TIME-TO-RUPTURE

OF

IN S U R F A C E - A C T I V E

POLYMER

MATERIALS

MEDIA

S. I . M i k i t i s h i n , a n d A . N. T y n n y i

UDC 678 : 539.4.019

O. A. Mikityuk,

Investigations of t i m e - t o - r u p t u r e of p o l y m e t h y l m e t h a c r y l a t e (PMMA) in liquid s u r f a c e - a c t i v e media [1, 2] showed that the relation log T(o) under t h e s e conditions is different in c h a r a c t e r f r o m the t e m p e r a t u r e t i m e dependence postulated by Zhurkov [3]. S i m i l a r o b s e r v a t i o n s w e r e p r e v i o u s l y made by Holland and T u r n e r [4] on silicate g l a s s t e s t e d in a i r , by B a r t e n e v and Bryukhanova [5] f o r p l a s t i c i z e d r u b b e r s , and by Gul' [6] for oriented PMMA. The t i m e - t o - r u p t u r e of m a t e r i a l s in t h e s e c a s e s is s a t i s f a c t o r i l y d e s c r i b e d by a p o w e r function [4]: (I)

~=eo--b

Time-to-rupture tests of PMMA in various medea (air, water, ethyl alcohol, acetone) showed that experimental results plotted in coordinates log T--log ~ lie on straight lines (see Fig. 1), i.e., obey the law ~-= ~

zo J

"c

y

\

0! ,,

-0'2

.\

b

Q~

a~

(2)

If it is b o r n e in mind that the s u r f a c e e n e r g y of m a t e r i a l s t e s t e d to f r a c t u r e in working media is reduced as a r e s u l t of adsorption phenomena [8] and if the r e l a tionship between s u r f a c e e n e r g y of solids and t h e i r a c t i vation e n e r g y for f r a c t u r e Uf is taken into account, the r e a s o n f o r the reduction in Uf of s p e c i m e n s tested in s u r f a c e - a c t i v e media b e c o m e s quite c l e a r .

-o,&,

0

,

w h e r e T 1 is t i m e - t o - r u p t u r e c o r r e s p o n d i n g to al, Uf is the fictitious (apparent [7]) activation e n e r g y for f r a c t u r e , which is l o w e r for liquid media than f o r a i r , its values being 60 k j o u l e / m o l e (for air), 26 k j o u l e / m o l e (for water), 1 9 k j o u l e / m o l e (for k e r o s e n e ) , 10.5 k j o u l e / m o l e (for ethyl alcohol), and 6 k j o u l e / m o l e (for acetone).

o\

"

rll Uf/It7 -

I

_

I

0Slog o, daN/ram2

Fig. 1. T i m e dependence of s t r e n g t h of PMMA in s u r f a c e - a c t i v e media: a) 20~ b) 50~ points r e l a t e to e x p e r i m e n t a l r e s u l t s , a n d c u r v e s to data calculated f r o m f o r m u l a (2). 1) Air; 2) water; 3) ethyl alcohol; 4) acetone; 5) k e r o s e n e .

Using f o r m u l a (2), we calculated the t i m e - t o r u p t u r e of PMMA in w a t e r and ethyl alcohol at 20 and 50~ and of p l a s t i c i z e d r u b b e r s SKS-30 and SKN-26 at 20-90~ The calculated r e s u l t s a g r e e quite well with e x p e r i m e n t a l data for r u b b e r s SKS-30 and SKN-26 [5, 9] and PMMA (see Fig. 1). In a c c o r d a n c e with f o r mula (2) the constants in f q r m u l a (1) derived by Holland and T u r n e r a r e B = T l a l U f / k T and b = U f / k T .

Institute of P h y s i c s and Mechanics, A c a d e m y of Sciences of the Ukrainian SSR, L ' v o v . 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 M a t e r i a l o v , Vol. 6, No. 4, pp. 118-119, July-August, 1970. Original a r t i c l e submitted June 30, 1969.

9 1973 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

Comparing (2) with the Zhurkov equation U.--~a

= ~o e

(3)

.

one can see that the e x p r e s s i o n

\

Uf/J

(4)

(analogous to Eq. (3)) at Uf = 7at c o r r e s p o n d s to Eq. (2) a c c u r a t e to the f i r s t t e r m of the expansion of function In ai/a (for ~l/a ~- 1/2). Thus, the t i m e - t o - r u p t u r e of p o l y m e r materials under a combined influence of mechanical s t r e s s and s u r f a c e - a c t i v e media in the time and t e m p e r a t u r e intervals investigated is satisfactorily d e s c r i b e d by Eq. (2). LITERATURE lg

2.

3. 4. 5. 6.

7. 8. 9,

534

CITED

A. I. Soshko, A. N. Tynnyi, and M. M. Gudimov, FKhMM, [Soviet Materials Science], no. 5, 1965. A. N. Tynnyi and A. I. Soshko, FKhMM [SMS], no. 1, 1967. S. N. Zhurkov and T. P . Sanfirova, DAN SSSR, 101,237, 1955. A. Holland and W. T u r n e r , J. Soc. Glass Technol., 24, 101, 1940; 32, 5, 1948. G. M. Bartenev and L. S. Bryukhanova, ZhTF, 288,287, 1958. V. E. Gul', Strength of P o l y m e r s [in Russian], Izd. Khimiya, 1964. G. M. Bartenev and Yu. S. Zuev, Strength and F r a c t u r e of High-Elasticity M a t e r i a l s [in Russian], Izd. Khimiya, 1964. V. L Likhtman, E. D. Shchukin, and P. A. Rebinder, Physicochemical Mechanics of Metals [in Russian], Izd~ AN SSSR, 1962. G. M. Bartenev, P l a s t m a s s y , no. 9, 1960.