NASA CR 137597

PREPARATION OF FOAM COMPOSITES

by Milan G. Maximovich

8 November 1974

'(NASA-CR-137597) PREPARATION FOR FOAM N75-17510COMPOSITES (Whittaker Corp.)

Uncl as10883

Reproduced by

NATIONAL TECHNICALINFORMATION SERVICE

US Department of CommerceSpringfield, VA. 22151

Prepared under Contract No. NAS2-8189 by

WHITTAKER CORPORATION

Research and Development Division3540 Aero Court

San Diego, California 92123

for

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Ames Research Center

Moffett Field, California

~CE.S 4~6 10

https://ntrs.nasa.gov/search.jsp?R=19750009438 2020-02-24T00:11:10+00:00Z

NOTICE

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SUMMARY

Methods were developed for the fabrication of fire resistant panelsutilizing polybenzimidazole (PBI) and Kerimid 601 resins along with glass,quartz, and Kevlar reinforcements. Stitched truss structure, bothunfilled and filled with PBI foam, were successfully fabricated andtested. Second generation structures were then selected, fabricated, andtested, with a PBI/glass skin/PBI foam sandwich structure emerging as theoptimum panel concept. Mechanical properties, smoke generation, and fireresistance were determined for the candidate panels.

iii

TABLE OF CONTENTS

Page

SUMMARY ................................ iii

LIST OF FIGURES . .... . . . ................. vi

LIST OF TABLES . .......... . ....... .. . . ..... . iii

1.0 INTRODUCTION . . ...... . . .... .......... . .. . 1

2.0 TECHNICAL DISCUSSION . .................. . 2

2.1 Initial Concepts ................... . .. 2

2.2 Material Selection . ................. . 4

2.2.1 Resins . . . . . ... . . . . . . . . . . . . .. 4

2.2.2 Reinforcements ................. 5

2.3 Fabrication of First Generation Structure . ...... .6

2.3.1 Initial Flat Laminates . ........... . 6

2.3.2 Truss Structure . . . .............. . 6

2.4 Testing of First Generation Structure . ........ 12

2.4.1 Fire Resistance Testing . ............ 122.4.1.1 Panel Preparation . ........ . . 12

2.4.1.2 Thermal Testing . . ............ 18

2.4.2 Physical and Mechanical Properties . ...... 332.5 Second Generation Structure Fabrication . ....... 33

2.6 Second Generation Structure Testing . ......... 38

2.6.1 Fire Resistance Testing . ........ . ..... 382.6.2 Mechanical Property Testing. . ......... 38

3.0 CONCLUSIONS AND RECOMMENDATIONS. . ............ . 44

APPENDIX A PROCEDURE FOR STITCHING TRUSS STRUCTURE . ...... 47

APPENDIX B TESTING OF FOAM COMPOSITE STRUCTURES . ....... 50

APPENDIX C WRD PRELIMINARY PROCESS SPECIFICATION . . . . . . . . 52

Precedinz page blank

LIST OF FIGURES

Figure Page

2-1 Panel Construction - Integrally Woven Fiberglass . ..... 2

2-2 Schematic for Fabrication of Stitched 3D Structure ..... 3

2-3 PBI Foam Filled Truss Structure . ...... .. . . . . . .. 4

2-4 Correlation of Primary Thermomechanical Char Yield withMolecular Structure . . . . . . . . . . . . . . . . . . . . . 4

2-5 Summary of Properties of Char Forming Foamed Polymers . . .. 4

2-6 Typical PBI Synthesis . .................. . 5

2-7 Kerimid 601 Chemistry . .................. . 5

2-8 Industrial Sewing Machine . . . ............. . . 8

2-9 Maranite Mandrels . . . . . . . . . . . . . . . . . . . . . . 9

2-10 PBI Fuam Blocks . . . . . . . . . ............ . 9

2-11 Unfilled Kevlar 49/Kerimid 601 Truss . ........... 10

2-12 181 E Glass/PBI Truss with Maranite Mandrel andPBI Foam Block . . .. .. . . . . . . . . . . . . . . . . 10

2-13 Cured 181 E Glass/Kerimid 601 Foam Filled Panel . . . 11

2-14 Ames T3 Thermal Test Facility, JP-4 Fuel . ......... 14

2-15 Back Side Thermocouple Placement, All Structures . ..... 15

2-16 Thermocouple Placement, Foam Filled Panels . ........ 16

2-17 Thermocouple Placement, Unfilled Panels . ...... . . . . 17

2-18 Thermocouple Placement, Skinned Sandwich . ......... 19

2-19 Kerimid/Kevlar, Filled vs. Unfilled . .......... . . 21

2-20 Kerimid/Glass, Filled vs. Unfilled . ............ 22

2-21 PBI/Glass, Fllled vs. Unfilled . ..... . ......... 23

ORIGINAL PAGE ISO' POOR QUALITYvi

Figure Page

2-22 Performance of Unfilled Structures . ............ 24

2-23 Performance of Filled Structures .............. .25

2-24 Panel 1, Unfilled PBI/Glass, Back Side Thermocouplesvs. Time ........... . . . . . . ........ . 26

2-25 Panel 4, Kerimid/Kevlar, Unfilled, Back Side Thermocouplesvs. Time . . . . . . . . . . . . . . . . . . . . . . . . .. . 27

2-26 Panel 8, Kerimid/Kevlar, PBI Foam, Back Side Thermocouplesvs. Time . . . . . . . . . . . . . . . . . . . . . . . . .. . 28

2-27 Panel 6, PBI/Glass, PBI Foam, Back Side Thermocouplesvs. Time . . . . . . . . . . . . . . . . . . . . . . . . .. . 29

2-28 Panel 9, Kerimid/Glass, Unfilled, Back Side Thermocouplesvs. Time . ..... ............ ........ . 30

2-29 Panel 12, Kerimid/Glass, PBI Foam, Back Side Thermocouplesvs. Time . ................. . ..... .. . . 31

2-30 Panel. 13, PBI Skin, No Truss, PBI Foam, Back SideThermocouples vs. Time ....... ........ .. . 32

2-31 Longitudinal Flexure, Unfilled . .............. 34

2-32 Transverse Flexure, Unfilled . ..... . ......... . 34

2-33 Longitudinal Flexure, Filled . ............... 35

2-34 Transverse Flexure, Filled .. . . ............... 35

2-35 NASA Data, All-PBI 48 kg/m 3 , 2.54 cm thick (3 lb/ft3 ,1 in. thick) Foam ................... . . 40

2-36 NASA Data, All-PBI 96 kg/m3, 0.64 cm thick (6 lb/ft3 ,1/4 in. thick) Foam Sandwich ...... -. ......... . . 41

2-37 NASA Data, K-601/Glass Skin 48 kg/m3 , 2.54 cm thick(3 lb/ft3 , 1 in, thick) PBI Core Sandwich . . . . . . . ... 42

vii

LIST OF TABLES

Table Page

2-1 Six Structures for Initial Fire Protection Evaluation . . . . 7

2-2 Physical Properties . ...... . . . . . . . . . . . . . . . 13

2-3 T3 Burn Tests ........................ ..... 20

2-4 Second Generation Panels .... ....... . . . . . . . .. 36

2-5 Smoke Density Results ............ ......... 39

2-6 Mechanical Properties..........' ......... .... 43

viii

1,0 INTRODUCTION

An area of great concern in present-day aircraft is the flammabilityand offgassing characteristics of the structural materials. Even when anaircraft fuselage survives a crash intact, lives may be lost in the sub-sequent fuel fire, as flames penetrate the cabin and/or gaseous by-productsof combustion overcome the passengers within. A prime objective of NASA-Ames Research Center is to develop aircraft structure that maintainsstructural integrity and a viable cabin atmosphere for a minimum of10 minutes under fuel fire conditions. Such structure would provide thetime required for a spilled fuel fire to burn out or for fire crews toextinguish the flames.

Another area of concern involves the fires that originate in therest rooms of commercial aircraft. Such fires, i.e. in trash receptacles,etc., often remain undetected until they develop into major conflagrationsand pose a serious threat to the lives of those aboard. Here, the firemust be contained to the rest room and must not penetrate into the maincabin, while the evolution of poisonous gasses from the burning structurecannot be tolerated.

These stringent performance requirements are not the only considera-tions that must be taken into account. For a design/material concept tobe viable, its economics must be attractive to the prime aircraft manu-facturer. Light weight (low density) is another imperative character-istic. In addition, many applications require highly cosmetic structureswith smooth, even surfaces or attractive color schemes needed for theconcept to achieve wide acceptance. The following report details theefforts by Whittaker Corporation, Research and Development Division (WRD)to develop attractive, moderately priced aircraft panel concepts thatexhibit outstanding fire resistance and performance in a fuel fireenvironment.

1

2.0 TECHNICAL DISCUSSION

2.1 Initial Concepts

Detailed design of aircraft structure was beyond the scope of thisprogram. Work was limited to the basic simple concept of a flat panelunit. Early tests of conventional sandwich panels by NASA-Ames showed atendency for panels to delaminate; i.e. for the skin to warp and debond,under impingement of the heat flux.

The general opinion was that a three-dimensional truss structurewith the skin mechanically attached to the truss cross members would berequired to maintain structural integrity throughout a 10-minute exposureto fuel fire conditions.

An obvious and direct approach is to utilize woven 3D reinforcements.A typical woven panel configuration is shown in Figure 2-1.

POROUS FACE- 3 PLIESINTEG WOVEN

WEB-1 PLYINTEG W V EN--

IMPERVIOUS FACE - 1 PLY, INTEG WOVEN2 PLIES, BONDED

Figure 2-1. Panel Construction - Integrally Woven Fiberglass

ORliGINAL PAGE IS2 OF POOR QUALT

Note the integral construction with the cross members and skins wovenas one unit. Unfortunately, such structures proved too costly to beincluded in the program. High set-up charges, long lead times, and highmaterial costs led to the decision to seek an alternate approach to 3Dstructure.

