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DYNAMIC FATIGUE OF SODIUM-SILICATE GLASSES WITH HIGH WATER CONTENT
S. Ito, M. Tomazawa
To cite this version:
S. Ito, M. Tomazawa. DYNAMIC FATIGUE OF SODIUM-SILICATE GLASSES WITH HIGH WATER CONTENT. Journal de Physique Colloques, 1982, 43 (C9), pp.C9-611-C9-614.
�10.1051/jphyscol:19829122�. �jpa-00222428�
JOURNAL DE PHYSIQUE
Colloque C9, supplement au n°12, Tome 43, deaembve 1982 page C9-611
DYNAMIC FATIGUE OF SODIUM-SILICATE GLASSES WITH HIGH WATER CONTENT
S. I t o and M. Tomozawa
Rensselaer Polytechnic Institute, Troy, N.I. 12181,U.S.A.
Résumé.- On étudie la manière dont dépend la résistance mécanique de la vi- tesse d'application des contraintes pour un verre de silicate de sodium ayant un contenu en eau élevé (jusqu'à 25% en poids) . Les verres ont été préparés par séchage de la solution commerciale de silicate de sodium dans un four ou dans un autoclave. La résistance mécanique a été mesurée par une méthode de flexion en quatre points pour des vitesses d'application des charges dif- férentes. Ces verres ont montré une forte dépendance de la vitesse, même dans l'huile de paraffine sèche ; elle augmente avec la teneur en eau. La valeur de n, mesure de cette dépendance est approximativement 5 pour les verres avec
^ 25% en poids d'eau. Parallèlement, le module d'Young décroit. On suggère que cette dépendance accrue résulte du mouvement d'eau sous l'action des contrain- tes appliquées. De plus, la valeur apparente du module d'Young décroit avec la vitesse de charge. Ce phénomène est expliqué par les propriétés visco-élas- tiques des verres.
A b s t r a c t . - The s t r e s s - r a t e dependency of the mechanical s t r e n g t h of sodium s i l - i c a t e glass with high water content (up t o ^25% by weight) was i n v e s t i g a t e d . The glasses were prepared by drying commercial sodium s i l i c a t e solution i n an oven or an autoclave. The mechanical strength of t h e glasses was measured by a four point bending method a t various s t r e s s r a t e s . These glasses showed a strong s t r e s s r a t e dependency even i n dired paraffin o i l and the dependency i n - creased with increasing water content; the value of n, a measure of the s t r e s s r a t e dependency, was approximately 5 for glasses with ^25 wt% water. At the same time Young's modulus decreased with increasing water, content. I t i s sug- gested t h a t stress-induced motion of water i s responsible for the increased s t r e s s r a t e dependency. In addition, the apparent value of Young's modulus de- creased with decreasing s t r e s s r a t e . This phenomenon was explained i n terms of the v i s c o - e l a s t i c property of t h e g l a s s e s .
1. I n t r o d u c t i o n . - Water i n t h e environment i s well known t o affect the mechanical strength of glass [ 1 , 2 ] ; the strength measured i n water i s about one h a l f of t h a t measured i n vacuum [ 3 ] , and the strength decreases with increasing loading time
( s t a t i c fatigue) and with decreasing s t r e s s r a t e (dynamic f a t i g u e ) [ 4 ] . On t h e other hand, very l i t t l e i s known about t h e effect of water i n glass on i t s mechanical s t r e n g t h . Recently, Wu [5] reported some data showing t h a t t h e e l a s t i c modulus and the s t r e n g t h of hydrated s i l i c a t e glass decreased with increasing water content, while McMillan e t a l [ 6 ] reported t h a t the bending strength of the soda-lime s i l i c a
glass with a small amount of water (below 780 ppm) was not influenced by the water content. So f a r , no research has been reported on d e t a i l s of t h e effect of the water in glass on the s t r e n g t h , e s p e c i a l l y on fatigue phenomenon.
