- Email: [email protected]
Mechanical properties
.~lul+,Pml,+Ncwnc+'+J~+d E'+U,++nc,'r+ng, 3 h ( 1 9 ' T H ) 133
1.43
133
MECHANICAL PROPERTIES (.)r i.~an i'/.e r .~ I.I F' K<.'k,,,, ,,4~t.~,mm' N'~.~/~.md L,~JhlmJh~ V ,I R iY,~.;I, E/TDA, [ht,~:.mm <~/ ['hy;m'al h'e,~t,arch
A (_] Evum,;, /~',.'/,'wHI ,'+c.,m'e t~e.ter
ThP h i g h e s t I_~rli)rity shuuht he I.)la('ed on
St."( )PE "l"he MPchanlcal Prol.mtLIvs W(.)rksh,.)l.~ was asked t,o ~teM wtt, il all I.)r(~blems <)r d e f l ) r m a Lion and flrac't,Llrv, ex~'vpL wit, h t,llv folh.)wmg Sl.~Vi'tl'm areas w h m h were asstgnPd t,o i~t,her w,,rkshol.,S defornlaLli.,n IJro,'et.;sIIlg, w,-'hls and t.hI,'k sec'l.ll.ms, ,-,rosic, i~ and w,-'ar, Hie ,'< )rrosion :~Sl.,,-'cl,s o r st.r,-,ss ~.'orl'< ~SlOt'~ Cl'a('k iiiI.~, Irra, lmt.i,.m crePp, anll n,m-,le.st.ru,'Lwe evaluaLi,.)n
{,}IP t'(_~IIIpP'+'hf'IISIP~.'II(~S,~; <.)r rl+lPchurll('a] ]lt'Ul)er tiPS r~sPart?Jl, P i i c o L i r a g l l l ~ a('{,iv~ ~)v.~t'Ja[.) b(¢.{,weP|l (i,) rtllCr<_)s('i)j.H(- and mai'lrosi'(~pl~' al_)
pr( )at.'h vs', (11) MP('h:.llll<~al J.)l'oJ_).~rLll-~s reSVLli"('ll
a|l(J
u thl-'r d tsvq din(-.s, (Hal) inv.,st, alsatians orl dtlT,-,r(-,nt ('lass~.s of r~iu t,Vl'ia Is', (iv) thP s,'lent.~l'~' a n d th<-, l.P,'hn
'T'<.)F' f'R I( )R ITY M EC'H ANICAL F'RI.)PF_:F{'T'IES F',SE A RCH
1 I N'T'R (.) EII.II"T I0 N
A I1 irH'rl-,asPd u tll[vrst,al~d Irlg o f m i('r< )s('OlJl(' a n d illa('l'(.),~('(-)i_)l(: m ~ v h a n l l ' a l prr)liPrt, iPs IS
A Pm'spe('twe
('rit, i<'ally rlPP(|.~l| iii 'all PnPrgy Lvt:hnoh-)gleS. FtPsear<'h urPas wit, h a high pid,Pnt,~al impact and a high prohahdHy o/' s+tcc+,ss over b<.)t,ll t.h~' short.vr an<| I<.)ngvr t.i-,|'nl are (i) c'onst, lt, tlt, lV<-, ri-,l:~it.lOl++.+ al1(l llullla,g,e,_ ai' ~'u rntllal.lon lawn, (li) crlt.i-,l'Ja f o r t,lle h~i'aJlzut.irm o f llPl'or mat ion;
t,ur,;m~ point Whil,-' in the, ~)()'s and 6()'s [h,-,
( l l i ) [.) red l t' t, l <.)n <-)1' {'alJLirP ra{,es;
(IV) ma{Prlals dPslgn anlJ subst, lt, uLablll|,V Research ari~a,~ {,hal liPPit ill(,r'Ptl,~ed mnphus~,~ to (Ievehq_~ {,hP h,'lSl4' undel'S{,andlll~ irrl].lort,all{, J'l)r {,by s ( ) l t l [ l ( m o[' t'lrltlt'al prol_) lems at'<-, <'<.)licP.rlivd Wlt, h (I)
C'lr~lck IIl.l<'h-'a{llm ~'l'i{,Prla,
(11) rP](-'van{ sllrfa~.'e and in{,erl'a('P i)rol .) eft ivs
M~,4'hani<'M l.)rol..-'rt.les r,-,s~,an'h
is at a
MIL'rosI.'()pI(' ,'.1|11~ inLicr(.)s(,oi31(, alq_~tuach,-,s t u (lt-~forr(l:lt, l(.H1 an(t flia(:~,ur( -, (:?v(.)lv(~(I us i~ssPn
t,lally in(l~,per.lent dlSCll.llln.s, (,hP 7()'s haw' I.)rotlghL Ir.:'r(-,aslngly eft'eCt, lW mlerucl.m I.),t.we.Pn t.h~ two. ,.qilnult.ane()Lisly, t h , ~'on sidvrallh-, Irlt'l'easv Ii1 sOphl.,~tl£'Cttltm that, has I_'.-'rva~l,-'d all ill' mat.t-,rials sc'ivn<'v has ma
mPt-ilatllSnlS
0[' J)ot,h d v f c ) r m a t , i