An attractive approach was then developed. It involved a stitchedstructure with the same general configuration of the woven 3D truss. Theuse of a one-ply fiber reinforced skin stitched as a 3D truss iseconomical, light weight, and lends itself readily to automated processing.Figure 2-2 shows a rough schematic for the fabrication of stitched 3Dstructure.

Stitch in progress

Direction

Previous Stitch

Rolls of Prepreg

Figure 2-2. Schematic for Fabrication ofStitched 3D Structure

It was possible that such structure in itself would prove an effec-tive fire barrier if suitable resins and reinforcements were chosen. Itwas also obvious that filling the truss sections with polybenzimidazole(PBI) foam would greatly increase the insulation characteristics of thefinal structure (retard heat transfer, etc.) and in general improve per-formance and enhance the fire resistance of the panels. Figure 2-3 showssuch a structure.

3

PBI Foam

Figure 2-3. PBI Foam Filled Truss Structure

The trade-off would be additional material and fabrication costversus improved fire resistance and performance. The empty and PBI foam

filled stitched truss structures were therefore selected as the benchwork

concepts for this study. The target ,densities for the final structures

are 96.1 and 134.6 kg/m (0.5 and 0.7 lb/ft2 of 1 in. thick structure),respectively.

2.2 Material Selection

2.2.1 Resins

The candidate resins for the work were identified by NASA-Ames andagain represent a trade-off of cost versus performance. Thermally stable,

high char forming polymers are needed for such structures, but unfortu-nately high performance is usually matched or exceeded'by high cost.Figures 2-4 and 2-5 summarize typical correlation of performance, cost,and structure.

14 - -POLYPIEINYLENE 5 100 10 n 00

E 12 POLYBENZIM.DOAZOLE R K%1I/

AR Y , ,, percent L5

Yield with MoHEOlecularCS Foamed Polymers

ORIGINAL PAG

020 20 40 60 60 1

Figure 2-4. Correlation of Primary Figure 2-5. Summary of PropertiesThermomec hanical Char of Char FormingYield witli Molecular Foamed PolymersStructure

ORIGINAL PAGE 1$4 OF POOR QUALITY

The high performance resin selected for truss fabrication was thepolybenzimidazole (PBI) system. The lower performance/lower cost resin

was Kerimid 601, a bismaleimide type polymer. Figures 2-6 and 2-7

illustrate the chemistry involved with PBI and Kerimid 601 resins

H2 N O 12 U2 C c 2 1

H NH 2 +(

+ 2H20 + 210H

Figure 2-6. Typical PBI Synthesis

2i CH2 NH2 METHYLINEDIANILINE

0 O

No' C) BIS M A L I MI O E

N CH2 OF METHYLENEC/ DIANILINE

0 0

CHAIN EXTENSION & CROSSLINKING VIAVINYL POLYMERIZATION & MICHAELSADDITIONS. NO VOLATILES.

Figure 2-7. Kerimid 601 Chemistry

In addition, the PBI polymer was selected as the foam material for

use in this study

2.2.2 Reinforcements

The selection of reinforcements was quite straightforward. Glass was

the prime candidate as it is low cost, readily available, and has high

temperature capability. Kevlar 49 fabric was included, as its low density

offered an opportunity to achieve significant weight savings. Other

materials such as quartz, graphite, fiberfax paper, alumina/boron/silica,

and zirconium/silicon fibers were available if the high temperature per-

formance of glass and Kevlar 49 proved inadequate.

5

2.3 Fabricationof First Generation Structure

2.3.1 Initial Flat Laminates

Small (15.3 cm x 15.3 cm), 4-ply, flat laminates were fabricated

from various resin/reinforcement combinations to confirm curing cycles

for the resin systems, check compatibility with the various reinforcements,

and to provide display pieces for the NASA-Ames exhibit at the 19th Annual

SAMPE Symposium held April 23 - 25 at Buena Park, California. Panels were

fabricated with the following compositions:

(1) Kevlar 49/PBI

(2) Kevlar 49/Kerimid 601

(3) E Glass/Kerimid 601

(4) Quartz/PBI

In all cases 181-style weaves were used.

The PBI prepreg was made to WRD specifications, while Kerimid was

processed to low (3 - 5%) volatile contents as were used in the truss

structures. Curing cycles were as follows:

Kerimid 601 Bag for autoclave cure. Heat at 1 - 20 K (2 - 4°F)

per minute to 455oK (360'F) under vacuum and

689 KN/m 2 (100 psi). Hold 1 hour at 455 0K (360'F),

cool. Postcure unrestrained for 16 hours at

511 0K (4500 F) in air.

PBI Place in press at ambient temperature; heat under

contact pressure at 1 - 20 K (2 - 4 0F) per minute to

450'K (350oF), apply 1379 KN/m2 (200 psi) pressure;heat in 280K (500F) increments to 642 0K (700 0F),

holding for 30 minutes at each increment. Hold

1 hour at 642 0K (700 0 F), cool.

All laminates appeared well consolidated and of good quality. The

Kevlar 49 darkened under the PBI cure cycle, but no quantitative evalua-

tion of this change was made.

2.3.2 Truss Structure

The next goal of the program was to fabricate a series of twelve 3D

first generation truss structures for test and evaluation. Table 2-1

lists the six initial types (2 structures per type) to be fabricated.

Panel dimensions of 30.5 cm x 30.5 cm (12 in. x 12 in.) were required for

this initial evaluation.

6

TABLE 2-1

SIX STRUCTURES FOR INITIAL FIRE PROTECTION EVALUATION

Empty Truss Structure PBI Foam Filled Truss

Structure

Target Density Target Density96.1 kg/m 134.6 kg/m

(.5 lb/ft of 1 in. thick) (.7 1b/ft 2 of 1 in, thick)

Compositions: Compositions:

1. Resin: Kerimide 601 4. Resin: Kerimide 601Reinforcement: Kevlar 49 Reinforcement: Kevlar 49

Filler: PBI Foam

2. Resin: Kerimide 601 5. Resin: Kerimide 601Reinforcement: E Glass Reinforcement: E Glass

Filler: PBI Foam

3. Resin: PBI 6. Resin: PBIReinforcement: E Glass Reinforcement: E Glass

Filler: PBI Foam

An initial full-size truss structure was fabricated using one ply of181 E glass/PBI prepreg. The apex of each triangular section was hand-

stitched to the top and bottom skin plies using glass thread. Triangular

shaped mandrels were cast of high temperature silicone rubber for the

cure. It was planned to use the pressure generated by the thermal expan-sion of the silicone rubber during cure to consolidate the trussstructure.

The initial cure with mandrels went to only 5600 K (550 0F). A laterfull postcure to 7280 K (850'F) was accomplished with maranite mandrels.

A second, well consolidated truss was fabricated with this procedure,but two problems arose. First, the hand-stitching process was far too

slow and laborious even for the purposes of the test program. Secondly,significant deterioration of the silicone rubber mandrels was observed,even in a 560 0 K (5500 F) cure. The latter problem was readily solved bythe use of aluminum mandrels for subsequent cures. An alternative to thehand-stitching was also found without major difficulty. An industrial

7

sewing machine, shown in Figure 2-8, was rented for the remainder of theprogram.

Figure 2-8. Industrial Sewing Machine

Glass thread was also readily available for this work. A detailedprocedure for the rapid stitching of one ply of prepreg to form the trussstructure was then developed and is attached as Appendix A.

The 181 E glass/PBI, 181 E glass/Kerimid 601, and Kevlar 49/Kerimid601 structures (4 each) were then stitched, using the procedure and equip-ment described above. Aluminum mandrels were then used for initial curesbelow 560 0 K (550'F). Maranite mandrels were used for postcures of unfilledtruss structures, while PBI foam triangular blocks were loaded into theremainder during the postcure. The truss matrix resin (PBI or Kerimid 601)was used to bond the foam blocks into place.

Figures 2-9 and 2-10 show the maranite mandrels and foam blocks,respectively. Figure 2-11 shows a cured Kevlar 49/Kerimid 601 truss,while Figure 2-12 shows an unfilled 181 E glass/PBI truss with bothmaranite mandrel and PBI foam block for comparative purposes. Figure 2-13shows a cured 181 E glass/Kerimid 601 foam filled truss after cure butbefore trimming.

8

lFigure 2-9. Maranite Mandrels

F i g Li e -1 0 P I o a m B l c k

9

Figure 2-11. Unfilled Kevlar 49/Kerimid 601 Truss

Figure 2-12, 181 E Glass/PBI Truss with Maranite Mandrel

and PBI Foam Block

10

Figure 2-13. Cured 181 E Glass/Kerimid 601Foam Filled Panel

Ii

11

The following cure schedules were used.

PBI Matrix Truss Cure - The initial step cure was accomplishedusing triangular aluminum mandrels and the following cure cycle:

Place in press at ambient temperature; heat under contact

pressure at 1 - 20K (2 - 40 F) per minute to 4500 K (350 0 F),

apply 1379 KN/ma (200 psi) pressure; heat in 280 K (500F)

increments to 5600K (550'F), holding for 30 minutes at each

increment. Hold 1 hour at 5600K (550'F), cool.

At this point the aluminum mandrels were removed. For the two foam

filled structures, the PBI foam was coated with powdered PBI adhesive and

placed in the truss. For the two unfilled structures, maranite mandrels

were now inserted for the postcure in nitrogen. All structures were post-

cured as follows:

Heat to 560 0K (550'F), hold 1 hour. Heat in 280 K (500F)increments to 7280K (850 0F), holding 30 minutes at eachincrement. Hold 1 hour at 728 0 K (850 0F), cool.

Kerimid 601 Matrix Cure - Aluminum mandrels were used for the

initial cure of all structures. The following cure cycle was used:

Heat at 1 - 20 K (2 - 4 0F) per minute to 4640 K (375 0F) under

vacuum and 689 KN/m2 (100 psi). Hold 1 hour at 464 0 K (375 0 F),cool.

