Kevlar KM2 Yarn and Fabric 

Strength Under Quasi-Static Tension 

by Thomas J. Mulkern and Martin N. Raftenberg 

ARL-TR-2865 October 2002 

Approved for public release; distribution is unlimited. 
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position unless 

so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the 

use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

ARL-TR-2865 October 2002 

Kevlar KM2 Yarn and Fabric Strength 

Under Quasi-Static Tension 

Thomas J. Mulkern and Martin N. Raftenberg 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited.
ii

Abstract 

Kevlar KM2, 600 denier, was Instron tested in quasi-static, uniaxial tension to determine its 

strength. Specimens included both single yarns and 68-yarn-wide, single-ply strips of plainwoven fabric (Style 706). Never-woven single-yarn specimens were tested with varying degrees 

of initial twist. Strength of the untwisted, never-woven yarn was 2.66 ± 0.04 GPa. The twist 

multiplier was 1.2. Single warp-oriented and fill-oriented yarns were extracted from Style 706 

fabric, tested, and found to have strengths of 2.06 ± 0.01 and 2.20 ± 0.05 GPa, respectively. The 

single-ply fabric specimens of both warp and fill orientations were tested and found to have 

strengths of 2.23 ± 0.04 and 2.67 ± 0.04 GPa, respectively. The strength effects of weaving, 

finishing, yarn extraction, and inter-yarn contact are discussed. 
iii

Acknowledgments 

The authors thank Philip M. Cunniff of the U.S. Army Natick Soldier Center and Dr. Brian Scott 

of the DuPont Corporation for very helpful discussions. We also thank Linda L. Ghiorse, Dr. 

Bruce Burns, and Edward Rapacki of the U.S. Army Research Laboratory, all of whom reviewed 

the manuscript and provided helpful comments. 
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v

Contents 

Acknowledgments iii

List of Figures vii

List of Tables ix

1. Introduction 1

2. Methods 2

2.1 Yarn Tests........................................................................................................................2 

2.2 Fabric Tests .....................................................................................................................4 

3. Results 7

3.1 Single-Yarn Tests............................................................................................................7 

3.1.1 Initial-Twist Effects on the Strength of Never-Woven Yarn .............................7 

3.1.2 Strength of Untwisted Yarn: Never-Woven, Extracted Warp, and 

Extracted Fill .....................................................................................................7 

3.2 Single-Ply Fabric Tests .................................................................................................10 

4. Discussion 10

4.1 Initial-Twist Effects on the Strength of Never-Woven Yarn ........................................10 

4.2 Strength of Untwisted Yarn; Never-Woven, Extracted Warp, and Extracted Fill........12 

4.3 Strength of Single-Ply Fabric–Warp and Fill................................................................13 

4.4 Single-Ply Fabric Strength Compared With Untwisted Yarn Strength.........................13 

5. Summary 14

6. References 17

List of Symbols 19

Report Documentation Page 21
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vii

List of Figures 

Figure 1. Plain weave construction, composed of two mutually orthogonal families of warp 

and fill yarns. .............................................................................................................................2 

Figure 2. Instron cord and yarn grip employed in the single-yarn tests. ........................................3 

Figure 3. Instron 4505 loading frame. ............................................................................................5 

Figure 4. An Instru-Met capstan webbing grip used in the tests. ...................................................6 

Figure 5. A specimen clamped in the Instron 4505 apparatus........................................................6 

Figure 6. Strength results for single yarns with various degrees of initial twist.............................8 

Figure 7. Strength results for never-woven single yarns vs. the degree of initial twist..................9 

Figure 8. Strength results for untwisted single yarns....................................................................10 

Figure 9. Strength results from the fabric tests.............................................................................11 

Figure 10. Strength results for untwisted yarns compared with those for fabric..........................13 
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ix

List of Tables 

Table 1. Strength of Kevlar yarns...................................................................................................1 

Table 2. Specimen initial twist for each single-yarn test series......................................................4 

Table 3. Y, TA, TB, TC series results. ...........................................................................................8 

Table 4. Y, XW, XF series results. .................................................................................................9 

Table 5. W and F series results. ....................................................................................................11 
x

