October 2010 

NASA/CR–2010-216854 

Flexible Material Systems Testing 

John K. Lin, Lauren S. Shook, Joanne S. Ware, and Joseph V. Welch 

ILC Dover, LP, Frederica, Delaware 
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October 2010 

NASA/CR–2010-216854 

Flexible Material Systems Testing 

John K. Lin, Lauren S. Shook, Joanne S. Ware, and Joseph V. Welch 

ILC Dover, LP, Frederica, Delaware 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

Acknowledgments 

The work presented herein was performed for NASA Langley Research Center and 

NASA Ames Research Center, under task order NNL09AC89D, in support of the 

Flexible Materials Systems Testing program. The authors would like to thank Charles 

Player from NASA Langley Research Center and Scott Murman from NASA Ames 

Research Center for their support. 

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Administration. 
Page i

Table of Contents

1. Introduction ............................................................................................................................. 1

2. Objective ................................................................................................................................. 1

3. Materials.................................................................................................................................. 2

3.1 Material Descriptions..................................................................................................... 2

3.2 Baseline Fiber Properties ............................................................................................... 3

3.3 Uncoated (Baseline) Fabric Properties........................................................................... 4

3.4 Coating Effort ................................................................................................................ 5

3.5 Fabric Density Determinations ...................................................................................... 6

4. Test Methods ........................................................................................................................... 8

4.1 Introduction.................................................................................................................... 8

4.2 Uni-axial Test Method ................................................................................................... 8

4.3 Shear Stress-Strain Test Methods .................................................................................. 9

4.3.1 Trellis-Frame Test ..................................................................................................... 9

4.3.2 Bias Extension Test ................................................................................................. 11

4.3.3 Cylindrical Biaxial Test........................................................................................... 12

5. Normal Stress-Strain ............................................................................................................. 13

5.1 F-111 Nylon Uni-axial testing ..................................................................................... 13

5.1.1 Warp Direction Pull Tests ....................................................................................... 13

5.1.2 Fill Direction Pull Tests........................................................................................... 16

5.1.3 Warp versus Fill Stiffness Comparison ................................................................... 19

5.2 HT1 Nomex Uni-axial testing...................................................................................... 21

5.2.1 Warp Direction Pull Tests ....................................................................................... 21

5.2.2 Fill Direction Pull Tests........................................................................................... 23

5.2.3 Warp versus Fill Stiffness Comparison ................................................................... 26

5.3 200 Denier Kevlar........................................................................................................ 27

5.3.1 Warp Direction Pull Tests ....................................................................................... 27

5.3.2 Fill Direction Pull Tests........................................................................................... 30

5.3.3 Warp versus Fill Stiffness Comparison ................................................................... 33

5.4 840 Denier Kevlar........................................................................................................ 34

5.4.1 Warp Direction Pull Tests ....................................................................................... 34

5.4.2 Fill Direction Pull Tests........................................................................................... 37

5.4.3 Warp versus Fill Stiffness Comparison ................................................................... 40

6. Shear Stress-Strain................................................................................................................. 42

6.1 Picture Frame Testing .................................................................................................. 42

6.1.1 F-111 Nylon Picture Frame Testing ........................................................................ 44

6.1.2 HT1 Nomex Picture Frame Testing......................................................................... 46

6.1.3 200 Denier Kevlar Picture Frame Testing ............................................................... 48

6.1.4 840 Denier Kevlar Picture Frame Testing ............................................................... 49

6.2 Bias Extension Testing................................................................................................. 51

6.2.1 F-111 Nylon Bias Extension Testing....................................................................... 51

6.2.2 HT1 Nomex Bias Extension Testing ....................................................................... 53

6.2.3 200 Denier Kevlar Bias Extension Testing.............................................................. 55

6.2.4 840 Denier Kevlar Bias Extension Testing.............................................................. 57

6.3 Inflated Cylinder Testing ............................................................................................. 59

6.3.1 HT1 Nomex Inflated Cylinder Testing.................................................................... 60

6.3.2 200 Denier Inflated Cylinder Testing ...................................................................... 62

6.4 Test Recommendations................................................................................................ 64

7. Summary ............................................................................................................................... 65
Page ii 

List of Tables 

Table 1: Textile material selection and rationale............................................................................. 3

Table 2: Fiber property comparison. ............................................................................................... 4

Table 3: Baseline fabric properties of uncoated materials. ............................................................. 5

Table 4: Test fabric properties......................................................................................................... 6

Table 5: Fabric density. ................................................................................................................... 7

Table 6: Fabric Thickness. .............................................................................................................. 8

Table 7: Manual inflated cylinder measurements.......................................................................... 60

Table 8: Inflated cylinder preload states. ...................................................................................... 60

List of Figures 

Figure 1: Textile stress and strains. ................................................................................................. 2

Figure 2: Uni-axial test setup in INSTRON test machine. .............................................................. 9

Figure 3: Trellis-Frame test setup in INSTRON test machine. ..................................................... 10

Figure 4: Camera Setup for Trellis Frame Test – Top View......................................................... 10

Figure 5: Bias extension sample in INSTRON test machine. ....................................................... 11

Figure 6: Camera Setup for Bias Extension Tests – Side View .................................................... 12

Figure 7: Cylindrical biaxial test setup.......................................................................................... 13

Figure 8: F-111 Nylon warp axial pull test, load cycle 1. ............................................................. 14

Figure 9: F-111 Nylon warp axial pull test, load cycle 10. ........................................................... 14

Figure 10: F-111 Nylon warp axial pull test, all ten load cycles................................................... 15

Figure 11: F-111 Nylon warp axial pull test, strain ratio cycle 1.................................................. 16

Figure 12: F-111 Nylon warp axial pull test, strain ratio cycle 10................................................ 16

Figure 13: F-111 Nylon fill axial pull test, load cycle 1................................................................ 17

Figure 14: F-111 Nylon fill axial pull test, load cycle 10.............................................................. 17

Figure 15: F-111 Nylon fill axial pull test, all ten load cycles. ..................................................... 18

Figure 16: F-111 Nylon fill axial pull test, strain ratio cycle 1. .................................................... 19

Figure 17: F-111 Nylon fill axial pull test, strain ratio cycle 10. .................................................. 19

Figure 18: F-111 Nylon axial pull test, cycle 1 warp vs. fill stiffness........................................... 20

Figure 19: F-111 Nylon axial pull test, cycle 10 warp vs. fill stiffness......................................... 20

Figure 20: HT1 Nomex warp axial pull test, load cycle 1............................................................. 21

Figure 21: HT1 Nomex warp axial pull test, load cycle 10........................................................... 22

Figure 22: HT1 Nomex warp axial pull test, all ten load cycles. .................................................. 22

Figure 23: HT1 Nomex warp axial pull test, strain ratio cycle 1. ................................................. 23

Figure 24: HT1 Nomex warp axial pull test, strain ratio cycle 10. ............................................... 23

Figure 25: HT1 Nomex fill axial pull test, load cycle 1................................................................ 24

Figure 26: HT1 Nomex fill axial pull test, load cycle 10.............................................................. 24

Figure 27: HT1 Nomex fill axial pull test, all ten load cycles....................................................... 25

Figure 28: HT1 Nomex fill axial pull test, strain ratio cycle 1...................................................... 25

Figure 29: HT1 Nomex fill axial pull test, strain ratio cycle 10.................................................... 26

Figure 30: HT1 Nomex axial pull test, cycle 1 warp vs. fill stiffness. .......................................... 26

Figure 31: HT1 Nomex axial pull test, cycle 10 warp vs. fill stiffness. ........................................ 27

Figure 32: 200 denier Kevlar warp axial pull test, load cycle 1.................................................... 28

Figure 33: 200 denier Kevlar warp axial pull test, load cycle 10.................................................. 28

Figure 34: 200 denier Kevlar warp axial pull test, all ten load cycles........................................... 29

Figure 35: 200 denier Kevlar warp axial pull test, strain ratio cycle 1.......................................... 29

Figure 36: 200 denier Kevlar warp axial pull test, strain ratio cycle 10........................................ 30

Figure 37: 200 denier Kevlar fill axial pull test, load cycle 1. ...................................................... 31
Page iii 

Figure 38: 200 denier Kevlar fill axial pull test, load cycle 10. .................................................... 31

Figure 39: 200 denier Kevlar fill axial pull test, all ten load cycles.............................................. 32

Figure 40: 200 denier Kevlar fill axial pull test, strain ratio cycle 1............................................. 32

Figure 41: 200 denier Kevlar fill axial pull test, strain ratio cycle 10........................................... 33

Figure 42: 200 denier Kevlar axial pull test, cycle 1 warp vs. fill stiffness. ................................. 34

Figure 43: 200 denier Kevlar axial pull test, cycle 10 warp vs. fill stiffness. ............................... 34

Figure 44: 840 denier Kevlar warp axial pull test, load cycle 1.................................................... 35

Figure 45: 840 denier Kevlar warp axial pull test, load cycle 10.................................................. 35

Figure 46: 840 denier Kevlar warp axial pull test, all ten load cycles........................................... 36

Figure 47: 840 denier Kevlar warp axial pull test, strain ratio cycle 1.......................................... 36

Figure 48: 840 denier Kevlar warp axial pull test, strain ratio cycle 10........................................ 37

Figure 49: 840 denier Kevlar fill axial pull test, load cycle 1. ...................................................... 38

Figure 50: 840 denier Kevlar fill axial pull test, load cycle 10. .................................................... 38

