NASA/TM-1998-208742

Room Temperature and Elevated

Temperature Composite Sandwich

Joint Testing

Sandra P. Walker

Langley Research Center, Hampton, Virginia

National Aeronautics and

Space Administration

Langley Research Center

Hampton, Virginia 23681-2199

November 1998

https://ntrs.nasa.gov/search.jsp?R=19990004379 2018-05-11T16:55:11+00:00Z
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Abstract

Testing of composite sandwich joint elements has been completed

to verify the strength capacity of joints designed to carry specified

running loads representative of a high speed civil transport wing.

Static tension testing at both room and an elevated temperature of

350°F and fatigue testing at room temperature were conducted to

determine strength capacity, fatigue life, and failure modes. Static

tension test results yielded failure loads above the design loads for the

room temperature tests, confirming the ability of the joint concepts

tested to carry their design loads. However, strength reductions as

large as 30% were observed at the elevated test temperature, where all

failure loads were below the room temperature design loads for the

specific joint designs tested. Fatigue testing resulted in lower than

predicted fatigue lives.

Introduction

Polymer matrix composite (PMC) bolted sandwich joints have been designed to transfer running

axial tension loads between wing panels at specific load levels as part of the High Speed Research

(HSR) Program. A single-row bolted sandwich joint was designed with the objective of transferring

5000 lb/in, and a multi-row bolted sandwich joint was designed to transfer 20,000 lb/in. The

objective of the tension testing was to verify the failure mode and load levels achievable from the

joint designs. Also, tension testing at 350°F was performed to evaluate the joint performances at the

elevated operating temperature representative of the Mach 2.4 cruise condition. All composite

facesheets were fabricated using the IM7/PETI-5 composite material system (Ref 1). The single-row

specimens were constructed with 25-ply 0° dominate facesheets, a 0.5 inch thick titanium honeycomb

core, and a single row of three, 0.375 inch diameter fasteners, spaced 2. inches apart. The multi-row

specimens had 44-ply 0 ° dominate facesheets, a one inch thick titanium honeycomb core, and three

rows of fasteners with three fasteners per row. The inner row of fasteners were 0.4375 inch in

diameter, the center row fasteners were 0.375 inch in diameter, and the outer row fasteners were

0.3175 inch in diameter, and all fasteners were spaced 2.25 inches apart.

The multi-row bolted sandwich joint specimens were tested in two splice joint configurations. A

composite honeycomb sandwich was joined with a similar composite honeycomb sandwich

configuration (PMC to PMC joint), and was also joined with a Titanium joint component

manufactured using the 4-sheet superplastically-formed diffusion-bonded process (SPF/DB)

developed by McDonnell Douglas Corporation. The latter joint specimen is designated as the PMC

to SPF/DB joint. A sketch of the PMC to PMC joint configuration is displayed in Figures 13 and a

sketch of the PMC to SPF/DB joint configuration is displayed in Figure 14. Both specimen

configurations were joined in a double shear design with titanium splice plates. The performance of

the PMC joint could then be evaluated for two splice joint applications.

The test objectives also include verifying the fatigue strength of the multi-row bolted joint

specimens. A summary of the number of composite sandwich joint specimens for each test condition
is presentedin Table 1.

Table 1. Composite Joint Test Specimens

Test Conditions

Room temperature

Static tension

Single-row Joint

1

Multi-row Joint

PMC to PMC PMC to SPF/DB

350°F Static tension 2 1 1

Room 0 1 ltemperature

Fatigue (R=-0.1)

All testing was conducted in the Thermal Structures Lab at NASA Langley Research Center. The

composite test specimens were designed and fabricated at Northrop-Grumman Corporation. The

SPF/DB specimen component was designed and fabricated at McDonnell Douglas Corporation.

Single-row Joint

The single-row joint test specimens were fabricated to be 6.0 inches wide and hence were designed

to transfer 30,000 lbs applied tensile load across the joint! Three single-row joint specimens were

tested to failure in tension. Specimen 1 was tested at room temperature and Specimen 2 and 3 were

tested at 350°F.