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1

1. Introduction 

Plies of plain-woven Kevlar fabrics are the usual components of “soft” body armor (National 

Institute of Justice Standard levels 1–3A.) According to the DuPont Corporation (undated), 

“Kevlar KM2 is a new, very high strength, high toughness [form of Kevlar] designed for 

improved ballistic fragmentation resistance and energy absorption capacity.” The various forms 

of Kevlar, such as KM2, 29, and 49, are all composed of the same paraphenylene 

terephthalamide (PPTA) monomer. The forms differ in the degree of crystallinity, which reflects 

the degree of molecular alignment and hydrogen bonding between neighboring molecules (Scott 

2001). 

Table 1 compares single-yarn quasi-static strength of KM2 to those of other forms of Kevlar. 

Here, σfail is the yarn strength, or maximum stress attained on a tensile stress-strain curve. The 

KM2 strength results were obtained from publications by H. H. Yang of DuPont. Note that KM2 

is distinguished by a relatively large value for σfail. 

Table 1. Strength of Kevlar yarns. 

Yarn Type σfail

(GPa)

Kevlar 29 2.9a 

Kevlar 49 2.9a 

Kevlar 68 3.1a 

Kevlar 119 3.1a 

Kevlar 129 3.4a 

Kevlar 149 2.3a 

KM2 3.3b 

a

Yang (1993), p. 26. 

b

Yang (2000), p. 219.

The strength values in Table 1 do not make clear the degree of initial twist applied to the yarn. 

One goal of the present study is to directly examine the dependence of strength upon the initial 

twist for the case of KM2. 

Yarns are generally not pretwisted in a woven fabric, so that strength measurements in untwisted 

single yarns are most relevant to fabric properties. Figure 1 sketches a single ply of a plain 

weave; this ply consists of a family of warp yarns orthogonal to a family of fill (weft) yarns. The 

creation of the ply involves the processes of weaving and finishing, both of which can incur 

damage to the individual yarns. A second goal of the present study is to bound the damage 

associated with these processes. To that end, 600-denier yarns aligned with the warp and the fill 

directions were extracted from a ply of KM2. Strengths of these extracted yarns were compared
2

Source: Reproduced from Warner (1995), p. 271. 

Figure 1. Plain weave construction, composed of two mutually orthogonal families of warp and fill 

yarns. 

with strength measurements for untwisted, never-woven yarns. Any damage incurred during 

yarn extraction would have contributed to the observed differences. 

Finally, quasi-static tensile data are presented from 68-yarn-wide specimens of plain-woven 

600-denier KM2 fabric (style 706) loaded along either the warp or the fill direction. Fabric 

strength results derived from these measurements are compared with strength results from 

untwisted single-yarn specimens. 

2. Methods 

2.1 Yarn Tests 

Each test involved a single yarn of Kevlar KM2 loaded in uniaxial tension. American Society 

for Testing and Materials (ASTM) Standard D2256-97 (ASTM 2000) provided guidance for the 

tests. An Instron 5500 tensile machine was employed with two Instron Cord and Yarn Grips 

(Figure 2). Each specimen had an initial length of 50 cm. Each end was clamped into the 

capstan grip and then wrapped once around the grip. At the start of the test, a central portion 

about 25 cm in length was not in contact with either grip. The crosshead separation rate was 

maintained at 2.12 mm/s. The specimen was elongated until rupture. The applied force was 

sampled 25 times/s. The maximum detected force value was denoted Ffail and converted to 

strength, σfail, by the following procedure: 
3

Source: Reproduced from Instron Corp. (undated), p. 6.5.

Figure 2. Instron cord and yarn grip employed in the single-yarn tests. 

A yarn of 600-denier KM2 contains 400 filaments (Scott 2001). A single filament has a circular 

cross-section and a nominal diameter of 12 μm (Yang 1993, pp. 28, 30), which corresponds to a 

filament cross-sectional area of 1.13×10-4 (mm)2

. A KM2 yarn’s cross-sectional area, Ayo, is 

therefore 0.0452 (mm)2

. The yarn’s strength is defined by 

yo

fail

fail A

F

σ = . (1) 

Six series of single-yarn tests were conducted and are denoted Y, XW, XF, TA, TB, and TC. 

