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Journal of Acoustic Emission, 4, 2/3, pp. S290-S293, 1985-04-01
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Acoustic emission study on multi-year sea ice in an Arctic field
laboratory
Sinha, N. K.
https://publications-cnrc.canada.ca/fra/droits
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https://nrc-publications.canada.ca/eng/view/object/?id=04537d2b-49d1-4df7-b636-6377d1a8ebeb https://publications-cnrc.canada.ca/fra/voir/objet/?id=04537d2b-49d1-4df7-b636-6377d1a8ebebSer THZ
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National
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construction
Acoustic Emission Study on Multi- Year
Sea Ice in an Arctic Field Laboratory
by N.K. Sinha
: . :: r r 7
Presented at
Second International Conference on Acoustic Emission
Lake Tahoe, Nevada. 28 Oct
-
1 Nov. 1985
Appeared ill
Journal of Acoustic Emission
Vol. 4, No. 213, April-September 1985
p. S290
-
S293
(IRC Paper No. 1349)
Reprinted with permission
Price $2.00
NRCC 25333
ABSTRACT
Acoustic emission, in conjunction with visual observation, was
monitored in a High Arctic field laboratory in multi-year
columnar-grained sea ice during uniaxial compression tests in a
wide range of loading rates.
AEobservations were compared
with the visual observation and an estimation of tensile
strength and its rate sensitivity was made from the data
obtained.
Dans un laboratoire de terrain de lfExtr6me-Arctique, on a
mesur6, tout en procgdant 3 une observation visuelle,
1'6mission acoustiaue
LEALclans de la glace-&e
mer
3grains
prismatiques
3g7--he
d'essais
de compression
ge.
Les
observations cc
ultats de
1
'observation
es, on a
estimg la
rB
Iet sa
The Second International Conference on Acoustic Rnission
ACOUSTIC EMISSION STUDY ON MULTI-YEAR SEA I C E I N AN ARCTIC FIELD LABORATORY
Nirmal K. S i n h a
D i v i s i o n of B u i l d i n g Research N a t i o n a l Research Council Canada
Ottawa, O n t a r i o , KIA OR6 INTRODUCTION
Most working t e m p e r a t u r e s i n i c e a r e v e r y c l o s e t o i t s m e l t i n g p o i n t . The b e h a v i o u r of p o l y c r y s t a l l i n e i c e a t t h e s e h i g h homologous t e m p e r a t u r e s i s v i s c o e l a s t i c , l i k e m e t a l s and a l l o y s a t e l e v a t e d t e m p e r a t u r e s , and e x h i b i t s h i g h t e m p e r a t u r e e m b r i t t l e m e n t . The t r a n s p a r e n c y of ice and t h e u s u a l l y l a r g e g r a i n s i z e f a c i l i t a t e d i r e c t v i s u a l o b s e r v a t i o n of t h e
f o r m a t i o n of m i c r o c r a c k s . These p r o p e r t i e s make i c e an a t t r a c t i v e m a t e r i a l f o r s t u d y of t h e f a i l u r e p r o c e s s i n c o n j u n c t i o n w i t h t h e measurements of a c o u s t i c e m i s s i o n ( 1 ) . The p r e s e n t work was c a r r i e d o u t i n t h e f i e l d i n March, 1984 d u r i n g t h e u n i a x i a l c o m p r e s s i v e s t r e n g t h t e s t i n g of f r e s h l y
sampled o l d s e a i c e . TEST SITE AND I C E TYPE
The High A r c t i c Weather S t a t i o n (76ON, llgOW) l o c a t e d on t h e e a s t e r n
s h o r e of Mould Bay, P r i n c e P a t r i c k I s l a n d , N.W.T., Canada, was used a s t h e
b a s e . Experiments were conducted a t -lO°C i n s i d e a mobile t r a i l e r s e r v i n g
a s t h e c o l d l a b o r a t o r y . The t e m p e r a t u r e of t h e l a b o r a t o r y , and hence of t h e t e s t , was c o n t r o l l e d by a commercial h e a t i n g l r e f r i g e r a t i n g u n i t o p e r a t i n g i n t h e h e a t i n g mode; t h e o u t s i d e a i r t e m p e r a t u r e s d u r i n g t h e days of t e s t i n g
were i n t h e r a n g e of -30 t o -40°C. T e s t s were c a r r i e d o u t on ( a ) i c e from
t h e c e n t r a l a r e a of a l a r g e ( a b o u t 1 km d i a m e t e r ) m u l t i - y e a r f l o e ,
d e s i g n a t e d a s "Norland F l o e " t h a t came i n t o t h e bay d u r i n g t h e 1983 summer and ( b ) i c e from a n o t h e r f l o e i n Deer Bay n e a r t h e abandoned w e a t h e r s t a t i o n of I s a c h s e n i n E l l e f Ringness I s l a n d . I c e a t b o t h of t h e s e s i t e s was
columnar-grained, w i t h t h e c - a x i s of t h e g r a i n s o r i e n t e d i n a p r e f e r r e d d i r e c t i o n i n t h e h o r i z o n t a l p l a n e p a r a l l e l t o t h e s u r f a c e of t h e i c e c o v e r . The a v e r a g e s a l i n i t y of i c e from Norland was 1.5O/00 and t h a t from I s a c h s e n was 0.5O/00.