The room temperature specimen was tension tested using hydraulic grips in a 220 kip test

machine. A photograph of the specimen mounted in the test machine is shown in Figure 1. The load

was applied to the end grip tabs of the joint specimen through the hydraulic grips using a grip

pressure of 5500 psi. The test machine was set in stroke control and a displacement rate of 0.01

in/rain was used to apply the load to the joint specimen. The applied load versus ram displacement is

plotted in Figure 2. The first indication of initial damage was observed at 31 kips, where a 10%

reduction in the load was recorded and a cracking noise was heard. Subsequently, loading of the

joint continued until an ultimate load of 40 kips was ob:ained. At the ultimate load, a 10 kip

reduction in the load was observed, and the test was stopped. Since the first load reduction was less

than 20%, which was considered in this test to indicate ultimate failure, the load of 40 kips was

considered the ultimate failure load. The measured back-to-back strains from strain gauges, SG3 and

SG4, located at the center of the specimen, are plotted in Figt re 3 with the applied load. The location

of SG2, SG4, and SG6 can be observed in Figure 1, where SG1, SG3, and SG5 correspond to the

same locations on the opposite facesheet, respectively. The strains measured from SG1 and SG2 are

plotted in Figure 4 with the applied load. At the ultimate fa lure load of 40 kips, a maximum strain

of 2530 _tin./in. was measured at SG4 in the center of the soecimen and a minimum strain of 1944

lain./in, was measured at SG2. Examination of the specimen after testing to failure showed bearing

damage at all three bolt hole locations in the composite sandwich specimen. A photograph indicating

the bearing damage is given in Figure 5. Later inspection of the specimen also revealed a confined

area of delamination in the composite laminate, in the neck d-?wn region to the grip end.
Theelevatedtemperaturespecimensweremodifiedto allowfor a pinnedconnectionto introduce

theloadanduseof anexistingovenin the 110 kip testmachine. A one inch diameterhole was

drilledin thecenteronthe compositegrip endtabanda 1.25inch diameterholewasdrilled in the

metallicgrip endtabto allowfor thepin connectionsoneachspecimen.Theovenenclosedboththe

specimenandfixturing asshownin Figure6. Prior to heatingthe specimenin the oven,coupon

samplesof thefiberglassmaterialthatwasbondedto thecompositegrip endswereheatedin anoven

to 350°F.Thefiberglassis usedto protectthecompositefromdamagewhenhydraulicgripsareused

andtherewereconcernsthatthefiberglassmaterialmightburn at thistesttemperature.No material

changeswereobservedwhenthefiberglasscouponswereheatednor whenthejoint specimenswith

the fiberglasstabsbonded to the compositematerialwere heated. Eight thermocoupleswere

mountedon the compositespecimen,four on eachfacesheet.The specimenswere heatedto

approximately350°Fwhile thetestmachinemaintaineda load of approximately200 lbs on the

specimens.Temperaturevariationswereminimalandall temperaturemeasurementsrangedbetween

348°Fand354°Fonthespecimenthroughoutthedurationof thetest. Whenthedesiredtemperatures

werereached,the specimenwasloadedusing a displacementrate of 0.01 in/min. The loaddisplacementdiagramandstrainmeasurementsaregivenin Figures7-9 for Specimen2 andFigures

10-12for Specimen3. Of thetwospecimenstestedat 350°F,Specimen2 failedat anultimateloadof

26kipsandSpecimen3 failedat 24kips. Unliketheroomtemperaturespecimentested,theelevated

temperaturetestsreachedanultimatefailureloadwithoutanyprior load reductions. The ultimate

strainmeasurementsrangedfrom 1641_tin./in.at thecentergaugeSG4to 1354_tin./in.atgaugeSG1

for Specimen2 andfrom 1560_in./in.at thecentergaugeSG3to 1288_tin./in.atSG6for Specimen

3. Also,unlike the room temperaturetestwhereall threebolt hole locationsdisplayedbearing

damage,bothelevatedtemperaturespecimenshowedsignificantbearingdamageonly at thecenter

andonesideboltholewith almostnovisiblebearingdamageat thethird bolt holelocation. A nonuniformdistributionof the loadbetweenfastenerswouldpartiallyattributeto thestrengthreduction

for theelevatedtemperaturetestspecimens.

