NASA / TM--2000-210482

A Damage Resistance Comparison

Between Candidate Polymer Matrix

Composite Feedline Materials

A. T. Nettles

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

National Aeronautics and

Space Administration

Marshall Space Flight Center • MSFC, Alabama 35812

September 2000
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TABLE OF CONTENTS

1. INTRODUCTION ............................................................................................................................. 1

3

2. MATERIAL USED ...........................................................................................................................

4

3. IMPACT TESTING ..........................................................................................................................

4

3.1 Visual Examination ...................................................................................................................

4

3.2 X Radiography ..........................................................................................................................

3.3 Cross-Sectional Examination .................................................................................................... 4

4. RESULTS .......................................................................................................................................... 6

4.1 High-Impact Level .................................................................................................................... 6

4.2 Low-Impact Level ..................................................................................................................... 14

20 5. CONCLUSIONS ..............................................................................................................................

6. FUTURE WORK .............................................................................................................................. 21

23 REFERENCES ......................................................................................................................................

iii

LIST OF FIGURES

1. Typical damage to impacted side of specimens at 2.5 ft-lb ..................................................... 7

2. Typical damage to nonimpacted side of specimens at 2.5 ft-lb .............................................. 8

,

.

X rays of specimens impacted at 2.5 ft-lb ............................................................................... tl

Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb ................................. I0

.

.

Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb,

flourescent dye enhanced ........................................................................................................ 12

Typical damage to impacted side of specimens at 1.8 ft-lb ................................................... 15

7. Typical damage to non-impacted side of specimens at 1.8 ft-lb ............................................. Io

8. Cross-sectional photomicrographs of specimens impacted at 1.8 ft-lb ................................... 18

LIST OF TABLES

1. Materials tested for impact resistance ..................................................................................... 3

LIST OF ACRONYMS

e-beam

IM

ksi

Msi

PEEK

PMC

RLV

SARTM

ZnI

electron beam

intermediate modulus

thousand square inches

million square inches

polyetheretherketone

polymer matrix composite

reusable launch vehicle

solvent assisted resin transfer molding

zinc iodide

vii

TECHNICAL MEMORANDUM

A DAMAGE RESISTANCE COMPARISON BETWEEN CANDIDATE POLYMER MATRIX

COMPOSITE FEEDLINE MATERIALS

1. INTRODUCTION

As part of NASA's focused technology programs for future reusable launch vehicles (RLV', D.a

feasibility study is underway of replacing metal feedlines with those made of polymer matrix coml_,,tt¢

(PMC) for transporting propulsion system liquid cryogen. The main advantage of using PMC's i_ in tl_.°

weight reduction potential that is so critical to the next generation of RLV's. The task consists of mT,nufacturing and testing several prototype composite feedlines made by various methods and then companng

them to see which method has the best cost and performance metrics needed. The methods used to manufacture the prototype feedlines are electron-beam (e-beam) curing, standard hand lay-up and autocla_ e

cure, solvent assisted resin transfer molding (SARTM), and thermoplastic tape laying.

One of the critical technology drivers for composite components is resistance to foreign object

impact damage. This is especially important in applications where leak paths must not develop in a

component (such as a feedline). The materials examined all have a 5-harness weave of intermediate

modulus 7 (IM7) as the fiber constituent (except for the polyetheretherketone (PEEK) thermoplastic.

which is unidirectional tape laid up in a bidirectional configuration). The resins tested were RS-E3

(e-beam curable), PEEK, Hexcel ®Incorporated 977-6, Cycom ® 823, PR 520, and Shade Industries SISE-I, (all epoxies). Since limited material was available for impact testing, relatively small specimens

were used; however, this was not a problem since the actual feedline would experience mostly contact

force damage rather than damage due to large deformation. The basis for this is from a study of impact

damage to composite feedlines where it was found that through the thickness leak paths developed as a

result of contact force damage. _ Impact damage resistance will be one of the critical parameters when

choosing a fiber/resin system since one of the main goals of future space vehicles is increased reliability.