In t h i s study, t h e s t r e s s r a t e dependency of the mechanical strength and t h e e l a s t i c modulus of the sodium s i l i c a t e glass with high water content were i n v e s t i - gated.
2. Experiment.- The glasses with high water content were prepared by drying commer- c i a l sodium s i l i c a t e solution (Na 2 0 ^8.9 wt%, Si0 2 ^28.7 wt%, H.0 <V62.4 wt%;
Na 2 0-3.3Si0 2 -24H 2 0 by mole r a t i o ) i n an oven a t 50^80°C for 5 ^ 7 days i n a i r (for
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19829122
C9-612 JOURNAL DE PTZYSIOUE
specimens with H 0 g r e a t e r than 20 wt%) and t h e n i n an a u t o c l a v e a t 8 0 ~ % 1 5 0 ~ ~ f o r 32.5 days i n 2.30 b a r 2 N2 ( f o r specimens w i t h H20 l e s s t h a n 20 w t % ) . The water con- t e n t s o f t h e s e g l a s s e s were determined from weight l o s s by drying t h e g l a s s a t 4 0 0 ' ~ f o r 2h. The dry g l a s s (Na20'3.3Si02. by mole r a t i o ) was prepared by h e a t i n g t h e g l a s s w i t h h i g b water content a t 400°C f o r 2h and s u b s e a u e n t l y m e l t l n g t h e d r i e d powder a t 1450 C f o r 5h. The g l a s s was annealed a t 530 C f o r 2h. The w a t e r c o n t e n t of t h e d r y g l a s s was determined approximately from t h e peak i n t e n s i t y o f IR spec- t r a [7]. The g l a s s e s were c u t i n t o samples %1.7 mm t h i c k , ' ~ 3 . 5 mm wide, %25 mm long with a diamond saw. The s u r f a c e o f the specimen was p o l i s h e d with S i c paper (600 g r i t ) . P r i o r t o t h e mechanical s t r e n g t h measurement, t h e c e n t e r r e g i o n o f one s u r - f a c e was abraded by a rougher S i c paper (240 g r i t ) , i n a d i r e c t i o n p e r p e n d i c u l a r t o t h e long a x i s o f t h e specimen. This s u r f a c e was p l a c e d on t h e t e n s i o n s i d e d u r i n g t h e mechanical t e s t i n g . A l l t h e p o l i s h i n g and abrading were performed i n p a r a f f i n o i l .
The mechanical s t r e n g t h was measured by a four p o i n t bending method a t f i v e d i f f e r e n t crosshead speeds (1.27
%0.00254 cm/min.) a t room temperature. The t e s t i n g was done i n p a r a f f i n o i l which had been d r i e d using P205 f o r one week, t o e l i m i n a t e
the e f f e c t o f environmental water. A t l e a s t 7 specimens were used t o o b t a i n one d a t a p o i n t .
The Knoop hardness number was measured w i t h a Kentron microhardness t e s t e r a t room temperature. The g l a s s s u r f a c e was p o l i s h e d , u s i n g diamond p a s t e . Within 15 min. a f t e r p o l i s h i n g , t h e i n d e n t e r was brought i n t o c o n t a c t with t h e g l a s s s u r f a c e f o r 30 s. with a 200 g load. The l e n g t h of t h e long dlagonal of t h e i n d e n t a t i o n was measured immediately a f t e r removing t h e load.
3. R e s u l t and Discussion.- F r a c t u r e s t r e n g t h v s . s t r e s s r a t e as a f u n c t i o n of w a t e r c o n t e n t i n the g l a s s i s shown i n Fig. 1. The g l a s s e s with high water content showed a s t r o n g s t r e s s r a t e dependency of t h e f r a c t u r e s t r e n g t h , even though t h e s t r e n g t h was measured i n p a r a f f i n o i l . The dependency i n c r e a s e d with i n c r e a s i n g w a t e r con- t e n t ; t h e v a l u e of n [ 8 ] , which was c a l c u l a t e d from t h e s l o p e o f t h e l i n e s i n Fig. 1, decreased with i n c r e a s i n g w a t e r c o n t e n t . On t h e o t h e r hand, t h e dry g l a s s showed l i t t l e s t r e s s r a t e dependency.