A summaryof the single row joint test results is presented in Table 2. With an increase in test

temperature from room to 350°F, a 37% decrease in the specimen strength capacity was observed.

All single-row joint specimens tested failed in a bearing mode.

Table 2. Single-row Joint Tension Testing Summary

Joint

Specimen

Test Temperature (°F)

1 70

2 350 26

3 350 24

Failure Load

(kips)

40

Failure Mode

Bearinl_

Bearin_

Bearing

Multi-row Joint

The multi-row splice joint test specimens were fabricated to be 5.55 inches in width, 29.55 inches

in length, and were designed to transfer 111 kips of applied tensile loading. Three PMC to PMC

specimens and three PMC to SPF/DB specimens were fabricated where two of each configuration were
to be tested in static tension and the remaining two were to be tested in fatigue. A sketch of a PMC to

PMC joint specimen and a sketch of a PMC to SPF/DB specimen, including strain gauge locations, are

given in Figures 13 and 14, respectively. As can be observed in the figures, both joining components

were tapered down under the outer splice plate to provide a smooth aerodynamic surface between the

splice plate and joining components. On the inner (spar) side, the PMC to PMC specimen was

designed with a flat inner splice plate and the PMC to SPF/DB specimen had a tapered T-section inner

splice plate. The tapering splice plate design was included to provide a more uniform fastener load

distribution. A photograph of the two specimens is shown ia Figure 15 where a top view (outer wing

surface side) of a PMC to PMC specimen and a bottom view (wing spar side) of a PMC to SPF/DB

specimen are shown.

The PMC to PMC specimens were instrumented with 22 back-to-back strain gauges as shown in

Figure 13. On each side, five gauges were located across the center of the splice plates and three were

located on each composite sandwich about 1.5 inches from the edge of the splice plate. The PMC to

SPF/DB specimens had a total of 17 strain gauges as shown in Figure 14. On the outer splice plate,

five gauges were located across the center as on the PMC to PMC specimen. Three back-to-back

gauges were located on the PMC sandwich about 2 inches from the edge of the splice plate. On the

SPF/DB component, four gauges were located on the outer surface and two on the inner surface. The

two back-to-back gauges were located 0.4 inch from the edge of the splice plate and the other two

gauges on the outer surface were located about 2.5 inches from the splice plate.

Static Tension Testing

All four static tension tests were conducted using the same fixtures for connecting the test

specimen to the 220 kip test machine. A photograph of one of the PMC to SPF/DB specimens

mounted in the test machine is shown in Figure 16. The specimen fixtures were designed and

fabricated at NASA Langley Research Center. Two steel plates are attached on each end of the

specimen by five steel 0.5 inch diameter bolts. The steel plates are also attached to the test fixture

through a pin connection on each end as pointed out in Figure 16. Back-to-back horizontal knife

edge supports are used to prevent out-of-plane displacement along the centerline of the test specimen

while it is being loaded in tension. Without this constraint, there would be significant out-of-plane

motion under tensile loads due to eccentricities in the specimen as was revealed by a finite element

analysis of the test specimen. 1

The room temperature tests were conducted with the test machine set on stroke control with an

applied displacement rate of 0.04 in./min. The applied load and displacement were monitored during

testing and testing continued until ultimate failure occurred, which is defined here as a 20% decrease

in the applied load. The load-displacement graph for the PMC to PMC joint specimen tested at room

temperature is shown in Figure 17. As can be observed in Ihe figure, the load continued to increase

until ultimate failure at 137 kips applied load. A gradual de crease in the slope near failure indicates

plastic behavior prior to ultimate failure. Ultimate failure appeared to be a consequence of shearing

1 Finite element analysis was performed by Young Kwon at Lockheed Georgia.

4
off of the fastener head. A photograph of the failed specimen is given in Figure 18. During loading,

an audible "crack" was identified at 61 kips and splice plate bending induced by fastener bending

became visible at 120 kips applied load. Examination of the failed specimen after removing the

splice plates showed significant beating damage in the composite sandwich. Back-to-back strains

measured at the center of the specimen splice plates are shown in Figure 19. The back-to-back strain

gauges SG17 and SG18 were at the center and SGI3 and SG22 were closest to the edge as indicated

in Figure 13. The maximum strain measured at failure was 14,174 p.in./in, at SGI7 in the center.