TEST METHODS
Unconfined u n i a x i a l c o m p r e s s i o n t e s t s were c a r r i e d o u t o v e r a wide s t r a i n r a t e r a n g e on h o r i z o n t a l l y o r i e n t e d machined samples w i t h f i n a l
dimensions of 50 x 100 x 250 mm. The l o n g a x i s of t h e g r a i n s was normal t o
t h e 100 x 250-mm f a c e s and t h e mean c - a x i s d i r e c t i o n was o r i e n t e d p a r a l l e l t o t h e l e n g t h of t h e specimen. T e s t p r o c e d u r e s were e s s e n t i a l l y s i m i l a r t o
t h o s e d e s c r i b e d i n r e f e r e n c e 2. The u n i v e r s a l t e s t machine used was a 50-kN
c a p a c i t y c o n v e n t i o n a l screw-driven machine c a p a b l e of a wide r a n g e of
c o n s t a n t cross-head r a t e s (%) o r nominal s t r a i n r a t e s ( i n s l a ) , where
L
i st h e specimen l e n g t h . The machine was k e p t i n s i d e t h e c o l d room ( F i g . l a ) .
A x i a l and t r a n s v e r s e specimen d e f o r m a t i o n s were r e c o r d e d by means of f o u r
d i s p l a c e m e n t gauges mounted d i r e c t l y on t h e specimen ( F i g . l b ) . Cracking
a c t i v i t y was monitored v i s u a l l y i n s i d e t h e c o l d room and marked on a c h a r t
r e c o r d e r by p r e s s i n g a remote-event marker. AE a c t i v i t i e s were m o n i t o r e d
The Second International Conference on Acoustic Enission
f r o z e n t o t h e specimen. The e l e c t r o n i c s f o r t h e l o a d - d e f o r m a t i o n r e c o r d i n g systems were d e s i g n e d t o o p e r a t e a t low t e m p e r a t u r e s and were k e p t i n s i d e t h e c o l d room. The e l e c t r o n i c s f o r t h e AE s y s t e m were k e p t i n a n o t h e r mobile t r a i l e r m a i n t a i n e d a t warm t e m p e r a t u r e s (+20°C). T h i s a r r a n g e m e n t , which was u n a v o i d a b l e a t t h a t t i m e , was most i n c o n v e n i e n t because of weather
c o n d i t i o n s . C o n s e q u e n t l y , AE m o n i t o r i n g was c a r r i e d o u t f o r o n l y t e n t e s t s . RESULTS F i g u r e 2 shows t h e g e n e r a l f e a t u r e s of a t e s t on I s a c h s e n i c e . AE was r e c o r d e d a t a t o t a l a m p l i f i c a t i o n of 76 db. A s s t r e s s approached maximm o r u p p e r y i e l d ( o f ) t h e a x i a l s t r a i n r a t e approached a peak v a l u e e q u i v a l e n t t o t h e nominal s t r a i n r a t e . I n a l l t h e t e s t s , t h e A . s t a r t e d some time a f t e r t h e b e g i n n i n g of l o a d i n g and t h e p r o d u c t i o n of t h e s e e v e n t s a p p r o a c h e d a n a l m o s t u n i f o r m r a t e a f t e r f a i l u r e . The example used h e r e a l s o shows an a b r u p t s l o w i n g down of t h e AE e v e n t s a f t e r u n l o a d i n g , a good i n d i c a t i o n t h a t t h e e v e n t s r e c o r d e d d u r i n g t h e l o a d i n g p e r i o d were i n d e e d caused by t h e d e f o r m a t i o n p r o c e s s e s a c t i n g i n t h e m a t e r i a l .