If possible, it would be desirable to use these feedlines without liners which add complexity and

weight to the hardware. This makes permeation-after-impact testing critical to the success of the program.

This type of testing is new and has not been extensively studied unlike compression-after-impact. Studies

that have been performed in this area mostly pertain to using liners in composite fuel tanks. 2"3The helicopter industry has been concerned about water ingression in honeycomb structures and has studied water

permeation-after-impact. 4 Their results indicate that a liner is needed for thin facesheets. However, none

of these studies examined the harsh thermal environment of cryogenic composite structures, nor do they

address gas permeation through a laminate due to microcracking. Gas permeation through composites has

been studied in the rocket nozzle industry since an ablative's performance is related to its permeability, 5

but this does not concern impact damage to the composite.
It is theintentof thisstudyto gaininsightinto therelativeresistanceto microcrackingdueto an

impacteventof somecandidateresinsbeingexaminedfor useonfeedlines.
2. MATERIAL USED

There were a total of six material systems tested in this study. These, along with some of their

laminate properties are presented in table 1.

All of the panels were visually inspected before test coupons were cut from them. Areas of the

panels had their cross sections examined as part of another test series and no panels contained voids of

any significance and all were well consolidated. Since material was limited, small impact specimens

were chosen for testing. These specimens were 2.25-in. squares.

Table 1. Materials tested for impact resistance.

Material

SystemI

IM7/977-6

IM7/PR 520

IM7/Cycom 823

IM7/SI-SE-1

IM7/RS-E3

IM7/PEEK

Manufacturing

Method

Hand Lay-Up with

Autoclave Cure

SARTMwith

Autoclave Cure

SARTMwith

Autoclave Cure

SARTMwith

Autoclave Cure

Hand Lay-Up With

E-BeamCure

Hand Lay-Up with

Hot Press Cure

Type Resin

Toughened

Epoxy

Toughened

Epoxy

Toughened

Epoxy

Epoxy

Epoxy

Polyetheret

herketone

Laminate

Density

(g/cm3)

1.35

1.58

1.63

1.55

1.55

1.59

Laminate

Modulus

(Msi)

10.4

10.2

11.7

10.2

12.1

11.5

Laminate

Tensile

Strength2

(ksi)

142.0

124.8

135.3

115.0

150.0

160.0

Laminate

Compression

Strength3

(ksi)

83.9

73.1

63.1

54.2

80.1

68.6

1Alllaminates made from 5-harness woven fabric [0/9012s (Except IM7/PEEKwhich is made from unitape [0,90,0,90]s).

2As specified in ASTM D 3039.

3As specified in ASTM D 3410M

3
3. IMPACT TESTING

A drop-weight impact test apparatus was used for the testing. The square specimens were

supported over a 2 × 2-in. square opening and impacted at the center with a 0.25-in. instrumented tup

(striker). A few sacrificial specimens were impacted and an impact level was chosen that would produce

obvious damage in most of the materials tested. This turned out to be a weight of 2.5 lbf dropped from a

height of 12 in. for an impact energy of 2.5 ft-lb. This was considered the upper threshold of the impact

severity and subsequent impact testing would be conducted at a level that would cause less damage.

Load-time data was gathered by a GRC International Dynatup ®930-1 software system for later

reduction if desired. Each type of material system was impacted twice at each of the two energy levels

tested to ensure repeatability. In all cases, the impacts were nearly identical in every way so repeatability

was not a concem.

An impact energy level of 1.8 ft-lb was also used to observe the damage resistance of these

materials at a lower severity of impact. The two impact levels used will often be referred to as high (2.5

ft-lb) and low (1.8 ft-lb) throughout this paper.

The damage resistance was evaluated in three ways: visual examination, x radiography, and

cross-sectional examination.