Specimens used in series Y were obtained from DuPont. Each specimen had never been woven 

and was untwisted. Nine different specimens were studied (Y1–Y9.) Specimens used in series 

TA, TB, and TC were also obtained from DuPont. These specimens were twisted prior to the 

test by the amounts τo, measured in turns per centimeter and given in Table 2. 
4

Table 2. Specimen initial twist for each single-yarn test series. 

Test

τo

(turns/cm)

Y 0.0 

XW 0.0 

XF 0.0 

TA 0.69 

TB 1.30 

TC 1.93 

Specimens used in series XW and XF were extracted from plies of style 706 fabric. This fabric 

is composed of plies of plain-woven 600-denier yarns of KM2. Six specimens of warp-direction 

yarns (XW1–XW6) and seven of fill-direction yarns (XF1–XF7) were studied. All warpdirection yarns were extracted from a single ply. All fill-direction yarns were extracted from a 

different single ply. The extraction procedure applied the ravel strip method (ASTM 1995). An 

individual yarn was gripped by hand at the edge of a single ply and pulled. 

2.2 Fabric Tests 

ASTM Standard D5035-95 (ASTM 1995) again provided guidance for the tests. The uniaxial 

tension tests were performed with an Instron 4505 load frame such as that shown in Figure 3. 

The Instron load cell was rated at 100-kN maximum load. Instru-Met capstan webbing grips 

(Figure 4) were used in place of the “wedge action grips” in Figure 3. Figure 5 shows a 

specimen clamped in preparation for a test. 

All specimens were created by the ravel strip method (ASTM 1995) from the same sheet of style 

706 fabric. Each specimen had an initial length of 1.219 m and a width of 68 yarns. Style 706 

KM2 fabric contains 34 yarns/in (Scott 2001), so the specimen’s width was 50.8 mm. At each 

end of the specimen, a length of 50 mm was clamped into the capstan grip. The specimen was 

then wrapped twice around each capstan grip. During each test, the load frame crossheads 

moved at the constant rate of 2.12 mm/s. Force was sampled 25 times/s. 

Specimens were pulled until rupture. Strength, σfail, was computed from the maximum force 

measurement, Ffail, using 

σ . fail

fail

yo

F

A = 68 (2) 
5

 “Wedge action grips” no. 5 were replaced with the capstan grips. 

 Source: Reproduced from Instron Corp. (1988), pp. 1–4, 5. 

Figure 3. Instron 4505 loading frame.
6

Figure 4. An Instru-Met capstan webbing grip used in the tests. 

Figure 5. A specimen clamped in the Instron 4505 apparatus.
7

Twelve specimens were tested. Six were elongated along the warp direction and had the fill 

direction associated with the width. These are Tests W1–W6. The other six were elongated 

along the fill direction and had the warp direction associated with the width. These are denoted 

Tests F1–F6. 

3. Results 

3.1 Single-Yarn Tests 

3.1.1 Initial-Twist Effects on the Strength of Never-Woven Yarn 

Results from series Y, TA, TB, and TC are presented in Table 3 and Figure 6. In this and in 

subsequent tables, “s.d.” denotes “standard deviation” and “s.e.” denotes standard error of the 

mean. The latter equals s.d./ N , where N is the number of tests in the series (Taylor 1997). All 

strength values from series Y are smaller than any values from TA, TB, or TC. There is overlap 

in strength values from the three series involving nonzero twist. 

The strength values were 2.66 ± 0.04 GPa for the nine Y series tests, 3.21 ± 0.05 GPa for the 

nine TA series tests, 3.36 ± 0.04 GPa for the eight TB series tests, and 3.28 ± 0.03 GPa for the 

six TC series tests. Thus, as illustrated in Figure 7, measurable strength increase occurred as the 

initial twist was increased from zero (Y) to 0.69 turns/cm (TA) to 1.30 turns/cm (TB). Further 

increase of initial twist to 1.93 turns/cm was accompanied by a slight decrease in strength (TC). 

