Radiation Effects on Polymers - American Chemical Society

Chapter 38 R a d i a t i o n - D e g r a d a t i o n Studies of the M e c h a n i c a l Properties of P o l y m e r Matrix Composites U s e d i n F u s i o n M a g n e t s

Downloaded by UNIV MASSACHUSETTS AMHERST on August 9, 2012 | http://pubs.acs.org Publication Date: November 12, 1991 | doi: 10.1021/bk-1991-0475.ch038

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S. Egusa , Tadao Seguchi , M. Hagiwara , H. Nakajima , S. Shimamoto, M. A. Kirk , and R. C. Birtcher 3

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1Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, Takasaki-shi, Gunma, 370-12 Japan Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki, 311-02 Japan Materials Science and Technology Division, Argonne National Laboratory, Argonne, IL 60439 When polymer matrix composites are used in superconduct ing magnets for fusion reactors, one of the most serious concerns is their resistance to changes in mechanical and electrical properties upon simultaneous irradiation with neutrons and γ -rays at 4.2 K. This chapter mainly describes the mechanical properties of polymer matrix composites tested at 77 K, 4.2 K, and at room tempera ture after Co γ -ray and neutron irradiations at room temperature and at 5 K. Based on the degradation behav ior, the mechanisms underlying the irradiation effects on polymer matrix composites are discussed with respect to factors such as composite type, test temperature, radiation type, and irradiation temperature. In the construction of superconducting magnets for Tokamak and Mir ror type fusion reactors, large amounts of polymer matrix composites are used as mechanical supporters and as electrical and thermal insulators. The magnets will be subjected to substantial quantities of neutrons and γ -rays during the fusion-reactor operation, thus leading to significant degradation of the magnet component materials such as insulators, stabilizers, and superconductors (1-4). Proba bly the degradation is most serious for composite organic insulators, because organic materials are usually less radiation resistant than inorganic materials (5). Thus the operating lifetime of the fusion magnets may be virtually determined by the radiation resistance of the composite insulators. From this point of view, several groups of workers have studied the irradiation effects on the mechanical and electrical properties of polymer matrix composites (6-11). The authors' group has also started such studies in 1983, mainly with regard to the composite mechanical properties (12-24). This chapter presents a review on 2

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0097-6156/91/0475-0591S06.00/0 © 1991 American Chemical Society In Radiation Effects on Polymers; Clough, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

RADIATION EFFECTS ON POLYMERS

592

the progress made by the authors i n understanding the i r r a d i a t i o n effects at a fundamental l e v e l . This chapter mainly describes the mechanical properties of polymer matrix composites tested at 77 K, 4.2 K, and at room temperature after C o γ -ray and neutron i r r a d i a tions at room temperature and at 5 K. Based on the degradation behavior, the mechanisms underlying the i r r a d i a t i o n effects on poly mer matrix composites are discussed with respect to factors such as composite type, test temperature, radiation type, and i r r a d i a t i o n temperature. Downloaded by UNIV MASSACHUSETTS AMHERST on August 9, 2012 | http://pubs.acs.org Publication Date: November 12, 1991 | doi: 10.1021/bk-1991-0475.ch038

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Experimental Section Most composites studied here were s p e c i a l l y prepared using the r e i n f o r c i n g f a b r i c s shown i n Table I , and matrix resins of epoxy and polyimide. The epoxy resin was t e t r a g l y c i d y l diaminodiphenyl meth ane (TGDDM) cured with diamino diphenyl sulfone (DDS), or d i g l y c i d y l ether of bisphenol A (DGEBA) cured with diamino diphenyl methane (DDM). The polyimide resin was polyaminobismaleimide (Kerimid 601). The composites thus prepared are shown i n Table Π. Commercially available Ε-glass f i b e r composites such as G-10CR, G-11CR (Spaulding Fibre Company, Inc.), and TIL-G1000 (*TORAY ) were also studied. The matrix r e s i n i n G-10CR was a s o l i d DGEBA cured f

Table I . Plain-Woven Glass Fabrics Used as Reinforcing F i l l e r Fabric

Fiber Type

Fiber Diameter

a

(nm)

