NASA/TP--2001-211302

Polymer Matrix Composite

Lines and Ducts

(National Research Announcement 8-21 Final Report)

A. T. Nettles

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

October 2001
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NASA/TP--2001-211302

Polymer Matrix Composite

Lines and Ducts

(National Research Announcement 8-21 Final Report)

A. T. Nettles

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

National Aeronautics and

Space Administration

Marshall Space Flight Center • MSFC, Alabama 35812

October 2001
TRADEMARKS

Trade names and trademarks are used in this report for identification only. This usage does not constitute an official

endorsement, either express or implied, by the National Aeronautics and Space Administration.

Available from:

NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076 1320

(301) 621 0390

National Technical Information Selwice

5285 Port Royal Road

Springfield, VA 22161

(703) 487 4650

ii
TABLE OF CONTENTS

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

2. TEST ARTICLE .............................................................................................................................. 3

2.1 Conventional Hand Layup ........................................................................................................ 4

2.2 Solvent-Assisted Resin Transfer Molding ................................................................................ 6

2.3 Thermoplastic Tape Laying ...................................................................................................... 7

3. TESTING ....................................................................................................................................... 10

3.1 Nondestructive Evaluation Testing ........................................................................................... 10

3.2 Proof Testing ............................................................................................................................. 11

3.3 Leak Testing .............................................................................................................................. 12

3.4 Cryogenic Testing ..................................................................................................................... 12

3.5 Burst Pressure Testing .............................................................................................................. 14

3.6 Damage Tolerance .................................................................................................................... 14

4. RESULTS ....................................................................................................................................... 15

4.1 Nondestructive Evaluation Testing ........................................................................................... 15

4.2 Proof and Leak Testing ............................................................................................................. 25

4.3 Cryogenic Testing ..................................................................................................................... 30

4.4 Burst Pressure Testing .............................................................................................................. 33

4.5 Damage Tolerance Testing ........................................................................................................ 35

4.6 Permeability After Impact Testing ............................................................................................ 50

5. ANALYSIS ...................................................................................................................................... 64

6. DISCUSSION AND CONCLUSIONS ........................................................................................... 66

REFERENCES ...................................................................................................................................... 67

iii
°

2.

3.

4.

5.

°

7.

8.

°

10.

11.

12.

13.

14.

15.

16.

17.

18.

LIST OF FIGURES

Drawing with dimensions of the common test article ........................................................... 3

Reusable tool used for HLU .................................................................................................. 4

Completed test article manufactured by HLU ...................................................................... 5

View of flange area on a feedline manufactured via HLU .................................................... 5

Microstructure of feedline manufactured via HLU:

(a) Longitudinal view and (b) radial view ............................................................................. 6

Completed test article manufactured via SARTM ................................................................ 6

View of flange area of a feedline manufactured via SARTM ............................................... 7

Microstructure of feedline manufactured via SARTM:

(a) Longitudinal view and (b) radial view ............................................................................. 7

A test article being manufactured by TTL ............................................................................ 8

Completed test article manufactured via TTL ...................................................................... 8

View of flange area of a feedline manufactured via TTL ..................................................... 9

Microstructure of feedline manufactured via TTL:

(a) Longitudinal view and (b) radial view ............................................................................. 9

Flash thermography image showing foreign object

(plastic tape) inclusion .......................................................................................................... 10

Schematic showing placement of array of foil markers ........................................................ 11

Thermograph of position El2 on test article No. 3 ............................................................... 11

Leak as detected by bubble-type solution in a test article ..................................................... 12

Location of 17 biaxial strain gauges on the test articles ....................................................... 14

Anomaly noted on thermograph of feedline HLU-2 ............................................................ 15

iv
19.

20.

21.

22a.

22b.

22c.

22d.

22e.

22f.

22g.

23.

24.

25.

26.

27.

28.

29.

LIST OF FIGURES (Continued)

Large inclusion found on feedline HLU-3 .......................................................................... 16

Cross section of plastic tape causing anomaly in figure 13 ................................................. 16

Dark regions and anomaly found in tube HLU-4 ............................................................... 17

No surface features, but strong thermal indication. Possible

"thin film" inclusion ............................................................................................................ 17

No surface features. Unknown source ................................................................................. 18

No surface features but strong thermal indication. The blurred

edges may indicate that this is a delamination from impact ................................................ 18

A bump is visible on the surface indicating an inclusion

with possible internal void ................................................................................................... 19

The surface of the tube shows signs of overworking during

fabrication. These regions may be thin, resin-starved zones

(indicated by the arrows) ..................................................................................................... 19

The surface of the tube has a small bump, which would

indicate an inclusion ............................................................................................................ 20

Possible voids along a seam ................................................................................................ 20

Anomalies on feedline HLU-6 ............................................................................................ 21

Thermography image of scuff on feedline HLU-7 ............................................................. 21

Thermograph of possible deep inclusion on feedline HLU-7 ............................................. 22

Anomalies in feedline HLU-8 ............................................................................................. 22

Thermograph showing thinning in feedline SARTM-2 ...................................................... 23

Thermograph of thinning in feedline SARTM-3 ................................................................ 24

Sample thermograms from feedline TTL-1 showing regions where

the tape was not well consolidated in acreage and voids in flanges .................................... 24

V
30.

31.

32.

33.

34.

35.

36.

39.

40.

41.

42.

43.

44.

45.

46.

47.

48.

LIST OF FIGURES (Continued)

Two areas of pinhole leaks on feedline HLU-5 ................................................................. 26

Samples of leak areas on feedline HLU-6 ......................................................................... 26

Feedline SARTM-1 showing three leak paths ................................................................... 27

Feedline SARTM-3 showing one large leak path .............................................................. 28

Cross section of leak area on feedline SARTM-1 .............................................................. 28

Cross section of leak area on feedline SARTM-3 .............................................................. 29

Feedline TTL-2 showing ring of leakage around flange

buildup area ........................................................................................................................ 29

Flange area of feedline TTL-3 showing gross leakage ...................................................... 30

Test article HLU-2 in test stand 300. Shown with full

insulation and half of the insulation removed ..................................................................... 31

Leakage across feedline SARTM-2 after first introduction

of LN 2 into the feedline ...................................................................................................... 32

Inside surface of SARTM feedlines: (a) No cryogenic

temperature and (b) LN 2 temperature excursion ................................................................ 33

Outside surface of SARTM feedlines: (a) No cryogenic

temperature and (b) LN 2 temperature excursion ................................................................ 33

Feedline HLU-2 after failing at 545-psi internal pressure ................................................. 34

Feedline HLU-7 after failing at 364-psi internal pressure ................................................. 34

Typical damage to impacted side of specimens at 2.5 ft-lb ................................................ 38

Typical damage to nonimpacted side of specimens at 2.5 ft-lb .......................................... 39

X rays of specimens impacted at 2.5 ft-lb .......................................................................... 40

Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb .............................. 41

Cross-sectional photomicrographs of specimens impacted

at 2.5 ft-lb, fluorescent dye enhanced ................................................................................. 43

vi
49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

61.

62.

63.

64.

65.

LIST OF FIGURES (Continued)

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

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

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

Schematic of impact apparatus ...........................................................................................

Schematic of leak detection apparatus ................................................................................

Specimen displaying a leak using a bubble-type leak detection fluid ................................

Surface views of impacted HLU specimens .......................................................................

Leak check images of HLU specimens ..............................................................................

Flow rate (permeability) versus applied pressure for specimen 3A ...................................

Flow rate (permeability) versus applied pressure for specimen 3B ...................................

Flow rate (permeability) versus applied pressure for specimen 4A ...................................

Flow rate (permeability) versus applied pressure for specimen 4B ...................................

Flow rate (permeability) versus applied pressure for specimen 5A ...................................

Flow rate (permeability) versus applied pressure for specimen 5B ...................................

Flow rate (permeability) versus applied pressure for specimen 6B ...................................

Surface views of electron beam-impacted specimens ........................................................

Examples of large areas of leakage on electron beam-cured laminates .............................

45

47

48

51

52

52

53

55

57

57

58

58

59

59

6O

61

62

vii
LIST OF TABLES

°

2.

3.

4.