I n Figure 1, t h e s t r e n g t h o f t h e abraded d r y g l a s s was seen t o b e lower than t h a t o f t h e g l a s s w i t h 15.9 w t % H20, while t h e g e n e r a l t r e n d appears t o be lower s t r e n g t h f o r h i g h e r water c o n t a i n i n g g l a s s e s . This apparent d i s c r e p a n c y i s probably due t o t h e d i f f e r e n c e i n t h e s u r f a c e microcrack geometry caused by t h e d i f f e r e n t hardness. Figure 2 shows t h e Knoop hardness vs.
w a t e r c o n t e n t . The hardness decreases with i n - c r e a s i n g water content of t h e g l a s s . Thus it i s
dry glass 0.8 -
Log Stress Rate I kg/mrn2. mi"
)FIG. 1. F r a c t u r e s t r e n g t h v s . s t r e s s r a t e f o r g l a s s e s w i t h v a r i o u s water c o n t e n t s . (Measured i n p a r a f f i n o i l a t room temperature;
2 s t a n d a r d d e v i a t i o n )
FIG. 2. Knoop hardness number
v s . water c o n t e n t i n g l a s s .
i s a c c e l e r a t e d by water i n g l a s s even when v i s -
c o e l a s t i c behavior i s a b s e n t . FIG. 4 . Apparent Young's Modulus Generally, s t r e s s i s known t o cause d i f f u - V S ' r a t e f o r with s i o n [14], and a l t e r t h e l o c a l c o n c e n t r a t i o n various water
r15.161 of t h e s o l u t e i n t h e s o l i d . Therefore. Standard deviation) expected t h a t a g l a s s w i t h high w a t e r con-
t e n t would deform e a s i l y and a microcrack
Crosshead speed
on i t s s u r f a c e would have a more rounded 254 mm/mln
t i p than t h a t of a dry g l a s s . In f a c t it was observed t h a t t h e abraded s u r f a c e of t h e specimens w i t h high w a t e r content be- came smooth i n d i c a t i n g t h e h e a l i n g e f f e c t . I f t h e crack geometry i s t h e same, t h e s t r e n g t h o f t h e d r y g l a s s would probably b e h i g h e r t h a n t h a t of t h e g l a s s with 15.9 w t % -
H20. 0 254 mrn/m~n
Some g l a s s e s used i n t h i s s t u d y showed -
an apparent Young's modulus which v a r i e s with crosshead speed as shown i n Fig. 3.
For t h e h i g h e s t water c o n t e n t (%25 wt%H20), and t h e low crosshead speed, i n a d d i t i o n , a p p a r e n t l y n o n - b r i t t l e f r a c t u r e was o b s e r - ved a s shown i n t h e lower curves i n Fig. 3.
The a p p a r e n t Young's modulus value was 0 o 1 0 2 o 3
c a l c u l a t e d from t h e load and t h e d e f l e c t i o n Oeflectlon ( m m )
of t h e specimen [9] and i s shown i n Fig. 4
as a f u n c t i o n of s t r e s s r a t e . From t h e f i - F I G . 3 . Load v s . d e f l e c t i o n a t gure, it i s seen t h a t t h e modulus d e c r e a s e s crosshead speeds glass with i n c r e a s i n g water content and t h e modu- w i t h 25.3 w t % w a t e r .