3.1.2 Strength of Untwisted Yarn: Never-Woven, Extracted Warp, and Extracted Fill 

Results from series XW and XF, involving single-yarn specimens that had been extracted from 

woven fabric, are presented in Table 4 and Figure 8. As stated in section 2.1, XW and XF 

specimens had been oriented along the warp and fill directions, respectively, prior to extraction. 

Results from untwisted, never-woven yarns, series Y, are added to Table 4 and Figure 8 for 

comparison. The strength values for the Y, XW, and XF series were 2.66 ± 0.04, 2.06 ± 0.01, 

and 2.20 ± 0.05 GPa, respectively. 

Yarns that were extracted from woven fabric (series XW and XF) exhibited smaller strength 

values than yarns that were not previously woven (series Y.) Of the extracted yarns, those that 

had been woven in the warp direction (XW) exhibited generally smaller strengths than those that 

had been woven in the fill direction (XF), although there was some overlap. 
8

Table 3. Y, TA, TB, TC series results. 

Test σfail

(GPa) 

Test σfail

(GPa)

Test σfail

(GPa)

Test σfail

(GPa)

Y1 2.84 TA1 2.99 TB1 3.40 TC1 3.24 

Y2 2.66 TA2 3.03 TB2 3.51 TC2 3.30 

Y3 2.58 TA3 3.13 TB3 3.46 TC3 3.13 

Y4 2.73 TA4 3.28 TB4 3.23 TC4 3.36 

Y5 2.42 TA5 3.38 TB5 3.25 TC5 3.33 

Y6 2.77 TA6 3.32 TB6 3.39 TC6 3.33 

Y7 2.78 TA7 3.23 TB7 3.33 — —

Y8 2.61 TA8 3.15 TB8 3.31 — —

Y9 2.56 TA9 3.38 — — — —

mean 2.66 mean 3.21 mean 3.36 mean 3.28 

s.d. 0.13 s.d. 0.14 s.d. 0.10 s.d. 0.08 

s.e. 0.04 s.e. 0.05 s.e. 0.04 s.e. 0.03 

Figure 6. Strength results for single yarns with various degrees of initial twist.
9

Figure 7. Strength results for never-woven single yarns vs. the degree of initial twist. 

Table 4. Y, XW, XF series results. 

Test σfail

(GPa)

Test σfail

(GPa)

Test σfail

(GPa)

Y1 2.84 XW1 2.03 XF1 2.27 

Y2 2.66 XW2 2.09 XF2 2.43 

Y3 2.58 XW3 2.07 XF3 2.16 

Y4 2.73 XW4 2.10 XF4 2.05 

Y5 2.42 XW5 2.02 XF5 2.17 

Y6 2.77 XW6 2.06 XF6 2.23 

Y7 2.78 — — XF7 2.06 

Y8 2.61 — — — —

Y9 2.56 — — — —

mean 2.66 mean 2.06 mean 2.20 

s.d. 0.13 s.d. 0.03 s.d. 0.13 

s.e. 0.04 s.e. 0.01 s.e. 0.05 
10

Figure 8. Strength results for untwisted single yarns. 

3.2 Single-Ply Fabric Tests 

Results from series W and F are presented in Table 5 and Figure 9. The strength for series W 

was 2.23 ± 0.04 GPa, and that for series F was 2.67 ± 0.04 GPa. Each value in series F is larger 

than any value in series W. 

4. Discussion 

4.1 Initial-Twist Effects on the Strength of Never-Woven Yarn 

The dependence of yarn strength upon the amount of initial twist has been previously studied in 

the case of Kevlar (Yang 1993, pp. 34, 35). Yang (1993) does not identify the type of Kevlar 

used in the study, but does report that the denier, gauge length, and strain rate were 1500, 

254 mm (10 in), and 0.0017/s (0.10/min), respectively. Yang (1993) defines a twist multiplier 

(TM) by 
11

Table 5. W and F series results. 