However, the strain measured at SG17 was suspiciously higher than the surrounding strain gauges,

raising the issue that SG17 may be defective. The next largest strain next to SG17 was 8871 _tin./in.

measured by SG15 where SG19 on the other side of SG17 measured 8823 Ixin./in. Back-to-back

strains measured on the composite are shown in Figure 20. The minimum strain measured was 4277

btin./in, by SG6 on the composite. The load-displacement graph for the PMC to SPF/DB specimen

tested at room temperature is shown in Figure 21 and a photograph of the failed specimen is shown

in Figure 22. An ultimate load of 123 kips was observed and the ultimate failure appeared to be due

to a tension failure of the inner splice plate along the outer row of fasteners. Bending of both splice

plates was apparent in the failed specimen as can be observed in Figure 22. Examination of the failed

specimen after removing the splice plates revealed no visible sign of beating damage in the PMC to

SPF/DB specimen. During loading, at 70 kips an audible "crack' was heard and as with the PMC to

PMC specimen, outer splice plate bending was also observed at 92 kips applied load. Measured

strains are plotted as a function of applied load in Figures 23-25. Figure 23 shows the measured

strains on the center of the upper splice plate (SG3 was at the center and SG1 and SG5 were the outer

most strain gauges as can be seen in the sketch in Figure 14). Figure 24 shows strains measured on

the SPF/DB component and Figure 25 shows strains measured on the PMC sandwich component. At

approximately 70 kips applied load, the load where the audible "crack" was heard, Figure 25 reveals

an almost instantaneous drop in the strains on one PMC facesheet with a corresponding instantaneous

increase in the strains on the opposing facesheet. The cause for this behavior is uncertain, but it

could possibly be attributed to a very localized failure of the inner PMC facesheet which caused the

outer facesheet to accept a localized instantaneous increase in load and consequently strain. As also

revealed in Figure 25, the subsequent instantaneous strain increase in the inner facesheet at

approximately 114 kips is also uncertain, but it may be due to another localized failure resulting in

instantaneous redistribution of the load.

For the elevated temperature tests, a Thermatron heater was used to blow hot air through a duct

and into an oven that was built to enclose the specimen. The oven box along with a specimen

mounted in the test fixture can be seen in Figure 16. The specimens were heated while the test

machine maintained a preset load of approximately 100 lbs. Six back-to-back thermocouples were

located on the specimen and monitored during heating until a nearly uniform temperature of 350°F

was reached. Once acceptable temperatures were achieved, load was applied to the specimens at the

displacement rate of 0.04 in./min. During the application of the load to the specimens, the

temperatures ranged from 342°F to 352°F on the PMC to PMC joint specimen and from 344°F to

350°F on the SPF/DB to PMC joint specimen. The load-displacement diagram for the PMC to PMC

specimen tested at 350°F is given in Figure 26. After an ultimate load of 110 kips was achieved, a

25% increase in the displacement was observed as the load slightly dropped. The specimen was then

considered failed and the applied load was removed. Examination of the specimen after testing

revealed a slight bending in the splice plates, apparently due to fastener bending. Removal of the

splice plates showed significant beating damage in the composite sandwich as can be viewed in Figure
27. The load-displacement diagram for the PMC to SPF/DI3 joint specimen tested at 350°F is given in

Figure 28. An ultimate toad of 105 kips was achieved before the inner splice plate experienced a

tension failure at the outer row of fasteners as shown in Figure 29. The appearance of the failed

specimen was very similar to the room temperature specimen which also experienced a tension failure

of the inner splice plate. After removal of the splice plate, examination of the specimen tested at

350°F showed severe bearing damage in the composite sandwich.

A summary of all the multi-row joint test specimen failare loads is given in Table 3. One can

conclude that the PMC to PMC joint has a slightly greater, 10% at room temperature and 5% at

350°F, strength capacity than the PMC to SPF/DB joint. A strength reduction of approximately 15-

20% can also be expected for each specimen type at the elevated operating temperature of 350°F.

