Specimens of graphite/epoxy composites and epoxy resins were exposed to electron and gamma radiation, followed by mechanical property and fundamental measurements. Measurement techniques included: scanning electron microscopy, X-ray diffraction analysis, and electron spin resonance spectroscopic analysis. Results indicate little or no change in flexural properties of miniature specimens of a graphite/epoxy composite and no change in failure mode at the fiber-resin interface and in the crystallinity of the fiber and the resin. Some doubt in the observation of stable flexural properties is cast by electron paramagnetic resonance spectra of a relatively large number of radiation-generated radicals. These generally lead to a change in cross-linking and in chain-scissioning which should alter mechanical properties

Fornes, R. E.

Gilbert, R. D.

Long, E. R., Jr.

Memory, J. D.

English

NASA Technical Reports Server

THE E F F E C T S  OF ELECTRON AND GAMMA RADIATION 
ON EPOXY-BASED MATERIALS 
Re E. FORNES, J. D. MEMORY, R. D. G I L B E R T  
NORTH CAROLINA STATE UNIVERSITY 
RALEIGH,  NORTH CAROLINA 
AND 
Em R. LONG, J R .  
MATERIALS D I V I S I O N  
NASA LANGLEY RESEARCH CENTER 
HAMPTON, V I R G I N I A  
LARGE SPACE SYSTEMS TECHNOLOGY - 1981 
THIRD ANNUAL TECHNICAL REVIEW 
NOVEMBER 16-19, 1981 
https://ntrs.nasa.gov/search.jsp?R=19820010402 2020-03-21T10:27:37+00:00Z
OBJECTIVES AND APPROACH 
R a d i a t i o n  e f f e c t s  on epoxy-based m a t e r i a l s  a r e  being s t u d i e d  a t  Nor th  
C a r o l i n a  S t a t e  U n i v e r s i t y  under a g r a n t  (NSG-1562) from the  M a t e r i a l s  D i v i s i o n  
of the  NASA Langley Research Center .  The r e s e a r c h  i s  conducted by members of 
t h e  School of T e x t i l e s ,  Department of T e x t i l e  Chemistry and Department of 
F i b e r  and Polymer Sc ience ,  and the  School of P h y s i c a l  Sc iences  and Applied 
Mathematics,  Department of Phys ics  and Department of Chemistry. The o b j e c t i v e s  
of t h i s  work a r e  t o  e v a l u a t e  the  e f f e c t s  of r a d i a t i o n  on the  mechanical  
p r o p e r t i e s  of epoxy-based s t r u c t u r a l  m a t e r i a l s  and t o  measure t h e  fundamental  
r a d i a t i o n - g e n e r a t e d  e v e n t s  which cause  the  changes i n  mechanical  p r o p e r t i e s .  
The approach t o  t h e s e  o b j e c t i v e s  is  t h e  exposure of specimens of g raph i t e /epoxy  
composites and epoxy r e s i n s  t o  e l e c t r o n  and gamma r a d i a t i o n ,  fo l lowed by 
mechanical  p r o p e r t y  and fundamental  measurements. This r e p o r t  w i l l  p r e s e n t  a 
p o r t i o n  of the  d a t a  which has been ga the red  t o  da te .  
OBJECTIVE 
EVALUATION OF THE EFFECTS OF R A D I A T I O N  ON THE MECHANICAL 
PROPERTIES OF EPOXY-BASED STRUCTURAL MATERIALS. 
MEASUREMENT OF THE FUNDAMENTAL, RAD I AT1 ON-GENERATED EVENTS 
W H I C H  CAUSE THE CHANGES I N  MECHANICAL PROPERTIES. 
APPROACH 
EXPOSURE OF SPECIMENS OF GRAPHITE EPOXY COMPOSITE AND 
EPOXY RESIN  TO ELECTRON AND GAMMA RADIATION. 
MEASUREMENT OF CHANGES I N  THE VALUES OF MECHANICAL AND 
FUNDAMENTAL PROPERTIES. 