Cryogenic testing series .......................................................................................................... 12

Materials tested for impact resistance .................................................................................... 36

Predicted and actual hoop strain data for feedline HLU #2 ................................................... 64

Predicted and actual hoop strain data for feedline HLU #7 ................................................... 65

viii
LIST OFACRONYMS

GHe

GN2

GRC

He

HLU

LH2

LN2

MSFC

NDE

ORNL

PEC

PEEK

PMC

SARTM

TP

TTL

UV

ZnI2

gaseoushelium

gaseousnitrogen

GlennResearchCenter

helium

handlayup

liquidhydrogen

liquid nitrogen

MarshallSpaceFlightCenter

nondestructiveevaluation

OakRidgeNationalLaboratories

ProductivityEnhancement Center

polyetheretherketone

polymermatrixcomposite

solventassistedresintransfermolding

TechnicalPublication

thermoplastictapelaying

ultraviolet

zinciodide

ix
TECHNICAL PUBLICATION

POLYMER MATRIX COMPOSITE LINES AND DUCTS

(National Research Announcement 8-21 Final Report)

1. INTRODUCTION

The Access-to-Space study identified the requirement for lightweight structures to achieve orbit

with a single-stage vehicle. 1 The use of composite components is critical to fulfilling that requirement. The

purpose of this task is to extend previous efforts with polymer matrix composite (PMC) feedlines and

ducts.

This Technical Publication (TP) outlines the results of a task that was awarded under National

Research Announcement 8-21. This task is an element under the Reusable Launch Vehicle Focused Technology Project Plan. The task is titled "Polymer Matrix Composite (PMC) Lines and Ducts" and its main

objective was to demonstrate the feasibility of manufacturing a large diameter composite feedline with a

90 ° elbow section and integral flanges. Other objectives of the task were to demonstrate PMC performance

under cryogenic environments, to demonstrate knowledge of the damage tolerance issues associated with

composite feedlines, and to evaluate feedlines manufactured by four different techniques. To accomplish

these objectives, an 8-in.-diameter composite feedline for liquid hydrogen (LH2) service was selected to be

designed because it is typical of those found in a launch vehicle main propulsion system.

While most feedline concepts currently use a metallic material, a small composite feedline was

successfully used on the Delta Clipper-Experimental Advanced flight vehicle. Larger feedlines of more

complexity need to be developed to realize even larger savings in weight. Typically, a composite feedline

can save over 50 percent mass to be manufactured via four different technologies: (1) Conventional hand

layup (HLU) and autoclave cure, (2) solvent-assisted resin transfer molding (SARTM), (3) electron beam

cure, and (4) thermoplastic tape laying (TTL).

NASA Marshall Space Flight Center (MSFC) was responsible for material selection and manufacture of the feedlines made via the HLU method. NASA Glenn Research Center (GRC) was responsible for

material selection and manufacture of feedlines made by the SARTM process. Oak Ridge National

Laboratories (ORNL) was responsible for material selection and manufacture of feedlines to be made by

the electron beam cure process. Automated Dynamics Incorporated manufactured feedlines by TTL.

The inspection, analysis, and testing of the feedlines was performed in-house at MSFC. As each

feedline was received, it was hydrostatically tested at 50 psi and inspected visually for leakage. If no gross

leakage was detected, nondestructive evaluation (NDE) of the feedlines was performed by the NDE team at

MSFC and consisted of flash thermography. Upon completion of NDE, the feedlines were given to the
mechanicaldesigngroupatMSFCforinstrumentation, cycliccryogenic,andpressurizationtesting.After

thisseriesof tests,afewfeedlineswerehydrostaticallyburstwhiletheothersweredestructivelytestedfor

microcracking.ThestrengthanalysisgroupatMSFCperformedananalysisofthefeedlinesandtheresults

werecomparedto themeasuredvaluesobtainedin thefull-scaletests.

A damagetolerancesubtaskwasalsoundertakenin this study.It consistedof testinglaminates

madefromthefourmanufacturingprocessesfor damageresistanceandpermeabilityafterimpacttesting.

Full-scaletestarticleswerealsoimpactedto seeatwhatthresholdleakagewouldoccur.

2
2. TEST ARTICLE

Within this task, a common test article was chosen to evaluate the different material systems and

manufacturing methods. A drawing of the test article is shown in figure 1.

._11.75 in.-_

8 in.

12in.

2

// _R16i, 0.06in.

0.245in.

RO.5_

Detail of Tube-to-Flange Buildup

Figure 1. Drawing with dimensions of the common test article.

The flanges on the ends are integral to the tube; i.e., the test article is one piece. An elbow section

was chosen to demonstrate a more complex geometry than a simple straight tube. The thickness dimensions of the tube's walls are approximate since the final dimensions would be heavily dependent on the

manufacturing process used.

At the beginning of the task, four different manufacturing methods were chosen for comparison.

These methods are (1) conventional HLU and autoclave cure, (2) SARTM, (3) electron beam cure, and

(4) TTL. Of these four techniques, test articles were made from three, although all types underwent some

coupon-level material testing. The electron beam cure technique never produced a full-scale test article.

The details of the material and layup of the other three follow.
2.1 Conventional Hand Layup

The most common method of producing composite parts for space hardware is HLU of prepreg

material with an autoclave cure. This was done at MSFC's Productivity Enhancement Center (PEC). The

material selected for this manufacturing method was IM7 carbon fiber with a toughened epoxy resin. Two

types of resin were used in this study. One was from Bryte Technologies, designated EX1522; the other

was from Hexcel ®, Incorporated, designated 977-6. The fiber architecture was a five-haxness satin weave.

The resin was impregnated into this and B-staged to produce the prepreg material used. The layup

sequence for the test article was [0/90,+45,+45,0/90] with buildups into the flanges. The prepreg was cut to

size and hand-laid on a male tube to form the part (fig. 2). Once the part was laidup, it was bagged and

autoclave cured at 350 °F.

Figure 2. Reusable tool used for HLU.

Eight tubes were made using this technique. Other tubes were made with different prepreg material, but they will not be included in this report. A photograph of a completed test article manufactured via

HLU is shown in figure 3. The total weight of the feedline was 6.7 lb. The outside surface is not smooth

since it was simply bagged and not against a tool. A closer view of the flange buildup area is given in

figure 4. Some creasing in the region between the tube and flange sections can be seen. This was typical of

all of the feedlines manufactured in this way. It is suspected that this is just a cosmetic anomaly and will not

adversely affect the performance of the feedline.

4
Figure3. CompletedtestarticlemanufacturedbyHLU.

':::iiii_ iiiiiiiiii"iii: '_" ii

Figure 4. View of flange area on a feedline manufactured via HLU.
Themicrostructureofthefeedlineintheacreageof thefeedlineisshownin figure5.Excellentply

consolidationis evident.Therelativelysmallresin-richareasobservedfor afive-haxnessweaveprepreg

alsonotesgoodcompaction.

(a) (b)

Figure 5. Microstructure of feedline manufactured via HLU:

(a) Longitudinal view and (b) radial view.

2.2 Solvent-Assisted Resin Transfer Molding

Another method used to make test articles was performed at NASA's GRC and consisted of SARTM.

This technique involved drawing the resin up through a fiber preform of the pax and then autoclave curing.

The fiber preform is braided with IM7 carbon fiber into the geometry of the final part. This preform is

placed over a male tool and a female mold placed over the preform. Resin is drawn through the preform by

placing a vacuum on one end of the elbow and resin with solvent added at the other end. Once the resin has

impregnated the entire perform, the pax is autoclave cured. The solvent is added to the resin to lower its

viscosity to aid in the wetting out of the preform.

The resin used to make the test article in this study was PR 520, a toughened epoxy manufactured

by Hexcel. However, test panels made with SI-SE-1 and Cycom ® 823 epoxies were tested during the

material characterization and damage tolerance phases of this program. A completed feedline manufactured via SARTM is shown in figure 6. A closer view of the flange area is given in figure 7. Both the inside

and outside surfaces of the tube axe smooth since they axe both tool sides.

Figure 6. Completed test article manufactured via SARTM.

6
Figure7. Viewof flangeareaof afeedlinemanufacturedvia SARTM.

Themicrostructureof thefeedlinein theacreageareais shownin figure8.As with thefeedline

manufacturedvia HLU,thisfeedlinealsodemonstratedexcellentconsolidationandcompactionwith no

voids.Thesolvent-assistedresindid anexcellentjob of wettingoutall of thefibersin thepreform.

(a) (b)

Figure 8. Microstructure of feedline manufactured via SARTM:

(a) Longitudinal view and (b) radial view.

2.3 Thermoplastic Tape Laying

Another method used to manufacture test articles was TTL. This method consists of laying tape

-_0.25 in. wide over a male mold and melting it into place as it is put down using a robotic head. The layup

sequence of the plies that were built up was [0,90,+45,-45] s with the 0 ° direction defined along the axis of

the tube. A photograph of a test article being manufactured using this method is shown in figure 9. For this

process, IM7 carbon fiber was used with a polyetheretherketone (PEEK) resin.