Table 3. Multi-row Joint Static Test Specimen Failure Loads

Test

Temperature

(°F)

Failure

PMC to PMC

Lc,ad (kips)

PMC to SPF/DB

70 137 123

350 110 105

Fatigue Testing

The fatigue tests were conducted in the same 220 kip test machine as the static tests. A

photograph of the PMC to PMC joint specimen mounted in the test machine is shown in Figure 30.

The fixture connecting the specimen to the test machine is smwn in the figure. It consisted of backto-back steel splice plates connected to another steel end fitting in a multifastener arrangement on

each end of the specimen. This differs from the static test fixture where a pin connection was

utilized. A 50 ft-lb torque was applied to each fastener used in the fixture to prevent slipping at the

fixture connection.

The test machine was set in load control to cycle betwec n 33,800 lb in tension and 6760 lb in

compression. This was equivalent to an R = -0.2, where R is the ratio of minimum applied load to

maximum applied load, with the peak load set at approximately 30% of the maximum static design

load. The majority of the cycling was conducted at one H,_, which was the maximum cycling rate

capability of the test machine. At approximately every 5000 cycles, the test machine cycling was

slowed to 0.01 Hz for five cycles to record test data at twice a second.

6
Both joint specimens tested failed in the same mode, with a transverse crack in the upper splice

plate occurring across the inner row of fasteners. The PMC to PMC joint specimen failure occurred

at approximately 42,000 cycles and the PMC to SPF/DB joint specimen failed at approximately

31,560 cycles. The splice plate crack was on the PMC side of the joint of the PMC to SPF/DB

specimen. During testing of the PMC to PMC specimen, out-of-plane bending of the top splice plate

was observed where the outer edges were observed to curve out away from the joint. There was also

an audible "crackling" sound present throughout the duration of the test. Load versus displacement

data are plotted in Figure 31. Shown is the load versus displacement test data during the first five

cycles that were recorded and the last five cycles that were recorded prior to failure. At failure, which

occurred at approximately 42,000 cycles, a change in slope in the load-displacement real time plot

was observed with a progressively decreasing slope for several cycles prior to stopping the test. Load

versus displacement test data for the PMC to SPF/DB joint specimen is shown in Figure 32. Once

again, the load and displacement test data during the first set of five cycles that was recorded and the

last set of five cycles that was recorded prior to failure is displayed. During testing of the PMC to

SPF/DB joint specimen, the doubler that was adhesively bonded on the bottom side of the SPF/DB

component at the location of the taper on the top side of the component, became disbonded from the

specimen and fell off the specimen at approximately 15,000 cycles. Overall out-of-plane bending

motion of the specimen was also more pronounced during cycling than that observed with the PMC

to PMC joint specimen. The lower fatigue life for the PMC to SPF/DB joint specimen might be

attributable to the increased bending motion. Unfortunately, both fatigue tests resulted in fatigue

lives much shorter than the 100,000 cycles predicted for the joint. Removal of the splice plates after

testing revealed no visible damage to the joint components in either fatigue specimen. A summary of

fatigue test results are shown in Table 4.

Table 4. Multi-row Joint Fatigue Test Summary

Fatisue Life, N

First 5 Cycles Recorded

Last 5 Cycles Recorded

PMC to PMC PMC to SPF/DB

42,335 31,568

1541-1545 i-5

41541-41545 30001-30005

Concluding Remarks

Composite sandwich splice joint element testing to verify the strength and fatigue life of the

specimen designs has been completed. Both single-row composite honeycomb sandwich and multirow composite honeycomb sandwich splice joint specimens were tested at both room temperature and

an elevated operating temperature of 350°F.

For the single-row joint specimens tested, the room temperature test failure load exceeded the

design ultimate load, however, the elevated temperature tests resulted in failure loads below the room

temperature design load. All specimens failed in a bearing mode with an approximately 30%

reduction in strength capacity at the elevated operating temperature of 350°F.

