Several multiply graphite polyimide composite specimens were examined by real-time infrared thermography in order to study the effects of moisture on their thermograms. Heat was injected from one side and IR emission detected on the opposite side using AGA Thermovision System-680. No differences between the thermograms of dry and water containing specimens were detected for defect-free specimens. However, the presence of trapped water in defective specimens modified the thermographic contrast significantly. It is concluded that: (1) IR thermography can be used to detect moisture in defective composites, and (2) because of the possibility of moisture camouflaging defects, IR thermography for subsurface defect detection should be supplemented by other techniques - such as acoustical imaging and X-radiography

Babcock, R. A.

Buckingham, R. D.

Kantsios, A. G.

Mcerlean, E. A.

Singh, J. J.

English

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I	 (	 I ,a
NASA Technical Memorandum 18649
EFFECTS OF MOISTURE. IN INFRARED THERMOGRAV11Y OF
RESIN MATRIX COMPOSITES
(NASA — TM-79649)	 FFFECTS CF MOISTURE IN	 N78-15464
INFRARED THEFMCGRAPHY OF RESIK MiATRIX
C01iPiCSITFS (NASA)	 18 p HC A02/4F A01
CSCL 14E	 hnclas(;3/35
	
01861
Jag J. Singh, Andronicos G. Kantsios, Edwin A. McErlean,
Robert A. Babcock, and Richard D. Backingham
January 1978
RVSA
	 JAN 1978
National Aeronautics and
Space Administration
r
Langley Res, arch Center
Harrnptun Virymia 113665
_ 
-mow
EFFECTS OF MOISTURE IN INFRARED THERMOGRAPHY
OF RESIN MATRIX :COMPOSITES
By
Jag J. Singh, Andronicos G. Kantsios, Edwin A. McE:rlean,
Robert A. Babcock, and Richard D. Buckinghcm*
ABSTRACT
Several multi-ply graphite polyimide composite specimen; were examined
by real-tim" infrared thermography in order to study the effects if moisture
on their thermograms. Ileat was injected from one side and IR emission
detected on the opposite side using AGA Thermovision System-680. No
differences between the thermograms of dry and water containing specimens
were detected for defect-free specimens. However, #-he presence of trapped
water in defective specimens modified the thermographic contrast signifi-
cantly. It has been concluded that: (1) IR thermography can be used to
detect moisture in defective composites and (2) because of the possibility
of moisture camouflaging defects, 1R thermography for subsurface defect
detection should be supplemented by other techniques - such as acoustical
imaging and X-radiography.
INTRODUCTION
Advanced graphite fiber-reinforced resin matrix composites have
emerged as strong candidates for aerospace applications. However,
structural integrity and full life cycle of these materials under normal
service environmental conditions must be demonstrated before they can
*Vought Corporation, Hampton, VA
•
I
i
ome in widespread use. It has been reported 1-6 that absorbed moisture
degrades the mechanical properties of these materials. rhis degradation is
generally attributed to the plasticizing effect of the moisture on the
matrix. Cyclic swelling and shrinkage caused by successive absorption
and desorption of water may also lead to substantial Internal stress result-
ing In mechanical deterioration. Thus the ability to detect the presence
of water in composites is important in determining their suitability for
continued service.
Infrared thrrmography has been successfully used 
7-9 
in detecting
subsurface defects in metals and composites. Subsurface defects in materials
cause differences in thermal conductance across them and these differences
are reflected in the thermograms of the test surfaces. Introduction of
water in composites may modify the thermal. gradients on the test eurface
since water is a better heat conductor in comparison with the voids,
delaminations and the matric resin itself. It is thus possible that th c
thermogram of a specimen in wet state would be different from its thermogram
in the dry state. The presence of water may even camouflage the defects
visible in the dry specimen. If the differences between the dry and wet
thermograms are significant, it will be necessary to supplement IR imaging
technique of defect detection by other techniques which are not influenced
b: ,
 the presence of moisture in the test specimen. On the other hand,
infrared thermography can be used for detecting moisture in composite
specimens if their wet and dry state chermograms are significantly different.
	 ►
The present studv was undertaken to investigate this latter possibility.
A number of multi-ply Hercules HTS graphite fiber-reinforced polyimide
omposite specimens (PMR-15) were selected for this study. Graphite-
I
polvimide composites were selected because NASA has been studying them
since 1976 for high temperature (600 K) airframe applications. They are
also prime candidates for use in the Shuttle program. The results are
discussed in the following sections.
Experimental Procedure