Test σfail

(GPa)

Test σfail

(GPa)

W1 2.33 F1 2.77 

W2 2.07 F2 2.69 

W3 2.18 F3 2.47 

W4 2.23 F4 2.75 

W5 2.31 F5 2.61 

W6 2.28 F6 2.72 

mean 2.23 mean 2.67 

s.d. 0.10 s.d. 0.11 

s.e. 0.04 s.e. 0.04 

Figure 9. Strength results from the fabric tests.
12

TM turns / in denier turns / cm denier = = τ τ o o () ( )

73 29 , (3a) 

and states without qualification that “a twist multiplier of 1.1 is optimal for Kevlar yarns” 

(p. 34). For the special case of 600 denier, equation (3a) reduces to 

TM 600denier = 084 . τ o . (3b) 

The least-squares-error parabolic fit to the four data points in Figure 7 is 

mean (σfail) = 2.66 GPa + (102 GPa Α cm) τo ! (0.366 GPa Α cm2

) τo

2

, (4) 

which is added to the figure. Here, τo is in turns/cm. This parabola attains its maximum of 

3.37 GPa corresponding to a τo of 1.39 turns/cm (3.54 turns/in). From equation (3b), the TM 

value associated with this maximum strength is 1.2, in agreement with the value of 1.1 cited by 

Yang. 

The initial increase in σfail with increasing τo has been attributed at least in part to frictional 

effects between filaments within the yarn. When a filament within a twisted yarn breaks, 

although it can no longer support an axial load at the breakage point, remote from that point the 

filament can still support a load because of frictional contact with neighboring yarns (Hearle 

1969; Warner 1995, pp. 268, 269). 

As noted in section 1 (Table 1), Yang (2000) reports a strength of 3.3 GPa for KM2 with no 

discussion of the corresponding degree of initial twist. This strength value is similar to our mean 

results of 3.21, 3.36, and 3.28 GPa from series TA, TB, and TC, respectively. On the other hand, 

this strength result in Yang (2000) is substantially larger than our result of 2.66 GPa from series 

Y. These comparisons strongly suggest that the result in Yang (2000) was based on specimens 

with non-zero initial twist. 

4.2 Strength of Untwisted Yarn; Never-Woven, Extracted Warp, and Extracted Fill 

As noted in section 3.1.2, untwisted yarns that had been extracted from woven fabric (series XW 

and XF) exhibited smaller strength values than untwisted yarns that were not previously woven 

(series Y). The damage that produced these strength reductions relative to the baseline Y series 

can be attributed to some combination of three possible sources: the weaving, the subsequent 

finishing (especially the scouring), and the yarn extraction procedure. 

As also noted in section 3.1.2, of the extracted yarns, those that had been woven in the warp 

direction (series XW) exhibited generally smaller strengths than those that had been woven in the 

fill direction (XF). This observation is consistent with the notion that greater damage was 

inflicted on the warp yarns than on the fill yarns during one or more of the weaving, scouring, 

and extraction processes. The weaving process involves several steps that can incur damage to 
13

yarns. The scouring process involves pulling the woven fabric along the warp direction, so that 

greater damage is generally inflicted upon warp yarns than on fill yarns. Finally, because the 

warp yarns were more crimped than the fill yarns, they are likely to have suffered more damage 

during extraction. 

4.3 Strength of Single-Ply Fabric–Warp and Fill 

Strengths found for fabric specimens pulled along the warp direction (series W) were without 

exception smaller than those found for fabric specimens pulled along the fill direction (series F.) 

This observation is qualitatively consistent with that of section 4.2, namely that XW yarns had 

generally smaller strength than XF yarns. The notion of greater damage inflicted on warp yarns 

than on fill yarns during the weaving and/or scouring processes is supported once again. The 

yarn extraction procedure discussed in section 4.2 does not apply to the W and F series. 

4.4 Single-Ply Fabric Strength Compared With Untwisted Yarn Strength 

Strength results from series W and F are compared with those from series Y, XW, and XF in 

Figure 10. 

Figure 10. Strength results for untwisted yarns compared with those for fabric.
14

The F series strength results (2.67 ± 0.04 GPa) are similar to Y results (2.66 ± 0.04 GPa.) The 

XF series strength results (2.20 ± 0.05 GPa) are substantially smaller than both the F series and 

Y series results. To summarize, XF < F = Y. The most plausible interpretation is that F and XF 

suffered equal strength degradations during weaving and scouring, and XF < F because of 

damage during extraction in the case of XF and/or inter-yarn contact in the case of F. 

