Kinetics of damage accumulation of rock salt during creep

Lelf. Appl. Engng Sci. Vol. 19. pp. 451-454 Pergamon Press Ltd., 1981. Printed in Great Britain

KIKKTICS OF DAMAGE ACCtJMUIATIOR OF ROCK SALT DUELINGCRBDP O.V.Kovaler, Yu.K.Litov, Yu.I.EmsnoVskl The USSR. B & D Institute of Haluqy Communicated (received

by

V.N.

, Leningrad

iiikolaevskii

October

3, 1980)

ABSTRACT Yicrofraoturing of rook salt specimen were deteofed experimentally usi the method of impulse eleotroma&netlo radiationn?IEB). The number of II&Rsi&nals was chosen es a measure of damage aocumulatlon in rock salt during creep in unlaxial ooapressire experiments. Using the results of these expermients the rupture curve of rook salt Is given and the kinetior of dama&es aooumulation is derived.

IlQTEODUCTIOl It is well known, that plastio deformation Is usually accompanied by conoentratlon of stressee and aocumulation of electrio ohafges on the internal defects of materials. When microfracturing st8rts, some p8rt of accumulated eleatrlo energy i8 dispersed in the form of impulse eleotromagnetlc radiation (IER) due to gas discharge between oraok surfaoes 1 . Bxperiments have shown that IKE parameters can be registered for rook salt at all stages of its

deformation up

to final rupture. So it enable8 us to determine In this paper the kinetiO8 of rook salt microfracturing In the oreep tests.

BXPFiBIMENTALPROCEDUBB Creep experiments in unlaxiol oompreselon were oarrled out on oylindrloal rook salt speolaene 0.064 m in height). 451

(0.032 m in dia.,

O.V.KOVALEV etal.

452

Fig.1 'phe experImenta

system:

1 - rook salt specimen; 2 - metal aoreen; 3 capaoitl9e sensor; 4 - selective amplifier; sealer 5-

The 98lu.e of applied compressire lo8d 8bOUt TO-80 per oent of the rupture load obtained In short

nents.

time experl-

The experimental system used In the present study Is

#hoan sehem&iO81~

in Fig.1, IEB parameters of the speci-

men during oreep were IUI8sUred with seleotire amplifier (4) and sealer (5). IEB slgn8ls were detected with the oapaoiti9e sensor (3) enosrred together with the specimen (1) Into the met8l aoreen (2). 'Phenumbers Ii of IBR signals were chosen as 8 measure of damage 8comnlllation, Mean values of lc 8t 8 given load were oaloulated from tests results of five 6peolmens. Yaxlmum relatloe error la 8 series of measurement did

not eroeed

10%.

EXFl3FUMBBTA.L RESULTS AND DISCUSSIOB !The d8a8ge faotor

r [2]

was used to evaluated the

miorafraoturing of material during oreep. Here

B*

Is

the number of IEB signals measured at the moment

when nmcrofraoturlng starte. From the definition of follows th8t end

It-

1 = 0, when the material Is in vlrC;ln

1, when the d8mge

is complete.

i

it

state

453

Kinetics of damage accumulation of rock salt during creep

typical 8 - t curve for rook salt is shown in Fig.2.

A

It can be seen from this regions

figure

that

number of distinot

a

n8y be observed.

Fig.2 A tgrpical

1 -

*

Cur-

ve rook salt

0

I+-

I 2mo

Region

I

ments

4000 6000 $000 t,s 023. At

this

ed due to short t-e plied

during

reoived oreep experl-

is develop-

stage the microfracWrin&

lo&din& and depends on the value

of ap-

load. Region Bc. The prooes;er of miorofxaot~~

down due to strain vefoped

harderlng

and defo~~tion

slow@&

anisotropy

de-

ia speofmen daring the oreep.

Regicn

the fraoturs

CD,. This

region represents

prooess,

materfill takea plme

the final. stageof

when the complete sod failure

At th2s atagethe damage faotor speed,

so the speo%xen life

ration

of this

separation

of the

of the etruotazre oomree. 1

grows at 8 ~i~i~~

is mstly

determined by tie

dm-

atage,

Experimental results oribed

is

represented

In Pig.2 are welZ des-

by the equation

where m is a rnaterirrl oonskawt( m = 6 at ~orplal taqwxratr is the time to rtlpbme, when [ = I. It is evident that for different tipf, of stress ci , whioh 1s $Xx-

t=eL

ed in eaoh experiment,

the time to rapture tr

ferent.

So one oan amwam that ti

stress

G

fe,a

imotion

is alrre difof applied

0. V. KOVALEV et al.

454

propa (2)

and (3)

=f(~)(~m~-~~,

vf

Let

have the relation 6

be a?~ arbitrary

t (em-f)= diifersntlablrr

funotion of time f, thm, dlfferentiatlngboth part6 of thl6 relation, w6 obtain

dt=

(4)

dt

It Is seen from this equation that the rat@ of damage faotor 1

is a funotion of the d%a%ge factor itself, appli-

ed strees C?Iand the loadfw rate

The author% expsesertheir gratitude to V.YA!Jikolaevaky aad B,S,Permjakov for valuable diaaussion.

1, Vorobyer 11.1.Xonio snd eleotronlo properiiesof alkali-halogen UryUtSlS. Tomk, 1968 (in Russian). 2. Litw Yu.X. Klnetlos of deetruotlon and strengthening of defornmble solids, (Dokl%dy Pkademil If&t&SSSR, 9979, t.245, X4,

809-811 (in Russian).