EFFECT STRESSES
OF
WORKING
AND TEMPERATURE
IN GLASS-REINFORCED
S~ M~ P e r l i n , and
MEDIA
A.
L~ A.
ON R E S I D U A L
PLASTICS
Borisen.ko,
Lo No O b i s h c h e n k o ,
To L o m a k i n
UDC 678 : 4.019.3
It is knowzl [1, 2] that the n a t u r e of working m e d i a and the t e m p e r a t u r e m a y substantially affect the intensity of p h e n o m e n a which take place both at the g l a s s - r e s i n i n t e r f a c e and in the p o l y m e r itself and which lead to changes in the n a t u r e of the s t r e s s distribution in the boundary zone and, consequently, in the p r o p e r t i e s of g l a s s - r e i n f o r c e d p l a s t i c s . The a i m of this investigation was to study these changes under the influence of distilled v~ater and l o w - and h i g h - s u l f u r p e t r o l e u m at elevated t e m p e r a t u r e s (50 and 80~ Residual s t r e s s e s w e r e d e t e r m i n e d by a p r e v i o u s l y d e s c r i b e d method [3]. The d i f f e r e n c e in principal s t r e s s e s obtained with the aid of an I P L 451 automatic p o l a r i m e t e r was s e p a r a t e d by a method of tangential s t r e s s e s . This made it p o s s i b l e to c a l culate tensile,tangential s t r e s s e s ((rl) and c o m p r e s s i v e radial s t r e s s e s (~2) in the p o l y m e t e r binder. Curves r e p r o d u c e d in Fig. 1 and r e p r e s e n t i n g the dependence of al and r 2 in the vicinity of the r e i n forcing e l e m e n t s on the t i m e of e x p o s u r e to the action of working m e d i a and on the e x p e r i m e n t a l t e m p e r a t u r e show that the variation in a 1 and in a2 a r e s i m i l a r in nature. The action of the working m e d i a in the by 3.5 and 1.0 k g / m m 2 r e s p e c t i v e l y .
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Fig. 1. The v a r i a t i o n in the r e s i d u a l s t r e s s e s in a g l a s s - r e i n f o r c e d plastic under the influence of working m e d i a at a) 20~ b) 50aC, and e) 80"C: 1, I) distilled w a t e r ; 2, II) l o w - s u l f u r p e t r o l e u m ; 3, Ill) h i g h - s u l f u r p e t r o l e u m ; 1, 2, 3) tangential s t r e s s e s a t ; I, II, HI) radial s t r e s s e s a 2. Gubkin Institute of P e t r o l e u m C h e m i c a l s and Gas I n d u s t r i e s , Moscow. T r a n s l a t e d f r o m F i z i k o K h i m i c h e s k a y a Mekhanika Materialov, Vol. 5, No. 5, pp. 638-639, S e p t e m b e r - O c t o b e r , 1969. 9 1972 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00.
533
f i r s t 100-200 h f i r s t produces a certain d e c r e a s e and then a sharp i n c r e a s e in these s t r e s s e s which pass through maxima. This points to a complex p h y s i c o chemical phenomena taking place both in the p o l y m e r and at the p o l y m e r - g l a s s interface. ~ ~ O
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4o
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Fig. 2. The Kinetics of water absorption at 1) 20~ 2) 50~ and 3) 80"C.
It is likely that, in these c i r c u m s t a n c e s , two main competing p r o c e s s e s take place: swelling, which leads to a d e c r e a s e in m o l e c u l a r interaction, and c r o s s linking, which i n c r e a s e s this interaction in the polymer. At first, as a r e s u l t of the weakening of m o l e c u l a r interaction due to swelling of the polymer, a d e c r e a s e in residual s t r e s s e s is o b s e r v e d ; later~ when c r o s s linking (chemical interaction of functional groups) b e gins to predominate, residual s t r e s s e s a r e increased.
P r o t r a c t e d (longer than 200 h) exposure to the action of a g g r e s s i v e media leads f i r s t to a sharp r e duction in residual s t r e s s e s which eventually r e a c h a certain constant level; this is associated with continued permeation of the working media into the polymer (leading to a reduction in m o l e c u l a r interaction) and with partial destruction of previously f o r m e d c r o s s - l i n k e d bonds. This p r o m o t e s the relaxation of s t r e s s e s which, as already mentioned, r e a c h a certain constant level. This level is different for different media and t e m p e r a t u r e s b e c a u s e of varying intensities of the relaxation phenomena. The l a r g e s t reduction in r e s i d u a l s t r e s s e s (94% for a s and 78% for a 2) was observed under the influence of distilled water and the s m a l l e s t (33 % f o r a 1 and 25% for a 2) in high-sulfur p e t r o l e u m (Fig. la). This is evidently a s s o c i a t e d with the highest permeating and plasticizing power of distilled water, illustrated by data on the i n c r e a s e d weight of specimens tested in this medium (Fig. 2). Raising the test t e m p e r a t u r e f r o m 20 to 80~ has a substantial effect on the residual s t r e s s e s in specimens under the influence of high- and low-sulfur petroleum. The reduction in the residual s t r e s s e s is i n c r e a s e d in the case of low-sulfur petroleum f r o m 50% for a I and 42% for a 2 to 75 and 67%, respectively, (Fig. lc, c u r v e s 1 and 3), the corresponding i n c r e a s e in the case of high-sulfur petroleum being f r o m 33 and 25~ to 57 and 38% (Fig. lc, curves 3 and III) respectively. This effect is evidently associated with the fact that permeating power of petroleum i n c r e a s e s with rising t e m p e r a t u r e , which leads to an i n c r e a s e in the intensity of relaxation phenomena in the polymer. Residual s t r e s s e s in specimens under the influence of water are almost completely relieved at r o o m t e m p e r a t u r e ; raising the t e m p e r a t u r e to 80~ produces no substantial changes in the p r o c e s s in question. LITERATURE 1.
2. 3.
534
CITED
Go D. Andreevskaya, High-Strength Oriented G l a s s - R e i n f o r c e d Plastics [in Russian], Izd, Nauka, 1966o P. M. Ogibalov and Yu. V. Suvorova, The Mechanics of Reinforced Plastics [in Russian], Izd. Khimiya, 1965. G. K. Shreiber, S. M. Perlin, L. N. Obishchenko, and L. A. Borisenko, FKhMM, [Soviet Materials Science], no. 6, 1967.