction in strength after environmental exposure.

Tear Strength

Tear properties depend not only on fiber properties but also on otherfactors such as fabric construction, coating, adhesion, etc. Because ofthe variations in these factors in this studv, it is difficr,,t to make adirect comparison in the interpretation of the results. Tongue and trapezoidtear strength is reported in pounds of tearing force or lead. The tearstrength data are also normalized to adjust for differences in fabric weightand are reported in pounds per ounce per square yard, Table III.

8

NAMC-80020-60

The aramid warp fabrics exhibit much greater resistance to tear thanthe polyester warp fabrics regardless of tear technique. The sample con-structed of a polyestc: warp and Kevlar filling (BPIIPK) would appear tobe a compromise between the low tear strength of the all polyester sampleand the higher values of the all Keviar sample.

CONCLUS IONS

The results of this ,valuation indicate that some damage is done tothe Kevlar aramid yarns during processing through the triaxial weaving process.The all aramid sample (B20K) yielded the highest breaking strength when normalizedon the bases of the uncoated fabric. Creasing, however, had a deleterious effecton the strength of the aramid warp samples.

On the basis of all around performance, the all aramid sample (B20K) andthe polyester warp and aramid fill construction (BP21PK) would be the bestchoices for use in LTA applications. Perhaps Kevlar warp yarns can be sizedand lubricated for improved manipulation through the triaxial machine. Inaddition to proper sizing, however, Kevlar aramid filaments must avoid criticalcompressive loading which is accentuated at any small radius of curvature ovpoint of concentrated pressure.

9

NADC-80020-60

RE FERENCES

(a) Mayer,, N. 'LTA Structures and Materials Technology" Proceedingsof the Interagency Workshop on Lighter Than Air Vehicles, -TTL Report R72-2, Jan 1975, M.I.T. Flight Transporation Lab.

(b) Marcy, W. L. "Parametric and Conceptual Design of Fully BuoyantAir Vehicles," Report No. NADC-76013-30 of 3 Jun 1977.

(c) Alexandroff, E. E. "Design Development and Testing of NewAerostat Material," Proceedings Eighth AFCRL Scientlfic BalloonSymposium 30 Sep - 3 Oct 1974; AFCRL-TR-0393, Special Reports,No 182.

(d) N. F. Doweave, Inc. "The Fabrication and Testing of CandidateAerostat. Envelope Materials Made From Triaxial Fabric,"Report No. NFD 77DI003, of 10 Nay 1977.

10

NADC-80020-60

0 03

r0->

-4 Ln

N %0~0 0 0

* * I',- '0 0

434

rz 0 01-

Nd 0f-I 43

NI %D co 0 0*q CI in- 0-4 N

~~"4

H #~~-443 4

'001 CN 0 co0

P4I N. 0 4 04 In'

H

i-I N1 0

00

4v4

oC 1.4

U N

r40

r4 . Z4 4,

Ud 44Cl 0~ 0' N3

1 4 -t4 Cd .4

NADc-80020..60

'H O Lco o

I CNI NC' cq\0 -f,- 0C\ co m

Lr~-4 ~ -4

tn N Lt

N n

rOI C1 %0 OnIt ntP c

-4-

C144

goH 0 MN l' "t

M C- 4 C- qC n DL ý -

-4 -4

C-4 cx ccJf I*n 0

H C1 q 0

9 rq tn .0go0

4.3 0

N co CCqJM

C4c C 4 54 '0 '

54 0 554'. 00 *o

N 4 00 eq I - 0

" "54 M Hn Nta 00 1 0%0 P 5.4

rz4 044-I-- t eq In

1. 12

NADC-80020-60

N~0 N* 0' co

H C-4

P4 ~ ~ 0. 00

0

m o n-fo

p-0 C1 -o -It0 .aOr4-

tn2cq C.4 O .n % 14

pq Tcn ce) a,,C;C

Ln0eq C*404 M2

N N -I~vs*.w 00040 'n

02

00. 000 0 %H -4~ C-44.- a% a%-44A a

1-4 M H4 Cq cH

WE-40

cn ; No

O41

"4 05.

-4 41-

0p 0024J ~ ~ ~ 4 00 ~i4.

9)0e r. a

0 41

0 4 0 "0 $44.H

.C 13

NADC-80020-60

500'-

DRY TWISTED YARNS10" GAGE LENGTHROOM TEMPERATURE

400 KEVLAR" 29

U,€'

0- 300

I-)Cl

"- 200'/inz DACRON')

LON

100.

0 5 10 15 20STRAIN, %

Figure 1. Yarn Suress Strain Curves of Dacron,

Nylon and Kevlar

14

NADC-80020-60

BASIC BIPLANE

Figure 2. Basic and Biplane Triaxial'Weave

15

DISTRIBUTION LIST

REPORT NO. NADC-80020 - 6 0

AIRTASK NO. AO3P-03PA/OOB/6WF41-41l-0O0lWORK UNIT NO. DH 814

No. of Copies

NAVAKsyscoM (AIR~94 . . . . . .

(2 for retention)Cl for AIR-03P 3 )

DT IC. . . . . . . . . . * * * * . * * * * * * * * , . * *1

Bell Aerospace, Nev Orleans, L& (Mr. 'James Bell)* . . .. . .

Grumman Aerospace Corp., Bethpage, NY (Mr. M. Epps) . . . . . .

McDonnell-Douglas Corps, Titusville, FL (Mr. J. J. Kessler) . *

Carnegie-Meilon UniversitY, Pittsburgh, PA (Professor C. M,. Adas) 1

Jet propulsion Laboratory, Pasadena, CA (Mr. V. C, Clarke,Jr.).

Martin Marietta, Denver, CO (0r. W. Marcy). . . . . . . . . 1

TCOM Corp., Columbia, MD (Mr. R. Ashford) . . . . . . . .. . .

LC Dover, Frederica, DE (Sp r. G. Durney) . . . . . . . . . .'.

Lockheed M4issiles & Space Corp., Sunnyvale, CA (tir. 11. Chappelle) 3

Goodyear Aerospace Corp*, Akron, Oil (Mr. D. Williams) . . . * • 1

j .. .. .