At this point, the aluminum mandrels were removed. For the PBI foam

filled structures, the foam was coated with Kerimid 601 lacquer and

placed in the structures. Maranite mandrels were placed in the unfilled

structures for postcure.

All structures were then postcured under contact pressure for 16 hours

at 511'K (4500 F) in nitrogen.

Table 2-2 gives the densities and resin contents of the final

structure.

2.4 Testing of First Generation Structure

2.4.1 Fire Resistance Testing

2.4.1.1 Panel Preparation. The twelve truss structures as describedpreviously (two structures each of six types) were prepared for testing in

the T3 tester, shown in Figure 2-14. Chromel alumel thermocouples wereused. Figures 2-15, 2-16, and 2-17 show the placement of thermocouples onthe filled and unfilled truss structures.

12

'TABLE 2-2

PHYSICAL PROPERTIES

Density, kg/m3 TrussSample Description/ Panel (ib/ft2 of a in Resin

Configuration No. ContentStructure)

PBI/Glass, unfilled 1 75 (.39) 35.1

3 77 (.40) 31.3

PBI/Glass, PBI foam 5 131 (.68) 30.2

6 129 (.67) 37.0

Kerimid/Glass, unfilled 9 87 (.45) 37.4

10 90 (.47) 37.6

Kerimid/Glass, PBI foam 11 121 (.63) 33.2

12 121 (.63) 37.4

Kerimid/Kevlar, unfilled 2 58 (.30) 54.4*

4 52 (.27) 35.0*

Kerimid/Kevlar, PBI foam 7 98 (.51) 38.1*

8 100 (.52) 44.4*

PBI Skin 96 kg/m3 13 32.6(6 lb/ft ) PBI core,no truss

* Calculated from weight data, as any known method that digests theKerimid 601 matrix also attacks Kevlar 49.

Note that the target goals were met or exceeded in every case.

The additional panel, no. 13, will be described in the followingsection.

13

AREA AREA

o a

"' . ,' ,,_

-- -- 7

OIL : -_ I AREA I 9-16 Btu/ft2secBURNER BURE ",~ Li !AREA 2 5.5-11 Btu/ft2 sec

A REA 3 - 22 Btu/f sec

Figure 2-14. Ames T3 Thermal Test FacilityJP-4 Fuel

I1" B-2 2" 1"

1" 1"

2"

8"

Figure 2-15. Back Side Thermocouple Placement,All Structures

15

-Center- i Center- 2

- Base Point

a 0

Back Side - 1 Back Side - 2 Back Side - 3

Figure 2-16. Thermocouple Placement, Foam Filled Panels

.c "

Base Point

-Back Side - 1 Back Side - 2 -Back Side - 3

Figure 2-17. Thermocouple Placement, Unfilled Panels

All thermocouple leads were bonded in place using Briskeat ceramic

adhesive, and cured 2 hours at '3390 K (150 0 F), with the exception of those

placed directly into the PBI foam. The latter were held in place by

simple mechanical friction. A 5.08 cm x 5.08 cm (2 in. x 2 in.) aluminum

patch was bonded over the center back side thermocouple, while a 2.54 cm

x 2.54 cm (1 in. x 1 in.) patch was bonded on all other external

thermocouples.

An additional panel, no. 13, was fabricated and prepared for testing.

This panel was based on a simple skinned sandwich approach; no truss

structure was used. A 96 kg/m (6 lb/ft3 ) PBI foam core was used in con-

junction with 1-ply, 181 glass reinforced PBI skins. The skins and foam

were precured to 645 0 K (700 0F). PBI adhesive was applied as a powder,and the structure was cocured to 7280 K (850 0 F) using the PBI cure cycle.

Thermocouples were attached in the same manner as for the truss structure.

Their location is shown in Figure 2-18. This panel was fabricated to

determine whether a simplified structural sandwich would exhibit adequate

performance. Such a structure would be much simpler and cheaper to

fabricate than woven or stitched truss panels, while exhibiting good

mechanical properties. The skinned foam panel no. 13 appeared stiff,

strong, and of good quality. In addition, a smooth cosmetic surface was

achieved, which would prove extremely difficult to accomplish with a

stitched truss structure. The question to be answered was whether this

panel would debond when tested in the T3 tester.

2.4.1.2 Thermal Testing. Tue painels were taken to NASA-Ames fot

testing by Ames technicians. Both WRD and NASA-Ames personnel observed

the tests. It was decided to test one each of the six panel types and

the skinned foam experimental specimen. The remaining panels, also one

each of the six types, were retained by NASA-Ames for later testing in an

aluminum-backed configuration.

Table 2-3 gives a description of the panels along with qualitativecomments and observations of those tested. Figures 2-19, 2-20, and 2-21

compare performance of foam filled vs. empty structures, while Figures

2-22 and 2-23 compare performance of various structure types. Figures

2-24 through 2-30 show the performance of the individual panels tested.

A number of conclusions can be drawn from these initial tests:

(1) The performance of unfilled structures was inadequate. Even in

the best case of PBI/glass, the back side temperature was too

high, i.e. near 700 0 K (800 0 F).

(2) Kevlar reinforced Kerimid 601 is not suitable for these applica-

tions. The structures burned vigorously under the testconditions.

ORIGINAL PAGE IS18 OF POOR QUALITY

Center

SBack Side - 1 Back Side -2 [ Back Side - 3

Figure 2-18. Thermocouple Placement, Skinned Sandwich

TABLE 2-3

T3 BURN TESTS

Panel

Sample Description/Composition No. Comments

PBI/Glass, unfilled 1 Almost no smoke or distortion

the entire run. Holds togethervery well, with the usual burn-away of resin off the center of

the fire face. (Note: No. 3thermocouple was replaced by acontact pyrometer on the back

side.)

PBI/Glass, PBI foam 6 Little smoke, moderate distor-tion (significantly less than

Kerimid), good stability to the

end of the run. The center of

the fire face is burned clean of

resin.

Kerimid/Class, unfilled 9 Severe smoking, the specimen

warps but stays together for

the test.

Kerimid/Glass, PBI foam 12 Some warping (normal), resinburned clean from glass at the

end of 10 minutes, virgin foamleft at the end of the 10-min.

test.

Kerimid/Kevlar, unfilled 4 Splits, smokes, then ignites.The face is gone and ignition of

back occurs in 20 seconds.

Complete burn-through and con-

sumption in 1 minute.

Kerimid/Kevlar, PBI foam 8 Smokes, ignites at fire face in

50 seconds. Face burns away,but structure stays intact. Somefissuring of foam, but no burn-

through in 10 minutes.

PBI Skin, 6 lb/ft PBI core, 13 Little smoking or initial surface

no truss effects, good dimensional stabil-

ity, good integrity the entire

10-min. run. Resin cleaned from

the center of the fire face by the

end of the run. (Note: No. 13 is

a PBI/181 glass skin, 1 in.,6 lb/ft, PBI core, no truss, no

stitching, bonded with PBI

adhesive.)

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Fiur 21. Ker imid/Kevlar, Filled vs. Unfilled:: ~ : : '::

. ....... .. i~i02.(Ceniter) Back Side T.C. ....... .. . ... .... --- : -..... .....--- -A. ..... ..IT: ..-: .. .'.~aa._ ! . [ i it2.... .. i

.(1500) -

(10001; - -I 1:.::v: nL11dI: - -

. I. .... . ..... ..... ., .

it e-

10 A .I . . . . . . 0 ... 60..... ........... .. .- .- - " .............. ......... ... . . . .i . . : .,: : ... :! . ... .. .... .L . . .. ......... . ... .

.ir 7.r m- s Fil eds. U

750

4IK Ii..;. : : ......... ....

.: Ii 'i'i" "t. { L:" .. I .7 .

...i .. ..... .........._ _. ......ifi ~ ~~. .. ,:,::. . ....... " . . ..!?;-:~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~~~. ............ii:-: ! l i .. # ! ... .; ;'! i; i,::i~~

:: {. [ I ... ":I , :.:.

100 20 100 . 400cOO60

~~. .. .. .... ..... . . .. i . . . . .. . . . .. ..q .! . , . ... . : . -. , . . I....-17-~1 .. . . .. .. ....,

•~ ~ ~ ~ ~ ~ ~ T 7-.,-- 1 ... T:....,..,. ,.

Exposure, seconds

Figure 2-20. Kerimid/Glass, Fill ed vs. Unfilled

*7V~~~~~I7~~~~. .FF.21

......;. . . 2' ; I ' ' F;

I ente )ack S~dtJi. T.: .I... ....

(1500- - I7 7 .1 ~

' ... ... .. .

(1000). ql

i'F ... F. ... ... .. .... J ;...

100. )'' '

j'L I; 1::: 1. ... ..

100 20M0 0 0 0.Exosre sec.onds .

Fiur 2-17B/Gas5ile0sUfle

j j IfIde~i r B'ck flk deH

I L1o(00P. .. . .. . .... " .. .

"0001 '|Burn-Through I ": "

.. .. ... -.

....... .. . .....

::: : I / il i:l iJ III : :il l i i ! :F I i = :

1111,~a 7F17 7 1' ... .. .. I.... V ... :. :

Ex1,re jeod

igre~/ 2-as efomneosUfle Srcue

]~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~-- -... --- .......... .. .... ............... I..

...(500 ! : t , .... ........ ...r .... ,,50 0 / / - ::-:::l- !i::: i :;i~ : :; :i!: W - i ; :;: !i: ;; : i !:i; [ !] :: ,;i:: ;.:: i :; : : ; :~ : :: ; : !:. .. -

•/ . .: : : • • : . ; : :. : . : ::- ; . . : -- . •7.7 .:. .. . :. . .: - . -: . . .. . -

100 200 300 400 500 ,.600

Exposure, seconds

Figure 2-22. Performance of Unfilled Structures

Ii -:": T it;!! 1' ':: w i : 7 ;

0 ). ... ... ...a : ........ .:... : ,.: : : -- --.