7
Figure9. A testarticlebeingmanufacturedbyTTL.

Figure10showsacompletedfeedlinemanufacturedbyTTL. A closerviewof theflangeareais

giveninfigure11.Thisareais particularlyroughwith obviousareasof nonconsolidationvisiblefromthe

surface.Thiswasof greatconcernsinceit couldfacilitatelea_ksandcompromisethestructuralintegrityof

thefeedline.A viewofthemicrostructureintheacreageofthefeedlineis givenin figure12.Poorconsolidationwith largeareasof delaminationcanbeseen.Thethermoplastictapeapparentlywasdifficult to

compactbytherobotichead.

Figure10.CompletedtestarticlemanufacturedviaTTL.

8
::::::::::::::::::::::::::::::::+: :-::: /:: ::::::,,::::::::::::::::::::::::::::::::::::::::::::::::::::-

, :::::::iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii::: :iiiiiiiiiiiiiiiii:::::iiii:iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii::::::: '

Figure 11. View of flange area of a feedline manufactured via TTL.

(a) (b)

Figure 12. Microstructure of feedline manufactured via TTL:

(a) Longitudinal view and (b) radial view.

9
3. TESTING

Section 3 outlines the tests performed during this study. Results axe presented in section 4.

3.1 Nondestructive Evaluation Testing

The feedlines were inspected using flash thermography, an NDE technique. Flash thermography

consists of hitting the test article with a pulse of heat and then monitoring the release of the heat with an

infrared camera. Areas that have anomalies will give off heat at a different rate than the rest of the tube, thus

identifying the location and general shape of possible defects. A sample picture of a thermography image

is shown in figure 13. In this figure, it can be seen that an anomaly appears (which turned out to be plastic

tape).

Figure 13. Flash thermography image showing foreign object

(plastic tape) inclusion.

The dark spots around the perimeter of the defect in figure 13 axe foil markers used to help identify

locations on the thermograms. Each test article was marked off with an array of foil markers as shown in

figure 14. This produced a grid pattern so each thermogram could be identified. For example, the dark gray

shaded area in figure 14 would be designated "position B2" and the light gray shaded area "position El2."

Due to the bend in the article, there is a smaller distance between the flanges along the inside radius of the

tube; thus, there axe only 11 areas along the inside radius versus 13 areas along the outside radius. A sample

thermogram with no anomalies is shown in figure 15.

10
01

)

O O

o _ F0il Markers

o o '"_..._ ,, o "c'_

o o o 10o

o

o o 12o

,.-, ,-, 12,-,

13 12in. 8in.

LL

13

16 in.

12 in.

"c'-10 c

N

,-,12^

v

T 401

12in. Do E o Fq

___ 2o 2 o 2c

-- O_ O

O O

O

in.

Figure 14. Schematic showing placement of array of foil markers.

F0ilMarkers

Figure 15. Thermograph of position E12 on test article No. 3.

3.2 Proof Testing

A hydrostatic proof test was performed on each test article to verify its integrity. The test articles

were proof pressure tested to 150 psi. The pressure was maintained for 60 sec and then reduced to zero psi.

This was repeated for a total of five cycles. The test article was visually observed for any leaks during the

test.

11
3.3 Leak Testing

Once proof testing was completed, the next series of tests performed were leak checks at 50 psi

using gaseous helium (GHe). The test article was enclosed in a bag (excluding the flange bolts and seal

joint) to capture any GHe leaking through the parent material. A probe connected to a helium (He) mass

spectrometer was inserted into the bag to sense for any He leakage. The test article sat for 10 min before a

leakage reading was recorded. If leaks were found, the test article was set aside and not used for cryogenic

testing. The tubes with leaks were taken to the damage tolerance facility in MSFC's PEC and examined

further to determine the possible cause of the leaks. Figure 16 shows a bubble-leak detect solution being

applied to one of the test articles manufactured by HLU. In this particular feedline, a line of small leaks was

apparent.

Figure 16. Leak as detected by bubble-type solution in a test article.

3.4 Cryogenic Testing

The cryogenic testing series was performed on a select number of feedlines that had passed the

proof and leak tests. These feedlines were tested at MSFC's test stand 300 and an outline of the testing

performed is given in tablel.

Table 1. Cryogenic testing series.

Test No.

1

2

3

4

5

Test

Leakage

10 Thermal/Pressure Cycles with LN 2

Leakage

15 Thermal/Pressure Cycles with LH 2

Leakage

12
A brief explanation of each of these tests follows:

Leakage: A pretest and posttest leak check was done on each test article. A pretest leak check

was performed after the test article was installed in the test stand. The test article was pressurized

to 50 psig with GHe and checked for lea_ks using leak check solution. A posttest leak check was

also performed on the test article after the 10 liquid nitrogen (LN2) cycle tests and the 15 LH 2

cycle tests. This posttest leak check was done prior to removal of the test article from the test

stand and was done in the same manner as the pretest leak check. If the test article passed the

posttest leak check, a more-refined leak check was performed using a GHe mass spectrometer to

quantify any leakage. This refined leak check was performed as described in section 3.3.

Thermal/Pressure Cycle Test with LN2: Each test article was subjected to 10 pressure and thermal cycles. The pressure was cycled from 0 tol00 psi. The temperature was cycled from LN 2

temperature to 140 °F. LN 2 was flowed through the test article at -_10 psi to chill it. Heated

gaseous nitrogen (GN2) was flowed through the test article to heat it. A typical thermal/pressure

cycle was performed as follows: Starting at ambient temperature and pressure, the test article

was chilled with LN 2 until the skin temperature reached a steady-state temperature. A dwell time

of 5 min at the steady-state temperature condition was maintained. While cold, the pressure

inside the test article was increased to 100 psi and dwelled for 1 min at the steady-state pressure

condition. The pressure was then vented and the test article was warmed to 140 °F temperature

using heated GN2, and dwelled for 5 min at the steady-state temperature condition. The test

article was chilled again and the testing was repeated for the total number of cycles required.

• Leakage: Like above.

• Thermal/Pressure Cycle Test With LH2: Performed 15 pressure and thermal cycles on the test

article using LH 2. This test was run in the same manner as the LN 2 test above.

• Leakage: Like above.

• The following instrumentation was used for each test article:

- 17 biaxial strain gauges.

- 5 skin temperature sensors.

- Fluid temperature sensors located on the facility immediately upstream and downstream of

the test article.

- One internal pressure measurement located on the facility.

- Video coverage of test article.

The location of the 17 strain gauges is shown in figure 17.

13
T_I 13 112

1 in,

/ 15

75in

¥11

1_.25in. _,,

8"_4

6

1 I

3.75m. -_

LeftSideView

12 _ U 14

1 in.

^ A

.,]'10

A _' 10.25in.

I1_17 7_

_- . ' .

3.75in.

t 6

RightSideView

Figure 17. Location of 17 biaxial strain gauges on the test articles.

3.5 Burst Pressure Testing

A hydrostatic burst pressure test was performed to determine strain versus pressure until failure.

Each test article was filled with water and pressure was slowly increased until failure. The test was done at

ambient temperature. Strain at each of the 17 gauges shown in figure 17 was recorded as well as internal

pressure. Video of the failure was also recorded. The test articles were mounted such that each flange was

rigidly fixed and immovable.

3.6 Damage Tolerance

All of the candidate materials were screened for damage resistance/damage tolerance. Flat panels

of the candidate materials were impacted with a drop-weight apparatus and assessed for damage and

resulting permeability. To assess damage, the specimens were visually examined and the damage digitally

documented. The specimens were then sectioned and polished for a through-the-thickness assessment of

the damage imparted by the impact event. This damage was enhanced with an ultraviolet (UV) dye solution

and then photographed under a UV light source to highlight the damage. Some specimens were tested for

permeability after impact.

14
4. RESULTS

Section 4 presents results of the NDE, leak, cryogenic, burst pressure, and damage tolerance testing

performed during the course of this study.

4.1 Nondestructive Evaluation Testing

The results of the flash thermography testing axe quite voluminous with a digital image of each grid

on each test article taken for 72 images per tube. Only indications of significance will be presented in this

section.

4.1.1 Test Articles Manufactured via Hand Layup

Eight HLU feedlines that were autoclave cured were inspected using flash thermography. Feedline

HLU-1 showed no anomalies. For feedline HLU-2, only one major indication was found. The abnormality

appears hot (white) which would indicate a void or inclusion of some material that blocks the flow of heat

into the tube. The thermogram for this anomaly is given in figure 18.