Figure 51: 840 denier Kevlar fill axial pull test, all ten load cycles.............................................. 39

Figure 52: 840 denier Kevlar fill axial pull test, strain ratio cycle 1............................................. 39

Figure 53: 840 denier Kevlar fill axial pull test, strain ratio cycle 10........................................... 40

Figure 54: 840 denier Kevlar axial pull test, cycle 1 warp vs. fill stiffness. ................................. 41

Figure 55: 840 denier Kevlar axial pull test, cycle 10 warp vs. fill stiffness. ............................... 41

Figure 56: Picture Frame Test Fixture – Frame Angle.................................................................. 42

Figure 57: Picture frame test load scenario. .................................................................................. 43

Figure 58: F-111 Nylon Item A time history................................................................................. 43

Figure 59: F-111 Nylon picture frame test, Item A shear stress-strain. ........................................ 44

Figure 60: F-111 Nylon picture frame test, Item B shear stress-strain.......................................... 45

Figure 61: F-111 Nylon picture frame test, Item C shear stress-strain.......................................... 45

Figure 62: F-111 Nylon picture frame test, shear stress-strain...................................................... 46

Figure 63: HT1 Nomex picture frame test, Item A shear stress-strain.......................................... 47

Figure 64: HT1 Nomex picture frame test, Items A, B & C shear stress-strain............................ 47

Figure 65: HT1 Nomex picture frame test, Item D shear stress-strain.......................................... 48

Figure 66: 200 denier Kevlar picture frame test, Item A and D shear stress-strain....................... 49

Figure 67: 200 denier Kevlar picture frame test, shear stress-strain. ............................................ 49

Figure 68: 840 denier Kevlar picture frame test, Item A shear stress-strain. ................................ 50

Figure 69: 840 denier Kevlar picture frame test, shear stress-strain. ............................................ 50

Figure 70: 840 denier Kevlar picture frame test, Item A and E shear stress-strain....................... 51

Figure 71: F-111 Nylon bias extension test, load ramp up cycle 1. .............................................. 52

Figure 72: F-111 Nylon bias extension test, load cycle 5. ............................................................ 52

Figure 73: F-111 Nylon bias extension test, cycles 2 through 5. .................................................. 53

Figure 74: HT1 Nomex bias extension test, load ramp up cycle 1................................................ 54

Figure 75: HT1 Nomex bias extension test, load cycle 5.............................................................. 54

Figure 76: HT1 Nomex bias extension test, cycles 2 through 5.................................................... 55

Figure 77: 200 denier Kevlar bias extension test, load ramp up cycle 1....................................... 56

Figure 78: 200 denier Kevlar bias extension test, load cycle 5. .................................................... 56

Figure 79: 200 denier Kevlar bias extension test, cycles 2 through 5. .......................................... 57

Figure 80: 840 denier Kevlar bias extension test, load ramp up cycle 1....................................... 58

Figure 81: 840 denier Kevlar bias extension test, load cycle 5. .................................................... 58

Figure 82: 840 denier Kevlar bias extension test, cycles 2 through 5. .......................................... 59

Figure 83: HT1 Nomex inflated cylinder test, Item B time history............................................... 61

Figure 84: HT1 Nomex inflated cylinder test, Item B shear stress-strain. .................................... 62

Figure 85: 200 denier Kevlar inflated cylinder test, Item B time history...................................... 63

Figure 86: 200 denier Kevlar inflated cylinder test, Item B shear stress-strain............................. 64
Page 1 

1. Introduction 

An experimental program has been undertaken to better characterize the stress-strain 

characteristics of flexible material systems to support a NASA ground test program for inflatable 

decelerator material technology. A goal of the current study is to investigate experimental 

methods for the characterization of coated woven material stiffness. This type of experimental 

mechanics data would eventually be used to define the material inputs of fluid-structure 

interaction simulation models. The test methodologies chosen for this stress-strain 

characterization are presented along with the experimental results. 

This report covers work performed by ILC Dover, LP (ILC) in support of the Flexible Materials 

Systems Testing program toward the investigation and characterization of the material properties 

of various coated woven materials which may be appropriate for use in inflatable decelerators. 

This task order (NNL09AC89D) consists of the materials testing and experimental results from 

four candidate materials. These activities were performed during the time frame of September 

2009 to May 2010. 

2. Objective 

A limited volume of mechanical property data is typically available when undertaking the 

structural analysis of inflatable aerodynamic structures fabricated with textile materials. The 

objective of this study is to provide a more comprehensive set of measured stress-strain behavior 

that will be used to support continued experimental and analytical work in this area. 

The particular stress-strain behaviors of interest for this work are shown below. 

• Normal stress versus strain 

• Transverse contraction versus axial strain 

• Shear stress versus shear strain 

Figure 1 is an illustration of these stress terms relative to the warp and fill axes of the woven 

fabric. With these two orthogonal axes of the weave we have limited our focus to that of an 

orthotropic lamina. 
Page 2 

Warp

τ

τ

τ

τ

Shear 

Fill

Stress Warp

τ

τ

τ

τ

Fill

Warp

τ

τ

τ

τ

Shear 

Fill

Stress

σ σ

Lateral Contraction

σ σ

Lateral Contraction

Warp

σw

σw

Fill

σ σf f

Normal Stresses

Warp

σw

σw

Warp

σw

σw

Fill

σ σf f

Fill

σ σf f

Normal Stresses

Figure 1: Textile stress and strains. 

Some degree of both inelastic and non-linear behavior is expected in the stress-strain behavior of 

textiles. We are interested in observing the differences between the load ramp up and load ramp 

down portions of stress-strain curves. We also have the objective to observe the strain which 

persists after the stress that produced it is removed. In mechanics this is typically referred to as 

permanent set. Although for textile materials, this apparent set may not necessarily be 

permanent. The set up of the experiments for this task placed an emphasis on assigning a 

magnitude to these tendencies. 

3. Materials 

3.1 Material Descriptions 

The number of materials selected for this experimental study was defined in the statement of 

work, which called for mechanical behavioral testing of six different coated fabrics. The fabrics 

ultimately selected were considered either “flight-like” materials or representative of materials 

used in wind tunnel experiments. The fabrics selected were Nylon, Nomex, and Kevlar. The 

coatings selected were chosen based on similar operational conditions for flight and wind tunnel 

testing. Silicone and urethane were selected to reduce the baseline porosity of the fabrics both for 

performance in anticipated wind tunnel studies and to represent the use of a coated fabric as the 
Page 3 

gas retaining layer of an inflated structural bladder in a flight article. The end-item fabrics 

specified for study are shown in Table 1. 

Table 1: Textile material selection and rationale. 

3.2 Baseline Fiber Properties 

Although the materials to be tested during this effort were intended to be coated, the base fiber is 

the primary contributor to structural performance of the end item. Therefore, from a comparative 

point of view, it is important to understand the differences between the types of base fiber used in 

this study. 

One of the main differences is that the polyamide (Nylon) is a flexible “melt” polymer, while the 

aramid fibers (Kevlar, Nomex) are more rigid, “non-melt” liquid crystalline polymers. The 

flexible chain polymers possess a random coil configuration and do not obtain a higher degree of 

order with increasing concentration. Conversely, the rigid polymers begin to align with 

increasing concentration and become structurally highly oriented polymer chains. Due to these 

random, flexible polymer chains, the Nylon has a significantly higher elongation than the Kevlar 

fibers. For the same reason, the rigid polymer chain materials have a higher tenacity and modulus 

than the Nylon. 
Page 4 

Table 2: Fiber property comparison. 

Though the Nomex (meta-aramid) and the Kevlar (para-aramid) fibers are both in the aramid 

family, the differences in their properties are striking. These differences are due to the location of 

the amide linkages on their aromatic rings. This causes the Nomex to have a lower modulus and 

tensile capacity, as well as a higher percentage of elongation, when compared to the Kevlar as 

noted in Table 2. 

3.3 Uncoated (Baseline) Fabric Properties 

Fabrics meeting the fiber, weave balance, and thickness targets that were outlined in the statement 

of work were identified and traded so as to provide a reasonable subset of materials for study. 

The baseline characteristics of the uncoated fabrics selected for study, including Nylon, Nomex, 

and Kevlar, are found in Table 3. 

Though many of a fabric’s performance characteristics are directly related to the amount of yarns 

packed into a given area, a fabric’s shear stiffness is directly dependent upon both the amount of 

yarns, as well as the weave type. Fabric properties can be tailored in a woven fabric development 

effort to the specific physical performance needs through the selection of yarn size twist, density, 

etc. for any or all of the 0o/90o/45o directions. In this effort, the fabric construction properties of 

0

o

/90o fabrics were considered when selecting materials for study. Choice of fabric construction 

properties were limited to those of existing, off-the shelf materials. The properties listed in Table 

3 indicate the baseline properties of the all the uncoated fabrics, prior to coating. 
Page 5 

Table 3: Baseline fabric properties of uncoated materials. 

3.4 Coating Effort 

The requirements developed for testing were that the Nomex and Kevlar fabrics be tested with a 

silicone coating and the Nylon be tested with a urethane coating. Different coating processes were 

used for the materials selected, based on the fabric and the coating being applied. 