Furthermore, according to this interpretation, the strength increase in the F series due to interyarn contact happened to offset the strength decrease incurred during weaving and scouring, 

thereby producing the result F = Y. 

F series strength increase arising from inter-yarn contact can be understood with the aid of 

Figure 1. In the plain weave pattern shown, each fill yarn is in direct contact with every warp 

yarn and hence in indirect contact with every other fill yarn. If a particular fill yarn were to 

undergo local rupture, that yarn should still be able to support a degree of axial tensile load 

because of frictional contact with other yarns. 

The W series strength results (2.23 ± 0.04 GPa) are substantially smaller than the Y series 

results. The XW series strength results (2.06 ± 0.01 GPa) are substantially smaller than the W 

series results. To summarize, XW<W<Y. The observation that W<Y implies that significant 

damage was incurred by warp yarns during weaving and finishing. The observation that XW<W 

can be attributed to damage during yarn extraction in the case of XW and/or to inter-yarn contact 

in the case of W (refer again to Figure 1). 

5. Summary 

Single yarns of 600 denier Kevlar KM2 were tested in quasi-static, uniaxial tension. The 

strength of never-woven, untwisted yarn specimens that were obtained from DuPont was 2.66 

± 0.04 GPa. 

Three different degrees of initial twist were imposed on never-woven yarns, 0.69, 1.30, and 

1.93 turns/cm. The corresponding strengths were 3.21 ± 0.05, 3.36 ± 0.04, and 3.28 ± 0.03 GPa, 

respectively. A parabolic fit was obtained to these strength vs. twist data. On the basis of this 

parabolic fit, a maximum strength of 3.37 GPa was found to correspond to an initial twist of 

1.39 turns/cm. The twist multiplier was found to be 1.2, in agreement with that reported for 

Kevlar in Yang (1993). It was proposed that the KM2 strength value of 3.3 GPa reported in 

Yang (2000) corresponds to a state of near-optimum twist. 

Warp-oriented and fill-oriented yarns were extracted from plain-woven, 600-denier KM2 fabric 

(Style 706). The strengths of extracted warp and fill yarns, tested in an untwisted state, were 

found to be 2.06 ± 0.01 and 2.20 ± 0.05 GPa, respectively. Comparison of these values with the 

never-woven, untwisted strength of 2.66 ± 0.04 GPa led to the conclusion that substantial 
15

strength degradation was incurred during one or more of the weaving, finishing (especially 

scouring), and yarn extraction processes. Furthermore, this degradation was significantly greater 

for warp than for fill yarns. 

Finally, 68-yarn-wide, single-ply specimens of plain-woven, 600-denier KM2 fabric were tested 

in quasi-static, uniaxial tension. Warp-oriented and fill-oriented fabric specimens had strengths 

of 2.23 ± 0.04 and 2.67 ± 0.04 GPa, respectively. These fabric strengths are larger than those 

found for extracted warp and fill yarns. The mechanism of frictional contact being adjacent 

yarns was speculated to account for the added strength in the case of woven fabric. 
16

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17

6. References 

American Society for Testing and Materials (ASTM). “Standard Test Method for Breaking 

Force and Elongation of Textile Fabrics (Strip Method).” ASTM Designation D5035-95, 

West Conshohocken, PA, July 1995. 

American Society for Testing and Materials (ASTM). “Standard Test Method for Tensile 

Properties of Yarns and the Single-Strand Method.” ASTM Designation D2256-97, West 

Conshohocken, PA, January 2000. 

DuPont Corporation. Kevlar KM2, Preliminary Information Bulletin, Wilmington, DE: 

DuPont, undated. 

Hearle, J. W. S. “Observed Extension and Breakage of Continuous Filament Yarns.” Structural 

Mechanics of Fibers, Yarns, and Fabrics. Volume 1, edited by J. W. S. Hearle, P. Grosberg, 

and S. Backer, New York: Wiley Interscience, pp. 213–253, 1969. 

Instron Corporation. The Series 4500 Floor Model Load Frame, Operators Guide. Manual No. 

M10-4500-5, Issue B, Canton, MA: Instron, June 1988. 

Instron Corporation. 1120 Series Operator’s Handbook. Canton, MA: Instron, undated. 