FoilTape

Figure 18. Anomaly noted on thermograph of feedline HLU-2.

15
A largeinclusionwasfoundontheinnerradiusof feedlineHLU-3. Thethermographsaxeshownin

figure19.Sincethisanomalywassolarge,thefeedlinewasscrappedfor subsequent testing.Thisprovided

anopportunitytodissecthefeedlinetodeterminethecauseof theanomaly.Uponsectioning,it wasfound

thattheanomalywasapieceof plastictapeundertheinnermostplyof prepreg.Thiscanbeclearlyseenin

figure20.

Figure19. LargeinclusionfoundonfeedlineHLU-3.

PlasticTape

........

Figure 20. Cross section of plastic tape causing anomaly in figure 13.

16
In feedlineHLU-4, darkbandsfoundthroughouttheacreageofthetube(bothcircumferentialand

axial),mostlikely indicateply overlapsandresinpockets.In figure21,thesedarkbandsareillustrated

alongwithaninclusion.Adelaminationwasfoundbelowaply spliceinthetubeacreage.Visualinspection

of theregionfoundasurfacecrackalongtheupperedgeof theindicationattheply splice.

Figure21. DarkregionsandanomalyfoundintubeHLU-4.

FeedlineHLU-5 showednumerousindicationsasoutlinedin figures22a-22g.

Figure22a.No surfacefeatures,butstrongthermalindication.

Possible"thin film" inclusion.

17
Figure22b.No surfacefeatures.Unknownsource.

Figure22c. No surfacefeaturesbutstrongthermalindication.

Theblurrededgesmayindicatethatthisis a

delaminationfromimpact.

18
Figure22d. A bumpisvisibleonthesurfaceindicatingan

inclusionwithpossibleinternalvoid.

Figure22e.Thesurfaceof therobeshowssignsof overworking

duringfabrication.Theseregionsmaybethin,resinstarvedzones(indicatedbythearrows).

19
Figure 22f. The surface of the tube has a small bump, which would

indicate an inclusion.

Figure 22g. Possible voids along a seam.

2O
For feedline HLU-6, indications 1, 2, and 3 in figure 23 appear on the surface as small bumps and

may be inclusions or ply wrinkles with embedded voids.

Figure 23. Anomalies on feedline HLU-6.

Feedline HLU-7 appears to have been scuffed and the indication shown in figure 24 is visible as a

scratch with exposed fibers. In addition, on feedline HLU-7, a faint surface ripple is visible, indicating a

deeply embedded inclusion. The thermograph is shown in figure 25.

CutFibers

Figure 24. Thermography image of scuff on feedline HLU-7.

21
Inclusion

Figure 25. Thermograph of possible deep inclusion on feedline HLU-7.

On feedline HLU-8, three small thermal abnormalities were detected as shown in figure 26. The

size of each indication was <0.25 by 0.5 in. At region A3, the indication correlates with a surface crack. At

position F3, the indication appears to be within the laminate. At position B 12, the indication is visible on

the surface as a scratch.

!iiiiiiiiiii!iiiiiii!iiiii!i!i iiiiiiiiiii!iiiiiiii!!iiiiii!i ii i iiii iiiiiiiiiiiii!iiiiiiiiiiiiii!i!ii!i !i!!iii!!iiii ! 

i i::::: :.::i:::: : : ::::i ::i:: ::

A3 B12

Figure 26. Anomalies in feedline HLU-8.

22
F3

Figure26. Anomaliesin feedlineHLU-8 (continued).

4.1.2 Test Articles Manufactured via Solvent-Assisted Resin Transfer Molding

Four feedlines, manufactured using SARTM, were inspected using flash thermography. Feedline

SARTM-1 showed no anomalies. Feedline SARTM-2 showed a ring of thinning that was detected on the

inside of the tube -_12 in. in from the flange. This is shown in figure 27.

Figure 27. Thermograph showing thinning in feedline SARTM-2.

Feedline SARTM-3 showed the same type of thinning at the same location as feedline SARTM-2.

A thermograph is presented in figure 28.

23
Figure28. Thermographofthinningin feedlineSARTM-3.

FeedlineSARTM-4showednomajoranomalies.

4.1.3 Test Articles Manufactured via Thermoplastic Tape Laying

Four feedlines manufactured via TTL were inspected using flash thermography. For feedline TTL-1,

the acreage of the tube appears to have many highly porous/low consolidation regions as indicated by the

many bright patches in the images. The bright regions in the flange thermograms coincide with missing

plies on its back surface. The fillet also shows many low consolidation/highly porous regions. Sample

thermograms showing these voids axe given in figure 29.

Acreage FlangeBuildup

Figure 29. Sample thermograms from feedline TTL-1 showing

regions where the tape was not well consolidated in

acreage and voids in flanges.

24
Acreage

Figure 29.

Flange

Sample thermograms from feedline TTL-1 showing

regions where the tape was not well consolidated in

acreage and voids in flanges (continued).

Feedlines TTL-2, TTL-3, and TTL-4 all demonstrate the same type of indications as feedline

TTL-1.

4.1.4 Test Articles Manufactured via Electron Beam Cure

No test articles manufactured by electron beam curing were produced for this study; therefore, no

testing was performed.

4.2 Proof and Leak Testing

All of the feedlines underwent a hydrostatic proof test and leak test before advancing to cryogenic

testing. Those tubes that leaked were taken to the damage tolerance laboratory for more detailed examination and documentation. This section presents the results of these tests.

4.2.1 Test Articles Manufactured via Hand Layup

Of the eight test articles manufactures by HLU, two leaked prior to cryogenic testing. Feedline

HLU-5 had two areas of linear pinhole leaks and feedline HLU-6 leaked at several sites. Figure 30 shows

the two areas of linear pinhole leaks in feedline HLU-5. The tube was pressurized with 20 psi of GHe and

a leak detect solution was squirted on the outside. The resulting trail of very small bubbles indicates very

small leaks.

25
..... ._ ", ,,,. ,. _ .. : _ . ii".... ,...,.,_ ..... :_"_,.,_,_,_.,_,:._,_:ii_:,._.:_i

Figure 30. Two areas of pinhole lea_ks on feedline HLU-5.

Figure 31 shows some of the lea_ks on feedline HLU-6. Note that these leaks form larger bubbles

than those on feedline HLU-5 (as shown in fig. 30). This indicates larger "holes," as does the fact that the

pictures in figure 31 were taken with the tube at only 3.5 psi. The area of lea_ks on feedline HLU-6 was

marked off into a grid pattern with each grid numbered so the lea_ks could be better identified.

Figure 31. Samples of leak areas on feedline HLU-6.

26
Figure31. Samplesof leakareasonfeedlineHLU-6 (continued).

4.2.2 Test Articles Manufactured via Solvent-Assisted Resin Transfer Molding

Of the four feedlines manufactured by SARTM, two leaked prior to cryogenic testing. Feedline

SARTM-1 demonstrated three areas of leakage and feedline SARTM-3 showed one area of leakage.

Figure 32 shows the three lea_ks in feedline SARTM-1. One of the lea_ks is large compared to the other two.

The feedline was pressurized at 5 psi when the photograph was taken.

Figure 32. Feedline SARTM-1 showing three leak paths.

27
Figure33showstheoneleakfoundinfeedlineSARTM-3.Duetothelargesizeofthebubbles,the

leakissignificant.Thefeedlinewaspressurizedat2.5psiwhenthisphotographwastaken.

Figure33. FeedlineSARTM-3showingonelargeleakpath.

Sincethesefeedlineswouldnotundergoanyfurthertesting,theyweresectionedat theareasof

leakageandphotomicrographstaken.Figure34showsthecrosssectionof feedlineSARTM-1inwhichan

airbubbleappearsto beresponsiblefor theleakageseen.Figure35showsthecrosssectionof feedline

SARTM-3.A smallregionof thepreformis resinstarvedandprovidedthelargeleakpathseen.

Figure34. Crosssectionof leakareaonfeedlineSARTM-1.

28
Figure35. Crosssectionof leakareaonfeedlineSARTM-3.

4.2.3 Test Articles Manufactured via Thermoplastic Tape Laying

Four feedlines manufactured via TTL were leak tested. All four feedlines showed leakage around

the flange buildup area. Figure 36 shows the leakage on feedline TTL-2. The feedline was pressurized at

5 psi for these leak tests. Some of the lea_ks axe very small while others are larger as evidenced by the larger

bubbles forming.

Figure 36. Feedline TTL-2 showing ring of leakage around

flange buildup area.