The Kevlar materials used in the IRVE II flight article were available in the coated condition, so 

no additional coating effort was required. Both of the Kevlar fabrics (Style 740 and Style 726) 

fabrics had been primed with a silicone infused solution to promote adhesion and then calendered 

with a Dow Corning Silicone Rubber. The silicone coating effort planned for the Nomex fabric 

was different in that it was performed not by calendering, which presses the rubber into the fabric 

filling the interstices under extreme load, but via a solution coating process. In this instance, 

there was sufficient adhesion without a prime coat (which can stiffen the fabrics by locking in 

yarns). The rubber was put into solution with solvent and then coated onto the fabric while 

passing under a knife with a predetermined gap; this pushes the rubber solution into the 

interstices as the fabric passes under the knife. The same base silicone was used to coat both 

fabrics, is relatively soft in comparison to many other rubbers and has a minimum elongation of 

400%. 

The urethane coating of the Nylon fabric that was planned for this effort was to have replicated 

the coating process used to coat the Isotensoid IAD wind tunnel model tested at the LaRC 

Transonic Dynamics Tunnel in 2009. That coating process applied a very thin (scrape coat) layer 

of an aromatic polyether urethane to the surface of the fabric to further reduce the porosity 

through the fabric. In the scrape coating process, the fabric passes under a blade, but there is no 

measurable gap between the fabric and the blade. Here, the solution is essentially scraped over 

the surface as the fabric passes under the blade. Using this process with the very thin Nylon 

ripstop applied only a very thin layer of coating to the fabric. 

Unfortunately, during the first run of the all the coating efforts that were planned, the allowable 

limit of volatile organic compounds (VOC's) found in the solvent solutions for that 24 hour 

period was exceeded, though only slightly. State and Federal statutes require that production stop 

while an investigation was conducted. This delay impacted the planned coating efforts and as a 
Page 6 

result only the HT1 construction of the Nomex fabrics was coated. The program schedule/funding 

source expired prior to receiving authorization to resume coating from State officials. Therefore, 

the testing matrix was revised and testing occurred only on the materials identified in Table 4. 

Table 4: Test fabric properties. 

* The ST numbers assigned to the Kevlar fabrics are ILC’s P/Ns of the coated goods 

The decision to leave the uncoated Nylon Ripstop, F-111 in the test matrix while the other 

uncoated Nomex fabric, HT48 was eliminated was made due to the baseline porosities of the 

fabrics, and the intended use of the F-111 in NASA Ames wind tunnel testing that was to be 

conducted at a later date. The F-111 is considered to have an extremely low porosity according to 

ASTM D 737 (0.5-3.0 ft3/minute at 0.5” water) compared to the Nomex HT48 (18.0 ft3/minute at 

0.5” water). The porosity of these fabrics is directly dependent upon their fabric constructions. 

The Nylon is a tightly packed plain weave/ripstop construction. The yarns used in both the warp 

and fill directions use 30 denier yarns which accommodates a tight packing condition with a 126 

x 132 yarns per inch. This fabric has proven repeatedly that it can take shape when in an air 

stream, and would function in the planned wind tunnel tests at NASA Ames. The Nomex HT-48 

chain weave is a much less dense construction made of 200 denier yarns in both the warp and 

filling directions and has a yarn density of 99 x 86 yarns per inch. This construction is much 

more porous and would not perform as needed in the wind tunnel experiments without the 

coating. 

3.5 Fabric Density Determinations 

Density determinations were made for each of the fabrics in this study using a Mettler Density 

Determination Kit, ME-33360. Three replicates of each of the four different fabrics evaluated in 

this study were used to obtain a mean density for that fabric. Considered a solid body, the density 

of the fabric was determined using a liquid of known density; this is also known as density 

measurements by hydrostatic weighingi. That liquid was distilled water and is considered a 

standard test liquid. 

To calculate each value per replicate, each sample was first weighed in air and then immersed 

into the distilled water bath. Then, from a series of weightings, the density (ρ) was calculated. 

Two variables, bath temperature and air buoyancy, were included in the calculations to obtain the 

most accurate result. In general, temperature has only a slight effect on any density change of a 

solid body and as such is often disregarded in density determinations; however, in the case of 

liquids, the density may change on the order of 0.1 - 1.0% per Co. Therefore, in this evaluation, 
Page 7 

the temperature of the water (24.5oC) in which the sample was immersed was included. The 

buoyancy of solids also has an effect on the density of a solid as each cubic centimeter of air 

weighs 1.0 - 1.2 milligrams. Any object that is being weighed in air is subject to buoyancy for 

each cm3 of its volume, meaning that with a density of 1 gm/cm3, an error of 0.1% could occur if 

buoyancy was not taken into consideration. Therefore, buoyancy was included in these 

calculations. 

Procedure: 

1. Using the density determination kit, distilled water was poured into the beaker so that a 

sample would be covered with at least 10mm of the liquid. 

2. The thermometer was inserted into the beaker and the entire set-up was placed on a 

bridge within in the balance. 

3. The sample holder was attached to the set-up while ensuring that there were no air 

bubbles created within the bath or along the holder. 

4. The balance tare read 0.0 grams 

5. A sample was weighed in air (W1) 

6. The wire holder was weighed in air (W2) 

7. The balance is tared again (W3) 

8. The weighed sample was placed on the wire holder and immersed in the bath 

9. Balance displays buoyancy (negative number) of the sample, (W4) 

10. Note the temperature to determine density of distilled water 

11. Density of water at 23.5oC is 0.9972 g/cm3

The equation used to calculate the density of each sample was: 

 W1 – W2 * 0.9972 

 W1 + W3 – W4 

 

Therefore, the densities listed below are the mean values densities of the fabric samples. 

Table 5: Fabric density. 
Page 8 

4. Test Methods 

4.1 Introduction 

Four different test methods were used in this program to measure and characterize the normal 

stress-strain and shear stress-strain behavior of textile materials for the inflatable aerodynamic 

decelerators. Two of the test methods, namely Uni-axial and Cylindrical Biaxial tests, have been 

used in previous programsii. These two tests were again used here, but with slight modification to 

include the capability of photogrammetry to capture additional data for comparison and 

correlation. In addition, two other shear stress-strain test methods, namely Trellis-Frame Testiii iv

and Bias Extension Testv

, have been refined with photogrammetry capability to measure shear 

stress-strain behavior for comparison and correlation with the Cylindrical Biaxial test method. 

The goal of using several test methods to measure the same mechanical behavior is to determine 

which shear modulus test method will be best suited for future wind tunnel test correlation. 

General test procedures were clearly defined in the internal Test Information Sheet with required 

test equipment and specimen preparation information. For test methods with special 

requirements, which are the case for this program, an additional test specimen was used to 

determine loading conditions. In the current test program, all tests were performed under 

laboratory ambient condition with standard room temperature, pressure and humidity. All test 

specimens, their quantity and quality (e.g. environmental conditioning), were prepared according 

to ASTM standards and/or best laboratory practices. 

Samples for the uni-axial, trellis-frame, and bias extension tests were performed using an 

INSTRON test machine, model number 1125. Calibration data showed the machine results to be 

within ±0.2%. Two extensometers from MTS Systems Corporation were used during testing, a 

9% extensometer (model number 632.11E-90) and a 50% extensometer (model number 634.12F24.) The data showed that the 9% extensometer was within ±0.2% and the 50% extensometer was 

within ±0.4%. 

Units of stress are reported in lbs/in, where the fabric thickness has been removed from the 

calculation. For fabrics, the stress is typically reported in units of load per width. The thicknesses

for each of the fabrics are given in Table 6. 

Table 6: Fabric Thickness. 

4.2 Uni-axial Test Method 

The uni-axial test, see Figure 2, is one of the most common test methods for determining the 

stress-strain characteristics of textile materials. This test method is performed according to ASTM 
Page 9 

D5035 -06(2008) e1 “Standard Test Method for Breaking Force and Elongation of Textile 

Fabrics (Strip Method)”. In the strip tensile test, a narrow strip of fabric specimen is used. For this 

particular test program, the test specimens, five samples per material per condition, were three 

inches wide by 6 inches long with raveled uni-axial threads along the edges. This width was 

chosen so that an extensometer could be mounted horizontally on the strip sample so that 

transverse strain could be measured in addition to the axial strain. INSTRON test machine with 

grips wider than the test sample width was used to pull the specimen. In this study, the test has 

been modified with additional features to include measurement of the transverse strain. Pin 

mounted extensometer was used to measure the strain. The INSTRON load cell was used to 

provide the measurement for stress. Since the stress-strain characteristics of a textile are typically

different in the orthogonal warp and fill fiber directions. Two sets of test samples are prepared for 

the uni-axial strip tensile method. One set of samples has the warp fibers running parallel to the 

axis of load application. A second set has the fill fibers running parallel to the axis of load 

application. 

Figure 2: Uni-axial test setup in INSTRON test machine. 

4.3 Shear Stress-Strain Test Methods 

Several inter-laboratory approaches have been developed and used by industry and academia to 

measure the shear stress-strain behavior of textile materials. In this study, three methods, namely 

Trellis-Frame Test (also known as Picture-Frame Test), Bias Extension Test and Cylindrical 

Biaxial Test, were performed on several textile materials for comparison and correlation. As 

mentioned above, all three test methods have been enhanced to include the use of 

photogrammetry. 

4.3.1 Trellis-Frame Test 

The objective of the Trellis-Frame Test, see Figure 3, is to measure the in-plane shear stress 

response to shear strain and shear strain rate by using a trellis-frame or picture-frame apparatus 

actuated by a tensile testing machine. The trellis-frame consists of four pinned corners and four 

clamped edges. Clamping mechanisms hold the cross-shaped fabric sample rigidly in the frame 

with no slippage. One corner of the frame is equipped with a locking pin to ensure proper 

installation of test specimen into the frame and the assembled fixture onto the INSTRON testing 

machine. During the test, the distance between the top and bottom corners of the frame is 

increased by the INSTRON testing machine, and thus reorienting the tows in the specimen in a 
Page 10 

shearing action. INSTRON crosshead force and motion were recorded for all cycles and 

photogrammetry pictures captured at specified loading condition as indicated in the Test 

Information Sheet. 