KS-1210 KS-1600 WTX-116E WTA-18W

E-Glass E-Glass T-Glass T-Glass

Number of Yarns per 25 mm

Number of Fibers i n a Yarn 200 400 200 400

7

9 7 9

Warp

Weft

53 41 60 44

48 32 58 34

a

E-glass composition (wU): Si0 (55.2), A l 0 ( 1 4 . 8 ) , Ca0(18.7), MgO(3.3), B 0 ( 7 . 3 ) , Na 0+K 0(0.5), F e 0 ( 0 . 3 ) , F (0.3), T i 0 ( 0 . 1 ) . T-glass composition (wt%): S i 0 ( 6 5 ) , A l 0 ( 2 3 ) , Ca0(

° ^ o ! ° C o γ-Hays

700 600 500 \i

400

^Habbit/VT2 CK-_

300

H

2

200 100 0 0

20

J i 1 J L 40 60 80 100 120 140 160 Absorbed Dose, D* or D (MGy)

180

T

Figure 12. P l o t of the ultimate f l e x u r a l strength at 77 Κ versus the absorbed dose i n the matrix for the 0° specimen of the g l a s s / polyimide I composite i r r a d i a t e d with neutrons or C o 7-rays. See the caption f o r Figure 11 for the symbols of data points. (Reproduced with permission from reference 18. Copyright 1987 Elsevier.) 60

In Radiation Effects on Polymers; Clough, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

38.

EGUSA ET AL.

Polymer Matrix Composites Used in Fusion Magnets

enhanced decrease i n the composite strength for the H2 neutrons i s d e f i n i t e l y ascribed to the a d d i t i o n a l r a d i a t i o n damage i n the compo s i t e due to the a and L i p a r t i c l e s (6,8,13,17,18). This i s be cause the B reaction has a large cross section for low-energy neutrons, and the f l u x of such neutrons i s much higher for the H2 neutrons than for the Rabbit or VT2 neutrons (25). As component materials to be used i n fusion magnets, therefore, boron-free glass f i b e r composites are recommended over the boron-containing glass f i b e r composites. From t h i s point of view, the e f f e c t s of the kind of glass f i bers and the type of f a b r i c weave on the composite degradation be havior were studied by using the r e i n f o r c i n g f a b r i c s shown i n Table I . The Ε-glass f a b r i c s of KS-1210 and KS-1600 (Kanebo Ltd.) were so selected as to d i f f e r from each other i n the number of f i b e r s i n a yarn and i n the number of yarns per 25 mm i n the warp and weft d i r e c t i o n s . The boron-free T-glass f a b r i c s of WTX-116E and WTA-18W (Nittobo Co.) were so selected as to be the counterparts of KS-1210 and KS-1600, respectively, with regard to the type of f a b r i c weave. The ultimate f l e x u r a l strength of a 0° specimen tested at 77 Κ a f t e r C o γ -ray i r r a d i a t i o n i s plotted i n Figure 13 as a function of the absorbed dose i n the matrix for the glass/epoxy I -IV compo s i t e s (24). I t i s seen that the i n i t i a l strength of the KS-1210 or WTX-116E f a b r i c composite i s 28-40% higher than that of the KS-1600 or WTA-18W f a b r i c composite, thus i n d i c a t i n g that the i n i t i a l strength i s dependent on the type of f a b r i c weave. I t i s also seen that the i n i t i a l strength i s less dependent on the kind of glass fibers. Following i r r a d i a t i o n the strengths of these composites decrease monotonically with increasing absorbed dose. Roughly speak ing, the dose dependence appears to follow a rather s i m i l a r pattern for a l l of these composites, thus suggesting that the degradation behavior of the composite f l e x u r a l strength depends neither on the type of f a b r i c weave nor the kind of glass f i b e r s . This r e s u l t i s consistent with a degradation mechanism such that the dose depend ence of the composite f l e x u r a l strength i s p r i m a r i l y determined by a change i n the matrix ultimate s t r a i n due to i r r a d i a t i o n (22). In agreement with t h i s mechanism, the composite degradation behavior i s e s s e n t i a l l y independent of the type of r e i n f o r c i n g f a b r i c for the glass/polyimide I -HI composites also (24). 7


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E f f e c t of I r r a d i a t i o n Atmosphere Composite insulators used i n fusion superconducting magnets are subjected to r a d i a t i o n under an i n e r t atmosphere of l i q u i d helium. I f the e f f e c t of i r r a d i a t i o n atmosphere on the composite degradation behavior i s s i g n i f i c a n t , the r e s u l t s obtained from i r r a d i a t i o n i n a i r can not be used as design data for fusion magnets. As an ap proach to t h i s problem, polymer matrix composites having various r a d i a t i o n resistance were i r r a d i a t e d with C o γ -rays i n a i r and i n argon under comparable dose rates. The ultimate f l e x u r a l strength of a 0° specimen tested at 77 Κ i s p l o t t e d i n Figure 14 as a function of the absorbed dose i n the matrix for the G-10CR, G-11CR, and TIL-G1000 composites (24). Com parison of the argon and a i r data points for each composite shows that the degradation behavior follows an i d e n t i c a l pattern regard60