Scott, B. R. Personal communication. DuPont Corporation, Wilmington, DE, 2001. 

Taylor, J. R. An Introduction to Error Analysis. Second Edition, Mill Valley, CA: University 

Science Books, 1997. 

Warner, S. B. Fiber Science. Englewood Cliffs, NJ: Prentice Hall, 1995. 

Yang, H. H. Kevlar Aramid Fiber. Chichester, U. K.: John Wiley, 1993. 

Yang, H. H. “Aramid Fibers.” Comprehensive Composite Materials, Volume 1, Fiber 

Reinforcements and General Theory of Composites, edited by T.-W. Chou, pp. 199–229, 

Oxford: Elsevier Science, 2000. 
18

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19

List of Symbols 

Ayo initial cross-sectional area of a yarn 

Ffail maximum force exerted on the specimen 

N number of tests in a given series 

σ

fail strength (maximum First Piola-Kirchhoff stress, corresponding to specimen 

failure)

τo initial twist of a yarn specimen 
20

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21
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 02747 

 1 VIRGINIA POLYTECHNIC INST 

 IMPACT BIOMECHANICS LAB 

 MECHANICAL ENGINEERING 

 S M DUMA 

 BLACKSBURG VA 24061 

 1 UNIVERSITY OF ALABAMA 

 ENGINEERING MECHANICS 

 S E JONES 

 PO BOX 870278 

 TUSCALOOSA AL 34587-0278 

 2 NORTHWESTERN UNIVERSITY 

 MECHANICAL ENGINEERING 

 H D ESPINOSA 

 W K LIU 

 EVANSTON IL 60208 

 1 UNIV OF MISSOURI ROLLA 

 CIVIL ENGINEERING DEPT 

 W SCHONBERG 

 ROLLA MO 65409-0030 

 1 JHU 

 MECH ENG 

 K T RAMESH 

 LATROBE HALL 

 3400 N CHARLES ST 

 BALTIMORE MD 21218 

 1 MIT 

 MATERIALS SCI AND ENG DEPT 

 D ROYLANCE 

 CAMBRIDGE MA 02139 

 1 BROWN UNIVERSITY 

 ENGINEERING 

 R J CLIFTON 

 PROVIDENCE RI 02912 

 1 SRI INTERNATIONAL 

 D SHOCKEY 

 333 RAVENSWOOD AVE 

 MENLO PARK CA 94025-3493 

 2 UC SAN DIEGO 

 MECH AEROSPACE ENGRNG 

 M A MEYERS 

 S NEMAT NASSER 

 9500 GILMAN DR 

 LA JOLLA CA 92093 

 1 NORTH CAROLINA STATE UNIV 

 DEPT MECH AND AEROSPACE 

 ENGINEERING 

 M ZIKRY 

 BOX 7910 

 RALEIGH NC 27695-7910 

 1 UNIVERSITY OF CINCINNATI 

 COLLEGE OF ENGINEERING 

 A TABIEI 

 787 RHODES HALL 

 PO BOX 210070 

 CINCINNATI OH 45221-0070 
NO. OF NO. OF 

COPIES ORGANIZATION COPIES ORGANIZATION

23 

 2 CALIFORNIA INSTITUTE OF TECH 

 AERONAUTICS AND APPLIED 

 MECHANICS 

 M ORTIZ 

 G RAVICHANDRAN 

 PASADENA CA 91125 

 1 UNIVERSITY OF ROCHESTER 

 MECHANICAL ENGR DEPT 

 D J QUESNEL 

 ROCHESTER NY 14627-0132 

 1 DYNA EAST CORP 

 W FLIS 

 3620 HORIZON DRIVE 

 KING OF PRUSSIA PA 19406-2647 