The specimens were first ultrasonically scanned to locate anv defects -
such as delaminations, fiber cracks, and debonds, etc. - that they may have.
They w_re then examined by the IR thermographic technique, 10 using the ACA
Thermovision System-680, in the spectral range of 3.0-5.6 Om. The ACA
system is capable of detecting temperature differences of the order of
0.2 K at 293 K object temperature. The thermographic measurements were made
on "dry" and "wet" conditions of the specimens. The specimens' linear
dimensions were 13 cm x 13 cm x 0.1 cm.
•
(a) Specimen Heating Procedure: A 13 cm x 13 cm Neater pad was
attached to one face of the specimen with the help of clamps along the edges,
as shown in figure 1. Thermocouples were attached to the rear side of the
heater pad. Current was applied t o the heating pad to bring the sample
through a temperature range of 300 to 350 K and the opposite face scanned for
IR emission. The same heating procedure was used for dry and wet specimens.
(b) ^rocedure for Introducing Water in the Specimen: The diffusion
coefficient of water through the polymeric matrix is low at ambient
temperatures. Consequently, the specimen had to be placed in a pressurized
cooker at 400 K to facilitate moisture difussion in it. The specimen was
first weighed and then inserted in a pressure cooker charged with water at
400 K (w.tter boiling point at 1400 Pa) and left there for 4 hours. Care was
3
taken to Insure that the specimen was in the steam atmosphere - not immersed
in water. The Specimen was then taken out of the cooker and weighed again
to determine the weight of water that had diffused into it. The table below
shows relevant weights for a selected specimen. The weight of water intake
Corresponds to about O.Oh percent of the weight of the dry specimen. This
weight should be compared with the moisture content of about 0.3 percent
calculated for a 24-ply T300/5208 specimen after exposure of 5 weeks in the
environment similar to that at Langley Air Force Base. 11
Specimen Weight Before	 Specimen Weight after	 Weight of Water
Introduction into Cooker	 Immersion in Steam for 4 Hours Intake
0.0594282 kgm	 0.0594142 kgm	 4.60 x 10-5 kgm
Results
Figure 2 shows a co-.Oarison between an IR thermogram and an ultra-
sonic C-scan of a typical specimen. Figure 2a shows an ultrasonic
transmission C-scan. The dark regions represent defective areas while
the clear (white) regions represent defect -free areas. Figure 2b shows
the "dry" IR thermogram of the same specimen. In this figure, dark
areas represent regions of poorer thermal conductance (and thus cooler),
while the white areas are the regions of normal thermal conductivity.
Notice that in figure 2b there are other thermal patterns which show across
the specimen face, in addition to those seen in figure 2a. These are
indicative of spatial differences in thermal conductance or perhaps surface
emittance effects. The spatial thermal conductance differences could arise
from excess/deficit resin concentration without an y mechanical defects
therein. The conventional techniques (ultrasonic scan, X-radiography, etc.)
cannot ' Pr ect such differences. It thus appears that IR scanning may
4
i	 A
provide additional information about the matrix thickness uniformity, which
i	 cannot be easily obtained by other techniques. Figure 3 shows au ultrasonic
transmission C-scan of a typical test sample. It shows a defect area on the
right. The defect is prominent in the lower portion and decreases in
severity towards the upper portion. Figure 4a is a thermogram of the same
specimen, taken from the front face in the dry state. Figure 4b represents
the wet thermogram under the same conditions. One can see that there is a
definite correlation between figures 3 and 4a. The defect area is quite
prominent in figure 4a. However, the prominence of the defect area is
considerably reduced in the wc•t thermogram seen in figure 4b. It thus
appears that changes in therma? contrast between the dry and moisture bearing
state of the sample can signal the presence of moisture in the specimen.
Figures 5a and 5b represent the "dry" and "wet" thermograms of the same
specimen, at the same temperature but from the rear face. The sharpness
of the thermal contrast seen in figure 4a is missing from figure 5a. Further-
more, the thermograms in figures Sa and 5b are not very different from each
other. These differences between figures 4 and 5 are discussed in the
following section.
DISCUSSION
The effect of an internal defect on heat distribution on the specimen
surface is illustrated in figure 6. When the specimen is dry, the defect
D acts as a heat barrier shadowing the region a-b on the opposite face.
The location of the defect D within the specimen determines its effectiveness
as a heat shield. Thus a thermogram of a dr y specimen should indicate if a
known defect is near face 1 or face 2. Now when the specimen is saturated
5
N	 L	 I	 j	 ,
t	 ...