'::': ' :: : ' ! .,. I I .L : :!; 1 .. I r . ' , . "....... ...... .... ......... ..... t-;!:i~ :: !:: ii:i -!r " : : ! : :

:I: :. i:.":: iK:* f: " . : 1 :l* *t7.i7 •." I0 i . . ' I I'ii i : . .. . ' . .. . ' I. ..i.... .. . .. .. .

"000 - ~*::w. .. .... ... i.... : .... i :... a. ..... .. : . 'Ba ck S J - 7I . . .

., : F ! :i: iii: :: iY :' ":'.::"F :'t:

.. . .. ...... :i ... : . ; " ' . - . t

",; ;'.i ::'.: ..... .. ;: ; :, ., " : :....:. . . :

w ' ia '

......... .... .... . ..... t . .i. .., , , ........... ... . .: ! , : : , i r

-I- l :-

" --:': ' " ": -''-:':-'iiiii:'- ... • "- , :tT:_i: " .U T :]

ioo -:i7:i~ii- ;::! " i ; .i i .. ... ........ . ... . ": .':, .......: i7 i ; !

...•. : . .. .. •" .. .' .. . . .. . : :. .: .. .. ... . .... .

7 .~ .. .. I[

..I . .. . . . . . . . ..". ';. . i ' ' : : ' .. ....... , " : . " . .

......... ..... ...... . "iiiil!:,. -!i: ... ..... ... ........... ..,. , ... .. ..

: ifji~ ~lj ':! ii: iii i ::::::: i]::7!!;: :'!i::!:,!i: ::1il l::;:':: ;::':: :.: ..:::i!: ~ i:.i!.:.:. l:

" .'.: .:; :: !;- I:: :I :. L -'"J L'E .: ! .i_-: .!b_ l::.:.;i . !.._,../: ;: liiI: ::1: i ::l ,i : i iiI I '' "iriii :FT :.I j ' Id ..L:ti: i ;.;:I:

100 200 300 400 500 600

Exposure, seconds

Figure 2-23. Performance of Filled Structures

. . . .... . . .. ...:I(1000) : :it it:~l: ':~: ' I

::J:: ...

: : 4i :: :It

N iiiii~i~iiii1: i7ii ii -- - ---------a'~s

i:7' 7::::j. T7~'' '"~"I

4 .:: .... .. '.. .. .... ..

II'd ;A : : ! ! i * :7 1:I I. ; :::::

... T :.: F;i i::i:l:j :;q I i it d l ::i:: :'::

V: j .... .... wq .;.:: q I!:,: Sk nn ed a !:I: ....... .... .. ...... .. ...... ... . .........i//iii

(500 P / Cl SS

... ..... .. !j:; ... . ....ii~li~ji~: I~ ~l:i~::

::.A:

t. :J: A d I

100 200 300 400 500 600

Exposure, seconds

Figure 2-23. Performance of Filled Structures

.. . 17i + .i ... ... ... .~i ..- ; ...... Ovn..............-.. -- ---- .. ...... ............. .. .. ..... .... ..... .

O .. . . . .: ... . .

S, .................: !:i -;+i :!: : ii i::ii : l + ' .. ....... ....A" ......:.::i7. i. : .::l : _!: .,.; ii , i :i i II

li- ili.ii:... : i .:: : i:. +~ i. .i : :::::::::::::i .i. i:: i : ... ......;- i- --~...ii li-' " + + , '......i -! i+ i i : il i + , II -i + I

... ...... :. ... .. .... ..

- . ..-: . . ., .. . .... .... ..... .... ... ... .

° < :i< i.. .. " :+" : .i. .::: ,

....i! .... ... .. ........ ....:. ..+ + : :T -+ . . . ....... : :,j

. i : i': + .... ...+ T++ 3' 1+ :

' " : ... :-!:: .. .............. .' ~~ ...... .::% :":: , ; : .: : ..: : :i i i .: !i'; : " ! : i:F~ .. ,! .,

--=-0I~il '' --+:: +- - --= .".i : .i' , + - ..

© ,-500 -, , +. -T+,,i . : ' , .......

.. .....' .^... -- ..... L. i .. .. , ......+ I :T : .. +.< ., .. . .'i.. .. .. . ... .

:iii' : " j i : : i : "! "! ": : .. .. ' : .. ... ......... :: .. .

': " i::.ii~~~~i :::ii!:i i <l: :i:i l:: "'!.:i:ir : : :: -:-< :,: : : + i i,;:: j: : i: i ! ! : : i . :

I- : T , i t ..: "' !_ I,+ : ' " ::: I

- 100 200 300 400. 500 1500Exposure, seconds

t'r-I

MFigure 2-24. Panel 1 Unf ilIled PBI/Glass,~Back Side Thermocouples vs. Time

----- 7- --1 ..... .. ..... .. ....... ... .

. . . .. .: .:... ... . .. . .'' : : .r

," '1 r::l : : 1: : : l t .-i !:iii !9 : i i': ii[: : : i ;: :u '.. .i~ :1' : i : : ', v: : : ,.. . . i -: • : - :.

7''

•~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~. -.. .-" .ve ............; ... ... .. ............ ;I "I n(1500)

0 00 - :: .. . " : ' :. :::.:.. .. ....... ." '

'" | ' ' l ' / . ... . .. . .. . . . . ... .... . .. .. . . . . . .. . .. .. . .. . . .. . . . ..1000 : . . .. : ... .:: .7:, !:EiiJ ~ ~ :. :i''~ iiil iiii i i :; :ii ::;: '::': : ::;:: :':;: : :

: :' : 'i~ : i:::: ::ii!: "x:.1 :: ::- :: :::: ::' .--- I : : : ": ::- ! : - r '

(~~~~~~l~ !0 ) = .. .. . .. ' : -: -, -: : ;- ; ...:. . .. . - ..... ":.... .. .. :....... .-- . •. .." -- --:: , " -3 ... ... .'. [.". .i' . ... . ' ' : "if : . . ... .iI~ i; I , ,. ,..... .. ......... .. ."....,,

, . ' . .. .... ... [ . . . . : . : . . ..... . .. . . : . . .: -" ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ .. .... ... ..... .. .....: :: ....... ..: ..... . :. . . - : : - .;:i:: Ov n:: i:: l :iii ii : ::i: ::! : :: ::!!~:i :::r ¢!: i i ii:,::: I1i! ! ii 1I i ;l :: {t !!!: :i : I ; i ;i 1 i;:i: .t ;:.:, ::.:';!: "iiii ..:l 'iii :ll::.:l:ft!iiE;::: l i', : 'i;: . :: : i:: I: i ;' :: :::;': :i :I: . : : !: i/: :Il l : ::i : : : :.:.t:

• .. ... : I100 0 -T:1: I

.. .. ... ... ... ... . ... .. ... ......... .... .::

'r: 'j: ''' 'I':: ~i~.

1:iiiiii : ,! iI 1iiiii:[i' i i i : i'.. : .. .. ... w:......::...:

I: !i. .... ... .

... .. ... ..... ... . .. : i iBid o c o . .. .u pl es .. . : 1 .. .. . :v s T::i: .:: .: : :: :: .: , : ::. . ... ... ... .. . .. ... . ... .. .. .. .

1:00 ) - a'::;: """:';i jliijj ~ ~ ;:::: i;iiiil~iiiiilii:::

500 j O::

... ... ... ... .

75 - : 77- LL;": """i~':: :::::: -'.

Ex os re seco-,7ndsT;- q

t i itI!i.... .... .. . .. I

Q) q . ... ... ...:

Figure 2-25. Panel 4, Kerimid/Kevlar, Unfilled,Back Side Thermocouples vs. Time

(1500) L".... .- ' -' "- '- -- --7 T- T " - .- - :T'T -" T ,: ,

S. .... "... ... i

1 0 - 1' ' : i : ' : ' : , ' :. . : .. ......"I ' .... .. ..... . ... .....-.::: :-

I:L:

[ ' .. I L K f. I........ ....... .,i

-- L 7 -R!- E I n i:i::l--~~i: ::

... ......

F50 'iI F :I

7 - i--i - - ----- -:i'-

4500 I..I. . ........

;'T

7.. :Ii:I' .,.i... I. . . ....L ..:.... ,:.. :...::?! 717: :!.! 112 :5:i }:. :L : .. . . .. ... .. ... . ...i i

.... .. ......I.:.i...I :. .I. : :". .'

500 200 300 400 500 600

Figure 2-26. Panel 8, Kerimid/Keviar, PBI Foam,

Back Side Thermocouples vs. Time

7F 7..:I~n4

L~?-f

-1) 10 200 30 400 00 60

Exosre scodFigure 2-26, Panel 8, Kerimid/Kevlar, PBI Foam,'"i;~~; :~

Back Side hermocoupls vs. Tim

... .. ...... .... .. ..- ' I ' " : : : m : " . .. .., I v , ? : .. .. i 1 ~ ., . L .. -, : : . .

.. ...... r - • . . .. ... . . .. ... ' , i , ... ..... .I , -.- I .. i --.c- F i , I,-- I-i~ i .T I Z [3 1i..IZ 7 ;:T t: ,,.% L ... .... .... .. ... ....... ....... .... ... ...... ...........(1500)- :i.:: iT T::':::: :::

:::: ii:.i~ i::::. :i::

...... , .I I .. : ..: : ::. i..... .!....: : : -: I : . .i .e.......: , : l tl.: :.-- .:.'.. .-- .- .... i ... : . ........ .

!l:': ;: .., :" " ..':t'11: iil l i ii1TZ :: iii:i:, l; ' i i~i 'i :: i : .1 ii ! ": ::ii.. :":"":. .... ! :.! 'll: ::... !

•~. ... ........ .: . , r . , : . . .. . . . . ... . .. ... ..

' " ' : ... ..': ..... . ' .. ':: ' : : : ' " : ::: il::' 1.! c i i ! : -a I ! i- -

: " ii ii!x. i i!. ! ! -i! i:i! '!!!i i: :/ :! :l iii! i:'...'"""": : : -' .i.:.:i .::.:

i i : 7 7 . 7 7- -1 . ...... ....

