The results of an experimental study of polyamide fatigue strength are presented. Multiple flexing tests were performed on specimens rotating at 3000 cycles/min with a symmetrical load cycle in various media, including air (with and without blowing),
1. In the uniaxial static elongation of geometrically similar samples, the strength characteristics (σB and σ0.2) and the relative elongation (ε) are practically independent of sample diameter. The relative contraction (ψ) increasing with falling d
In the hydrometallurgical treatment of ores the main losses of uranium are due to the leaching process. It is therefore of interest to study substances which catalyze the transfer of uranium to solution. Studies into the effect of variable-valency el
The strength of concrete was investigated. It was found that in the case of charging individual concrete components into TMs mounted on the chassis of KrAZ and KamAZ trucks, high-grade concrete cannot always be prepared with such a technological sche
Some authors believe [1-4] that dental porcelain is r e s i s t a n t to all chemicals except hydrofluoric acid. Such a belief was not conductive to studies of the influence of active media whose composition approaches that of liquids p r e s e n t in the oraI cavity on the strength and durability of dentalporcelain mate rial s. As in the case of l o w - s t r e n g t h silicate glass , the p r e s e n c e of s u r f a c e - a c t i v e media should also reduce the strength of dental porcelain. The aim of this investigation was to study the influence of certain s u r f a c e - a c t i v e media on the strength of grade F L - 1 dental porcelain (62.3% feldspar; 17% quartz; 4.05% spodumene; 9.75% b o r i c acid) tested in bending. The specimens in the f o r m of rods m e a s u r i n g 6.5 =~6.5 • 55.5 mm were compacted under a p r e s s u r e of 250 kg/mm2; the moisture content of the starting mixture was 8~. A f t e r compacting the specimens were fired for 5 rain at 915 ~ C and furnace cooled. Specimens p r e p a r e d in this way complied with the specification for a v e r a g e quality m a t e r i a l s . Faulty specimens (with c r a c k s , b l i s t e r s , etc.) were d i s c a r d e d . We investigated the influence of the following media: 20% h y d r o c h l o r i c acid solution; 20% lactic acid solution; 50% acetic acid solution; a mixture of samples of saliva taken f r o m 10 men 20-22 y e a r s olds with intact teeth. The composition of these media a p p r o a c h e s m o s t closely that of liquids p r e s e n t in the oral cavity, since the concentration of c e r t a i n acids in various m i c r o r e g i o n s of the mouth i n t e r i o r (especially in places w h e r e food p a r t i c l e s a r e entrapped) can be quite high. To d e t e r m i n e the influence of active media on the strength of grade F L - 1 porcelain, the specimens w e r e i m m e r s e d in the media studied and held (with control specimens) in a t h e r m o s t a t at 37* C f o r 30days. a f t e r which they were s u b j e c t e d t o bending tests on a universal machine . The shackle t r a v e r s e rate was 5 m m / m i n and the distance between supports 20 ram. Between four and six specimens of each batch were tested in the media in which they had been held; the remaining s p e c i m e n s , a f t e r being wiped with a f i l t e r paper, w e r e tested in air. T e s t r e s u l t s are r e p r o d u c e d in Table 1. It wilI be seen that the strength of grade F L - 1 porcelain may be i n c r e a s e d under the influence of c e r t a i n active media. This effect is evidently a s s o c i a t e d with partial dissolution of the m a t e r i a l held in these media. Since the strength of porcelain, like TABLE 1 that of glass , is determined mainly bythe size of defects ( m i c r o - and m a c r o c r a c k s ) , and since the d i s Bending strength (kg/ solution of the m a t e r i a l studied leads to an i n c r e a s e cm 2) a f t e r holding in a in the c u r v a t u r e radii of the crack tips and to a c o r r e medium pH Medium sponding reduction in the s t r e s s concentration in tests in a i r tests in the these regions, the strength of the m a t e r i a l i n c r e a s e s . medium The strength of porcelain F L - 1 specimens tested Air 615 in the a g g r e s s i v e media is l o w e r than that of s p e c i 615 627 20~o lactic acid 1.74 mens tested in air. This indicates that the material 598 1.26 50% acetic acid 602 562 under s t r a i n is influenced m o r e by active media than 621 20% HCI by air. The reduction in s t r e n g t h depends on pH of -0.72 488 Saliva 580 507 the medium, i.e., on its chemical activity (see Table 1)o 7.9
L'vov State Institute of Medicine. Institute of Physics and Mechanics, Academy of Sciences of the Ukrainian SSSR, L'vov. Translated from Fiziko-Khimieheskaya Mekhanika Materialov, Vol. 6, No, 5, p. 114, September-October, 1970o Original article submitted January 9, 1970. 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 $15.00.
As the chemical activity of the media in relation to the m a t e r i a l tested i n c r e a s e s , its strength d e c r e a s e s , Thus, the h y d r o c h l o r i c acid solution is chemically m o r e active than acetic and lactic acid solutions. It m a y t h e r e f o r e be postulated that when poreelain F L - 1 is deformed in the s u r f a c e - a c t i v e media studied, the reduction in its strength is due to a chemical reaction between porcelain and the media.
2. 3. 4. 5. 6.
A. L. Rin$, Zahn~irztliche Welt-Reform, 1960, No. 17, 529-533. W. N. Hattemer, Zahn~rztliche Rundschau, 1961, No. 3, 86-90. K. Fuhr, Zahn~rztliche Welt-Reform, 1965, No. 6, 195-199. V. A. Lysenko, Proceedings of a Stomatologieal Conference [in Russian], 99-104, Moscow, Strength of Glass [inRussian], Izd., Mir, 1969. S. I. Mikitishin and A. N. Tynnyi, ZL, No. 7, 1968.