29
Thesefeedlinesalsoshowedleakageat theflangetransitionareas.Someof theseleakswereso

exceptionallylargethatmaintainingpressurein thefeedlinewasdifficult. Figure37showstheflangeon

feedlineTTL-3. Thetubewasonlyat2 psiandit canbeseenthattheleakdetectsolutionisbeingsplatteredintotheair sincetheleakis of suchagrossnature.

Figure37. Flangeareaof feedlineTTL-3 showinggrossleakage.

4.3 Cryogenic Testing

Only the feedlines that did not leak were accepted for cryogenic testing as outlined in section 3.4.

None of the TTL feedlines met these criteria. Only HLU and SARTM feedlines (those that did not leak)

could be tested. Each feedline was installed in the test facility with one flange end firmly fixed and the

other flange end free. These end conditions allowed for movements in the test setup due to the temperature

changes from the test fluid. Each feedline was insulated using a foam clamshell-type arrangement. This

allowed for ease of installation, removal, and reuse of the insulation. Figure 38 shows a photograph of

feedline HLU-2 insulated and installed in test stand 300 for cryogenic testing and a photograph of the

feedline with half of its insulation removed and some of the instrumentation visible. The mating flanges to

the composite feedline were made of stainless steel. Differences in the coefficient of thermal expansion

between the two different flange materials were considered during selection of the proper seal for the

flanges. The composite flange was designed with a flat face and the mating stainless steel flange was

machined with a seal groove in its face. An Omniseal ®, part No. 348-374-0101, manufactured by SaintGobain Performance Plastics, was selected to seal the flanges. The following presents the results of the

cryogenic tests with LN 2 and LH 2.

3O
Figure38. TestarticleHLU-2 inteststand300.Shownwithfull

insulationandhalfof theinsulationremoved.

4.3.1 Test Articles Manufactured via Hand Layup

The first feedline to undergo cryogenic testing was feedline HLU-2. It passed all the thermal and

pressurization cycle testing. No lea_ks ever developed in this feedline. The pressure, temperature, and strain

data are recorded and stored in a digital format for comparison to analysis. After the cryogenic testing of

HLU-2 with LH 2, a posttest leak check was made. Using a GHe mass spectrometer, the leakage measured

from the feedline was <2.0 × 10 8 sccs GHe. This value was essentially the background He in the room

where the measurement took place. The conclusion was the feedline was not leaking and passed its cryogenic tests.

The second feedline to undergo cryogenic testing was feedline HLU-7. It passed all the thermal

and pressurization cycle testing. No lea_ks ever developed in this feedline. The pressure, temperature, and

strain data axe recorded and stored in a digital format for comparison to analysis. After the cryogenic

testing of HLU-7 with LH 2, a posttest leak check was made. Using a GHe mass spectrometer, the leakage

measured from the feedline was <1.4 × 108 sccs GHe. This value was essentially the background He in the

room where the measurement took place. The conclusion was the feedline was not lea_king and passed its

cryogenic tests.

31
4.3.2 Test Articles Manufactured via Solvent-Assisted Resin Transfer Molding

SARTM-2 was the first feedline of this type to be tested. During the first cryogenic cool-down

cycle with LN2, strain gauge readings were being lost. Upon closer inspection, it was noted that LN 2 was

pouring out from the insulation around the feedline. The insulation was removed and it appeared that the

LN 2 was seeping out of the tube across its entire acreage. The cryogenic testing was stopped and a GHe

leak check was performed. The feedline was filled with 10 psi of GHe and a leak detect solution was

sprayed over the feedline. Leakage was observed over the entire area of the feedline. Figure 39 shows the

extent of the leakage on this tube. Feedline SARTM-4 was then filled with LN 2 and yielded the same

results as feedline SARTM-2. Cryogenic testing on these feedlines was terminated at this point.

Figure 39. Leakage across feedline SARTM-2 after first introduction

of LN 2 into the feedline.

Feedline SARTM-2 was then dissected for inspection as to the mechanisms behind this gross leakage. Figure 40 shows a view of the inside surface of the tube after a UV dye was placed on the surface. For

comparison, a SARTM tube that did not undergo cryogenic testing is also shown. Many matrix cracks can

be seen on the specimen that saw one temperature drop to LN 2 temperature.

32
(a) (b)

Figure 40. Inside surface of SARTM feedlines: (a) No cryogenic

temperature and (b) LN 2 temperature excursion.

Figure 41 is a view of the outside of a SARTM feedline that saw a temperature drop to LN 2. A

section of a SARTM feedline that did not experience cryogenic temperatures is also shown for comparison.

(a) (b)

Figure 41. Outside surface of SARTM feedlines: (a) No cryogenic

temperature and (b) LN 2 temperature excursion.

4.4 Burst Pressure Testing

Feedline HLU-2 was hydrostatically tested for burst strength. The feedline was installed such that

both flanged ends were rigidly fixed to prevent any movement. A maximum pressure of 545 psi was reached

and then the feedline catastrophically failed. A photograph of the failed feedline is shown in figure 42. A

longitudinal split is seen on most of the feedline with a radial split occurring about three quarters of the way

up the tube.

33
_iiii_iiiiiiiiiTTTTTTTiTiT_T!T_T_T_T_i_iiiiiiiiiiiii_iii_i_!_i_iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii__iiiiiiiiiiiiiiiii

Figure42. FeedlineHLU-2 afterfailingat545-psinternalpressure.

FeedlineHLU-7 wasthenhydrostaticallytestedfor burststrength.It wasalsoinstalledsuchthat

bothflangedendswererigidly fixedtopreventanymovement.A maximumpressureof 364psiwasreached

andthenthefeedlinecatastrophicallyfailed.Photographsof thefailedfeedlineaxeshownin figure43.

A largesplitaboutonefourthof thetubelengthis seenalongoneside.

(a) (b)

Figure43. FeedlineHLU-7 afterfailingat364-psintemalpressure.

34
4.5 Damage Tolerance Testing

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

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

component such as a feedline. The materials examined all have a five-haxness weave of IM7 as the fiber

constituent (except for the thermoplastic, which is unidirectional tape laidup in a bidirectional configuration). The resins tested were RS-E3 (electron-beam curable), PEEK (thermoplastic), 977-6, Cycom 823,

PR 520, and SE-SA-1 (all epoxies). Since a limited amount of material was available for impact testing,

relatively small specimens were used. This was not a problem since the actual feedline would experience

mostly contact force damage rather than damage due to large deformation. This is based on a previous

study on impact damage to composite feedlines which found that through the thickness leak paths

developed as a result of contact force damage. 2 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.

It would be desirable to use these feedlines without liners that 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 as extensively studied as compression after impact. Studies that have been

performed in this area mostly pertain to using liners in composite fuel tanks. 3,4 The helicopter industry has

been concerned about water ingression in honeycomb structures and has studied water permeation after

impact. 5 The results indicate that a liner is needed for thin face sheets. 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, 6 but this does not

concern impact damage to the composite.

It is the intent of this study to gain insight into the relative resistance to microcracking due to an

impact event of some candidate resins being examined for use on feedlines.

35
4.5.1 Material Used

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

properties, axe presented in table 2.

Material

System1

IM7/977-6

IM7/PR 520

IM7/Cycom823

IM7/SI-SE-1

IM7/RS-E3

IM7/PEEK

Table 2. Materials tested for impact resistance.

ManufacturingMethod

HLUwith autoclavecure

SARTM2with autoclavecure

SARTMwith autoclavecure

SARTMwith autoclavecure

HLUwith electron beamcure

HLUwith hot press cure

Type Resin

ToughenedEpoxy

ToughenedEpoxy

ToughenedEpoxy

Epoxy

Epoxy

Polyetheretherketone

Laminate Laminate

Density Modulus

(g/cm3) (Msi)

1.35 10.2

1.58 10.2

1.63 10.2

1.55 10.2

1.55 10.2

1.59 11.5

Laminate Laminate

Tensile Compression

Strength3 Strength4

(ksi) (ksi)

130.0 83.9

124.8 73.1

120.0 63.1

115.0 54.2

120.0 80.1

160.0 68.6

1 All laminatesmadefrom five-harnesswovenfabric [0/9012s (exceptIM7/PEEKwhich is madefrom unitape[0,90,0,90]s).

2 SARTM

3 ASTMD 3039

4 ASTMD 3410M

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 squares 2.25 in. on a side.

4.5.2 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

were gathered by a GRC 930-I 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 concern.

36
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 TR

The damage resistance was evaluated in three ways: (1) Visual examination, (2) radiography, and

(3) cross-sectional examination.

4.5.3 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.