,. ... . ...

'. .. . .. ..... ... :7. . . . .

t'(000 .... 30.00.00

750ur 2-7. Pane 6,PT/las PIFom

7Back Side T c vs. Time

77- ...... ........i~i l~i::: l:iilli ;1::: ... . ...... :........ .. ........ ...

77t-- 7F 7 7-F -7 .... ... TC-::: ;: : '

liii ll: illii~ ~i .......... .... .... . TC-: :'::; !:Iiilli'ii~: I~l:: lll!I :'.I:i(500)ij iiii iii : ii::':::I :!:::r:~: ~'~'' :t:::::: :i~l I'''ii~iil:;iii~l~~iii :i~ii~iIl77-~500-::

:::::: I77 77. -7- -

:.::.: ::i::i:i I:li'!: j :~jil jl!! s:!: ; :!.!j 1: i:

::::::Ik::

E~oo :Ii: ii100 200 300 400 500 600ii ij/jiliiljl;: lj:-:~ I:I:.I:.;:: :::: :

:'!:':'::!::; iiii lil~iExposure, secondsi :liiiiilIlFigure 2-27. Panel 6, PBI/Glass, PBI Foamlii:: ::: ''

3C - : :::: :iii;:":"" : ':'Back Side Thermocouples vs. Time~I:I: :1::::1:

. . .-7 .. .. . ..... . . .. .. "... ... ..... .- ........... --. . . .. .. ..... -..-. - .. . . .. . . .. ........ . . . . ... . . .. .-.. .. ...-.: ~ ~i I,+ ; : ________': . i i I•

ooo-

Fj, (!:n ......(15 0 0 ) . . .. .. .... . ... .. ---- ,-

750 -1I

00 : : .. I

101003040 0 0

+ ! + -' l I [ =+ l... ...... ..

... .. .. ..... e r m i /. ........... .... i..ll eBack Si -e The mo ou e s... i... ....

TI- t I' /. . . i ;/ .i: i !:::.T'C .. -i A ......... ...ii~ i :.~ ii: ii.!: r - : . i - - t -5 . T .

m " + +...... ... .. .... . .. _. .. .." : ., . F + ! - - :L

(50) - I- t17 -71/": ,I ,I' . . .. . . . . . . ..... .............' ".

.. ........ ... .. . .. . .

....0 . . I 7 . . . . .. . .. .... .. . . .

100 500 300 400 500 600

Expos1ure. seconds

Figure 2 28 Panel 9 Kerimid/Glass Unfilled

Back Side Thermocouples vs. Time

(1500) 17000 7b: o I *, :'.:i i ,7 : : i I .. :

(:7o ) ... . 2" . ... .:..... : :: : .: : .

L .. .. :. i.i... i '/ =

(1000)- . e

750 1 j ~~.. . . .............. .... .......

1:7

I ! ~ l ! , ilii~ i:. ! i[ ... ..... .. ..L ,. .. iiL !:i!:.l:L::: ,. .,

,. . .... . . ... . .:I I

.. ... ..... .' .. -:: ; :

[: i t .: F :! ' ' : 7....

! i ]T! ii I: :: :::Y: .................

(500)- If :..TCT+

.0. .. ... :. .... ...

[I"": :

100 200 300 400 500 600

Exposure, seconds

Figure 2-29. Panel 12, Kerimid/Glass, PBI Foam,Back Side Thermocouples vs. Time

-7; 7Ct Ld.i! .. . 7 .. : i ! 1 : )_ .: .. ........... .... ....... ....

A s.. . ... .... .. .. ... ... . ..........."< ; : 17 ! 7 :! :. .. ... .... .. .. - .. .± _!: - ,k j : . ..- ~

( 500)- . .n

.i::< ... ....- -i V '- - .: ; : ... . . . . . . . . ., i < ! -.. " - -= - ... . . . . .. .. ...... .... ...I"... .I " ...

-1000) -i

750 : "i : . . .i .... .... K I I 7 0 I _____' ___'..... ....... ::. - - - - , - -- - . ..

I l: i ] I: : .. . . . .i, i ! : : i :!

7.1j

100 200 300 400 500 600

............ ...... . ..F ... .... .-"._' .-- ." "." ... .. .. .. .. V

-7Exposure, seconds

Figure 2-30. Panel 13, FBI Skin, No Truss, FBI Foam,

Back Side Thermocouples vs. Time

50- -m " -. '{' .... . 17 . . . ' : :

.... .. . . . . . . . . . . . . . . . ..... .. ..... .. . ... ...... : .

-5.0 :.I. i ;i; i .:: 1;ji! :i;.l .!; -i ...... !,, :: -- ;:':1t':.. . =.. .. ' ............. .....

:i~l =i !...m ....... .... .. i _ -' . . .... . ... . . .. . .

1. T -::. :

]

:. qigur 2-30. Pane Ti~~i !{:i, !!il 13, . I Sk,:.F in No Truss PB' :!i:!F oam,Bac Side Thrmcupe vs. Tim

(3) Although the all-PBI structures are definitely superior inperformance,'a PBI foam filled Kerimid 601/glass panel mayprovide good performance at a lower price.

(4) Th@ skinned panel approach is definitely viable and performedas well as the best truss structure panel. This conceptshould certainly be developed further.

2.4.2 Physical and Mechanical Properties

The density of thb thirteen panel types was previously given inTable 2-2. Simple weighing and measuring techniques were used, Trimmedsections of the various panels were used to determine resin pontent of thevarious truss and skin materials. The Kevlar reinforced material had tobe evaluated by weight calculations, as any known method that attachedthe Kerimid matrix also attacked the Kevlar reinforcing fibers.

An attempt was made to determine the flexural strength and modulusof the various structures. This proved to be impractical, due to theunusual geometry of the truss structure. The panels would buckle anddeform, but not fail. Figures 2-31 through 2-34 illustrate typicaldeformation encountered in testing. The difficulty arises in that thesize of the geometric details in the specimen is very large when comparedto the dimensions of the testing fixtures. This made it impossible to runmeaningful flexural test data on specimens of moderate size. WRD hasdeveloped an attractive approach for a meaningful test of larger panelsthat is beyond the scope of the present program. This approach isattached as Appendix B.

2.5 Second Generation Structure Fabrication

A discussion was held between WRD and NASA-Ames personnel at the con-clusion of the initial set of thermal tests. It was decided that the setof panels shown in Table 2-4 would be fabricated.

For Items A, B, and C, NASA-Ames was sent a 15.24 by 15.24 cm (6 by 6in.) and a 30.5 by 30.5 cm (12 by 12 in.) piece of each type for theirtesting and evaluation. The rest of the panels were used for mechanicalproperty data. For Items D, E, and F, one panel each was retained by WRPfor mechanical property testing, while the remaining panels were sent toNASA-Ames for evaluation.

The truss structures were fabricated with no difficulty, using

procedures and cure cycles described in Section 2-3. However, two

significant problems were encountered and overcome.

33

Figure 2-31. Longitudinal Flexure, Unfilled

Figure 2-32. Transverse Flexure, Unfilled

34

ti

Figure 2-33. Longitudinal Flexure, Filled

Figure 2-34. Transverse Flexure, Filled

L 35

TABLE 2-4

SECOND GENERATION PANELS

Number of

Type Truss Panels

(A) PBI/181 Glass with foam 2

2.54 cm (1 in.) thick no foam 2

(B) Kerimid 601/Glass with foam 2

2.54 cm (1 in.) thick no foam 2

(C) Kerimid 601/Kevlar 49 with foam 2

2.54 cm (1 in.) thick

(D) 1 Ply PBI/Glass S<in 3

32 kg/m (2 lb/ft ) foam

core (PBI), no truss,

2.54 cm (1 in.) thick

(E) 1 Ply Kerimid 601YGlass Skin 3

32 kg/m (2 ib/ft ) foam

core (PBI), no truss,

2.54 cm (1 in.) thicjk

(F) 1 Ply PBI/Glass Skin 2

96 kg/m' (6 lb/ft ) foam

core (PBI), no truss,

.635 cm (.125 in.) thick

Total 18

36

(1) Uneven Foam Quality. Some significant variation in foam

quality (i.e., porosity and density) was encountered throughoutthe program. Although the problem was not severe, it wascertainly not desirable to have a sizeable scrap rate. The dif-ficulty was identified as originating from heat distortion inthe. foam mold during cure. This allowed molten PBI to melt and"puddle" before foaming, with the result that variations indensity and porosity occurred. A larger, stiffened tool (inthis case, utilizing a large press and picture frame structureas the tool) resolved the problem.

(2) Skinned Panel Fabrication. When the glass/PBI skins were bondedto the 32 kg/m (2 lb/ft3 ) foam, a number of difficulties were

encountered. When cured at 7280K (850 0F), the foam distortedunder pressure and unsatisfactory panels resulted. When a lowerbonding temperature was used, the adhesive did not cure to ahigh molecular weight, and the resulting bond was weak andbrittle. Local and massive delaminations were encountered.

It was therefore determined that the full 728 0 K (8500 F) curewas needed for good bonding of the skins to the foam. New48 kg/ma (3 lb/ft) PBI foam was made, but it also distortedunder light pressure. Analysis revealed that significant phenolremained in the foam, even after a 728 0K (850 0F) hold of 4 hourswas added to the foam cure cycle. The phenol acts as a plasti-cizing agent and causes a thermcplastic yielding to occur inthe foam. This phenol had been driven out when small, thin foamsections had been fabricated in earlier work. The recent workinvolved 10 cm (4 in.) or thicker foam slabs as would be usedin production of large numbers of foam parts. Here, the phenoldid not readily escape during a standard PBI cure cycle.

The solution to the problem was to apply a vacuum to thefoam blocks during the final extended high temperature cure.This effectively removes the phenol from the foam. The resultingPBI is readily bonded to the.glass/PBI skins without thermo-

plastic distortion under light pressure.