F i g u r e  1 
RADIATION EFFECTS ON FLEXURAL PROPERTIES OF A GRAPHITE/EPOXY COMPOSITE 
The f l e x u r a l  p r o p e r t i e s  of m i n i a t u r e  (25 m x 13 mm x 0.51 mm) 
u n i d i r e c t i o n a l  specimens of T300/5208 composite f o r  e l e c t r o n  r a d i a t i o n  
exposures  i n  vacuum f o r  doses  up t o  and i n c l u d i n g  8  x l o 9  rads  a r e  shown i n  
f i g u r e s  2a and 2b. The specimens were f a b r i c a t e d  a t  Langley Research Center  
from prepreg  m a t e r i a l .  The f i b e r  d i r e c t i o n  was i n  the  d i r e c t i o n  of specimen 
l e n g t h  ( l o n g i t u d i n a l ) ,  so t h e  f l e x u r a l  p r o p e r t i e s  were f iber-dominated.  Each 
datum p o i n t  is t h e  mean of t e n  specimens. The 95 pe rcen t  conf idence-of - f i t  
bands f o r  t h e  mean a r e  a l s o  shown. The s t r e n g t h  appears  t o  s l i g h t l y  i n c r e a s e  
wi th  dose ,  approximate ly  f o u r  pe rcen t  a t  8 x  10' r a d s ,  whi le  t h e  modulus 
a p p e a r s  u n a f f e c t e d .  However, the  s i z e  of t h e  conf idence  band i s  s u f f i c i e n t l y  
l a r g e  t h a t  the  l o c a t i o n  of t h e  mean is u n c e r t a i n  t o  t h e  e x t e n t  t h a t  l a r g e r ,  
perhaps  s i g n i f i c a n t ,  changes i n  f l e x u r a l  p r o p e r t i e s  w i t h  r a d i a t i o n  could  have 
occurred.  The a p p r e c i a b l e  u n c e r t a i n t y  i n  the  l o c a t i o n  of t h e  mean does s u g g e s t  
t h a t  a n  a d d i t i o n a l  emphasis on q u a l i t y  c o n t r o l  of specimen p r e p a r a t i o n  and /o r  
t e s t i n g  procedures  may be necessary .  
FLEXURAL MODULUS FOR FOUR-PLY. UNlDlRECTlONAL T30015208 
COMPOSITE SPECIMENS. LONGITUDINAL FIBER DIRECTION 
+ MEAN OF 10 SPECIMENS 
1. 5 x loll A LIMITS FOR 95 PERCENT CONFIDENCE 
r 
1.301 i i i 4 i i i i x i o 9  
DOSE. rads 
FLEXURAL 
MODULUS. 
PASCALS 
1. 4 
FLMURAL STRENGTHS FOR FOURPLY, UNIDIRECTIONAL T300h208  
COMPOSITE SPECIMENS. LONGITUDINAL FIBER DIRECTION. 
@ MEAN OF 10 SPECIMENS 
A LIMITS FOR 95 PERCENT CONFIDENC 
24 x 10' v F QB LOCATlQN OF THE MEAN 
r 
n 
" A 
" 
A 
A 
* '  * *  
* * 
I! * 
V v " v * 
, I  V 
1 i i 4 i i i i Ax109 
DOSE, rads 
F i g u r e  2  
RADIATION EFFECTS ON FLEXURAL PROPERTIES OF A GRAPHI'I'E/POLYIMIDE COMPOSITE 
S i m i l a r  exposures  t o  e l e c t r o n  r a d i a t i o n  have been made on f l e x u r a l  
u n i d i r e c t i o n a l  C6000/PMR15 composi te  specimens ,  w i t h  a  l o n g i t u d i n a l  f i b e r  
o r i e n t a t i o n .  The e f f e c t s  on f l e x u r a l  p r o p e r t i e s  were v e r y  s i m i l a r  t o  
t h o s e  j u s t  shown f o r  t h e  g r a p h i t e / e p o x y  composite m a t e r i a l .  I n  f i g u r e s  3a and 
3b, f l e x u r a l  d a t a  f o r  specimens of t h e  ~6000/PMR15 composite wi th  a  t r a n s v e r s e  
f i b e r  o r i e n t a t i o n  a r e  shown f o r  r a d i a t i o n  doses  a l s o  up t o  and i n c l u d i n g  8 x  
10' rads .  The specimens were f a b r i c a t e d  a t  Langley Research C e n t e r  from n e a t  
r e s i n  and tows of g r a p h i t e  f i b e r .  For t h e  t r a n s v e r s e  f i b e r  d i r e c t i o n ,  t h e  
means sugges t  no change i n  e i t h e r  modulus o r  s t r e n g t h .  But, a g a i n  t h e  
u n c e r t a i n t y  i n  the  l o c a t i o n  of the  mean may have masked a  more a p p r e c i a b l e ,  
perhaps  s i g n i f i c a n t ,  change due t o  the  r a d i a t i o n .  Transverse -o r ien ted  f i b e r ,  
u n i d i r e c t i o n a l  f l e x u r a l  specimens of the  g raph i t e /epoxy  composite w i l l  be 
s t u d i e d  i n  t h e  f u t u r e .  Specimen p r e p a r a t i o n  and t e s t i -ng  procedures  w i l l  be a n  
impor tan t  c o n s i d e r a t  i o n  whi le  p lanning and conduct ing t h e s e  t e s t s .  