4.5.4 Radiography

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

was a zinc iodide (ZnI2) solution containing Kodak PhotoFlo TM to help the penetraxlt flow into all cracks

and delaminations that may have been formed. The ZnI 2 solution is opaque to x rays and shows 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 (2.5 ft-lb) since the next energy level

used (1.8 ft-lb) did not produce enough damage to be readily seen on an x ray.

4.5.5 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-caxbide paper of progressively finer grit sizes: 240, 400, 600,

800, 1,000, and 1,200. 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 a UV light source, any damage

present would then be highlighted and much easier to detect.

4.5.6 Visual Examination After Impact (High-Level Impacts)

Figure 44 shows the impacted side of each specimen tested at the high (2.5 ft-lb) 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

span 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 45 shows the back (nonimpacted) side of each type of specimen tested at the high (2.5 ft-lb)

energy level. All samples show backface fiber breakage of varying magnitudes. The 977-2 is the least

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

37
IM7/PR520 IM7/SI-SE-1

IM7/977-6 IM7/Cycom823

IM7/RS-E3 IM7/PEEK

Figure 44. Typical damage to impacted side of specimens at 2.5 ft-lb.

38
IM7/PR520 IM7/SI-SE-1

IM7/977-6 IM7/Cycom823

IM7/RS-E3 IM7/PEEK

Figure 45. Typical damage to nonimpacted side of specimens at 2.5 ft-lb.

39
4.5.7 Radiography After Impact (High-Level Impacts)

Figure 46 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 figures 44 and 45. The 977-6-resin system has noticeably

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

massive damage directly under the impact zone. Delaminations emanating from the impact can be seen in

the Cycom 823, RS-E3, and PEEK resin systems.

IM7/PR520 IM7/SI-SE-1

IM7/977-6 IM7/Cycom823

Figure 46. X rays of specimens impacted at 2.5 ft-lb.

4O
IM7/977-6 IM7/PEEK

Figure 46. X rays of specimens impacted at 2.5 ft-lb (continued).

4.5.8 Cross-Sectional Examination (High-Level Impacts)

Figures 47 show 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 fax less damage than the others

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

IM7/PR 520

IM7/SE-SE-1

Figure 47. Cross-sectional photomicrographs of specimens impacted at 2.5 ft-lb.

41
IM7/S977-6

IM7/Oycom823

IM7/RS-E3

Figure 47. Cross-sectional photomicrographs of specimens impacted

at 2.5 ft-lb (continued).

42
Figure 47.

IM7/PEEK

Cross-sectional photomicrographs of specimens impacted

at 2.5 ft-lb (continued).

Figures 48 show fluorescent 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 damage free. The PEEK specimen shows good damage resistance;

however, damage does exist throughout the thickness of the specimen. The severity of damage to the

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

system is seen to have delamination and matrix cracking within all plies although the photograph in figure

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

where damage is readily visible.

IM7/PR520

Figure 48. Cross-sectional photomicrographs of specimens impacted

at 2.5 ft-lb, fluorescent dye enhanced.

43
IM7/SI-SE-1

IM7/977-6

IM7/Oycom823

IM7/RS-E3

Figure 48. Cross-sectional photomicrographs of specimens impacted

at 2.5 ft-lb, fluorescent dye enhanced (continued).

44
IM7/PEEK

Figure 48. Cross-sectional photomicrographs of specimens impacted

at 2.5 ft-lb, fluorescent dye enhanced (continued).

4.5.9 Visual Examination After Impact (Low-Level Impacts)

Figure 49 shows the impacted side of each specimen tested at the low (1.8 ft-lb) 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]

IM7/PR520 IM7/SI-SE-1

Figure 49. Typical damage to impacted side of specimens at 1.8 ft-lb.

45
IM7/977-6 IM7/Cycom823

IM7/RS-3 IM7/PEEK

Figure 49. Typical damage to impacted side of specimens at 1.8 ft-lb (continued).

Figure 50 shows the back (nonimpacted) side of each type of specimen tested at the low (1.8 ft-lb)

energy level. All samples show backface fiber breakage of varying magnitudes. The 977-6 and RS-E3

resin systems have barely noticeable backface damage. What little damage is present in these two systems

is limited to less than two stitches, but never three or more. This type of damage could easily be overlooked

during a routine inspection of a part.

46
IM7/PR 520 IM7/SI-SE-1

IM7/977-6 IM7/Cycom823

IM7/RS-E3 IM7/PEEK

Figure 50. Typical damage to nonimpacted side of specimens at 1.8 ft-lb.

47
4.5.10 Radiography After Impact (Low-Level Impacts)

No radiographs were taken of these specimens since such little damage was formed and an x-ray

signature of the damage would yield no information.

4.5.11 Cross-Sectional Examination After Impact (Low-Level Impacts)

Figure 51 shows photomicrographs of the cross section 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 amount of 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 is undamaged. The PEEK resin showed similar damage with some small delaminations and

matrix cracking in or near the bottom ply.

IM7/PR520

_: ":*::i_::_ii_i}_'_'i_ _:iiiiiiii_i_i_::i_iiiii::::iiiii::iiii!ii::i::iiii:i::iii i::::::i_i)!::i_::ii_::i ii::i::iiiilj:ii ii:.iiiii:,::ii_ i i i::i iiiii::ii::ii:;iiii: iiiiiiii::::i::iiiiiiii!::::iii::::ii_::i::i::iii!i!!_i

IM7/SE-SE-1

IM7/977-6

Figure 51. Cross-sectional photomicrographs of specimens impacted

at 1.8 ft-lb.

48
IM7/Cycom823

FarView

CloseView

IM7/RS-E3

IM7/RS-E3

Figure 51. Cross-sectional photomicrographs of specimens impacted

at 1.8 ft-lb (continued).

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

two pictures axe presented to include the entire range of damage.

49
4.5.12 Conclusions of the Damage Tolerance Study

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.

4.6 Permeability After Impact Testing

As composite laminates are being considered for use in liquid propulsion systems, microcracking

due to foreign object impact damage becomes very important, especially if a tank or feedline is to be

unlined. If a component that carries liquid or gaseous hydrogen develops an area of microcracking, hydrogen can leak out of the component and pose a serious threat to the vehicle. Since it has been shown in the

past that no visible impact damage can cause a composite feedline to lea_k,2 a better understanding of the

material's resistance to microcracking is needed. Microcracking also occurs due to thermal and mechanical

stresses and fatigue; however, this study will deal only with foreign object impact damage, a very real

threat to all composite parts. The most quantifiable way of determining how much leakage may occur after

an impact event is to test the material for permeability. Permeability testing has been used in the past for

composites to determine the porosity of rocket nozzle material. 6 Fluid permeability has been tested on

some composite structures to be used as fuel tanks. 3,8 ASTM standard D 1434 exists for gas permeability

testing of plastic film and sheeting and it is from this test methodology that the one in this study was

adapted.

For this study, flat panel specimens were manufactured from material that was used in this feedline

program. These specimens were representative of two of the caxbon/polymer systems being evaluated for

use in constructing feedlines for future launch vehicles. These were panels manufactured via HLU and

electron beam curing. There was not enough material left to perform permeability tests on impacted specimens manufactured via SARTM or TTL. A drop-weight impact tester with a 0.25-in. diameter tup was

used to impart varying levels of damage from almost nondetectable to near penetration. The specimens

were then secured in a fixture that could supply a positive pressure of GHe on one side and allow a leak

detection solution to be applied to the other side. This gave a qualitative assessment of permeability after

impact. The specimens were then secured in an apparatus that could give quantitative results.

4.6.1 Experimental Procedure

This section will explain how the impact and subsequent permeability testing was performed.

Results will be given in section 4.6.2.

4.6.1.1 Specimens. The HLU specimens were manufactured from caxbon/epoxy prepreg that was

in a five-haxness satin weave form. A 36×24-in. panel was laidup in a bidirectional configuration on a flat

aluminum tool. This gave the laminate a layup sequence of [0/90,0/90] s. The panel was then vacuum

50
baggedandautoclavecuredaccordingto themanufacturer'srecommendedcurecycle.Theelectronbeam

laminatesweremanufacturedin the samemanner,only insteadof anautoclavecure,electronbeam

radiationwasusedto curethelaminates.Thecuredlaminateswerethencutinto 3×3-in.specimens.The

nominalthicknessof thespecimenswas10mil.