Figure 3: Trellis-Frame test setup in INSTRON test machine. 

Three cameras were used to capture photogrammetry data during the testing. As seen in Figure 3, 

the cameras were placed at different heights and locations across the front of the INSTRON. 

Figure 4 shows a top view layout of the camera locations. 

Figure 4: Camera Setup for Trellis Frame Test – Top View 
Page 11 

In this study, six test specimens were made for each material and condition. One sample was used 

for initial set up to determine maximum loading condition. Test specimens were marked and cut 

from automated cutting equipment using CAD file. Dimensionally the width of the cross is 8 

inches and the length is 13 inches. After the specimens have been marked and cut, 

photogrammetry dots are adhered to the test specimens according to the engineering instruction. 

The INSTRON crosshead speed for the trellis frame tests was 5 in/min. This gave an average 

shear strain rate of 0.012 rad/sec. 

4.3.2 Bias Extension Test 

Bias Extension Test, see Figure 5, is used to measure the in-plane combined shearing and tensile 

responses of a given textile material sample with a set displacement and cross head speed. This 

test is considered to be an alternate method to the Trellis-Frame test. In terms of test setup it is 

similar to ASTM D5035 -06(2008) e1 “Standard Test Method for Breaking Force and Elongation 

of Textile Fabrics”. However, test specimen preparation requires special attention. One critical 

aspect of the sample preparation in the bias extension test is yarn orientation which must be ±45° 

to the edges of the grippers. During the test, the specimen is clamped into the grips with zero (i.e. 

minimum) preload. As the distance of the crossheads of the testing machine separates the tows at 

the center zone (a pure shear zone) of the sample reorient in shear. The INSTRON crosshead 

speed for the bias extension tests was 1.25 in/min. This was selected in order to give an average 

shear strain rate equal to that used for the trellis frame tests. 

Figure 5: Bias extension sample in INSTRON test machine. 

In this study, six test specimens were made for each material and condition. One sample was used 

for initial set up to determine appropriate values for photogrammetry measurements and the 
Page 12 

maximum extension. Data will be used to validate the calculations based on the linear length 

measurements taken as part of this procedure. Data will also be used to report on test article 

flatness as load is applied. Flatness is an important assumed condition for the bias extension test. 

These measurements would take place at a set of discrete load points using photogrammetry. Test 

specimens were marked and cut from automated cutting equipment using CAD file. After the 

specimens have been marked and cut, photogrammetry dots are adhered to the test specimens 

according to the engineering instruction. Again, three cameras were placed to capture the 

photogrammetry data during the testing. Figure 6 shows a side view of the camera locations for 

the bias extension tests. 

Figure 6: Camera Setup for Bias Extension Tests – Side View 

4.3.3 Cylindrical Biaxial Test 

In this study the inflated cylinder torsion test, see Figure 7, was the third method selected to 

characterize the shear stress-strain behavior of the textile materials. In the inflated cylinder 

torsion test torque versus twist angle is measured for an inflated cylinder where one end cap has a 

free rotational degree of freedom and the other end cap has a free axial degree of freedom. 

Photogrammetry measurements were taken at zero and maximum torque values (both directions). 

Using well known relations from engineering mechanics the applied torque can be converted to 

the resulting shear stress and the twist angle can be converted to shear strain. 
Page 13 

Figure 7: Cylindrical biaxial test setup. 

In this study, five test specimens were made for each material and condition. A nominal length to 

diameter aspect ratio of 3:1 or greater is recommended for the inflated cylinder torsion test. Each 

sample will run through a break in cycle as its preconditioning. Test specimens were marked and 

cut from automated cutting equipment using CAD file and then assembled into cylindrical tubes. 

After the specimens have been assembled, photogrammetry dots are adhered to the test specimens 

according to the engineering instruction. Each test article will be tested at a given set of discrete 

internal pressures. These pressures will be selected so that the shear modulus dependence on the 

biaxial preload state is known. A regression will be performed to estimate the shear modulus at a 

state of zero biaxial preload. 

5. Normal Stress-Strain 

5.1 F-111 Nylon Uni-axial testing 

5.1.1 Warp Direction Pull Tests 

The F-111 Nylon warp direction measured normal stress-strain behavior for the stress interval [0, 

37] lbf/in is shown in Figure 8 through Figure 10. Figure 8 shows the first load cycle for all the 

samples tested. Similarly, Figure 9 shows the stress-strain data for the tenth load cycle. The 

results for the first load cycle exhibit non-linearity in the ramp up portion of the load curve, where

two points of inflection are observed. The first load cycle also exhibits significant inelastic 

behavior both in hysteresis and strain set. The results for the tenth load cycle showed much less 

inelastic behavior, but the non-linearity increased. Figure 10 shows all ten load/unload cycles for 

the test item A. 
Page 14 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0

5

10

15

20

25

30

35

40

Item A

Item B

Item C

Item D

Figure 8: F-111 Nylon warp axial pull test, load cycle 1. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0

5

10

15

20

25

30

35

40

Item A

Item B

Item C

Item D

Figure 9: F-111 Nylon warp axial pull test, load cycle 10. 
Page 15 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0

5

10

15

20

25

30

35

40

Item A

Figure 10: F-111 Nylon warp axial pull test, all ten load cycles. 

Figure 11 and Figure 12 show the transverse to axial strain ratios for warp axial pulls of the F-111 

Nylon material. The strain ratio is observed to be highly loading dependent in the early portions 

of the loading histories. The relative sample to sample agreement of the strain ratio data is 

observed to be less than that observed for the normal stress-strain data. At stresses above 10 

lbf/in, the strain ratio was observed to be between 0.25 and 0.40 for the first load cycle. For the 

tenth load cycle the strain ratio was observed to be between 0.20 and 0.27 for stresses greater than 

10 lbf/in. 
Page 16 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 5 10 15 20 25 30 35 40 0

0.2

0.4

0.6

0.8

1

Item A

Item B

Item C

Item D

Figure 11: F-111 Nylon warp axial pull test, strain ratio cycle 1. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 5 10 15 20 25 30 35 40 0

0.1

0.2

0.3

0.4

0.5

Item A

Item B

Item C

Item D

Figure 12: F-111 Nylon warp axial pull test, strain ratio cycle 10. 

5.1.2 Fill Direction Pull Tests 

The F-111 Nylon fill direction measured normal stress-strain behavior for the stress interval [0, 

37] lbf/in is shown in Figure 13 through Figure 15. Figure 13 shows the first load cycle for all 

the samples tested. Similarly, Figure 14 shows the stress-strain data for the tenth load cycle. The 

results for the first load cycle exhibit non-linearity in the ramp up portion of the load curve. The 

first load cycle also exhibits significant inelastic behavior both in hysteresis and strain set. The 
Page 17 

strain set resulting from the first load cycle was approximately 10%. The results for the tenth 

load cycle showed much less inelastic behavior. Figure 15 shows all ten load/unload cycles for 

the test item A. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0.25 0

5

10

15

20

25

30

35

40

Item A

Item B

Item C

Item D

Item E

Figure 13: F-111 Nylon fill axial pull test, load cycle 1. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0.25 0

5

10

15

20

25

30

35

40

Item A

Item B

Item C

Item D

Item E

Figure 14: F-111 Nylon fill axial pull test, load cycle 10. 
Page 18 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0.25 0

5

10

15

20

25

30

35

40

Item A

Figure 15: F-111 Nylon fill axial pull test, all ten load cycles. 

Figure 16 and Figure 17 show the transverse to axial strain ratios for fill axial pulls of the F-111 

Nylon material. The strain ratio is observed to be highly loading dependent in the early portions 

of the loading histories. The relative sample to sample agreement of the strain ratio data is 

observed to be less than that observed for the normal stress-strain data. At stresses above 10 

lbf/in, the strain ratio was observed to be between 0.24 and 0.34 for the first load cycle. For the 

tenth load cycle the strain ratio was observed to be between 0.21 and 0.25 for stresses greater than 

10 lbf/in. 
Page 19 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 5 10 15 20 25 30 35 40 0

0.1

0.2

0.3

0.4

0.5

Item A

Item B

Item C

Item D

Item E

Figure 16: F-111 Nylon fill axial pull test, strain ratio cycle 1. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 5 10 15 20 25 30 35 40 0

0.1

0.2

0.3

0.4

0.5

Item A

Item B

Item C

Item D

Item E

Figure 17: F-111 Nylon fill axial pull test, strain ratio cycle 10. 