FLEXURAL MODUU FOR FOUR-PLY, UNlOlRLCTIONAL C60001PMM5 
COMPOSm SPECIMENS. TRANSVERSE FIBER DIRECTION. 
! 
I A n 
FLEXURAL 
MODULUS, 1 
PASCALS * 
+ MEAN OF 10 SPECIMENS 
- -  L I M I T S  FOR 95 PERCENT CONFIDENCE 7 
FOR LOCATION OF THE MLAFL 
._i --d ; 5 6  i 8 x 1 0 ~  
DOSE, rads 
FLEXURAL STRENGTHS FOR FOUR-PLY, UNIDIRECTIONAL C6000/PMRl5 
COMPOSITE SPECIMENS. TRANSVERSE FIBER DIRECTION 
12 o 107 + MEAN OF 10 SPECIMENS 
L I M I T S  FOR 95 PERCENT CDNF IDENCE 
FOR LOCATENOFTHE %Ahi 
A 
* 
V 
8.0 
(b 1 V 
7.00 I u i i 4 5 6 7 8x109 
DOSE, rads 
F i g u r e  3 
SCANNING ELECTRON MICROSCOPY OF FIBER/RESIN COMPOSITES 
Photographs from scanning e l e c t r o n  mic roscop ic  a n a l y s i s  of t h e  f a i l u r e  edge 
of a f l e x u r a l  specimen are shown i n  f i g u r e  4a f o r  ~ 3 0 0 1 5 2 0 8  and i n  f i g u r e  4b 
f o r  C6000lPMR15. N e i t h e r  p a i r  of photographs shows a  d i f f e r e n c e  i n  the  f a i l u r e  
mode a t  the  f i b e r - r e s i n  i n t e r f a c e  due t o  r a d i a t i o n  exposure.  S ince  t h e  
f i b e r - r e s i n  i n t e r a c t i o n  is more mechanical  i n t e r l o c k i n g  than chemical  
i n t e r a c t i o n ,  t h e  l ack  of change i n  t h e  f a i l u r e  mode had, t o  a  c e r t a i n  e x t e n t ,  
been a n t i c i p a t e d ,  
SCANNING ELECTRON PHOTOGRAPHS OF TYE FAILURE EUGE OF 
FLEXURAL SPECIMENS OF GRAPHIWEPOXY COMPOSITE. 
DOSE = 0 rads DOSE = 8 x lo9 rads 
SCANNING ELECTRON PHOTOGRAPHS OF THE FAILURE EDGE OF 
FLEXURAL SPECIMENS OF GRAPHITVPOLY IMlDE COMPOSITE 
DOSE = 0 rads (b DOZE = 5 x lo9 rads 
F i g u r e  4 
X-RAY DIFFRACTION ANALYSIS OF GRAPHITE/EPOXY COMPOSITE 
F igure  5a is a  p a i r  of X-ray d i f f r a c t i o n  photographs of T300/5208 composi te  
w i t h  no r a d i a t i o n  exposure and wi th  a  r a d i a t i o n  dose of 8 x 10' rads .  There i s  
no change i n  e i t h e r  the  d i f f u s e  s c a t t e r  due t o  the  r e s i n  o r  t h e  broad d i f f u s i o n  
peak a long t h e  equa to r  due t o  t h e  g r a p h i t e  f i b e r .  There fo re ,  t h e  r a d i a t i o n  d i d  
not a f f e c t  t h e  c r y s t a l l i n i t y ,  e i t h e r  of the  amorphous r e s i n  o r  of the  g r a p h i t e  
f i b e r  which o r i g i n a l l y  c o n s i s t e d  of e i t h e r  very smal l - s i ze  c r y s t a l l i n e  
s t r u c t u r e  o r  numerous d e f e c t s .  A l ack  of change i n  c r y s t a l l i n i t y  conf i rms t h a t  
a tomic  displacement  i s  not one of the  e f f e c t s  of e l e c t r o n  r a d i a t i o n .  F igure  5b 
is  a mic rodens i tomet r i c  t r a c e  of the  photographs.  The ampl i tudes  of t h e  t r a c e s  
conf i rm t h a t  no d i f f e r e n c e s  e x i s t .  