The 48 kg/m3 (3 lb/ft3 ) foam proved significantly superiorto the 32 kg/m 3 (2 lb/ft3 ) foam in strength and uniformityand was therefore used in fabricating the panels for theprogram.

37

2.6 Second Generation Structure Testing

2.6.1 Fire Resistance Testing

As previously mentioned, panels were sent to NASA-Ames for a series

of evaluations, i.e., T-3 testing, smoke generation, and toxicity tests.

The toxicity tests were not run during the course of the program, but

the other two series of evaluations were carried out by NASA-Ames personnel.

Table 2-5 summarizes the results of the smoke generation tests. All WRD

panels far outperformed a commercial type aircraft panel. However, the

all-PBI structures were outstanding, and significantly superior to all

other candidate systems.

There was no apparent difference between the performance of the

truss structure versus the skinned foam configuration.

Figures 2-35, 2-36, and 2-37 summarize results obtained by NASA-Ames

during T3 flame testing of the new panel concept. A constant heat flux

of 11.4 - 12.5x10 watt/n (10 - 11 BTU/ft 2 /sec) as measured before and

after testing with a calorimeter was maintained throughout the test.

From the results it may be concluded that the performance of the 0.64 cm

(1/4 in.) thick panels was unacceptable and approximately equivalent to

that of the unfilled truss structure. The all-PBI resin sandwich again

shows performance significantly superior to that displayed by a panel

with Kerimid 601 matrix surface skins. All panels were thermocoupled in

the same manner as the first generation panels described earlier.

2.6.2 Mechanical Property Testing

Triplicate flatwise tension and flatwise compression tests were run

on all structure types at room temperature and 3350 K (160 0 F). Table 2-6

summarizes this data. The results are the average of three determinations.

Again, as with flexural strength tests, significant problems were

encountered in obtaining meaningful data. The tensile tests were fairly

straightforward. With a low density foam, low flatwise tension resultswere expected. There is little material on the foam surface for the

adhesive to adhere to. Little significant difference was seen in the

strength of the various structures.

With flatwise compression tests, it is difficult to determine what

the results mean. The light foam is quite resiliant and does not "fail",as would a rigid foam. The load simply builds under compression as the

foam block is compressed 25%, 50%, or more. The "break" or failure point

was taken as a discontinuity in the stress/strain curve, indicating a

38

TABLE 2-5

SMOKE DENSITY RESULTS

Specimen WeightSample %7 Test Ds Ds Ds Ds Time Te Area

Before After Loss Condition 90 sec. 2 min. 4 min. max Dm e Density

Commercial type 10.53 g 8.16 g. 22.5 flame 49.71 50.18 53.20 61.81 12 min. 30 sec. .570 (1 in.)aircraft panel 10.53 g 9.52 g 9.6 no flame 12.00 13.88 15.70 26.48 4 min.

Kerimid 601/PBI, 10.7365 g 10.2381 g 4.64 flame 4.46 4.46 5.40 5.72 6' 30" " .458 (1 in.)no truss core 10.1671 10.0142 1.50 no flame .28 .28 .57 1.15 9 min. 0

Kerimid 601/PBI, 7.86 flame .28 .56 1.13 1.68 9 min. w .540truss 1.06 no flame 0 0 0 0 0 0

PBI/181/PBI, 2.18 flame 0 0 0 0 0 0 .687truss 3.15 no flame 0 0 0 0 *

Kerimid 601/Kevlar/ 6.64 flame .28 .28 .28 2.24 16 min. m .671PBI foam, truss .91 no flame 0 0 0 0

PBI/PBI foam, flame 0 0 0 .28 10 min. m .566no truss no flame 0 0 0 0 (

Kerimid 601/181, flame 2.24 2.79 3.33 8.01 11 min. 0 .417truss no flame 0 0 0, 0 0

PBI/118, flame 0 0 0 0 0 0 .364truss no flame 0 0 .28 .28 4 min. 0

i i• . ~'K.- 'I

I ___7 S;I T 7

0 j ' rii I: :l:~ :': '

"' ' I I" .' ' , , ( , . . ,':' : : . .. .iii :1 ' ' . :~I:::," ' ":. I; : I : ' : ::[ "i~ :: l z''' : i ; ' : , : *, : , . .. . . : ' ] : , : , I ': ;::

S - : fT' K [ : " .. . . .. . .. .,. .. .. . .. . . " I _

. ' K ' - - + _. _ _ . _L I i ,iJ. ._ ; . .K . .. .i l '+ I ... . .. . .L 4 - -

I i

( 500 )Ji .

_ ,. . ..

500 . .. . . ... . . . ....... . . .. .. .. . . . . ... ... ...

I : ' ' : ' i " : ' " ' ' ' ' " : ' : ' : ' ' : ' ' ' ; " " ' " ' "

1000 F"; J: l1i~i -: i r

::A;:

F'' I I':

i . . Ii I* H i ii i

"j K K"I

. " ".",.T

;. .. . . . ....-. . . . ... ..K ... . .. K . . . .

.~~~~~. . K ........7

..

. .... .. ' '.. . . .. ..L ..I

i ' ' 4 -. {. ..

00200 300 400 500 600

~~Figure 2-35. NASA Data, All-PBI 48 kg/r, 2.54 cm thick (3 ib/ft3 , 1 in. thick) Foam

I: :t 7:

C" 1 -0 200 300''':''

".

.1_

:I I::i: ilExposure, seconds 600i/i~ii';-''"

iii~-i iiiilii~ii ;il~~i: :j'~ii' I:. 1:

Q) :~:Fi g u r e 2 -35i: : ~ . N A S A D a t a , A l l -P B I 4 8 k g/l:: : I I : I: : : : .3 , 2 .5 4 c m t h i c k ( 3 l b / f t 3 , i n . t h i c k ) F o am1. : : l:; : L:. i : : : :

lWid i-jj:l!

Pit

-t7 ... !It titra'ac'e u heE tit e din tt:. Z 1! ii -I;;

jili 1:1 ij :tit iJ -.1 1:I! . .., .I ... -1 1 i : I - . 1. 1 .L 71 t :;:i i; it i:; :Ittit; t :4

:7 . .. . .... .... . .. .... . .. .... ... . ........." Ll

!it(1500 it ... ...

t: j : i !;; it It l :: it it 1 iti ' : : :! : .......... ... .....it. ........ ....

it .. ..1 !;; , it I l i t1000

L i: i::):, tit tA:L l !Tli: .. ....

it ;:It it s: iT ii:

... .... .........

it t: l i

:it t

tt:, : - ;: !::i :::I; i i; I i it i;

1:, 1 t:. i: it. fit J,: i.t :; ;:T k !i s, i t !it 1 i ; t;: t! 1!

.. .. .. .... ... .. .. ... i t I; I I; ; : 1; : l : f !; : i i : 1 :1 : :i i :i ; i ; ! ! i: 1 ; , : i ! i : : : i : : t ::! 1 : : ; 1:it : ,1. 1; : i P ; 1 1 :: i it it I: i it I i!:! !i

- 7 : , . , . .: : t i i t I i i , ' f i t j ; :1 1 : ! f I : :

it i t l:;i t: I

(looo:tii i!A jt:.i;T 11 :T

I ! I ! : : I : i t i"i.: 7

i t i t;

.......

V :T ii; tl:V !,

750 !it it 1 ;j tit 1;it it iti ; 1: llil ii , ! i- it i i. iti t i i;: it l! t ;!i' fil T, T! ji 1 i; 1.1;!: :WI i I: tit i!: li: I It it :N 1 1:!.::!: 1 i i 1 !.1 !i.: i It: i 1::

i i 1 I i. i t i l i: i t: Iti j ';.I :tit .. .... .... ... ...... :7;: it t i:::it; i 1; i : 1; l 1 ; 1! 1. !

it 1: 1:Ii 7 -- 71 7, --7

7

it(500 ] : T i t : : i ll I i I; .... i . . d ! i .... .........1 !::, fit t : i t i! 1' ::::'

... ...... .. ....5 0 0 - ': ::: i i;;! : 1:.1 ! -4. . . . t; 1 1; 1 . I !itii ; ;:;: j; t: ::, ii : i , !f tit : f. - L LL it ittit It: i: 1- 1 i:!

1 : 1 : itl: :tit ;..i

1*!,: it I i;! it t !: l:jt .t t i 1 !: :ii t ; 1 . t I ; i

F 1: 1;: it ;i:7ii.th 1-: :7117- T

it it i

is

it T -7 ..............

it :T

ti t. ......If

.11:1

100 200. 300 400 500 60

Exposure, seconds

Figure 2-36. NASA Data, All-PBI 96 kg/m3, 0.64 cm thick (6 lb/ft3l, 1/4 in. thick) Foam Sandwich

I T : . . ... . . . .. .. ... . .. .. i . .... .... ..7 t(1500)-r.'v

, 1~*i~

7. .- ..t .t 7-7 4 17-

q. . .uve drops ou6. . ..

g ~~~~~ ~ ~ - is .. . ... : "' .... .... . .... .."... .

goes -6 0 Ol . a secon I

. .. . . ....... . . . . . .

(000) t :~j7500 7.

.. . .. I. ... i .... ..... .. .. .....$4 7-,7 q ' .. . .. ; i :l . .. .. .. . : -' . : i: :. , '.i:i : [::.;I ; :: :i::

•~~~Z ." .. .. .. . . . . :7 . . .' .. .. .. . . . . ...... . .:•

50 it . I -:i '. .. ;.:.. ! .... i.. . .. . .i .. .... . . . . .......... ...-' ! ' t . . . . .c ' ..... ..

__________________ 1 ~~ it ------

:-:- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 7 it :;i:- ... ... .= ... '' : r .. : : :::: t": 7E" : :-

i00 230 300 4 0 500 600itosre teod

Figure 2-37. NASA Data, K-601/Glass Skin 48 kg/m3, 2.54 cm thick

(3 lb/ft 3 , I in. thick) PBI Core Sandwich

TABLE 2-6

MECHANICAL PROPERTIES

Flrtw 1se Tenslon I Flatwis CompressionSample Description IKN/m (Ib/in.) KN/m (1b/in.)