5.1.3 Warp versus Fill Stiffness Comparison 

The F-111 Nylon warp and fill normal stress-strain data for the first load cycle is shown in Figure 

18. From this curve we see the relative difference in stiffness in these two principle yarn 

directions. For the F-111 Nylon material tested, we observed that the warp direction of the 

material had the higher stiffness in the first load cycle. The warp and fill normal stress-strain data 
Page 20 

for the tenth load cycle is shown in Figure 19. From this curve we observed only a small stiffness 

difference in the tenth load cycle. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0.25 0

5

10

15

20

25

30

35

40

Warp Item A

Fill Item A

Figure 18: F-111 Nylon axial pull test, cycle 1 warp vs. fill stiffness. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0.25 0

5

10

15

20

25

30

35

40

Warp Item A

Fill Item A

Figure 19: F-111 Nylon axial pull test, cycle 10 warp vs. fill stiffness. 
Page 21 

5.2 HT1 Nomex Uni-axial testing 

5.2.1 Warp Direction Pull Tests 

The HT1 Nomex warp direction measured normal stress-strain behavior for the stress interval [0, 

172] lbf/in is shown in Figure 20 through Figure 22. Figure 20 shows the first load cycle for all 

the samples tested. Similarly, Figure 21 shows the stress-strain data for the tenth load cycle. The 

results for the first load cycle exhibit non-linearity in the ramp up portion of the load curve, where

two points of inflection are observed. Depending on the modeling objectives a linear stress-strain 

approximation could yield acceptable results for the ramp up portion of cycle 1. The first load 

cycle also exhibits significant inelastic behavior both in hysteresis and strain set. The strain set 

was observed to be approximately 50% of the strain maximum for the first load cycle. The 

results for the tenth load cycle showed much less inelastic behavior. After a small initial region 

of loading, the tenth cycle stress-strain response was close to linear behavior. Figure 22 shows all 

ten load/unload cycles for one of the samples tested. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Item A

Item B

Item C

Item D

Item E

Figure 20: HT1 Nomex warp axial pull test, load cycle 1. 
Page 22 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Item A

Item B

Item C

Item D

Item E

Figure 21: HT1 Nomex warp axial pull test, load cycle 10. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Item A

Figure 22: HT1 Nomex warp axial pull test, all ten load cycles. 

Figure 23 and Figure 24 show the transverse to axial strain ratios for warp axial pulls of the HT1 

Nomex material. The strain ratio is observed to be loading dependent through the entire load 

range for cycle 1. At stresses above 50 lbf/in, the strain ratio was observed to be between 0.5 and 

0.7 for the tenth load cycle. The relative sample to sample agreement of the strain ratio data was 

not significantly different from that observed for the normal stress-strain data. 
Page 23 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.5

1

1.5

2

Item A

Item B

Item C

Item D

Item E

Load Decreasing

Load Increasing

Figure 23: HT1 Nomex warp axial pull test, strain ratio cycle 1. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.2

0.4

0.6

0.8

1

Item A

Item B

Item C

Item D

Item E

Figure 24: HT1 Nomex warp axial pull test, strain ratio cycle 10. 

5.2.2 Fill Direction Pull Tests 

The HT1 Nomex fill direction measured normal stress-strain behavior for the stress interval [0, 

172] lbf/in is shown in Figure 25 through Figure 27. Figure 25 shows the first load cycle for all 

the samples tested. Similarly, Figure 26 shows the stress-strain data for the tenth load cycle. The 

results for the first load cycle exhibit non-linearity in the ramp up portion of the load curve, where

two points of inflection are observed. The first load cycle also exhibits significant inelastic 
Page 24 

behavior both in hysteresis and strain set. For an approximate maximum induced strain of 16%, 

the strain set was observed to be 9% for the first load cycle. The results for the tenth load cycle 

showed much less inelastic behavior. Similar to the warp direction, the tenth cycle stress-strain 

response was close to linear behavior after a small initial region of loading. Figure 27 shows all 

ten load/unload cycles for one of the samples tested. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Item A

Item B

Item C

Item D

Figure 25: HT1 Nomex fill axial pull test, load cycle 1. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Item A

Item B

Item C

Item D

Figure 26: HT1 Nomex fill axial pull test, load cycle 10. 
Page 25 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Item A

Figure 27: HT1 Nomex fill axial pull test, all ten load cycles. 

Figure 28 and Figure 29 show the transverse to axial strain ratios for fill axial pulls of the HT1 

Nomex material. The strain ratio is observed to be loading dependent through the entire load 

range for the first cycle. At stresses above 50 lbf/in, the strain ratio was observed to be between 

0.30 and 0.45 for the tenth load cycle. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.5

1

1.5

2

Item A

Item B

Item C

Itrem D

Load Increasing

Load Decreasing

Figure 28: HT1 Nomex fill axial pull test, strain ratio cycle 1. 
Page 26 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.2

0.4

0.6

0.8

1

Item A

Item B

Item C

Item D

Figure 29: HT1 Nomex fill axial pull test, strain ratio cycle 10. 

5.2.3 Warp versus Fill Stiffness Comparison 

The HT1 Nomex warp and fill normal stress-strain data for the first load cycle is shown in Figure 

30. The warp and fill normal stress-strain data for the tenth load cycle is shown in Figure 31. 

From this curve we see the relative difference in stiffness in these two principle yarn directions. 

For the material tested, we observed that the warp and fill stiffness of the material was very 

similar in both the first and tenth cycles. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Warp Item A

Fill Item A

Figure 30: HT1 Nomex axial pull test, cycle 1 warp vs. fill stiffness. 
Page 27 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.05 0.1 0.15 0.2 0

50

100

150

200

Warp Item A

Fill Item A

Figure 31: HT1 Nomex axial pull test, cycle 10 warp vs. fill stiffness. 

5.3 200 Denier Kevlar 

5.3.1 Warp Direction Pull Tests 

The 200 denier Kevlar warp direction measured normal stress-strain behavior for the stress 

interval [0, 189] lbf/in is shown in Figure 32 through Figure 34. Figure 32 shows the first load 

cycle for all the samples tested. Similarly, Figure 33 shows the stress-strain data for the tenth 

load cycle. The results for the first load cycle exhibit a smaller degree of non-linearity than was 

observed in the Nylon and Nomex materials. The first load cycle also exhibits significantly less 

inelastic behavior that was observed with the Nylon and Nomex materials. The strain set was 

observed to be approximately 20% of the strain maximum for the first load cycle. Other than the 

impact of the strain set, the results for the tenth load cycle were very similar to those of the first. 

Figure 34 shows all ten load/unload cycles for one of the samples tested. 
Page 28 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Item B

Item C

Item D

Item E

Figure 32: 200 denier Kevlar warp axial pull test, load cycle 1. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Item B

Item C

Item D

Item E

Figure 33: 200 denier Kevlar warp axial pull test, load cycle 10. 
Page 29 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Item B

Figure 34: 200 denier Kevlar warp axial pull test, all ten load cycles. 

Figure 35 and Figure 36 show the transverse to axial strain ratios for warp axial pulls of the 200 

denier Kevlar material. The strain ratio is observed to be loading dependent through the entire 

load range for all cycles. Other than a minor shift down, the cycling did not have an impact on 

the ratio. The overall magnitude of the ratio for the 200 denier Kevlar is large in comparison to 

the Nylon and Nomex materials. In all cases the ratio was greater than 1.0 and under some loads 

it was greater than 2.0. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.5

1

1.5

2

2.5

3

Item B

Item C

Item D

Item E

Figure 35: 200 denier Kevlar warp axial pull test, strain ratio cycle 1. 
Page 30 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.5

1

1.5

2

2.5

3

Item B

Item C

Item D

Item E

Figure 36: 200 denier Kevlar warp axial pull test, strain ratio cycle 10. 

5.3.2 Fill Direction Pull Tests 

The 200 denier Kevlar fill direction measured normal stress-strain behavior for the stress interval 

[0, 189] lbf/in is shown in Figure 37 through Figure 39. Figure 37 shows the first load cycle for 

all the samples tested. Similarly, Figure 38 shows the stress-strain data for the tenth load cycle. 

The results for the first load cycle exhibit non-linearity in the ramp up portion of the load curve. 

The stress-strain response was bi-linear in nature with low stiffness at low loads and then a 

significantly higher stiffness at higher loads. Similar to the warp direction, the first load cycle 

exhibits significantly less inelastic behavior than was observed with the Nylon and Nomex 

materials. The strain set was observed to be approximately 28% of the strain maximum for the 

first load cycle. The results for the tenth load cycle showed less of a bi-linear response where the 

initial low stiffness linear region was not present in the stress-strain curve. Figure 39 shows all 

ten load/unload cycles for one of the samples tested. 
Page 31 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Item A

Item B

Item C

Item D

Item E

Figure 37: 200 denier Kevlar fill axial pull test, load cycle 1. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Item A

Item B

Item C

Item D

Item E

Figure 38: 200 denier Kevlar fill axial pull test, load cycle 10. 
Page 32 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Item A

Figure 39: 200 denier Kevlar fill axial pull test, all ten load cycles. 

Figure 40 and Figure 41 show the transverse to axial strain ratios for fill axial pulls of the 200 

denier Kevlar material. The strain ratio is observed to be loading dependent through the entire 

load range for all cycles. The cycling did not have an impact on the ratio. Similar to the warp 

direction, the overall magnitude of the ratio is large in comparison to the Nylon and Nomex 

materials. In all cases the ratio was greater than 1.0. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.5

1

1.5

2

2.5

3

Item A

Item B

Item C

Item D

Item E

Figure 40: 200 denier Kevlar fill axial pull test, strain ratio cycle 1. 
Page 33 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 50 100 150 200 0

0.5

1

1.5

2

2.5

Item A

Item B

Item C

Item D

Item E

Figure 41: 200 denier Kevlar fill axial pull test, strain ratio cycle 10. 