WlDE ANGLE X-RAY PHOTOGRAPHS OF T300f5208 COMPOSITE 
WITH AND WITHOUT amsuRE TO ELECTRON RADIATION. 
DOSE = 0 rads DOSE = 8 x lo9 rads 
MICRODENSITOMETER TRACES OF WlDE ANGLE X-RAY 
PHOTOGRAPHS OF T300/5208 
w 
DOSE = 8 x lo9 cads 
"Ilc,J,pW, 
DOSE = 0 rads 
F i g u r e  5 
ELECTRON SPIN RESONANCE SPECTROSCOPIC ANALYSIS OF RADIATION EFFECTS 
The major e f f e c t  of r a d i a t i o n  upon polymeric m a t e r i a l s  i s  t h e  c r e a t i o n  of 
chemical  r a d i c a l s ,  which a r e  groups wi th  unpaired e l e c t r o n s  i n  molecu la r  
o r b i t a l s .  The p resences  of these  unpaired e l e c t r o n s  i n  a  specimen a r e  measured 
by e l e c t r o n  s p i n  resonance ( o r  e l e c t r o n  paramagnet ic  resonance)  spec t roscopy .  
The specimen i s  s imul taneous ly  s u b j e c t e d  t o  a  f i x e d  f requency s i g n a l  and a  
sweeping magnetic f i e l d .  A t  a  p a r t i c u l a r  combination of s i g n a l  and f i e l d ,  
c h a r a c t e r i s t i c  of the  e l e c t r o n ' s  environment,  t h e  unpa i red  e l e c t r o n ' s  s p i n  i s  
f l i p p e d  and a  ne t  a b s o r p t i o n  of energy i s  d e t e c t e d .  Usua l ly ,  the  a b s o r p t i o n  i s  
d e t e c t e d  i n  i t s  f i r s t  d e r i v a t i v e  form, a s  shown i n  f i g u r e  6a f o r  t e t r a g l y c i d y l  
diamino d ipheny l  methane, TGDDM, which has  been cured wi th  diamino d ipheny l  
sulphone,  DDS. The s i g n a l  of d i p h e n y l p i c r y l h y d r a z y l ,  DPPH, is  a l s o  shown 
because i t  i s  inc luded  wi th  t h e  specimen f o r  c a l i b r a t i o n  purposes.  The epoxy 's  
s i g n a l  shown i n  f i g u r e  6a is due t o  r a d i a t i o n - g e n e r a t e d  r a d i c a l s ,  t h e  number of 
which v a r i e s  wi th  dose. The s i g n a l  magnitude, p o s i t i o n ,  and s t r u c t u r e  vary  
w i t h  r a d i a t i o n  dose a s  shown i n  f i g u r e  6b. 
ELECTRON SPIN RESONANCE SPECTRA OF ELECTRON-IRRADIATED EPOXY 
DPPH 
g ; 2.0036 
ELECTRON SPIN RESONANCE OF ELECTRON-IRRADIATED EPOXY (TGDDM-DDS) 
EPOXY (TGDDM-DDS) 
F i g u r e  6 
25 C 
u 
ELECTRON RADIATION-GENERATED RADICAL CONCENTRATIONS AND DECAYS I N  EPOXY RESINS 
The v a r i a t i o n  of r a d i c a l  c o n c e n t r a t i o n  i n  the  cured epoxy r e s i n  TGDDM-DDS 
wi th  dose a f t e r  room tem e r a t u r e  exposures  t o  e l e c t r o n  r a d i a t i o n  is shown i n  is f i g u r e  7a. For 1.3 x 10 r a d s ,  t h e  r a d i c a l  c o n c e n t r a t i o n  a t  t h e  end of 
exposure  is  approximate ly  1.9 x lo1* s p i n s f g ,  o r  one s p i n  f o r  eve ry  55 
molecules.  F igure  7b shows t h e  decay i n  r a d i c a l  c o n c e n t r a t i o n  a t  room 
tempera tu re  wi th  t ime a f t e r  exposure.  Two r a d i c a l  d i s t r i b u t i o n s  a r e  p r e s e n t ,  
a s  sugges ted  by the  sha rp  change i n  t h e  s l o p e s  of the  curves  i n  f i g u r e  7b,  one 
w i t h  a  h a l f - l i f e  on the  o r d e r  of twelve minutes and ano the r  wi th  a  much longer  
h a l f - l i f e .  Consequent ly ,  the  t o t a l  number of s p i n s  per gram which o c c u r r e d  
over  a  long exposure pe r iod  was much l a r g e r  than  t h e  va lue  a t  t h e  end of 
exposure  and may have amounted t o  only  s e v e r a l  molecules p e r  sp in .  The c u r r e n t  
l i t e r a t u r e  s u g g e s t s  t h a t  each s p i n  would probably ,  i n  the  end, g e n e r a t e  a  
c r o s s - l i n k  o r  cha in  s c i s s i o n .  I n  c o n t r a s t ,  based upon the  mechanical  d a t a  
d i s c u s s e d  e a r l i e r ,  t h e  r a d i c a l s  w i t h i n  t h i s  epoxy may have decayed i n  a  p rocess  
of s e l f - h e a l i n g .  But, we must a l s o  p o i n t  ou t  t h a t  the  EPR d a t a ,  because of t h e  
l a r g e  r a d i c a l  concent r a t  i o n ,  can be sugges t ing  a  review of the  t echn iques  used 
f o r  t h e  measurements of mechanical  p r o p e r t i e s .  