4.6.1.2Impact Testing. The 3-in.-squaxe specimens were impacted at various levels using a dropweight apparatus. The impactor consisted of a 0.25 in. semispherically ended tup that was attached to a

dynamic load cell to gather instrumented impact data, should it be needed for future analysis. (None of the

instrumented data were used in the study presented in this paper). The falling mass had a total weight of

2.51 lb and drop heights of 4, 6, 8, 10, and 12 in. were used. The specimen was simply supported over a

2-in.-square opening. A schematic of the impact set up is given in figure 52. Two specimens were impacted

from each drop height to give 10 impacted specimens in order to check for repeatability of results. After

each specimen was impacted, images of both the front and back surface damage were recorded with a

digital camera at a magnification of approximately × 5.

__ Guideposts D,.__

FallingWeight _ [ ] _ vel°city Flag

_lnstrumented Tup _ VelocityDetector

SpecimenSupport

[--

Figure 52. Schematic of impact apparatus.

51
4.6.1.3LeakCheck.Afterall specimenshadbeenimpactedandthesurfacedamagerecorded,the

specimensweremountedinanapparatustocheckforleakageofGHewhenapositivepressurewasapplied

to oneside.A "bubble-type" leak detector solution was used and a digital image was made of the leaks for

each specimen. A schematic of the apparatus used to check for leaks is shown in figure 53. A sample image

of a leak is given in figure 54.

k DetectionSolution

6

®

NeopreneGaskets

Figure 53.

GHeinatPressure

Schematic of leak detection apparatus.

Figure 54. Specimen displaying a leak using a bubble-type leak

detection fluid.

52
4.6.1.4Permeability Testing. After the specimens had thoroughly dried from the leak detection

procedure, they were ready for permeability testing. A more detailed analysis of the permeability testing

and apparatus can be found elsewhere. 9

4.6.2 Results

This section presents results of the impact testing, the leak check testing, and the permeability

testing.

4.6.2.1 Impact Testing of Hand Layup Specimens. Ten specimens manufactured via HLU were

impacted, two at each of the five energy levels. The resulting visual surface damage is presented in

figure 55. Duplicates axe not presented since the visual damage was nearly identical in every case. Damage

in some form can be noted on all specimens, even those impacted at the smallest impact energy of 0.84 fl-lb.

Front,Specimen2,2.51ft-lb Back,Specimen2, 2.51ft-lb

iiiiiiiiiiii!_i_i_iiiiii_;;i=iiiiii iiiii! ̧ ̧

Front,Specimen3,2.09ft-lb Back,Specimen3, 2.09ft-lb

Figure 55. Surface views of impacted HLU specimens.

53
Front,Specimen4, 1.67 ft-lb Back,Specimen4, 1.67 ft-lb

iiiii  ̧ ! iiiiiiiiiiiiiiiiiliiiii ii iiiii!i_

Front,Specimen5, 1.26ft-lb Back,Specimen5, 1.26 ft-lb

Front,Specimen6, 0.84 ft-lb Back,Specimen6, 0.84 ft-lb

Figure 55. Surface views of impacted HLU specimens (continued).

54
4.6.2.2 Leak Check Testing of Hand Layup Specimens. Figure 56 shows photographs of the

specimens when subjected to a pressure of 10 psi on one side and a bubble-type leak detection solution

placed on the other. Results from all specimens are included since these results did not show the duplication that was seen in the visual results. The impact energy level is included below each image.

Specimen2A,2.51ft-lb Specimen2B,2.51ft-lb

Specimen3A,2.09ft-lb Specimen3B,2.09ft-lb

Specimen4A,1.67ft-lb Specimen4B,1.67ft-lb

Figure 56. Leak check images of HLU specimens.

55
Specimen5A,1.26ft-lb Specimen5B,1.26ft-lb

Specimen6A,0.84ft-lb Specimen6B,0.84ft-lb

Figure 56. Leak check images of HLU specimens (continued).

All samples, with the exception of 6A, showed leakage. The larger the bubbles axe in the pictures,

the higher the leak rate. Specimen 2B was difficult to photograph due to the extremely large bubbles that

were forming. Specimen 2A can be seen to rapidly expel the leak detect solution and form relatively large

bubbles. As the impact damage becomes less severe, the bubbles become smaller. In fact, in specimens 5A

and 6B, the leak rate is such that the leak detection fluid forms a fine "foam" that emanates from the

impacted area.

4.6.2.3 Permeability Testing of Hand Layup Specimens. Figures 57-63 show plots of flow rate

versus pressure for the samples tested. Specimen 6A showed no permeability (as would be expected from

fig. 56) and specimens 2A and 2B had such high flow rates that measurements could not be taken.

A polynomial curve fit to the data is given in each figure.

56
0.025

0.02

A

0.015

0.01

0.005

Specimen3A

ImpactEnergy= 2.09 ft-lb

Rate= 4.92×10-5 p2 _ 8.12×10-4 P + 3.11×10-3

, , , | ,,K , , , , _

5 10 15 20 25 30

Pressure(psi)

Figure 57. Flow rate (permeability) versus applied pressure for specimen 3A.

0.035

0.03

0.025

_-_ 0.02

,m

® 0.015

0.01

0.005

Specimen3B

ImpactEnergy= 2.09 ft-lb

Rate= 3.18×10-5 p2 + 4.3210 -4 P + 3.77×10-4

j2y

, ,,_, I , ,, , I, , , ,I , ,, , I, ,, , I , , ,,

5 10 15 20 25 30

Pressure(psi)

Figure 58. Flow rate (permeability) versus applied pressure for specimen 3B.

57
0.007

0.006

0.005

_._.0.004

.__

•_ 0.003

t',,,'-

0.002

0.001

Specimen4A

Impact Energy= 1.67 ft-lb

Rate=

, , , ,ID--r'_, , , I , , , , I , , , , I , , , , I , , , , I , , , ,

5 10 15 20 25 30 35

Pressure(psi)

Figure 59. Flow rate (permeability) versus applied pressure for specimen 4A.

0.0035

0.003

A 0.0025

0.002

.E

0.0015

0.001

0.0005

Specimen4B

ImpactEnergy= 1.67ft-lb

Rate= 1.84×10-6 p2 + 8.29×10-5 P - 1.68×10-4

, , , , I , , , , I , , , , I , , , , I , , , ,

5 10 15 20 25

Pressure (psi)

Figure 60. Flow rate (permeability) versus applied pressure for specimen 4B.

58
0.001

0.0008

A

0.0006

,m

0.0004

0.0002

Specimen5A

ImpactEnergy= 1.26ft-lb

Rate= 9.05xl 0-7 p2 _ 6.92xl 0-7 p2+ 2.82xl 0-5

,,,, I,,,, I,,,, I,,,, I,,,, I,,,, I,,,,

5 10 15 20 25 30 35

Pressure(psi)

Figure 61. Flow rate (permeability) versus applied pressure for specimen 5A.

e_

9×10-5

Specimen5B

ImpactEnergy= 1.26 ft-lb

8×10-5

7×10-5

6×10-5

5×10-5

4×10-5

3×10-5

2×10-5

1 ×10 -5

20

/

_p2 + 1.91×10-6 P- 2.42×10-5

30 40 50 60 70

Pressure(psi)

Figure 62. Flow rate (permeability) versus applied pressure for specimen 5B.

59
0.004

0.0035

0.003

'_ 0.0025

•_ 0.002

,'," 0.0015

0.001

0.0005

Specimen6B

ImpactEnergy = 0.84ft-lb

_Rate = 5.96×10-2 p2+ 5.09×10-4 P - 1.52×10-4

, _I_,, I , , , , I , , , , I , , , , I , , , , I , , , ,

10 20 30 40 50 60

Pressure(psi)

Figure 63. Flow rate (permeability) versus applied pressure for specimen 6B.

In general, the larger the impact energy, the higher the flow rate for a given applied pressure, which

is expected. A noticeable exception is specimen 5B, which showed a very low flow rate, even though it was

hit harder than specimen 6B. The amount of nonlinearity in flow rate versus applied pressure also varied

between samples; however, most of the nonlinearity is observed at the lower pressures, and as the applied

pressure increased, the lineaxity of the flow rate versus pressure increased.

4.6.2.4 Impact Testing of Electron Beam Specimens. Ten specimens were impacted, two at each

of the five energy levels. The resulting surface damage is presented in figure 64. Duplicates axe not

presented. Specimen 1 (impact energy of 0.84 ft-lb) is not shown since no visible damage was present. In

addition, the front of specimen 2 is not shown for the same reason. Damage is relatively light compared to

comparable specimens made from the HLU technique and presented in figure 55. Less plastic deformation

is seen in the electron beam-cured specimens. However, from the cross-sectional results given in figure 51,

it can be seen that despite little surface damage, significant internal damage can be present in the impacted

electron beam-cured specimens.