5.3.3 Warp versus Fill Stiffness Comparison 

The 200 denier Kevlar warp and fill normal stress-strain data for the first load cycle is shown in 

Figure 42. The warp and fill normal stress-strain data for the tenth load cycle is shown in Figure 

43. For the first load cycle, the warp direction is stiffer than the fill direction. This is due to the 

initial low stiffness region in the fill direction bi-linear response. Other than an offset resulting

from the respective strain sets, the warp and fill stress-strain responses are very similar for the 

tenth load cycle. 
Page 34 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Warp Item B

Fill Item B

Figure 42: 200 denier Kevlar axial pull test, cycle 1 warp vs. fill stiffness. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0

50

100

150

200

Warp Item B

Fill Item B

Figure 43: 200 denier Kevlar axial pull test, cycle 10 warp vs. fill stiffness. 

5.4 840 Denier Kevlar 

5.4.1 Warp Direction Pull Tests 

The 840 denier Kevlar warp direction measured normal stress-strain behavior for the stress 

interval [0, 491] lbf/in is shown in Figure 44 through Figure 46. Figure 44 shows the first load 

cycle for all the samples tested. Similarly, Figure 45 shows the stress-strain data for the tenth 
Page 35 

load cycle. The results for the first load cycle exhibit non-linearity in the ramp up portion of the 

load curve. The stress-strain response was bi-linear in nature with low stiffness at low loads and 

then a significantly higher stiffness at higher loads. The strain set was observed to be 

approximately 38% of the strain maximum for the first load cycle. The results for the tenth load 

cycle showed less of a bi-linear response where the initial low stiffness linear region was not as 

large in the stress-strain curve. Figure 46 shows all ten load/unload cycles for one of the samples 

tested. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Item B

Item C

Item D

Item E

Figure 44: 840 denier Kevlar warp axial pull test, load cycle 1. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Item B

Item C

Item D

Item E

Figure 45: 840 denier Kevlar warp axial pull test, load cycle 10. 
Page 36 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Item B

Figure 46: 840 denier Kevlar warp axial pull test, all ten load cycles. 

Figure 47 and Figure 48 show the transverse to axial strain ratios for warp axial pulls of the 840 

denier Kevlar material. The strain ratio is observed to be loading dependent through the entire 

load range for all cycles. Other than some differences at low load, the cycling did not have an 

impact on the ratio. The overall magnitude of the ratio for the 840 denier Kevlar was similar to 

that of the 200 denier Kevlar. In all cases the ratio was greater than 1.0 and under some loads it 

was greater than 2.0. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 100 200 300 400 500 600 0

0.5

1

1.5

2

2.5

3

Item B

Item C

Item D

Item E

Figure 47: 840 denier Kevlar warp axial pull test, strain ratio cycle 1. 
Page 37 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 100 200 300 400 500 600 0

0.5

1

1.5

2

2.5

3

Item B

Item C

Item D

Item E

Figure 48: 840 denier Kevlar warp axial pull test, strain ratio cycle 10. 

5.4.2 Fill Direction Pull Tests 

The 840 denier Kevlar fill direction measured normal stress-strain behavior for the stress interval 

[0, 491] lbf/in is shown in Figure 49 through Figure 51. Figure 49 shows the first load cycle for 

all the samples tested. Similarly, Figure 50 shows the stress-strain data for the tenth load cycle. 

The results for the first load cycle exhibit non-linearity in the ramp up portion of the load curve. 

The stress-strain response was bi-linear in nature with low stiffness at low loads and then a 

significantly higher stiffness at higher loads. The strain set was observed to be approximately 

28% of the strain maximum for the first load cycle. The results for the tenth load cycle showed 

less of a bi-linear response where the initial low stiffness linear region was not present in the 

stress-strain curve. Figure 51 shows all ten load/unload cycles for one of the samples tested. 
Page 38 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Item A

Item B

Item C

Item D

Item E

Figure 49: 840 denier Kevlar fill axial pull test, load cycle 1. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Item A

Item B

Item C

Item D

Item E

Figure 50: 840 denier Kevlar fill axial pull test, load cycle 10. 
Page 39 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Item B

Figure 51: 840 denier Kevlar fill axial pull test, all ten load cycles. 

Figure 52 and Figure 53 show the transverse to axial strain ratios for fill axial pulls of the 840 

denier Kevlar material. The strain ratio is observed to be loading dependent through the entire 

load range for all cycles. The cycling did not have an impact on the ratio. The overall magnitude 

of the ratio for the 840 denier Kevlar was similar to that of the 200 denier Kevlar. In all cases the

ratio was greater than 1.0 and under some loads it was greater than 2.0. 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 100 200 300 400 500 600 0

0.5

1

1.5

2

2.5

3

Item A

Item B

Item C

Item D

Item E

Figure 52: 840 denier Kevlar fill axial pull test, strain ratio cycle 1. 
Page 40 

Axial Stress (lbf/in)

-εtrans

/εaxial

0 100 200 300 400 500 600 0

0.5

1

1.5

2

2.5

3

Item A

Item B

Item C

Item D

Item E

Figure 53: 840 denier Kevlar fill axial pull test, strain ratio cycle 10. 

5.4.3 Warp versus Fill Stiffness Comparison 

The 840 denier Kevlar warp and fill normal stress-strain data for the first load cycle is shown in 

Figure 54. The warp and fill normal stress-strain data for the tenth load cycle is shown in Figure 

55. For the first load cycle, the fill direction is stiffer than the warp direction. This is due to the 

initial low stiffness region being larger on the warp direction response. Other than an offset 

resulting from the respective strain sets, the warp and fill stress-strain responses are very similar 

for the tenth load cycle. 
Page 41 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Warp Item B

Fill Item B

Figure 54: 840 denier Kevlar axial pull test, cycle 1 warp vs. fill stiffness. 

Axial Strain (in/in)

Axial Stress (lbf/in)

0 0.005 0.01 0.015 0.02 0.025 0.03 0

100

200

300

400

500

600

Warp Item B

Fill Item B

Figure 55: 840 denier Kevlar axial pull test, cycle 10 warp vs. fill stiffness. 
Page 42 

6. Shear Stress-Strain 

6.1 Picture Frame Testing 

The picture frame apparatus used in the testing had a bearing to bearing side length of 10 inches. 

The test article for the picture frame shear testing had a slightly shorter edge length of 8.0 inches. 

The apparatus with a test article installed is shown in Figure 3. The INSTRON crosshead 

extension along with the apparatus side length was used to calculate the shear strain. Shear strain 

was calculated as φ

π

θ = −

2

, where φ is the frame angle as shown in Figure 56. 

Figure 56: Picture Frame Test Fixture – Frame Angle

The crosshead extension along with the load cell force was used to calculate the shear stress. 

This included calculating the shear force as 

2cosφ

FL F = where FL is the load cell force and the 

nominal shear stress as 

L

F

σ = where L is the side length of the picture frame fixture. 

Engineering shear strain versus shear stress is shown plotted in the figures of this section. Shear 

strain is reported in radians, and is the angle between the warp and fill fibers as the fabric is 

loaded. The test cycles were defined in terms of maximum/minimum load cell force. The test 

cycles always started out with a pulling action on the pivot points of the fixture and then a 

pushing action as shown in Figure 57. The results for the pulling portion of a load cycle were 

generally positive shear strain and stress. Conversely, the push portions of the load cycle were 

generally negative shear strain and stress. 
Page 43 

Pull Load Push Load

Figure 57: Picture frame test load scenario. 

During the first load cycle of this testing, the INSTRON crosshead was paused twice for 

photogrammetry picture taking. A sample time history plot showing these pauses is shown in 

Figure 58. Although the strain was held at a constant value for the pictures, the actual load 

relaxed significantly during the time it took to take the photos. As a result of this, the plots in this 

section include the 2nd through the 5th cycles. 

Time (s)

Extension (in)

Load (lbf)

0 200 400 600 800 1000 1200 -2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-4

-3

-2

-1

0

1

2

3

Crosshead Extension 4

Load Cell Force

Figure 58: F-111 Nylon Item A time history. 
Page 44 

6.1.1 F-111 Nylon Picture Frame Testing 

The results for the F-111 Nylon shear stress-strain are shown plotted individually for each test 

article and then in one plot where all the curves are overlaid. We observe some change in shear 

stiffness with continued cycling for the Nylon. Other than an offset in shear strain, the response 

of items A and B were similar. The induced shear strain range for Item C was larger than it was 

for Items A and B. 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Item A

Figure 59: F-111 Nylon picture frame test, Item A shear stress-strain. 
Page 45 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Item B

Figure 60: F-111 Nylon picture frame test, Item B shear stress-strain. 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Item C

Figure 61: F-111 Nylon picture frame test, Item C shear stress-strain. 
Page 46 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Item A

Item B

Item C

Figure 62: F-111 Nylon picture frame test, shear stress-strain. 

6.1.2 HT1 Nomex Picture Frame Testing 

Test articles identified as A, B, and C were tested as described in Section 6.1. The results for 

these test articles are shown in Figure 63 and Figure 64. Figure 63 shows the results for the test 

article identified as Item A. Similar to the Nylon material, we observe some change in shear 

stiffness with continued cycling for the HT1 Nomex. In Figure 64 we see that articles A through 

C are in relatively good agreement with each other. A shear stress strain response was observed 

that was less stiff in the push portion of the load cycle as it was in the pull section. This result 

was also observed for the Nylon test articles in the previous sub-section. There was one 

additional HT1 Nomex test article, identified as Item D, that had a much more consistent 

response relative to the pull and push portions of the load cycle. All five load cycles are shown 

for Item D in Figure 65. For Item D there were no pauses in the loading for photogrammetry. 