INITIAL RADICAL CONCENTRATIONS IN EPOXY RESIN AFER ELECTRON IRRADlATlON 
R A D I C A L  
CONCENTRATION, 
spins/g 
L- L- u 
0 10 20 3 0  40 50 60 70 80 W ID3 110 120 1 3 0 ~ 1 0 ~  
(a) DOSE, rads 
ROOM-TEMPERATURE DECAY OF ELECTRON-RAWON-GENERATE0 
RADICALS I N  EPOXY RESIN 
DOSE 
R A D I C A L  
CONCENTRATION, 20 x 1 0 ' ~  o 130 x1o6 rads 
0 100 
spins/g 0 MI 
M 
. 30 
* a 
I I -- - I 
0 100 200 7 ' i  1220 
(b) POST IRRADIATION TIME, m i r  
F i g u r e  7 
GAMMA RADIATION-GENERATED RADICAL CONCENTRATIONS AND DECAY I N  EPOXY RESIN 
Rad ica l  c o n c e n t r a t i o n s  i n  epoxy r e s i n  f o r  a  range of doses  from gamma r a d i -  
a t i o n  a r e  shown i n  f i g u r e  8a. The c o n c e n t r a t i o n s  up t o  t h e  maximum dose  
s t u d i e d ,  6 x lo7 r a d s ,  a r e  approx imate ly  twice  t h a t  f o r  e l e c t r o n  r a d i a t i o n .  
The h i g h e r  d e n s i t y  may be due t o  t h e  f a c t  t h a t  t h e  gamma exposures  were 
conducted a t  c ryogen ic  t empera tu res ;  hence,  s h o r t - l i v e d  s p e c i e s  were t r apped .  
T h i s  appears ,  t o  an  e x t e n t ,  t o  be t h e  c a s e  from t h e  decay d a t a  shown i n  f i g u r e  
8b. P r e s e n t l y ,  t h r e e  r a d i c a l  d i s t r i b u t i o n s ,  each wi th  d i f f e r e n t  h a l f - l i v e s ,  
a r e  b e l i e v e d  t o  be w i t h i n  t h e s e  decay da ta .  The c o n c e n t r a t i o n  a t  
end of exposure  and t h e  decay dur ing  exposure  s u g g e s t ,  a s  i n  t h e  case  of t h e  
e l e c t r o n  r a d i a t i o n ,  t h a t  t h e  t o t a l  s p i n  fo rmat ion  was s u f f i c i e n t  t o  cause  
changes i n  mechanical  p r o p e r t i e s ,  u n l e s s  s e l f - h e a l i n g  was the  dominant 
p rocess .  A d d i t i o n a l  s t u d i e s  u s i n g  EPR f o r  t h e  s t u d y  of epoxy r e s i n  a f t e r  
e l e c t r o n  and gamma r a d i a t i o n  w i l l  be conducted t o  measure r a d i c a l  d e n s i t i e s  a t  
h i g h e r  doses  and r e l a t e d  t o  t h e  mechanical  d a t a ,  both  f o r  t h i s  and o t h e r  epoxy 
systems.  