with water, the defect D will trap some water in it and will no longer act
as an effective heat shield. Consequently, the presence of water should bu
signaled by the disappearance of (or reduction in the intensity of) the cold
spot present in the thermogram of a defective dry specimen. The change in
thermal contrast between the dry and wet state will be more marked when the
defect is near the surface studied. This explains the differences between
figures 4 and 5. A reflection ultrasonic C-scan (shown in figure 7)
confirmed that the defect was nearer the front face than the rear face.
When the specimen has no defects, the water is taken up uniformly by
the polymer, rendering it plastic. The water thus absorbed in the specimen
should affect general heat conduction through it without cau" .I.ng any
localized effects. The dry and wet thermograms from defect-free specimen
should thus be similar.
CONCLUDING REMARKS
Present study indicates that the presence of moisture in composites
modifies the surface temperature distribution associated with regions of
anomalous thermal conductance in the specimen - such as cracks, voids, and
delaminations. Thus a comparison between the thermogram of a defective
test specimen, as received, and its thermogram in the "dry" state can indicate
if the test specimen had any moisture in it. The technique cannot however
provide a quantitative measure of moisture content in the test specimen.
Nor can it be used to provide information about the water content of a
defect-free specimen. In general, however, specimens that have seen some
service usually develop enough small defects to render this technique usable
in most practical cases. In view of the fact that the moisture associated
6
i
with the defects tends to camouflage them, it is Suggested that infrared
imaging technique for subsurface defect detection be supplemented by other
techniques (such as acoustical imaging and X-radiography) not influenced by
the presence of water in the test specimen.
7
^	 ,	 ^	 ^	 1	 I	 I	 r
REFERENCES
1. (- E. Browning and J. T. liartness: Proceedings of Third Conference on
Composite Materials Testing and Design, pp. 284-302 (Williamsburg, VA,
March 21-22, 1973).
2. C. E. Browning: Proceedings of 28th Conference of Society of Plastic
Industry held at Washington, DC (Feb. 1973).
3. J. Hertz: Final Contract Report No. NASA 8-27435 (.tune 1973).
C. E. Browning: Workshop on the
Lrix Composites held at Battelle's
2, 1975).
(Proceedings of a Symposium on Environ-
Materials held at Montreal, Canada,
4. C. D. Shirrel; J. D. Halpin; and
Environmental Durability of Resin Ma
Columbus Laboratories (Sept. 30-Oct.
5. ASTM Special Publication No. 602
mental Effects on Advanced Composite
June 22-27, 1975).
6. H. W. Bergman and C. W. Dill: National SAMPE Tech. Conf. Series;
Vol. 8, p. 244, 1976.
7. R. D. Dixon, G. D. Lassahn, and A. Digiallonardo: Materials Fvaluation,
Vol. 30, 73-77, 1972.
8. G. .1. Trezek and S. Balk: Materials Evaluation, Vol. 34, 172-176, 1976.
9. R. S. Williams and K. L. Reifsnider: Materials Evaluation, Vol. 35,
50-54, 1977.
10. AGA Thermovision 680 Operating Manual, Publ. 556.053 AGA Infrared
Systems AB, c. 1973.
11. J. Unnam and D. R. Tenney: AIAA Paper No. 77-400 (presented at the
AIAA-ASME 1801 Structures, Structural Dynamics, and Materials Conference,
held at San Diego, CA, Mar. 21-23, 1977).
8
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DEFECTIVE AREA
- NO;A-DEFECT I VE AREA
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(F IGURE 2A,- ULTRASONIC SCAN OF A Irt'ICAL SPECIMEN CONTAINING DEFECTS,
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FIGURE 2B/- TNERMOGRAM Or SAME SPECIMEN SNOWING DEFECTIVE AND
NONOEFECTIVE AREAS.
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FIGURE 3,- ULTRASONIC SCAN OF THE TEST SPECIMEN, (THIS SPECIMEN
HAS BEEN USED IN FIGURES 3, L!, 5, AND 7,)
4(A) DRY
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FIGURE 4.- [HERMOGRAM OF DRY AND VIET TEST SAMPLE - FRONT FPCE
i5(A) BY 5($) WE]
ilGURE S.- THERMOCRAPti OF DRY AND MET TEST SAMPLE - REAR "ACE,
^,	 I	 I	 r
ETHIS FACE IS SCANNED BY THE IR CAMERA (FACE #1)
AB Z
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HEAT ENTERS THIS FACE ( FACE 91)
FIGURE 6,- EFFECT OF DEFECT ON HEAT PROPAGATION THROUGH A
COMPOSITE SPECIMEN,
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iI Holism  No	 --	 — Uovernment Aeeasron No 3	 Reriwont's Catalog NO
NASA TM 78649
—	 -4 Title and Subt-tle 5	 Remit Date
1 ,lnudl	 1978
Effects of Moisture	 in	 Infrared Tilt- rmographv of	 Resin 6	 Perfsxmr	 organrratronCode
.ti trix	 Composites 1:00
1 Auth.xtsl
,I;1};	 .1.	 S ingh,	 r111d ro11 il'lrs	 C.	 h:Itlt s iUS, 8	 Pet lotmrrsg01yon,Ntnun Nrtr,rt No
Edwi ► 1	 A.	 McErlean.	 Ro1wrt	 A.	 Babcock,	 Richard	 11.	 Ruckin)'•I __^
10	 Wnr ► Unit No
505-02-33-04V r'erf,xm ng Organ Falion Name and Addis►
NASA Lati> , ley Research 11	 Contract or Grant No
Hampton, VA
	