Additional testing would be needed to determine if the extended pauses for photogrammetry 

during the first load cycle impacted the stiffness measured in the push portions of the load cycle. 
Page 47 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -4

-3

-2

-1

0

1

2

3

4

Item A

Figure 63: HT1 Nomex picture frame test, Item A shear stress-strain. 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -4

-3

-2

-1

0

1

2

3

4

Item A

Item B

Item C

Figure 64: HT1 Nomex picture frame test, Items A, B & C shear stress-strain. 
Page 48 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 -4

-3

-2

-1

0

1

2

3

4

Item D

Figure 65: HT1 Nomex picture frame test, Item D shear stress-strain. 

6.1.3 200 Denier Kevlar Picture Frame Testing 

For the 200 denier Kevlar picture frame testing two of the five test articles were in particularly 

good agreement as shown in Figure 66. In this figure we see that the shear stress strain response 

did not change as the load cycling increased. Figure 67 shows the picture frame shear stressstrain response for all the articles tested for the 200 denier Kevlar. The test article identified as

Item E had a lower shear stiffness as compared with the other samples. 
Page 49 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 -0.6

-0.4

-0.2

0

0.2

0.4

0.6

Item A

Item D

Figure 66: 200 denier Kevlar picture frame test, Item A and D shear stress-strain. 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 -0.6

-0.4

-0.2

0

0.2

0.4

0.6

Item A

Item B

Item C

Item D

Item E

Figure 67: 200 denier Kevlar picture frame test, shear stress-strain. 

6.1.4 840 Denier Kevlar Picture Frame Testing 

The results for the 840 denier Kevlar picture frame testing are shown in Figure 68 through Figure 

70. The tendency for the shear stiffness results to be less stiff in the push direction repeat again 

for this material. Of the four materials in this study, the 840 denier Kevlar had the largest relative 

change between the push direction and pull direction shear stiffness. This result can be seen in 

Figure 68, where the shear stress-strain data is shown plotted for the test article identified as Item
Page 50 

A. For the five 840 denier Kevlar articles tested with the picture frame apparatus, four of the five 

were in relatively good agreement as shown in Figure 69. Test Item E had a significantly 

different shear stress-strain response and is shown plotted in Figure 70 with Item A for 

comparison. 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Item A

Figure 68: 840 denier Kevlar picture frame test, Item A shear stress-strain. 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Item A

Item B

Item C

Item D

Item E

Figure 69: 840 denier Kevlar picture frame test, shear stress-strain. 
Page 51 

Engineering Shear Strain (rad)

Shear Stress (lbf/in)

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 -2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Item E

Item A

Figure 70: 840 denier Kevlar picture frame test, Item A and E shear stress-strain. 

6.2 Bias Extension Testing 

Bias Extension test results are presented in the next four sub sections for the four materials under 

consideration in this task. The sample size used for this testing had a height of 8.6 inches and a 

width of 3.5 inches. INSTRON load and crosshead extension were the two primary 

measurements taken during the testing. Cross head extension was converted into engineering 

shear strain in the pure shear region of the test article. This was calculated as φ

π

θ 2

2

= − and 













−

= +

−

0

0

1

(2 ) cos

cos cos

φ

δ

φ φ

H W

 where H = sample height, W= sample width, and δ = 

displacement. 

Some iterative numerical analysis is required to convert the load and extension into the shear 

stress in the pure shear region of the sample. This numerical analysis has not yet been conducted 

for these results. As a result, the experimental plots in this section will plot load versus 

engineering shear strain. The result plots only show the ramp up portion of the first cycle where 

the crosshead was paused for photogrammetry pictures. The subsequent cycles where the 

crosshead was not paused have both the ramp up and ramp down portions of the loading included. 

6.2.1 F-111 Nylon Bias Extension Testing 

The F-111 Nylon bias extension shear stiffness behavior for the shear strain interval [0, 0.097] 

rad is shown in Figure 71 through Figure 73. Figure 71 shows the ramp up for the first load cycle 

of all samples tested. Figure 72 shows the shear stiffness results for the fifth load cycle. The first 

cycle load versus shear strain response during the ramp up for the Nylon had an initial non-linear 

region followed by a linear region. The first load cycle resulted in a shear strain set that was 

approximately 67% of the maximum induced shear strain of the cycle. The results for the fifth 
Page 52 

load cycle showed a predominantly linear response during the load ramp up. Figure 73 shows 

load cycles 2 through 5 for one of the samples tested. From this figure we see that subsequent 

cycling had no effect on the shear stiffness in this strain range. The load cycles do exhibit some 

degree of hysteresis in the stress-strain response.

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.2

0.4

0.6

0.8

1

1.2

Item A

Item B

Item C

Figure 71: F-111 Nylon bias extension test, load ramp up cycle 1. 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.2

0.4

0.6

0.8

1

1.2

Item A

Item B

Item C

Figure 72: F-111 Nylon bias extension test, load cycle 5. 
Page 53 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.2

0.4

0.6

0.8

1

1.2

Item A

Figure 73: F-111 Nylon bias extension test, cycles 2 through 5. 

6.2.2 HT1 Nomex Bias Extension Testing 

The HT1 Nomex bias extension shear stiffness behavior for the shear strain interval [0, 0.097] rad 

is shown in Figure 74 through Figure 76. Figure 74 shows the ramp up for the first load cycle of 

all samples tested. Figure 75 shows the shear stiffness results for the fifth load cycle. The first 

cycle load versus shear strain response during the ramp up for the Nomex was predominantly 

linear. The first load cycle resulted in a shear strain set that was approximately 8% of the 

maximum induced shear strain of the cycle. The results for the fifth load cycle showed a greater 

degree of non-linearity during the load ramp up. Figure 76 shows load cycles 2 through 5 for one 

of the samples tested. From this figure we see that subsequent cycling had no effect on the shear 

stiffness in this strain range. The load cycles do exhibit some degree of hysteresis in the stressstrain response. 
Page 54 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

1

2

3

4

5

6

7

Item A

Item B

Item C

Figure 74: HT1 Nomex bias extension test, load ramp up cycle 1. 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

1

2

3

4

5

6

7

Item A

Item B

Item C

Figure 75: HT1 Nomex bias extension test, load cycle 5. 
Page 55 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

1

2

3

4

5

6

7

Item A

Figure 76: HT1 Nomex bias extension test, cycles 2 through 5. 

6.2.3 200 Denier Kevlar Bias Extension Testing 

The 200 denier Kevlar bias extension shear stiffness behavior for the shear strain interval [0, 

0.097] rad is shown in Figure 77 through Figure 79. Figure 77 shows the ramp up for the first 

load cycle of all samples tested. Figure 78 shows the shear stiffness results for the fifth load 

cycle. The first cycle load versus shear strain response during the ramp up for the 200 denier 

Kevlar was predominantly linear. The first load cycle resulted in a shear strain set that was 

approximately 10% of the maximum induced shear strain of the cycle. Figure 79 shows load 

cycles 2 through 5 for one of the samples tested. From this figure we see that subsequent cycling 

had no effect on the shear stiffness in this strain range. The load cycles do exhibit some degree of 

hysteresis in the stress-strain response. 
Page 56 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.2

0.4

0.6

0.8

1

1.2

Item A

Item B

Item C

Figure 77: 200 denier Kevlar bias extension test, load ramp up cycle 1. 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.2

0.4

0.6

0.8

1

1.2

Item A

Item B

Item C

Figure 78: 200 denier Kevlar bias extension test, load cycle 5. 
Page 57 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.2

0.4

0.6

0.8

1

1.2

Item A

Figure 79: 200 denier Kevlar bias extension test, cycles 2 through 5. 

6.2.4 840 Denier Kevlar Bias Extension Testing 

The 840 denier Kevlar bias extension shear stiffness behavior for the shear strain interval [0, 

0.097] rad is shown in Figure 80 through Figure 82. Figure 80 shows the ramp up for the first 

load cycle of all samples tested. Figure 81 shows the shear stiffness results for the fifth load 

cycle. Similar to the Nomex and 200 denier Kevlar, the first cycle load versus shear strain 

response during the ramp up for the 840 denier Kevlar was predominantly linear. The first load 

cycle resulted in a shear strain set that was approximately 10% of the maximum induced shear 

strain of the cycle. Figure 82 shows load cycles 2 through 5 for one of the samples tested. From 

this figure we see that subsequent cycling had no effect on the shear stiffness in this strain range. 

The load cycles do exhibit some degree of hysteresis in the stress-strain response. 
Page 58 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.5

1

1.5

2

2.5

3

3.5

Item A

Item B

Item C

Figure 80: 840 denier Kevlar bias extension test, load ramp up cycle 1. 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.5

1

1.5

2

2.5

3

3.5

Item A

Item B

Item C

Figure 81: 840 denier Kevlar bias extension test, load cycle 5. 
Page 59 

Engineering Shear Strain (rad)

Load (lbf)

0 0.02 0.04 0.06 0.08 0.1 0.12 0

0.5

1

1.5

2

2.5

3

3.5

Item B

Figure 82: 840 denier Kevlar bias extension test, cycles 2 through 5. 

6.3 Inflated Cylinder Testing 

Inflated cylinder torsion test results are presented in the next two sub sections for the HT1 Nomex 

and 200 Denier Kevlar materials. During the experimental program problems developed with the 

F-111 Nylon and 840 denier Kevlar materials. The F-111 material tested as part of the Isotensoid 

program had a very light coating applied as discussed in Section 3.4. As a result of the coating 

problems discussed in this section we were not able to coat the F-111 material for this task. 