A few low-amplitude AE e v e n t s were r e c o r d e d ( F i g . 2) b e f o r e a v i s u a l l y i d e n t i f i a b l e c r a c k formed, p r o d u c i n g a r e l a t i v e l y l a r g e s i g n a l . These
c r a c k s were a few mm wide and a few mm t o a few cm l o n g , t h e l e n g t h p a r a l l e l t o t h e l o n g a x i s of t h e g r a i n s . S i n c e t h e c r o s s - s e c t i o n a l s h a p e of t h e g r a i n s was i r r e g u l a r b u t c o u l d be r e p r e s e n t e d by a n e l l i p s e w i t h t h e major a x i s i n t h e r a n g e of 1 t o 4 cm,
AE
a s s o c i a t e d w i t h a v i s i b l e c r a c k i n d i c a t e d t h e c r e a t i o n of a n o p e n i n g comparable i n s i z e t o t h e g r a i n s . These o b s e r v a t i o n s a r e s i m i l a r t o p r e v i o u s o b s e r v a t i o n s made i n columnar-grained f r e s h w a t e r i c e ( 1 ) . Sea i c e , however, e x h i b i t e d a n o t h e r t y p e of v i s i b l e c r a c k t h a t was n o t o f t e n n o t i c e d i n f r e s h w a t e r i c e . These c r a c k s were s m a l l ( 1 mm o r l e s s ) and t h e y d i s a p p e a r e d immediately a f t e r t h e i r f o r m a t i o n . The s i z e s of t h e s e c a v i t i e s were comparable t o t h e s i z e of t h e s u b g r a i n s i n s e a i c e . Most of t h e low a m p l i t u d e AE e v e n t s r e c o r d e d i n s e a i c e , f o r example i n F i g . 2, were t h o u g h t t o be a s s o c i a t e d w i t h t h e i n i t i a t i o n s of t h e s e s m a l l c a v i t i e s . M o n i t o r i n g AE d u r i n g t h e c o m p r e s s i o n t e s t s g r e a t l y s i m p l i f i e s t h e i d e n t i f i c a t i o n of t h e l a r g e c r a c k s , and t h e a s s o c i a t e d i n f o r m a t i o n on t i m e , s t r e s s , s t r a i n and l o c a t i o n . Formation of t h e f i r s t l a r g e c r a c k s i n a m a t e r i a l d u r i n g compression d o e s n o t n e c e s s a r i l y d e t e r m i n e i t s c o m p r e s s i v e s t r e n g t h . However, t h e s e c r a c k s may l e a d t o f a i l u r e by f r a c t u r e u n d e r t e n s i l e mode of l o a d i n g . By i n v o k i n g G r i f f i t h s ' t h e o r y ( 1 ) t h e o b s e r v a t i o n s made on t h e f o r m a t i o n of t h e f i r s t l a r g e c r a c k s i n f r e s h w a t e r i c e d u r i n g compression t e s t s c o u l d be u s e d t o e s t i m a t e t h e t e n s i l e s t r e n g t h and i t s dependence on t h e r a t e of l o a d i n g . A few of t h e p r e v i o u s r e s u l t s on columnar-grained ice a r e p r e s e n t e d i n F i g . 3, a l o n g w i t h t h e o b s e r v a t i o n s1
p r e s e n t l y made on t h e f o r m a t i o n of t h e f i r s t l a r g e c r a c k s i n m u l t i y e a r s e ai c e . The stress r a t e s r e p r e s e n t t h e averag.e stress r a t e s up t o t h e
I
f o r m a t i o n of t h e s e c r a c k s . R e s u l t s on f r e s h w a t e r i c e r e p r e s e n t t h e a v e r a g e of t h e f i r s t t h r e e c r a c k s i n t h e laboratory-made i n c l u s i o n - f r e e i c e . The t e n s i l e s t r e n g t h s were d e t e r m i n e d by Kubo ( 3 ) on n a t u r a l r i v e r i c e which c e r t a i n l y c o n t a i n e d i n h e r e n t f l a w s . I n g e n e r a l , t h e r e s u l t s a r e e n c o u r a g i n g , p a r t i c u l a r l y t h e s i m i l a r r a t e e f f e c t i n b o t h t y p e s o f i c e . There i s a s t r o n g i n d i c a t i o n t h a t t h e multi-year s e a i c e c o u l d be s i g n i f i c a n t l y lower i n t e n s i l e s t r e n g t h t h a n t h e same t y p e of f r e s h w a t e r i c e i n t h e stress r a t e r a n g e s t u d i e d h e r e . No d a t a a r e a v a i l a b l e now on d i r e c t t e n s i l e s t r e n g t h of m u l t i y e a r columnar-grained s e a i c e .