3.1 Visual Examination

After each impact event, the specimen surface damage was recorded as a digital image. Both

sides of the specimen were observed and recorded.

3.2 X Radiography

Each impacted specimen was subjected to a dye penetrant soak for at least 24 hr. The dye

penetrant was a zinc iodide (ZnI) solution containing Kodak PhotoFlo TM to help the penetrant flow into

all cracks and delaminations that may have formed. The ZnI solution is opaque to x rays and shows up

when an x-ray image of the specimen is made, thus forming a map of the damage within the specimen.

This technique was only used on specimens impacted at the high-energy level since the test at the lowenergy level did not produce enough damage to be readily seen on an x ray.

3.3 Cross-Sectional Examination

After the specimens were x-rayed, they were sectioned through the center of the impact area with

a diamond-wafering blade. The halved specimens were then mounted in polymethylmethacralate for

subsequent edge polishing and microscopic examination. The specimens were sectioned parallel to the

warp fibers on the outer surfaces of the specimens, or parallel to the outer 0 ° fibers on the IM7/PEEK

specimens. The edges were wet polished with silicon-carbide paper of progressively finer grit sizes: 240,

4
400, 600, 800, 1000, and 1200. A fluorescent dye was placed on the polished edges of the specimen and

wiped off so that the dye remained in any cracks in the specimen. Upon exposure to an ultraviolet light

source, any damage present would then be highlighted and much easier to detect.

5
4. RESULTS

4.1 High-Impact Level

4.1.1 Visual Examination

Figure 1 shows the impacted side of each specimen tested at the high-energy level. In all cases,

except the 977-6 resin, a distinct dent is seen in each of the specimens. Fiber breakage is observed in all

of the specimens. The 977-6 resin possesses a relatively long crack across the outer warp fibers that

spans the distance of the impacted zone. The PR 520 has short cracks at or near the indentation formed,

as does the PEEK. The remaining three have fiber breakage within the indentation.

Figure 2 shows the back (nonimpacted) side of each type of specimen tested at the high-energy

level. All samples show back face fiber breakage of varying magnitudes. The 977-6 is the least severe

while the RS-E3 and Cycom 823 are the most severe where it appears near penetration occurred.

4.1.2 X Radiography

Figure 3 shows x rays of each type of resin system tested at the high-impact energy level. These

x rays correspond to the visual observations of figure 1 and figure 2. The 977-6 resin system has

noticeably less damage than the others. The Cycom 823 and RS-E3 systems appear as dark round circles

indicating massive damage directly under the impact zone. Delaminations emanating from the impact

can be seen in the Cycom 823, and RS-E3 and PEEK resin systems.

4.1.3 Cross-Sectional Examination

Figure 4 shows photomicrographs of the cross section of each type of resin system tested at the

high-impact energy level. The 977-6 and PEEK resins appear to have far less damage than the others

tested. The Cycom 823 and RS-E3 resins show near penetration.

Figure 5 shows fiuorescent-dye-enhanced photographs of these cross sections. This technique

better shows the extent of damage present in the specimens. The 977-6 specimen only has two short

delaminations near the outer plies and minor fiber breakage on the top ply. The plies in the center of the

specimen appear to be completely undamaged. The PEEK specimen shows good damage resistance;

however, damage exists throughout the thickness of the specimen. The severity of damage to the Cycom

823 and RS-E3 resin systems are even further highlighted by the fluorescent dye. The PR 520 resin

system had delamination and matrix cracking within all plies, although the photograph in figure 4 does

not clearly show this and is a good argument for using a fluorescent dye penetrant even on samples

where damage is readily visible.

6
IM7/PR 520 IM7/SI-SE-1

IM7/977-6 IM7/Cycom 823

IM7/RS-E3 IM7/PEEK

Figure 1. Typical damage to impacted side of specimens at 2.5 fl-lb.
IM7/PR 520 IM7/SI-SE-1

IM7/977-6 IM7/Cycom823

.........