Without the coating, the F-111 Nylon cylinders could not hold pressure in the testing. The 840 

denier Kevlar cylinders presented a problem of excess skew in the weave of the fabric. Under 

just the influence of the inflation pressure the cylinders rotated as much as 20 degrees. This 

rotation put an offset in the data such that only a small clockwise rotation could be made before 

the fixture hardware would bottom out. As a result, using this data would most likely 

misrepresent the properties of the material. The numerical data for these 840 denier Kevlar tests 

has been provided to the customer but shear stress-strain data is not plotted in this report. 

The graphs in this section plot shear stress versus shear strain in the material. End cap rotation 

was converted into engineering shear strain using measurements of the cylinder circumference 

and length. This was calculated as 

L

rφ

γ = where φ = twist angle, r = radius of cylinder, and L = 

length of cylinder. Applied torque was converted into shear stress using 

J

Tr

τ = where T = 

applied torque, r = radius of cylinder, and J = cylinder polar moment of inertia. For the test 

cylinder, 3J = 2πr . 

Table 7 details the manual measurements made during cylinder testing for circumference and 

length. With the inflation load we get a hoop and axial preload state which has the effect of 

increasing the shear stiffness. Testing was conducted at inflation pressures of 1.0 and 7.0 psi. 
Page 60 

Table 8 details the hoop stress preload states for these two inflation pressures. During the 7.0 psi 

testing the torsion cycling resulted in increasing the leakage of the test article. As the leakage 

increased the pressure fell below 7.0 psi so that a uniform preload state was not maintained. 

These pressure changes are not shown in the shear stress-strain plots, but are included in the time 

history data provided to the customer. 

Table 7: Manual inflated cylinder measurements. 

Table 8: Inflated cylinder preload states. 

6.3.1 HT1 Nomex Inflated Cylinder Testing 

Figure 83 shows the time history data for the HT1 Nomex cylinder identified as Item B. Between 

0.0 and 1000 seconds torque testing was conducted at an inflation pressure of 1.0 psi. From time 

1000 to 1600 torque testing was conducted at an inflation pressure of 7.0 psi. The full +/- 70 

degree twist angle range of the fixture was used in both cases. Figure 84 shows the shear stressstrain data that was calculated from the torque and twist angle measurements. We see a 

significant increase in the shear stiffness when changing the pressure from 1.0 to 7.0 psi. The 

data for test articles Item A and Item C are included in the data set provided to the customer. 
Page 61 

-80

-60

-40

-20

0

20

40

60

80

0 200 400 600 800 1000 1200 1400 1600 1800

Time (s)

Twist Angle (deg)

-800

-600

-400

-200

0

200

400

600

800

Torque (in-lbs)

Twist Angle Torque

Figure 83: HT1 Nomex inflated cylinder test, Item B time history. 
Page 62 

-8

-6

-4

-2

0

2

4

6

8

-0.15 -0.1 -0.05 0 0.05 0.1 0.15

Shear Strain (rad)

Shear Stress (lbf/in)

Shear Stress 1psi

Shear Stress 7psi

Figure 84: HT1 Nomex inflated cylinder test, Item B shear stress-strain. 

6.3.2 200 Denier Inflated Cylinder Testing 

Figure 85 shows the time history data for the 200 denier Kevlar cylinder identified as Item B. 

Between 0.0 and 1000 seconds torque testing was conducted at an inflation pressure of 1.0 psi. 

From time 1500 to 2500 torque testing was conducted at an inflation pressure of 7.0 psi. The full 

+/- 70 degree twist angle range of the fixture was used in both cases. Figure 86 shows the 

calculated shear stress strain data that was calculated from the torque and twist angle 

measurements. We see a significant increase in the shear stiffness when changing the pressure 

from 1.0 to 7.0 psi. The data for test articles Item A and Item C are included in the data set 

provided to the customer. 
Page 63 

-80

-60

-40

-20

0

20

40

60

80

0 500 1000 1500 2000 2500 3000

Time (s)

Twist Angle (deg)

-500

-400

-300

-200

-100

0

100

200

300

400

500

Torque (in-lbs)

Twist Angle Torque 1 psi Torque 7 psi

Figure 85: 200 denier Kevlar inflated cylinder test, Item B time history. 
Page 64 

-5

-4

-3

-2

-1

0

1

2

3

4

5

-0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10

Shear Strain (rad)

Stress Stress (lbf/in)

1 psi 7 psi

Figure 86: 200 denier Kevlar inflated cylinder test, Item B shear stress-strain. 

6.4 Test Recommendations 

Based on the material testing and data taken throughout this study, several recommendations for 

future work were compiled for each test type. This section details the lessons learned and 

recommendations for future test phases. 

Uni-axial testing in this program addressed measurements of hysteresis and strain sets after 

loading. An additional measurement recommended for future uni-axial testing would be the 

degree to which the observed strain set is permanent. Samples would have a gauge length 

marked on them in the axial and lateral directions. After the samples are removed from the 

INSTRON, the axial and lateral gauge length would be measured as a function of time. This 

information would be important to better understand the effect of break in cycling of the samples. 

For the trellis frame testing, it should be noted that samples were installed on the trellis frame 

apparatus without any initial tension, per the test procedure. It was difficult to repeatedly install 

the samples without the presence of some slack in the setup. Ideally, all the points would be 

planar at the beginning of the test trellis frame shear test. The presence of the slack resulted in out 

of plane effects that should be able to be quantified once the photogrammetry data is post 

processed. The presence of this slack also made the no load photogrammetry measurements quite 

challenging since in the state of slack the sample could be easily be due to small amounts in the 
Page 65 

out of plane direction. For future efforts with this fixture, some type of tensioning frame is 

recommended to develop a repeatable minimum load taut condition prior to loading the frame. 

The inflated cylinder test articles clearly exhibited circumference changes as the cylinders were 

torqued. The current procedure could only accommodate manual measurement of the 

circumference. It is recommended for future testing that a string potentiometer style device be 

used to measure the circumference in real time and that this data be recorded on the data 

acquisition system. This improvement would allow more data to be gathered in less time. It 

would also eliminate the need lock in a specific twist angle while the measurements are 

conducted. 

While conducting the INSTRON testing for the bias extension and trellis frame test samples, the 

INSTRON crosshead was paused and held constant so that photogrammetry pictures could be 

taken. A single camera was used and had to be moved between the three planned camera 

positions. This procedure had many disadvantages relative to accuracy and the labor time to 

complete the test. While a strain state was locked in, the load dropped off significantly due to 

inelastic effects that were not desired. This action of pausing the crosshead also was problematic 

for the INSTRON itself. The INSTRON software had the tendency to crash after a pause 

interval. A sufficient number of photogrammetry cameras are now available at ILC such that the 

testing can be conducted without any pauses at all. This improvement will shorten test times and 

increase the consistency of the trellis frame shear test results. 

7. Summary 

Textile material load versus elongation characteristics have been experimentally determined for 

the PAI-DAE program Flexible Material Systems Testing task. This testing was carried out for a 

set of four materials that have been considered for inflatable aerodynamic decelerators. Uni-axial 

strip tensile testing was implemented to measure the normal stress-strain behavior of the 

materials. Three test procedures were implemented to measure the shear stress-strain behavior of 

the materials. Follow on work in this area could include the following: 

• Post processing and analysis of the photogrammetry data taken during the bias extension 

and picture frame shear testing. 

• Review of the macro photography data and correlate the observed weave shear angle with 

the shear strain calculated from the test data. 

• Performance of the iterative curve fitting to establish experimental shear stress data for 

the bias extension testing. 

The results for this work will enhance the predictive capability of inflatable aerodynamic 

decelerator finite element numerical models by providing this experimental data for the material 

law implementations. The results will also directly support a ground test program for inflatable 

decelerator material technology. 

 

i

 Reference ASTM D297-93, 16.3 Density by Hydrostatic Method 

ii Welch, Joseph V., “PAI-DAE Program – Experimental Mechanics Study, Stress-Strain Behavior of 

Isotensoid Woven Fabric Material,” Final Report submitted to NASA Langley Research Center, February 

18, 2010. 

iii Harrison, P., Wiggers, J., Long, A.C., and Clifford. M.J., “Continuous Fiber Reinforced Composites – 

Determination of the In-plane Shear Stress Response to Shear Strain and Shear Strain Rate, Using the 

Picture-Frame Test,” Internal Test Standard, Polymer Composites Research Group, University of 

Nottingham, 1st Edition, August 1, 2002. 
Page 66 

 

iv Cao, J., et al., “Characterization of Mechanical Behavior of Woven Fabrics: Experimental Methods and 

Benchmark Results,” Composites: Part A, pp 1037-1053, Elsevier, 2008. 

v

 Cao, Jian and Peng, Xiongqi, “Bias Extension Test Standard,” Advanced Materials Processing 

Laboratory, Department of Mechanical Engineering, Northwestern University, 8/2003. 
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Flexible Material Systems Testing

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Lin, John K.; Shook, Lauren S.; Ware, Joanne S.; Welch, Joseph V.

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NASA Langley Research Center

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An experimental program has been undertaken to better characterize the stress-strain characteristics of flexible material 

systems to support a NASA ground test program for inflatable decelerator material technology. A goal of the current study is 

to investigate experimental methods for the characterization of coated woven material stiffness. This type of experimental 

mechanics data would eventually be used to define the material inputs of fluid-structure interaction simulation models. The test 

methodologies chosen for this stress-strain characterization are presented along with the experimental results.

15. SUBJECT TERMS

Fabric; Flexible materials; Inflatable decelerator; Stress-strain

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