605

606


m CL 3L

n

4->

1600 1400

en

Str

c 1200 —

Ί

I

I

1

I

Glass/Epoxy

•

I

1

I

I

1000

r-t

c_

800

lex


03

1

I - W Composites (0°) Fabric (O) KS-1210 ( · ) WTX-116E (•) KS-1600 (•) WTA-18W

600

liCi)

4->

400 —

E

4-»

200

Z)

0

1

„ ±

J

L

L

L_i

0 20 40 60 80 100 120 140 160 180 200 220 Absorbed Dose (MGy)

Figure 13. Plot of the ultimate f l e x u r a l strength at 77 Κ versus the absorbed dose i n the matrix f o r the 0° specimens of the g l a s s / epoxy I -IV composites i r r a d i a t e d with Qco 7-rays. (Reproduced with permission from Cryogenics, 1991, 31, 7-15. Copyright 1991 Butterworth.) 6

I

"Ί

I

1200

Γ

1 1

Ί

Glass Fiber

1000 Lïï

I

I

I

Γ

Composites (0°) (O.D.o) in Argon ( · . • . • ) in Air

800 TIL-G1000

\

600

• G-10CR

400

\G-11CR \

200 0

0

10 20 30 40 50 60 70 80 90 100 Absorbed Dose (MGy)

Figure 14. Plot of the ultimate f l e x u r a l strength at 77 Κ versus the absorbed dose i n the matrix f o r the 0° specimens of the G10CR, G-11CR, and TIL-G1000 composites i r r a d i a t e d with C o 7rays i n argon and i n a i r . (Reproduced with permission from Cryogenics, 1991, 31, 7-15. Copyright 1991 Butterworth.) 60



38. EGUSA ET AL.

Polymer Matrix Composites Used in Fusion Mag

less of the irradiation atmosphere for all of these composites. This is also the case for other kinds of composites such as the glass/epoxyV and glass/polyimide I composites (24). It is reasona ble to conclude, therefore, that the presence or absence of oxygen during irradiation has essentially no influence on the degradation behavior of a polymer matrix composite. It should be pointed out, however, that irradiation in air versus argon must produce some differences in the radiation damage at the specimen surface by the presence and absence of oxidative degradation (33). The fact that the composite degradation behavior is s t i l l independent of the irradiation atmosphere (Figure 14) strongly suggests that the composite strength is fairly insensitive to small flaws which will be formed at the specimen surface by oxi dative degradation during irradiation in air. Such insensitivity is most likely ascribed to the presence of reinforcing fibers in the composite. The presence of fibers is, in fact, known to interfere with the propagation of matrix cracking in the composite (34). Conclusions We have reviewed the mechanical properties of polymer matrix compo sites tested at 77 K, 4.2 K, and at room temperature after 60co r ray and neutron irradiations at room temperature and at 5 K. The most general characteristic of the composite degradation behavior is that the dose dependence of the composite flexural strength depends not only on the matrix resin in the composite but also on the test temperature. The complicated dose dependence can be explained sys tematically by a mechanism in which the degradation of the composite flexural strength is primarily determined by a change in the matrix ultimate strain due to irradiation. In agreement with this mecha nism, the type of fabric weave and the kind of glass fibers have essentially no influence on the dose dependence of the composite flexural strength. Another important characteristic of the composite degradation behavior is that the radiation sensitivity of the epoxy and polyimi de matrix composites is higher for neutrons than Co 7-rays, thus indicating that the decomposition efficiency of the matrix resin depends on the type of radiation. Thus it is concluded that the results of simulation irradiation with Co 7-rays or accelerated electrons are unreliable as sources of design data for fusion super conducting magnets. As to the effect of irradiation temperature, the data points obtained so far suggest that there is no significant difference in the composite degradation behavior for 5 Κ and roomtemperature irradiations. 60