7
Similarly with the multi-row composite honeycomb sandwich splice joints tested statically, the

room temperature test failure loads exceeded the design ultimate load, and the elevated temperature

test failure loads were slightly lower than the room temperature design load. For the PMC to PMC

joint specimens tested, the room temperature ultimate failure mode was due to fastener head shear

off. At the elevated test temperature, a 20% reduction in the strength capacity and a change in the

failure mode due to bearing damage was observed. However, bearing damage was observed in both

specimens tested. For the PMC to SPF/DB splice joint tested, both the room and elevated temperature

tests exhibited the same ultimate failure mode where an inner splice plate tension failure occurred at

the outer row of fasteners. A 15% reduction in strength was observed for the elevated temperature

test. Although there was no bearing damage observed for the room temperature specimen, significant

bearing damage was present in the elevated temperature PMC to SPF/DB test specimen.

Fatigue testing at a maximum tensile load of 33.8 kips with an R=-0.2 of the multi-row joint

specimens resulted in a fatigue life of 42,000 cycles for the PMC to PMC joint specimen and a

fatigue life of 31,500 cycles for the PMC to SPF/DB joint specimen tested. Both specimens failed due

to a tension crack at the inner row of fasteners on the outer splice plate. The fatigue lives achieved

for these tests were lower than the predicted fatigue life of 100,000 cycles.

References

1. Hou, T.H.; Jensen, D.J.; and Hergenrother, P.M.: Processing and Properties of IM7/PETI composites. Journal

of Composite Materials, Vol. 30, Issue 1, January 1996, p.109-12.
Figure 1. Single-row joint specimen mounted in test machine using hydraulic grips for the room

temperature test.

50000

40000

30000

Load, lbs

20000

10000

0

O.Oi

F

I I I I I

0.02 0.04 0.06 0.08 0.10

Displacement, in.

Figure 2. Load versus displacement for the room temperature single-row joint test.
50000 _

Figure 3.

40000

30OOO

Load, Ibs

20OO0

100OO

SG3

--- SG4

iP_ _'

I I I LI I

0 500 1000 1500 2000 2500

Strain, pin/in

I

30OO

Back-to-back measured strains at the center of the room temperature joint specimen.

50000 I

40000 t_

3OOO0

Load, Ibs

20000

1000O

SG1

--- SG2

J.t

r # I

r

I 1 I I I I

0 500 1000 1500 2000 2500 3000

Strain, pin/in

Figure 4. Measured strains from strain gauges SG1 and SG2 of the room temperature joint

specimen.

10
Bearing damage

Figure 5. Single-row joint Specimen 1 after testing to failure.

11
Figure6.Single-rowjoint specimenmountedin testmachinefor elevatedtemperaturetesting.

30000

2O00(

Load, Ibs

15000

10000

5000

0 I I I

0.00 0.02 0.04 0.06 0.08 0.10

Displacement, in.

Figure 7. Load versus displacement for Specimen 2 tested at 350°F.

12
30000 -

Figure 8.

25000

20000

Load, lbs

15000

10000

5000

_ __-7_sG3 /y

o I I I I

0 500 1000 1500 2000

Strain, p.in/in

Back-to-back measured strains at the center of Specimen 2 tested at 350°F.

30000 _

Figure 9.

SG1

)

25000 - - -- SG2 _Sr_

20000 - _J

Load, Ibs

15OO0

10000

5000

I I I I

0 500 1000 1500 2000

Strain, _in/in

Measured strains from strain gauges SG 1and SG2 on Specimen 2 tested at 350°F.

13
30000 I

25000 I"

20000

Load, Ibs

15000

1OOOO

5000

0 I I I

0.00 0.02 0.04 0.06 0.08

Displacement, in.

I

0.10

Figure 10. Load versus displacement for Specimen 3 tested at 350°F.

30000 -

25000

20000

Load, lbs

15000

10000

5OO0

r #r

_ /

i J

/

0 I I I I

0 500 1000 1500 2000

Strain, lainhn

Figure 11. Back-to-back measured strains at the center of Specimen 3 tested at 350°F.

14
30000

25000

20000

Load, Ibs

15000

1OOO0

5000

-- SG1

I I I I

0 500 10O0 1500 2000

Strain, pin/in

Figure 12. Measured strains from strain gauges SG 1 and SG6 on Specimen 3 tested at 350°F.