The Second International Conference on Acoustic hission
REFERENCES( 1 ) S i n h a ,
N.K.
(1982) A c o u s t i c e m i s s i o n and m i c r o c r a c k i n g i n i c e . Proc. J o i n t Conference on Experimental Mechanics, S o c i e t y of Experimental S t r e s s A n a l y s i s / J a p a n S o c i e t y f o r Mechanical E n g i n e e r s , Honolulu/Maui, Hawaii, May, 1982, P a r t 11, p. 767-772.( 2 ) S i n h a , N.K. (1984) U n i a x i a l compressive s t r e n g t h of f i r s t y e a r and m u l t i - y e a r s e a i c e . Can. J. Civ. Eng., 11 (11, p - 82-91.
( 3 ) C o n s t r u c t i o n Bureau, South Manchurian Railway Company Study on R i v e r I c e ( i n J a p a n e s e ) (1941) T r a n s l a t i o n : U.S. Army CRREL, Trans. 50, 1955. (Y. Kubo, c h i e f e n g i n e e r of t h e p r o j e c t , p u b l i s h e d a b r i e f summary of t h e p r o j e c t i n Seppyo, 20 ( 6 ) 1958, p. 161-165.)
F i g u r e 1. Experimental arrangement showing ( a ) t e s t s y s t e m and (b)
l o c a t i o n s of AE d e t e c t o r s and d i s p l a c e m e n t gauges on t h e specimen a t -lO°C.
The Second International Conference on Acoustic hission
TEST 1 8 4 7-
6-
5-
0 CL 2 4-
b \L u Q " w U " 3 - u CL C I " 2-
U N L O A D E D I I 0 I D O z o o 3 oa 4 0 0 500 T I M E , t , s F I G U R E 2 S T R E S S , S T R A I N A N D A E H I S T O R I E S F O R I S A C H S E N I C E A T - 1 0 ° C S U B J E C T E D T O - 5 - 1 E n = ~ x ~ ~ FIRST CRACKS 6 0 -IO°C, 4-5 mmN -30°C. 4-5 rnm FRESH WATER 5-2 ICE 0 -lO°C, 2-3 mm
F I G U R E 3
STRESS R A T E D E P E N D E N C E O F STRESS A T F I R S T C R A C K O R T E N S I L E S T R E N G T H
T h i s paper i s being d i s t r i b u t e d i n r e p r i n t form by t h e I n s t i t u t e f o r Research i n C o n s t r u c t i o n . A l i s t of b u i l d i n g p r a c t i c e and r e s e a r c h p u b l i c a t i o n s a v a i l a b l e from t h e I n s t i t u t e may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , I n s t i t u t e f o r Research i n C o n s t r u c t i o n , N a t i o n a l Research C o u n c i l of C a n a d a , O t t a w a , O n t a r i o ,
KIA
OR6.C e document e s t d i s t - r i b u 6 sous forme de t i r 6 - 3 - p a r t p a r 1' I n s t i t u t de r e c h e r c h e e n c o n s t r u c t i o n . On peut o b t e n i r une l i s t e d e s p u b l i c a t i o n s de 1' I n s t i t u t p o r t a n t s u r