INITIAL RADICAL CONCENTRATIONS I N  EPOXY RESIN 
AFTER GAMMA IRRADIATION 
1 A. 
RADICAL  
CONCENTPATION, 14 
spins/g 121 l;vo;; , , , 
4 
2 
0 10 M 30 40 50 60x10~ 
DOSE, rads 
ROOM-TEMPERATURE DECAY OF GAMMA-RADIATION-GENERATED 
RADICALS IN EPOXY RESIN 
RADICAL 
CONCENTRATION. 
DOSE 
A 53.2 x 1f16 rads 
12 1 x lo6 rads 
F i g u r e  8 
5 - 
(b) 
I 1 I 1 I A__- 
25 50 75 100 125 150 175 
POST IRRADIATION TIME. min 
SUMMARY 
The s tudy  a t  North Caro l ina  S t a t e  U n i v e r s i t y  has ,  t o  d a t e ,  shown l i t t l e  o r  
no change i n  f l e x u r a l  p r o p e r t i e s  of m i n i a t u r e  specimens of a  g raph i t e /epoxy  
composite due t o  exposure t o  e l e c t r o n  and t o  gamma r a d i a t i o n .  ( A  s tudy of j u s t  
the  f l e x u r a l  p r o p e r t i e s  of specimens of a  g r a p h i t e / p o l y i m i d e  composite a l s o  
showed l i t t l e  o r  no change due t o  exposure t o  r a d i a t i o n . )  I n  a d d i t i o n ,  no 
change i n  f a i l u r e  mode a t  t h e  f i b e r - r e s i n  i n t e r f a c e  and i n  the  c r y s t a l l i n i t y  of 
t h e  f i b e r  and t h e  r e s i n  has  been found. The absence of changes a t  t h e  
f i b e r - r e s i n  i n t e r f a c e  and i n  the  c r y s t a l l i n i t i e s  was expected.  However, t h e  
o b s e r v a t i o n  of only  a  smal l  change i n  f l e x u r a l  p r o p e r t i e s  was a  p l e a s a n t  
s u r p r i s e .  Some doubt i n  t h e  o b s e r v a t i o n  of s t a b l e  f l e x u r a l  p r o p e r t i e s  i s  c a s t ,  
though, by e l e c t r o n  paramagnet ic  resonance s p e c t r a  of a r e l a t i v e l y  l a r g e  number 
of r a d i a t i o n - g e n e r a t e d  r a d i c a l s .  The l a t t e r  g e n e r a l l y  l ead  t o  a  change i n  
c r o s s - l i n k i n g  and i n  c h a i n - s c i s s i o n i n g  which should  a l t e r  mechanical  
p r o p e r t i e s .  Consequent ly ,  the  measurements of f l e x u r a l  p r o p e r t i e s  w i l l  
c o n t i n u e ,  both  f o r  the  epoxy d i s c u s s e d  i n  t h i s  r e p o r t  and f o r  s i m p l e r  epoxy 
systems.  Also,  fundamental  a n a l y s i s  w i l l  be conducted f o r  the  h i g h e r  doses  
used i n  t h e  mechanical  p r o p e r t y  s t u d i e s .  EPR and o t h e r  fundamental  methods 
w i l l  be used t o  b e t t e r  unders tand the  chemical  changes and mechanisms caused by 
t h e  r a d i a t i o n .  
SUMMARY 
RESULTS 
I. - NO MAJOR CHANGES I N  FLEXURAL PROPERTIES OF SPECIMENS OF A 
GRAPHITE EPOXY COMPOSITE FOR R A D I A T I O N  DOSES UP TO 5 x lo9 rads. 
2. - NO CHANGES I N  THE FA l LURE MODE AT THE F I  BER-RESI N l NTERFACE OR 
I N  THE CRYSTALLINITY OF THE FIBER OR THE P E S l N  FOR R A D I A T I O N  
DOSES U P  TO 5 x 109 rads. 
3. - A H I G H  CONCENTRATION OF RADIATION-GENERATED RADICALS W I T H  
MULTIPLE DECAY CONSTANTS FOR DOSES U P  TO 130 Mrads. 
FUTURE WORK 
I. - CONTINUED STUDY OF FLEXURAL PROPERTIES OF EPOXY-BASED 
MATER l ALS FOR SEVERAL EPOXY SYSTEMS. 
2. - FUNDAMENTAL ANALYSIS  FOR CHARACTER I Z A T I O N  OF R A D I A T I O N  
EFFECTS ON THE CHEMICAL STRUCTURE OF EPOXY RESINS 
P i g u r e  9 


The effects of electron and gamma radiation on epoxy-based materials

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server