,4 29.55 in. _"

u !

0 0 0 " 0 0 0 j 0

_13 1- i 0

-e -e -e ql-C_ e .... _ r---ell

Inner

0 0 "12

0 "10!

0 0 "8

AT

f 5.55 in.

Figure 13.

if 2 m

II

0 0 0 ;1 0 0 0 0

6" 0

0 0 0 2_3 0 0 0 4- 0

4_5 0

o o o ,,; o o o o

II

Outer

Schematic drawing of PMC to PMC multi-row joint specimen including strain gauge

locations.

15
= 29.55 in.

......... ........ li' ._,' .........,,:il---:I--l--- Of"l'_---IT---Ir--_lO,'' 0 " Ol ]l 0 r I 0 I ..15 J! O0

A I : ..,3 O' O, 0 0 0 0 "16 1

............... __, , , ___<,__'__ __-

Inner

AT

f 5.55 in.

SPF/DB

i

S PMC

A-A

......... i .... , .... t---.--t---;: r

I -6: -8: o, o, o,, o o o 10 - I o

I I II

"7' "9 '---'- ,_ ,_.... _ , , 2- o

,

, k .... ,_....... o,o,o. o , _---, @5 o o o o

' ' ' O' ©' 0" 0 0 0 0

I I I I -- I -- II

J- - - -L -----J-- - -- 41

Outer

Figure 14. Schematic drawing of PMC to SPF/DB multi-row joint specimen including strain

gauge locations.

16
PMC

Honeycomb

PMC

Sandwich

Titanium

Splice

Plate

Titanium

Splice

Plate

PMC

Honeycom

Sandwich

Titanium

SPF/DB

Figure 15. Multi-row joint test specimens.

17
/- Pin Connection

Steel Plate

Oven

Knife Edge

Supports

PMC to SPF/DB

Test Specimen

Figure 16. Multi-row joint static tension testing configuration.

18
140000 12-- F

80000p /

L°a° "s/ /

°°°_I //

4oo_ I

20001 _ I I I I

0.0 0.1 0.2 0.3 0.4

Displacement, in.

I

0,5

Figure 17. Load versus displacement of the PMC to PMC joint specimen tested at room

temperature.

Figure 18. Failed PMC to PMC joint specimen tested at room temperature.

19
140000 --

120000 --

100000 -

80000 -

Load, lbs

60000

40000_

20000

o I

0 2000 4000

_SG17

.... SG18

.... SG13

---- SG22

I I I I I I

6000 8000 10000 12000 14000 16000

Strain, _n/in

Figure 19. Strains measured at the center of the splice plate for the PMC to PMC joint specimen

tested at room temperature.

20
140000 --

120000 -

100000 -

80000 -

Load, Ibs

60000 -

40000 -

20000 F,:i

0

0

SG3

.... SG4

.... SG1

--- SG6

I I I I I I

6000 8000 10000 12000 14000 16000

Strain, pin/in

Figure 20. Strains measured on the composite sandwich for the PMC to PMC specimen tested at

room temperature.

21
140000 -

120000

100000

80OOO

Load, Ibs

60000

40000

20000

0

0.0

I I I I I

0.1 0.2 0.3 0.4 0.5

Displacement, in.

Figure 21. Load versus displacement for the PMC to SPF/DB joint specimen tested at room

temperature.

Figure 22. Failed PMC to SPF/DB specimen tested at room temperature.

22
140000

120000

100000

800O0

Load, lbs

60000

40000

SG1

.... SG3

.... SG5

20000

Figure 23.

0 I I I

0 2000 4000 6000 8000

Strain, lain/in

Strains measured at center of top splice plate for the PMC to SPF/DB joint specimen

tested at room temperature.

140000

Figure 24.

120000

100000

80000

Load, lbs

60000

40OO0

20000

SG7

.... SG9

.... SG14

0 1 I I

0 2000 4000 6000 8000

Strain, _n/in

Strains measured on the SPF/DB component for the PMC to SPF/DB joint specimen

tested at room temperature.

23
1_000 -

120000

100000

80000

Load, lbs

60000

40000

-- SG11

.... SG16

.... SG12

---- SG17

20000

Figure 25.