li of t h e g l a s s e s c o n t a i n i n g 23.1% and
25.3% w a t e r were markedly dependent on t h e s t r e s s r a t e , while t h e moduli o f t h e dry g l a s s and t h e g l a s s c o n t a i n i n g 15.9 w t % w a t e r were independent o f t h e s t r e s s r a t e . These r e s u l t s s u g g e s t t h a t t h e g l a s s with high w a t e r c o n t e n t shows v i s c o - e l a s t i c be- h a v i o r . Using two p a r a l l e l Maxwell models [ l o ] , t h e v i s c o e l a s t i c b e h a v i o r was an- alyzed and t h e e l a s t i c modulus a t i n f i n i t e s t r e s s r a t e was c a l c u l a t e d and i s shown i n Fig. 5. The modulus decreased g r a d u a l l y up t o %20 w t % , and then r a p i d l y w i t h i n - c r e a s i n g w a t e r c o n t e n t . This can be a t t r i b u t e d t o t h e gradual loosening o f t h e g l a s s s t r u c t u r e due t o t h e i n c r e a s i n g number of broken ZSi-0- bonds by water. Be- yond 20 w t % H20, s t r u c t u r a l loosening becomes a c c e l e r a t e d s i n c e t h e g l a s s t r a n s i t i o n temperature approaches room temperature [ l l ] where a l l t h e measurements were made.
;he* a'load i s applied t o t h e g l a s s w i t h h i g h
The s t r e s s r a t e dependency o f t h e s t r e n g t h 100-
namely, dynamic f a t i g u e , has been u s u a l l y ex- 80.
p l a i n e d by a c o r r o s i o n r e a c t i o n [ I ] of t h e glass w i t h atmospheric w a t e r o r a s u r f a c e energy r e - 6 0 -
d u c t i o n [12,13] due t o w a t e r a d s o r p t i o n . How- -
e v e r , i n t h i s s t u d y , t h e e f f e c t of t h e w a t e r i n ": 40-
t h e environment i s considered n e g l i g i b l e , s i n c e ,
t h e s t r e n g t h was measured i n d r i e d p a r a f f i n o i l Z' and i n f a c t , t h e n value o f t h e dry g l a s s , 50, 2
sured i n t h e presence o f water. This observa- was much h i g h e r than t h e u s u a l n value [4] mea- - 20.
t i o n s u g g e s t s t h a t t h e dynamic f a t i g u e o f t h e 2
g l a s s c o n t a i n i n g w a t e r i s induced by t h e water l o .
i n t h e g l a s s . .g 0 8
I t i s n o t c l e a r whether o r n o t t h e o b s e r -
ved v i s c o e l a s t i c behavior h a s an i n f l u e n c e on z 06.
t h e s t r e s s - r a t e dependency o f t h e s t r e n g t h .
However, a s shown i n Fig. 1, t h e g l a s s con- 0 4 .
t a i n i n g 15.9 w t % w a t e r shows dynamic f a t i g u e , even though it shows e l a s t i c behavior ( i n
H2°
-005%
1 5 9&/. T;$~-r
$/HA+-
23i0,,,
,,v-
253yy+
- 2 - 1 0 1 2 3 4
Fig. 4 ) , i n d i c a t i n g t h a t t h e f a t i g u e tendency LO^ Stress Rate
(kg/mm2 rnm )
C9-614 JOURNAL DE PHYSIQUE
w a t e r c o n t e n t , t h e w a t e r i n t h e g l a s s is expected t o d i f f u s e t o a crack t i p , where a l a r g e t e n s i l e s t r e s s e x i s t s because of t h e s t r e s s concentration. %6<' I t i s p o s s i b l e t h a t t h e w a t e r d i f f u s e d t o t h e
crack t i p reduces t h e s t r e n g t h o f t h e g l a s s -
causing t h e dynamic f a t i g u e phenomenon. For
example, t h e r e a r e i n d i c a t i o n s [17,18] t h a t t h e !4 -
f r a c t u r e toughness decreases with d e c r e a s i n g
TI=
0