RT 335"K [ 160-F] RT 335*K [ 160F]

(A) PI3/181 Glass, foam filled, 106 (15.4) 92 (13.4) 231 (33.5) 233 (33.8)2.54 cm (1 in.) thick

Same, unfilled 142 (20.6) 119 (17.2) 61 ( 8.9) 53 ( 7.7)

(B) Kerimid 601/Class, foam filled, 138 (20.0) 79 (11.5) 361 (52.3) 297 (43.1)2.54 cm (I in.) thick

Same, unfilled 75 (10.9) 148 .(21.5) 43 ( 6.2) 40 (5.8)

(C) Kerimid 60!/Kevlar 49, foam filled, 170 (24.6) 110 (16.0) 303 (44.0) 258 (37.4)2.54 cm (1 in.) thick

(D) 1 Ply PBI/Glass Skin, 233 (33.8) 274 (39.8) 858 (124.4)* 654 (94.8)*48 kg/ma (3 lb/fc ) foam core (PBI),no truss, 2.54 cm (1 in.) thick

(E) 1 Ply Kerimid 601!Class Skin, 76 (11.0) 74 (10.8) 80 (11.6)* 84 (12.2)*48 kg/m (3 ib/ft ) foam core (PBI),no truss, 2.54 cm (1 in.) thick

(F) 1 Ply I1'B/Glass Skin, 181 (26.3) 227 (32.9) n.a.* n.G.*96 kg/nm (6 1b/ft ) foam core (PBI),no truss, .635 cm (.125 in.) thick

* Difficult or impossible to find a "break" point. Specimen compressesas load builds; returns to initial.condition when load is removed.See discussion in text.

failure somewhere in the structure. The specimen remained intact andcould still be loaded to a significantly higher level. When the compressivestress was removed, the specimen returned to normal dimensions with onlyminor signs of failure.

In the case of the thin sandwich (Structure E), no discontinuity

could be found as the specimen compressed, so no "break" point could be

recorded. These anomalies should be taken into account when consideringthe data obtained. Direct comparisons of these results to data generated

on rigid conventional structures (i.e., honeycomb sandwich, rigid foam,etc.) are misleading and may not be valid. Again, the necessity of care-

fully designing meaningful tests for these complex sandwich/foam/truss

type structures cannot be overemphasized. Unfortunately, elaborate and/or

expensive test specimens and fixtures were beyond the scope of this

program.

3. CONCLUSIONS AND RECOMMENDATIONS

All structures tested showed some'degree of flame resistance under

the test conditions of this program. Kevlar 49 reinforcement is leastdesirable for such applications as it burns vigorously in the T3 testingenvironment. The performance of unfilled truss structures and of 0.64 cm(1/4 in.) thick sandwich is not adequate. The skinned sandwich/PBI foamcore panels did not debond or delaminate under T3 test conditions andproved the most satisfactory concept for a number of reasons.

(1) The skinned sandwich panels are much simpler to fabricate andtherefore significantly less expensive than truss structure.

(2) Aircraft manufacturers are familiar with the procedures requiredfor the fabrication of such structure.jut LtLk £~UtL~1LLL UL b.UL DLLULUute

(3) Smooth, cosmetic surfaces can be readily achieved with theskinned foam panel concept. Such surfaces cannot be easilyproduced on truss structure panels.

(4) The skinned panels are far more familiar to aircraft manufac-turers and would probably be accepted and utilized much morereadily than would the unfamiliar truss structure panels.

(5) The truss structures show essentially no performance advantagesover the skinned foam panels.

The performance of the glass/PBI skin/PBI core structures was quitesuperior to that achieved with glass/Kerimid 601 skin/PBI core panels.A large advantage in smoke generation for the PBI matrix was observed, aswell as superior performance in T3 testing.

44

It is therefore recommended that the 181 E glass/PBI skin/PBI foamsandwich structure be selected for further development work aimed at theevaluation and production of highly fire resistant aircraft panels. Theconcept shows superb perfonmance, relatively low production costs, andmoderate material costs in volume. WRD believes it is highly probablethat the goal of a structure capable of protecting human life for at least10 minutes in a fuel fire condition can be achieved using the approachdeveloped in this work.

It is also recommended that more sophisticated, comprehensive mechanicalproperty testing be included as a vital part of any new effort in thisarea.

45

APPENDIX A

PROCEDURE FOR STITCHING TRUSS STRUCTURES

The procedure for the fabrication of the stitched truss structuresfor fire protection panels follows.

PREPREG PROCESSING FOR FIRE PROTECTION PANELS, 12 IN. x 12 IN. FINISH

DIMENSIONS

1. Cut two pieces prepreg, 14 in. x 17 in., 'A' and 'C'.

2. Cut one piece prepreg, 13 in. x 31 in., 'B'.

3. Scribe center line on all three pieces.

B' 13 x 31 in. L'A' and 'C' 14 x 17 in.

(2 pieces)

4. Place 'B' over 'A' and match center lines, and arrange so that approxi-

mately 0.5 in. of 'A' extends beyond each edge of 'B'. Staple in

place and stitch the two pieces together, being sure the stitching

line is straight and I to the long sides of prepreg. Tie each end of

threads and remove staples

'A'

'B'stitching

47receding page blank47.

5. Fold back one side of 'A' to expose seam. Place form tool on material

against seam and scribe a line along opposite edge of form tool.

6. Scribe a line approximately midway between the seam line and the line

scribed in Step 5.

7. Place the stitched assembly over 'C' and line up the center line of

'C' with the line scribed in Step 6. Each edge of 'C' should extend

beyond edges of 'B'.

8. In this position staple 'C' to 'B' and stitch together along line on

'B' in Step 5. Tie each end of threads and remove staples.

stitch line 'B' to 'A'

'A' . stitch line 'B' to 'C'

'A'

Sof 'C'

These two seams now form one side of triangular cell.

9. Lay out assembly on flat surface with 'C' down flat on surface.

10. Fold back both sides of 'A' and the seam 'B' to 'A' so that the seam

'B' to 'C' is exposed.

11. Place one edge of form tool against the exposed seam and scribe on

'C' along the opposite flat side of form tool.

12. Keeping unit in same position, drop 'B' over 'C', and keep piece 'A'

folded so that the seam 'B' to 'A' is exposed.

13. Place one edge of form tool against this exposed seam and scribe on

'B' a line along the opposite flat side of form tool.

14. Line up these two scribe lines (Steps 11 and 13) and staple into

place.

15. Stitch along this line. This stitch completes all three sides for the

initial cell.

48

16. Before tying the thread ends, be sure form tool will fit through the

cell. If not, remove last 'set of stitches and adjust stitching lineto accommodate form tool. Tie ends of thread, and remove staples.

of 'A'

7'B'

NOTES:

It must be borne in mind that Steps 4 through 16 are critical. The

straightness of the seams and the parallelism of the seams 'B' to 'C'set the pattern for the entire assembly.

To continue the stitching process, the unit is laid out next with 'A'

side down and scribe lines made on 'A' and 'BI, next on 'B' and 'C',etc.

Each time a cell is completed, the form tool fitting should be checked

before tying the thread ends.

Periodical measurements should be taken to assure uniform distancesbetween seams. If these distances vary greatly, wrinkling and/or

stretching will occur when completed assembly is cured.

49

APPENDIX B

TESTING OF FOAM COMPOSITE STRUCTURES

C O R P 0 R A T 1 0 N

TO: Milan Maximovich DATE: 25 July 1974

LOCATION: SDE-74-67

FROM: K. R. Berg

LOCATION:

SUBJECT: Testing Foam-Composite StructureHJO 4521-001

Flexural tests were conducted on the finished panels using a

3"x8" specimen. The standard test method that is called out

for honeycomb structure (flexural testing) is a four pointloading beam test. The test apparatus consisted of a flexural

- fixture having a lower support span of 6" and a load nose span

of 2". The specimen was loaded with 3/4" wide pads at all of

the contact points.

The test proved to be unsatisfactory due to the geometry of the

internal structure. Early skin buckling occurred due to the cell

size, and crushing occurred at the load points.

As a result of this test a modification was made to the upper load

nose. The 2" span was replaced with a 3"x3" load pad, still using

the 6" span for the lower support. This improved the situation to

a certain degree as it enabled the load to be applied over

approximately three of the triangular structures. Even with this

modification, it is concluded that a structure of this configuration

should not'be tested in this manner. A comparison based on this test

with results obtained from honeycomb structures tested in accordance

with the standard test method is not therefore recommended.

WRD would recommend an alternate test. A test apparatus would be

built that would accor.modate this type of structure and which could

be used on honeycomb structure of an equivalent nature. This would

allow comparison between the two structures and provide reliable data

on the foam-composite structure.

The test apparatus (see Figure 1) would consist of a rigid (1" alum.)

mounting plate which would be covered with a rubber diaphragm, The

test panel would be mounted on the rubber diaphragm and secured around

the edges. Air pressure would then be applied to the opposite side

of the diaphragm causing the specimen to be loaded uniformly over a

large area. The load would be transferred uniformly from the skin

surface into the internal structure allowing it be loaded structurally

similar to typical applications. This would result in reliable data.

Deflection measurements would be taken as the air pressure was

increased giving a direct relationship between load and deflection.

The ultimate failure load of the panel would also be determined.

K. R. Berg

50 ORIGINAL PAGE IS

OF POOR QUALYT

CROSS SECTION VIEW

DEFLECTORSPANEL AREA

S12.0 x 12.0.

RUBBER DIAPHRAGM .ALUIIINUM BASE PLATE

FIGURE 1. PANEL TEST METHOD.