23665
—'	 -
13	 Type of Report and Peruxf Covered
Technical Memorandum ^^S►uns,xing Agency Name and Address
Nat ional Aeronaut ics and Space Admintstrat ion 14	 %punwrring Agency Code
Washington, DC
	
20546
15 Supptrmrntar y Notes
Infrared Thermogr.tphy can be used 	 to detect	 mr.Isture	 in composites having voids/
det,•,•ts.
16 Abstract
Several	 nutlti-ply graphite polyimide composite specimens were examined by real-time
infrared	 thermography
	
in order ter studv the effects of moisture on their thernutgrams.
Heat was	 injected from one side and lR emission detected on the opposite side using i
ACA Thermovision System-6130.	 No differences between the thermograms of dry and water
containing specimens were detected for defect-free specimens.
	 However, the
presence of trapped water 	 in defective specimens modified
	 the thermographic contrast
significantly.
	 It	 has heen concluded that: 	 (1)	 IR thermography can be used 	 to
detect moisture
	 in defective composites and 	 (2)	 because of the possibility of
moisture camouflaging defects, 1R thermography for subsurface defect detection
should be supplemented by other techniques - such as acoustical
	 imaging and
Y-rad iographv.
i
17 Key Words (Suggested by Author(0) 18
	 Distribution Statement
Composites, Moisture,defects, 	 Infrared unclassified - unlimited
Thermographv, Nondestructive Evaluation. Star Category - 35
19 Security	 Ctassif	 (of this reportl 20.	 Security Classd	 lot this page) 21,	 No. of Pages 22	 Price*
Unc lass if ied Vnrlassif ied 16 $4.00
For sale by the National iechnrcal Infamation Service Springfield Virginia 11161
^	 !	 I	 1	 I


Effects of moisture in infrared thermography of resin matrix composites

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