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Literature Cited (1) Brown, B.S. J. Nucl. Mater. 1981, 97, 1. (2) Wiffen, F.W. J. Nucl. Mater. 1985, 133 & 134, 32. (3) Scott, J.L.; Clinard, F.W. Jr.; Wiffen, F.W. J. Nucl. Mater. 1985, 133 & 134, 156. (4) Kulcinski, G.L.; Dupouy, J.M.; Ishino, S. J. Nucl. Mater. 1986, 141-143, 3. (5) Hay, R.D.; Rapperport, E.J. Oak Ridge National Laboratory Re port; ORNL/TM-2643 (1976). In Radiation Effects on Polymers; Clough, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


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(6) Coltman, R.R. Jr.; Klabunde, C.E. J. Nucl. Mater. 1983, 113, 268. (7) Takamura, S.; Kato, T. Advan. Cryogenic Engrg. Mater. 1984, 30, 41. (8) Tucker, D.S.; Fowler, J.D. Jr.; Clinard, F.W. Jr. Fusion Technol. 1985, 8, 2696. (9) Weber, H.W.; Kubasta, E.; Steiner, W.; Benz, H.; Nylund, K. J. Nucl. Mater. 1983, 115, 11. (10) Yamaoka, H.; Miyata, K. Advan. Cryogenic Engrg. Mater. 1986, 32, 161. (11) Nishijima, S.; Okada, T.; Miyata K.; Yamaoka, H. Advan. Cryo genic Engrg. Mater. 1988, 34, 35. (12) Egusa, S.; Kirk, M.A.; Birtcher, R.C.; Hagiwara, M.; Kawanishi, S. J. Nucl. Mater. 1983, 119, 146. (13) Egusa, S.; Kirk, M.A.; Birtcher, R.C. J. Nucl. Mater. 1984, 126, 152. (14) Egusa, S.; Kirk, M.A.; Birtcher, R.C.; Hagiwara, M. J. Nucl. Mater. 1985, 127, 146. (15) Egusa, S.; Nakajima, H.; Oshikiri, M.; Hagiwara, M.; Shimamoto, S. J. Nucl. Mater. 1986, 137, 173. (16) Egusa, S.; Hagiwara, M. Cryogenics 1986, 26, 417. (17) Egusa, S.; Kirk, M.A.; Birtcher, R.C. J. Nucl. Mater. 1987, 148, 43. (18) Egusa, S.; Kirk, M.A.; Birtcher, R.C. J. Nucl. Mater. 1987, 148, 53. (19) Egusa, S.; Udagawa, Α.; Hashimoto, O.; Ono, T.; Yamamoto, Y.; Sonoda, K. J. Mater. Sci. Lett. 1988, 7, 503. (20) Egusa, S.; Seguchi, T.; Sugiuchi, K. J. Mater. Sci. Lett. 1988, 7, 973. (21) Egusa, S. J. Mech. Behavior of Mater. 1988, 1, 1. (22) Egusa, S. J. Mater. Sci. 1988, 23, 2753. (23) Egusa, S. J. Mater. Sci. 1990, 25, 1863. (24) Egusa, S. Cryogenics, in press. (25) Birtcher, R.C.; Blewitt, T.H.; Kirk, M.A.; Scott, T.L.; Brown, B.S.; Greenwood, L.R. J. Nucl. Mater. 1982, 108 & 109, 3. (26) Hanna, G.L.; Steingiser, S. In Composite Materials: Testing and Design; American Society for Testing and Materials, ASTM STP 460; 1969, 182-191. (27) Nishijima, S.; Nishiura, T.; Ikeda, T.; Okada, T.; Hagihara, T. Advan. Cryogenic Engrg. Mater. 1988, 34, 75. (28) Hartwig, G.; Knaak, S. Cryogenics 1984, 24, 639. (29) Takeda, N.; Kawanishi, S.; Udagawa, Α.; Hagiwara, M. J. Mater. Sci. 1985, 20, 3003. (30) Greenwood, L.R. Proc. 4th ASTM-EURATOM Symp. Reactor Dosimetry; Gaithersburg, MD, 1982; 783-792. (31) Burns, W.G.; Jones, J.D. Trans. Faraday Soc. 1964, 60, 2022. (32) Egusa, S.; Ishigure, K.; Tabata, Y. Macromolecules 1980, 13, 171. (33) Chapiro, A. Radiation Chemistry of Polymeric Systems; Intersci ence; New York, 1962; 360-361. (34) Broutman, L.J. In Modern Composite Materials; Broutman, L.J.; Krock, R.H., Eds.; Addison-Wesley Publishing Company; Massachu setts, 1967; Chapter 13. RECEIVED January

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Radiation Effects on Polymers - American Chemical Society

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