60
Back,Specimen2, 1.26ft-lb

Front,Specimen3, 1.67ft-lb

_sss:_

N_iN_

Back,Specimen3, 1.67 ft-lb

Front,Specimen4, 2.09 tt-lb Back,Specimen4, 2.09 ft-lb

Figure 64. Surface views of electron beam-impacted specimens.

61
4.6.2.5 Leak Check Testing of Electron Beam Specimens. As the impacted electron beam specimens were being checked for visual leakage after impact, it was noted that most of the specimens were

demonstrating gross leakage across the specimen, away from the impact site. A panel that had not been

impacted was tested and it too showed gross areas of leakage. Since there was so much permeability of the

specimen before impact, permeation after impact testing was not performed for these specimens.

Figure 65 shows examples of this gross permeability on the electron beam-cured laminates.

Specimen 1 showing gross leakage on one side of the specimen.

Specimen 6 showing leakage across certain areas ot the laminate.

Figure 65. Examples of large areas of leakage on electron

beam-cured laminates.

62
Close-upviewof abovespecimenshowingleakageatstitch.

Figure 65. Examples of large areas of leakage on electron

beam-cured laminates (continued).

4.6.3 Conclusions

For permeability after impact testing, the residual flow rate usually has a nonlinear dependence on

the applied pressure, increasing more rapidly as a higher pressure is applied. Thus, the permeability cannot

be stated as a constant per unit of applied pressure.

The HLU four-ply laminates tested in this study showed leakage after impact, even when visible

damage could only be detected with magnifying techniques. The qualitative measurement of leakage with

the bubble-type leak detector solution corresponded with the qualitative permeability measurements.

The electron beam-cured laminates demonstrated gross areas of leakage/permeability across the

laminate that seemed to be clustered in areas. About one-half of the electron beam specimens demonstrated

this type of gross leakage.

63
5. ANALYSIS

A limited series of analysis was performed to compare to the actual data gathered while testing the

feedlines. The model was built using PATRAN 8.5, then translated to ANSYS 5.5 for analysis. Detailed

information can be obtained in the MSFC structural mechanics team report, "Stress Analysis of Marshall

Space Flight Center LH 2 Composite Test Article Number 1, Drawing Number 96M00001" dated June 19,

2001, and labeled as report number ED22-01-100. For briefness, only the highlights will be presented in

this TR

Table 3 shows the predicted and actual value of the 17 strain gauges (in the hoop direction) shown

in figure 17 for feedline HLU #2. The tube was assumed fixed-fixed, and the internal pressure was 150 psi.

Table 3. Predicted and actual hoop strain data for feedline HLU #2.

Predicted Actual

GaugeNo. (microstrain) (microstrain) % Difference

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

592

520

520

1444

1324

1313

1426

1064

1124

1287

597

576

457

1025

993

1028

424

463

472

Badgauge

2104

Badgauge

Badgauge

1413

404

407

2271

491

423

Badgauge

968

885

2417

-28.4

-10.9

-9.21

58.9

-0.087

-62.1

-63.8

76.5

-17.8

-26.5

-5.5

-10.9

135.3

64
Table 4 shows the predicted and actual value of the 17 strain gauges (in the hoop direction) shown

in figure 17 for feedline HLU #7. The tube was assumed fixed-fixed, and the intemal pressure was 150 psi.

Table 4. Predicted and actual hoop strain data for feedline HLU #7.

Predicted Actual

GaugeNo. (microstrain) (microstrain) % Difference

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

520

1444

1324

1313

1426

1064

1124

1287

597

576

457

993

Badgauge

Badgauge

732

3123

1336

Badgauge

2200

1651

2330

2112

1881

701

803

527

Badgauge

1443

Badgauge

40.7

116.3

0.92

67.6

15.8

119.0

87.9

46.2

17.4

39.0

15.2

45.3

From these data, it can be seen that prediction of the elastic response of the feedline is not easy. In

fact, the data from the two tests differ significantly, although all test conditions were held constant. This is

most probably due to the method in which the tubes were made. To get a five-harness weave to lie down

across an elbow shape with the fibers running in a particular direction is a daunting task to say the least. In

addition, there axe ply drops and seams that are not accounted for in the model. In fact, many of the

measured values on a given gauge on the two feedlines tested actually bracket the predicted value, thus no

determination of the validity of the model can be made with such large variations in the actual test data.

65
6. DISCUSSION AND CONCLUSIONS

The difficulty in developing an all-composite cryogenic feedline without a liner present becomes

obvious in this study. The majority of the full-scale test articles that were manufactured either leaked

before any testing began or leaked after just one cycle of LN 2. The only test articles that survived the entire

cryogenic cycling and pressurization were two that were manufactured by the HLU and autoclave cure

procedure. The feedlines that were made by SARTM sustained microcracking across their entire acreage

after one cycle of LN 2. These microcracks caused gross permeation and the testing was stopped. The

feedlines manufactured by TTL seemed to suffer from a lack of consolidation. Leak paths around the

flange buildup area developed on all four test articles manufactured. The radius of the flanges themselves

showed severe leak paths to the point where maintaining a pressure in the feedline was difficult.

Unfortunately, full-scale test articles manufactured by electron beam curing never came to fruition

during this study; however, the material was evaluated for damage tolerance testing. The results showed

that this material is not as tough as the epoxy system used for the HLU processing.

66
REFERENCES

1. Access-to-Space Summary, Office of Space Systems Development, NASA Headquarters, 1994.

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

Feedline," NASA TP-3583, Marshall Space Flight Center, AL, September 1995.

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

Technology, p. 20, November 1989.

. Murry, C.F.; Newhouse, N.L.; Schimenti, J.D.; et al.: "Development of Composite Pressure Vessels

With Nonmetallic Liners," AIAA, SAE, ASME, and ASEE, 28th Joint Propulsion Conference and

Exhibit, Nashville, TN, July 1992.

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

American Helicopter Society National Technical Specialists' Meeting on Rotorcraft Structures,

Williamsburg, VA, October 1995.

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

Mechanical Engineers, Symposium on Computational Mechanics of Porous Materials, Tucson, AZ,

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, Marshall Space Flight Center, AL,

July 1990.

8. Brydges, W.T.; Gulati, S.T.; and Baum, G.: "Permeability of Glass Ribbon-Reinforced Composites,"

Journal of Materials Science, Vol. 10, pp. 2044-2049, December 1975.

9. Nettles, A.T.: "Permeability Testing of Impacted Composite Laminates for Use on Reusable Launch

Vehicles," NASA/TM 2001-210799, Marshall Space Flight Center, AL, February 2001.

67
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

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1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE

October 2001

4. TITLE AND SUBTITLE

Polymer Matrix Composite Lines and Ducts

(National Research Announcement 8-21 Final Report)

6. AUTHORS

A.T. Nettles

3. REPORT TYPE AND DATES COVERED

Technical Publication

5. FUNDING NUMBERS

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

George C. Marshall Space Flight Center

Marshall Space Flight Center, AL 35812

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

NRA 8-21 TA 7.5

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REPORT NUMBER

M-1029

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AGENCY REPORT NUMBER

NASA/TP--2001-211302

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Prepared by the Materials Manufacturing and Processes Department, Engineering Directorate

12a. DISTRIB UTION/AVAILABILITY STATEM ENT

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12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Since composite laminates are beginning to be identified for use in reusable launch vehicle propulsion systems, a task

was undertaken to assess the feasibility of making cryogenic feedlines with integral flanges from polymer matrix

composite materials. An additional level of complexity was added by having the feedlines be elbow shaped. Four

materials, each with a unique manufacturing method, were chosen for this program. Feedlines were to be made by

hand layup (HLU) with standard autoclave cure, HLU with electron beam cure, solvent-assisted resin transfer

molding (SARTM), and thermoplastic tape laying (TTL). A test matrix of fill and drain cycles with both liquid

nitrogen and liquid helium, along with a heat up to 250 °F, was planned for each of the feedlines. A pressurization to

failure was performed on any feedlines that passed the cryogenic cycling testing. A damage tolerance subtask was

also undertaken in this study. The effects of foreign object impact to the materials used was assessed by crosssectional examination and by permeability after impact testing. At the end of the program, the manufacture of the

electron beam-cured feedlines never came to fruition. All of the TTL feedlines leaked heavily before any cryogenic

testing, all of the SARTM feedlines leaked heavily after one cryogenic cycle. Thus, only the HLU with autoclave

cure feedlines underwent the complete test matrix. They passed the cyclic testing and were pressurized to failure.

14. SUBJECT TERMS

composite materials, feedlines, impact, permeability

15. NUMBER OF PAGES

8O

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