IM7/RS-E3 IM7/PEEK

Figure 2. Typical damage to nonimpacted side of specimens at 2.5 ft-lb.

8
IM7/PR 520 IM7/SI-SE-1

IM7/977-6 IM7/Cycom823

{

IM7/RS-E3 IMT/PEEK

Figure 3. X-rays of specimens impacted at 2.5 ft-lb.

9
IM7/PR 520

IM7/SE-SE-1

IM7/977-6

IM7/Cycom823

Figure 4. Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb.

10
IM7/RS-E3

IM7/PEEK

Figure 4. Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb (continued).

11
IM7/PR520

IM7/SE-SE-1

IM7/977-6

Figure 5.

IM7/Cycom823

Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb, flourescent

dye enhanced.

12
IM7/RS-E3

Figure 5.

IM7/PEEK

Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb, flourescent

dye enhanced (continued).

13
4.2 Low-Impact Level

4.2.1 Visual Examination

Figure 6 shows the impacted side of each specimen tested at the low-energy level. Fiber breakage

is observed in most of the specimens in the form of short cracks emanating from the indentation on the

surface. The RS-E3 resin has a long, fine crack that runs from the lower left to the upper right of the

figure and very little indentation is observed. The mechanics behind these small cracks is unknown, but

they have been noted in a previous study. 6

Figure 7 shows the back (non-impacted) side of each type of specimen tested at the low-energy

level. All samples show back face fiber breakage of varying magnitudes. The 977-6 and RS-E3 resin

systems have barely noticeable back face damage. What little damage is present in these two systems is

limited to less than two fiber rows in length, but never as long as three. This type of damage could be

easily overlooked during a routine inspection of a part.

4.2.2 X Radiography

No x radiography was performed for these specimens since such little damage was formed and

an x ray signature of the damage would yield no information.

14
• %_.,:_

• :_:_:_

IM7/PR 520

_ i_i_

IM7/SI-SE-1

i_i _!_ i_!ii_:ili : ̧ ̧ i_i_'_i _ !?

ill!ii'_ii_i

IM7/977-6 IM7/Cycom 823

IM7/RS-E3 IM7/PEEK

Figure 6. Typical damage to impacted side of specimens at 1.8 ft-lb.

15
IM7/PR 520 IM7/SI-SE-1

IM7/977..-6 IM7/Cycom 823

IM7/RS--E3 IM7/PEEK

Figure 7. Typical damage to nonimpacted side of specimens at 1.8 ft-lb.

16
4.2.3 Cross-Sectional Examination

Figure 8 shows photomicrographs of the cross sections of each type of resin system tested at the

low-impact energy level. The fluorescent dye technique was employed on all of these specimens since

visible light did not readily detect all of the damage present. The 977-6 and the PEEK resins showed the

least damage as they did for the high-impact energy level. The 977-6 resin showed a short delamination

at the bottom plies and some matrix cracking within the bottom ply, but the majority of the cross section

was undamaged. The PEEK resin showed similar damage with some small delaminations and matrix

cracking in or near the bottom ply.

The RS-E3 resin system had extremely long delaminations emanating from the impact damage.

so two pictures are presented to include the entire range of damage.

17
IM7/PR 520

IM7/SE-SE-1

lM7/977-6

IM7/Cycom823

Figure 8. Cross-sectional photomicrographs of specimens impacted at 1.8 ft-lb.

18
Far View

CloseView

IM7/RS-E3

IM7/PEEK

Figure 8. Cross-sectional photomicrographs of specimens impacted at 1.8 ft-lb (continued).

19
5. CONCLUSIONS

From the results in this study, it appears that the 977--6 resin system is far superior to the others

tested for microcracking resistance to impact damage. The PEEK resin system also demonstrated good

impact resistance. The Cycom 823 and RS-E3 demonstrated poor impact resistance as many

delaminations and microcracks were found in these specimens at the low-impact energy level.