 1 SOUTHWEST RSRCH INSTITUTE 

 ENGR AND MAT SCI DIV 

 C E ANDERSON 

 6220 CULEBRA ROAD 

 PO DRAWER 28510 

 SAN ANTONIO TX 78228-0510 

 1 UNIV OF TEXAS AT AUSTIN 

 INSTITUTE FOR ADV TECH 

 S BLESS 

 4030 2 W BRAKER LANE 

 AUSTIN TX 78759 

 1 MISSION RESEARCH CORP 

 R EISLER 

 735 STATE ST 

 SANTA BARBARA CA 93102 

 1 DUPONT ENG 

 B SCOTT 

 101 BEECH ST 

 PO BOX 80840 

 WILMINGTON DE 19880-0840 

 1 APPLIED RESEARCH ASSOCIATES 

 D E GRADY 

 SUITE A 220 

 4300 SAN MATEO BLVD NE 

 ALBUQUERQUE NM 87110 

 2 DIR LLNL 

 D LASSILLA 

 TECH LIB 

 PO BOX 808 

 LIVERMORE CA 94550 

 5 DIRECTOR 

 SANDIA NATIONAL LABS 

 R BRANNON 

 L CHHABILDAS 

 E HERTEL 

 M KIPP 

 TECH LIB 

 PO BOX 5800 

 ALBUQUERQUE NM 87185-5800 

 3 DIR LANL 

 G T GRAY 

 TECH LIB 

 PO BOX 166 

 LOS ALAMOS NM 87454 

 1 US ARMY NGIC 

 T SHAVER 

 2055 BOULDERS RD 

 CHARLOTTESVILLE VA 

 22911-8318 

ABERDEEN PROVING GROUND

 1 COMMANDER 

 US ARMY ATC 

 CSTE DTC AT SL V 

 T E SANDERSON 

 400 COLLERAN ROAD 

 APG MD 21005-5059 

 49 DIR USARL 

 AMRSL SL BE 

 E DAVIS 

 D NEADES 

 AMSRL WM 

 J SMITH 

 AMSRL WM M 

 L GHIORSE 

 S GHIORSE 

 E RIGAS 

 G HAGNAUER 

 P MOY 

 D VIECHNICKI 

 AMSRL WM MA 

 S MCKNIGHT 

 AMSRL WM MB 

 T BOGETTI 

 B CHEESEMAN 

 R DOOLEY 

 B FINK 

 G GAZONAS 

 D HOPKINS 

 C HOPPEL 

 R LIEB 

 AMSRL WM MC 

 J LASALVIA 

 M STAKER 
NO. OF 

COPIES ORGANIZATION 

24

ABERDEEN PROVING GROUND (CONT)

 AMSRL WM T 

 B BURNS 

 T BJERKE 

 N GNIAZDOWSKI 

 F GREGORY 

 K KIMSEY 

 L MAGNESS 

 W WALTERS 

 AMSRL WM TA 

 W BRUCHEY 

 M BURKINS 

 W GILLICH 

 W GOOCH 

 M NORMANDIA 

 AMSRL WM TD 

 K FRANK 

 T HADUCH 

 M N RAFTENBERG (6 CPS) 

 E RAPACKI 

 S E SCHOENFELD 

 D CASEM 

 T WEERISOORIYA 

 M SCHEIDLER 

 T MOYNIHAN 

 H MEYERS 

 Y HUANG 

 S BILYK 
NO. OF 

COPIES ORGANIZATION 

25 

 1 RAFAEL BALLISTICS CTR 

 M MAYSELESS 

 PO BOX 2250 

 HAIFA 

 ISRAEL 

 2 DSTL BIOMEDICAL SCIENCES 

 G COOPER 

 W TAM 

 PORTON DOWN 

 SALISBURY 

 WILTSHIRE SP4 0JQ 

 UNITED KINGDOM 

 1 DSTO 

 AERONAUTICAL AND MARITIME 

 RESEARCH LABORATORY 

 J J WANG 

 PO BOX 1500 

 SALISBURY SA 5108 

 AUSTRALIA 

 1 DLO R&P 

 P GOTTS 

 SKIMMINGDISH LANE 

 CAVERSFIELD 

 BICESTER OXON 

 OX27 ATS 

 UNITED KINGDOM 

 1 ARL ERO 

 S SAMPATH 

 AERO MECH ENG 

 223 MARYLEBONE RD 

 LONDON NW1 5TH 

 UNITED KINGDOM 

 6 AMC SCI & TECH CTR 

 EUROPE 

 T J MULKERN 

 POSTFACH 81 

 55247 MAINZ KASTEL 

 GERMANY