0 I I I I

0 2000 4000 6000 8000

Strain, pi_in

Strains measured on the PMC sandwich co_lponent for the PMC to SPF/DB joint

specimen tested at room ten_perature.

24
120000

100000

80000

Load, lbs

60000

40000

20000

B

0 I I I I I

0.0 0.1 0.2 0.3 0.4 0.5

Displacement, in.

Figure 26. Load versus displacement for the PMC to PMC joint specimen tested at 350°F.

Figure 27. PMC to PMC joint specimen after testing at 350°F and having the splice plates removed

for examination of the composite sandwich components.

25
120000

100000

80000

Load, Ibs

60000

40000

20000

0 I I I I I

0.0 0.1 0.2 0.3 0.4 0.5

Displacement, in.

Figure 28. Load versus displacement for the PMC to SPF/DB joint specimen tested at 350°F.

Figure 29. Failed PMC to SPF/DB joint specimen tested at 350°F.

26
Figure30.PMCtoPMCjoint specimenmountedin testmachineforfatiguetesting.

27
40000/I- .... cycles: 1541 - 1545

/

30000 I

201300 _

Load, Ibs /

-10000 / I I I I

-0.02 0.00 0.02 0.04 0,06

Displacement, in,

I

0.08

Figure 31. Load versus displacement test data for the PMC to PMC joint specimen tested under

cyclic loading.

40000-

30000-

20000 -

Load, Ibs

10000 -

0

-1000C

-0.02

.... cycles: 0 - 5

cycles: 30001-30005 /

S ,`p

irlt

/

I I I I I

0.00 0.02 0.04 0.06 0.08

Displacement, in.

Figure 32. Load versus displacement test data for the PMC to SPF/DB joint specimen tested under

cyclic loads.

28
I Form Approved REPORT DOCUMENTATION PAGE OMa_.o_*01_

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for rewewing instructions, searching existing data sources,

gethe_ng ar_. maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of informat_c_, =ndu¢l ng suggestions for reducing this burden, to Washington Headquarters Servces, Directorate for Information Operations end Reports, 1215 Jefferson

Daws H_ghway, SuRe 1204, Ad=ngton, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reducbon Proect 0704-0188), Washington, DC 20503.

1, AGENCY USE ONLY (Leave blank) 2. REPORT DATE

November 1998

4. TITLE AND SUBTITLE

Room Temperature and Elevated Temperature Composite

Sandwich Joint Testing 537-06-34-20

6. AUTHOR(S)

Sandra P. Walker

7. PERFORMINGORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

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

National Aeronautics and Space Administration

Washington, DC 20546-0001

11. SUPPLEMENTARY NOTES

3. REPORTTYPE AND DATES COVERED

Technicai Memorandum

5. FUNDING NUMBERS

8. PERFORMING ORGANIZATION

REPORT NUMBER

L-17746

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASAFFM-1998-208742

12a. D|SiH|BUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Unclassified-Unlimited

Subject Category 27 Distribution: Standard

Availability: NASA CASI (301) 621-0390

13. ABSTRACT (Maximum 200 words)

Testing of composite sandwich joint elements has been completed to verify the strength capacity of joints

designed to carry specified running loads representative of a high speed civil transport wing. Static tension

testing at both room and an elevated temperature of 350oF and fatigue testing at room temperature were

conducted to determine strength capacity, fatigue life, and failure modes. Static tension test results yielded failure

loads above the design loads for the room temperature tests, confirming the ability of the joint concepts tested to

carry their design loads. However, strength reductions as large as 30% were observed at the elevated test

temperature, where all failure loads were below the room temperature design loads for the specific joint designs

tested. Fatigue testing resulted in lower than predicted fatigue lives.

14. SUBJECT I_HMS

tension testing, room and elevated temperature, composite sandwich joint

17. SECURITY CLASSIFICATION

OF RB=ORT

Unclassified

NSN 7540-01-280-5500

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

15. NUMBER OF PAGES

33

16. PRICE CODE

A03

20. LIMITATION

OF ABSTRACT

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z-39-18

29e-I(_