The use of a fluorescent dye to highlight damage gives a better indication of damage when

examining the cross section of an impacted specimen.

20
6. FUTURE WORK

The next step in this damage tolerance study is to perform permeability testing of impacted

samples. While cross-sectional examination gives a good idea of the relative resistance to impact damage

of a resin system, resistance to permeability after an impact event is really the driver behind choosing a

resin system for ducts and feedlines.

Correlation between permeability rate and microcracking as observed in cross sections will be

made to gain a qualitative assessment of visual damage to permeability rates.

21

REFERENCES

o

.

.

.

.

.

Nettles, A.T.: "Impact Damage Resistance of Carbon/Epoxy Tubes for the DC-XA Liquid Hydrogen

Feedline," NASA TP-3583, MSFC, September 1995.

Randazzo, S.: "Fuel Resistant Coatings for Metal and Composite Fuel Tanks," AGARD, Fuel Tank

Technology, p. 20, 1989.

Murry, C.F.; Newhouse, N.L.; Schimenti, J.D.; and Tiller, D.B.: "Development of Composite

Pressure Vessels With Nonmetallic Liners," Proceedings, The 28th AIAA, SAE, ASME, and ASEE

Joint Propulsion Conference and Exhibit, AIAA Paper 92-3853, Nashville, TN, pp. 192-210. Juh

6-8, 1992.

Weems, D.B.; and Fay, R.E.: "A Moisture Barrier for Composite Sandwich Structure," Proceedin_ _.

The First American Helicopter Society National Technical Specialists 'Meeting on Rotorcraft

Structures, Williamsburg, VA, October 30, 1995.

Stokes, E.H.: "'Permeability of Rayon Based Polymer Composites," Proceedings, American Society

of Mechanical Engineers, The First Symposium on Computational Mechanics of Porous Material,,

Tucson, AZ, pp. 45-51, April 28-May 8, 1992.

Lance, D.G.; and Nettles, A.T.: "Low Velocity Instrumented Impact Testing of Four New Damage

Tolerant Carbon/Epoxy Composite Systems," NASA TP-3029, MSFC, July 1990.

23
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September 2000 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

A Damage Resistance Comparison Between Candidate

Polymer Matrix Composite Feedline Materials

6. AUTHORS

A.T. Nettles

7. PERFORMING ORGANIZATION NAMES{S) AND ADDRESS(ES)

George C. Marshall Space Flight Center

Marshall Space Flight Center, AL 35812

9. SPONSORING/MONITORING AGENCYNAME(S)ANDADDRESS{ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

8. PERFORMING ORGANIZATION

REPORT NUMBER

M-992

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AGENCY REPORT NUMBER

NASA/TM--2000-210482

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13. ABSTRACT (Maximum 200 words)

As part of NASA's focused technology programs for future reusable lauch vehicles, a task is underway to

study the feasibility of using the polymer matrix composite feedlines instead of metal ones on propulsion

systems. This is desirable to reduce weight and manufacturing costs. The task consists of comparing

several prototype composite feedlines made by various methods. These methods are electron-beam curing,

standard hand lay-up and autoclave cure, solvent assisted resin transfer molding, and thermoplastic tape

laying. One of the critical technology drivers for composite components is resistance to foreign objects

damage. This paper presents results of an experimental study of the damage resistance of the candidate

materials that the prototype feedlines are manufactured from. The materials examined all have a 5-harness

weave of IM7 as the fiber constituent (except for the thermoplastic, which is unidirectional tape laid up in

a bidirectional configuration). The resin tested were 977-6, PR 520, SE-SA-I, RS-E3 (e-beam curable),

Cycom 823 and PEEK. The results showed that the 977-6 and PEEK were the most damage resistant in all

tested cases.

14.SUB.,ECTTERMS

composite materials, impacts, microcracking

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