,APPENDIX C

WHITTAKER RESEARCH AND DEVELOPMENT PRELIMINARY PROCESS SPECIFICATION,FABRICATING COMPOSITE SANDWICHES WITH PBI

SYNTACTIC FOAM CORE AND PBI/GLASS SKINS

SPECIFICATION

PROCESS -PRELIMINARYTYPE:

SPECIFICATION NO. :2013

TITLE: FABRICATING COM-MOSITE SA,'DWICHES WITH PBI

SYNTACTIC FOAM CORE AND PBI/GLASS SKINS

PREPARED BY: R. REED CHECKED BY:.Prograr i ina i ',

APPROVED BY: B. L. DUFT APPROVED BY:

Manager Engineering

APPROVED BY:

REVISIONS

LTR DATE PAGE LTR DATE PAGE LTR DATE . PACE

52 ORIGINAL PAGE TSOiF "-POC. ,UA,-r

SPECIFICATION NO. 2013

PAGE I OF 7

REVISION Original

1.0 SCOPE

1.1 The objective of this specification is to establish the generalprocessing requirements for fabricating composite sandwichesutilizing PBI syntactic foam core and PDI/glass skins.

1.2 This specification is applicable to all work accomplished by WhittakerResearch & Development and any and all sub-contractors thereof un-less specifically stated otherwise. This specification establishesthe-minimum requirements for utilizing the subject materials and noeffort has been made to detail specific "hardware" requirements.

2.0 APPLICABLE DOCUMENTS

2.1 Mil-Specifications

2.2 NRD Specifications

2.2.1 NRD 2004, Barrier Material for Imidite Laminates

2.2.2 NRD 1004, Imidite 1850 Acceptance Specification

2.3 Commercial Specifications

2.4 Other

3.0 MATERIALS

3.1 Imidite foam compound SA & PC

3.2 Imidite 1850

3.3 TFE 30/112 barrier material

3.4 Miscellaneous materials

3.4.1 Release agents

3.4.2 Bagging materials

53

SPECIFICATION NO. 2013

PAGE 2 OF 7

REVISION

4.0 EQUIPNMNT

4.1. Oven capable of operation at 850°F

4.2 Vacuum pump

4.3 Heated platen press - 6500F (optional)

4.4 Autoclave (optional)

5.0 QUALITY ASSURANCE

5.1 All materials shall be qualified for shop use per the applicableacceptance specification.

5.2 The following sections of the Narmco Quality Assurance manual areapplicable:

QAM 61.3361.3561.4461.5261.54

6.0 GENERAL

6.1 Safety

6.1.1 There are no special safety requirements applicable tothis specification.

6.2 Storage

6.2.1 All raw materials shall be stored in their originalcontainers and shall be protected from contamination.

6.2.2 All applicable materials shall be stored at roomtemperature.

54

2013SPECIFICATION NO.

PAGE 3 OF 7

REVISION

7.0 PROCEDURE

7.1 Preforming

7.1.1 Prepare a suitable flat preform mold to contain the PBI.syntactic foam powder. The flat molds can be of anysuitable material such as aluminum, plastic (epoxy, etc.)plaster or wood.

7.1.2 Place a film of suitable release material (PVA, cellophane,FEP) in bottom of mold.

7.1.3 Charge mold with calculated weight (density x volume x 1.15= weight of foam powder) of foam powder. Screed level andcover with release film.

7.1.4 The charged mold can then be either vacuum bagged for ovencure or placed in a heated platen press for the followingcure:

7.1.4.1 Raise temperature uniformily to 250 0 ± 10F(foam temperature) and apply 15 psig (28 in-hg).Hold at temperature for 30 ' 5 minutes. Coolto 1500 F or less under pressure before removingfrom mold.

7.2 Preform contouring

7.2.1 If the shape of the finished article is other than flatwith uniform thickness then a contouring operation must beaccomplished.

7.2.2 The foam preform sheets can be contoured by any of severalmethods - depending upon shape and facilities available.

7.2.3 Place the preformed sheet in either a 300OF ± 10*F ovenor between the platens of a press regulated at 3000F ± 100FHold 10 minutes or until preform softens. Remove preformand drape over a heated mandrel or form into cavity asrequired.

NOTE: This operation may be accomplished utilizingmatched tooling.

55

SPECIFICATION NO. 2013

PAGE 4 OF 7

REVISION

7.2.4 Vacuum bag shaped preforms to tool utilizing a 4000 F

service bagging material such as Capran(R)80, a high

temperature nylon, or other suitable material. Pull

minimum (1/2 - 1 in.Hg) vacuum only to seat bag. Insert

mandrel in oven regulated at -350'F ± 10 0F and allow

mandrel and foam to stabilize at oven temperature. Pull

maximum vacuum to conform foam to mandrel shape and allow

to cool to 1500F or less under maximum vacuum. Remove

foam from mandrel.

7.2,5 Note: The mandrel or tool should be covered with a suitable

release agent or film. Typical of these are:

7.2.5.1 Release agents

TFE 30 - sintered to tool

Vydax - sintered to tool

Frecote

7.2.5.2 Films

3M's TB5 Glass/TFEFEP

Capran 80

7.3 Inner Skin Layup

7.3.1 Tool.preparation

7.3.1.1 Tool should be cleaned with steel wool and

solvent.

7.3.1.2 Coat tool with silicone resin DC 20 or equivalent

and bake per manufacturer's recommendations. Re-

move excess silicone by abrading with fine steel

wool.

7.3.1.3 Coat the tool surface with a release agent such

as TFE 30, Vydax or Frecote. Note: TFE 30

must be sintered into a continuous film by heating

the tool surface to 800 0 F. This can be accomplished

by utilizing a propane torch.

56

SPECIFICATION NO. 2013

PAGE 5. OF 7

REVISION

7.3.2 Cut the required number of Imidite 1850 prepreg plies perdrawing - note warp direction.

7.3.3 Utilize heat guns and irons regulated to 500 0F ± 200 F(approx.) and heat tack prepreg to tool or mandrel.

7.3.4 Cover prepreg with 1 ply of perforated cellophane and i - 3

plies of glass breather. Bag with PVA or similar material.

7.3.5 Pull maximum vacuum and place in an oven. Raise temperatureto 300 0F,2 - 3°F per min. Reduce temperature as soon as300'F is reached. Allow to cool to room temperature undermaximum vacuum.

7.3.6 Remove bag, breather and cellophane and lightly sand to

remove resin rich spots.

7.4 Inner Skin-Foam Sub-Assembly

7.4.1 Prefit foam core sections to inner skin. Interference buttjoints should be made if possible. If excessive gaps doexist an adhesive tape (Imidite 2801 on 112/112 scrim) shouldbe interposed at the foam core butt joints.

7.4.2 Cover the layup with 2 plies TFE 30/112 barrier material and3 - 4 plies of 1500 type glass breather.

7.4.3 Vacuum bag with 5 mil thick soft aluminum foil utilizingDow-Corning silicone sealant 93-046 and primer QA-2-1011

as required to form and/or seal the bag.

7.4.4 Place in an oven and draw maximum vacuum. Cure to thefollowing schedule:

a. Utilize a uniform heating rate of I - 3±F/min.

b. Raise temperature to 650 - 700'F.

c. Hold @ 650 - 700*F for 120 ± 10 min.

d. Cool under vacuum to 150'F or less.

7.4.5 Remove bag, breather and barrier.

57

SPECIFICATION NO. 2013

PAGE 6 OF 7

REVISION

7.5 Machining

7.5.1 The skin-core sub-assembly can be machined to the desiredphysical configuration by conventional means such assanding, grinding and routing.

7.6 Outer Skin Layup

7.6.1 Repeat steps 7.3.2 and 7.3.3 except the material is tackedto the c6re.

7.6.2 Cover layup with 2 plies TFE 30/112 barrier material and

3 - 4 plies of 1500 type glass breather.

7.6.3 Bag per 7.4.3

7.6.4 Cure per 7.4.4

7.6.5 Remove bag, breather and barrier and remove part from tool.

7.7 Postcure

7.7.1 Post curing to be accomplished in an inert atmosphere suchas nitrogen or argon.

7.7.2 Place the part in a suitable chamber - one that will maintainan inert gaseous envelope around the part and postcure as

fol 0ow1s:

a. Utilize a 1/2 - 10F/min heating rate.

b. Raise temperature to 400 0F and hold 2 hours.

c. Raise temperature to 500F and hold 2 hours.

d. Raise temperature to 600'F and hold 2 hours.

e. Raise temperature to 650'F and hole 2 hours.

f. Raise temperature to 700 0F and hold 24 hours.

58

SPECIFICATION NO. 2013

PAGE 7 OF 7

REVISION

7.7.2 (cont'd)

g. Raise temperature to 750'F and hold 24 hours.

h. Raise temperature to 8000F and hold 8 hours.

i. Raise temperature to 850 °F and hold 8 hours.

j. Cool under inert atmosphere to 4000 F or less.

7.8 -Part Finish

7.8.1 For certain application it may be found advantageous toseal the part against moisture absorbtion and to enhanceits high temperature oxidation stability. Dow-CorningDC-7146 silicone resin has been found excellent for thispurpose.

7.9 Process Variations

7.9.1 The processes described herein are general in nature andshould not be construed as the only acceptable ones.

7.9.2 Typical variations to the processes described herein andknown to produce good quality composites are:

7.9.2.1 The foam core sections may require a completecure (to 600 0 F) and postcure (to 850'F) afterforming to shape to eliminate shrinkage priorto prefitting.

7.9.2.2 Preformed core may be cured directly to pre-viously cured PBI/glass skins and effect agood bond.

7.9.2.3 PBI glass prepreg may be cured directly to pre-viously cured and postcured foam core and effecta good bond.

7.9.2.4 The skin-core bonding-cure cycles may requirepressures in excess of that obtainable with avacuum bag type cure. This is generally depen-dent upon skin thickness, profit accuracy andgeneral complexity of the layup. Maximumvacuum and 15-20 PSIC autoclave pressure hasbeen adequate for assemblies fabricated to date.

59