and I'rac'Lure IS n(~w I)~lng vonslcl(-,red, an(| all II'l{,Pl,~ra{,IO|l c)vi-Jr ('omph-'x I(.)a(tmg lli,,-;t.orlPs (Stl('l'l ,'lS a]{,Prllat, lllg~ i'|'P~la all(J ['~[iLVtlP) IS
(iv) r e i ' l w v r y , lecryst,alllzaLion, and r)hasP t,ransf()rma{l~mS ooc'urrlng s~multanPouslv w it,h dPl'<)rmat i(.)11
J~PIn{2, a{,[,PITII)[,Pd 'T'h~ glaring vx('ept, lon t,(.i t,his i.)rogrvs:slng suphist, lcat, lon an
O0'Jb b4 If;/'Tali)(Kih 4)I 3;J%~ LPb
,,_~F:I,,i,~n~! Sl~q~siq,n,J.i..; A , L,du,,aririvlPrlnJ.Pd m ille '~{'l.i'ie|l,~ri{J,,
( I l l ) {,hP erJ'P('[l,; o f L'hPmll'aJ . ~ n v i r o n r I l e t l { , s ,
1 :} 4
Stl<'h a rapid ~levelopment, ul hot, h t,he breadt.h and delJt, h o1' ultderst,anding pt'ovldes exciting scten{.ll'l~' c'haJlenges, and i[+ portends a rapidly m~'reasing us+,[uhlf,ss of the results or such resean'lh. In some cases, t,he I1npa~'t 1311 Lo('hn<)h)gl('al a
mal+,rtals developments; ['or example, I11 t,he ..)pt,lmlzat, l
ehalll'P
(i) [1 SLIII'('eHS IS u n l ' e r t , a l l l .
Fin',.dly, t,hero are arras of mPchanl('aJ pr<)l'~ ert, leS research where Lhe Impact, of any rest.llt, s on te<'hnoh)gieal i.mfl.flerns w()ul
f~rmant'e <)r st,ru,'lural ,'oml.,.menl,s, t,hey will be highly seh-,<'tlW In terms or l,he alloys aiM <'omput, at, ional Lechnlques used. rl"he basic r e s e a r ( ' h IJl'OIb'q'aI11 18 nee
B. Outline, The main body c~l" t,he repm't summartzes out, stal;
M A T E R I A L S AND ENVIRf)NMEN'T'S
,4 Materials T o the h e n e r i t or met'Ironical properties research,
arl u1(.'reasJrlg L e n t l e n c y
can
he
1 3h
ol.lservm.I b.i integrut,e the un~lersLun~linl4 gall"md fl'(ml d i f f e r e n t kblds ot' mat.m'tals met.aJs and alloys, c e r a m i c s , s e m l c o n d u c L o r s allqI illlllelIL.IIN, I.i(.Ilylllel'S ailc.ILlm(ilri.ilic)I.iS nla l m'nals It, us u m e a s u r e ~)t' the Sol~hust, icat, non~ (~t' t,he t'iHd t h a t sm'h old t nme classul'ucaLu~ms llave hlst, Ill significance atilt m'e being re IJh_lce(I I.)y cah'gurle,'~ Sll('h aS {,WCI phase rl'lal,e rmls, mal,ermls w i t h a high F'eierls stress i)r a h~w i'leavage sl, rengl,h, aml the I~ke. II in t,hus m~L eXlJel'telt that Sl~ecufll' " n e w m u l e r i a l s " re, lUre' a redu'el'tlon or the ii~e(,hau~ul'uJ i_)rol.~rLues research el't'~)rt,, rut, her, they sl..mht t.-, ilwl.)rl)(_)ral,e(I ii~t,o (li'~g~)mg I)iOb.'~'arnn l i) Ira)aden t.he base ~)1' un~lerst,andnng. T h e (llst, inct, l~m I_)el.,Weell "acallemnl'" and "l'e:ll l i f e " materials is also I.lel:()mlrl~, I)hlrr'ed. Mal,erl;.lJs foi elec't,i'li'aI a n d rn;..l~a,l l e l l c al.)ldlca t, loIIS ill'e ot't,en plli'e nm{,als
(tt t,o derive alfl~ropriale SUlmrl.~SlLll)l~ laws [ih;.It ',.dlow ()lie t , I . ) i ' a h . ' u l a t e ( w h e n e v e r I,)nSll)le) tile InelanLie t_)eh,'lVlUr i)f [lie i'oln
I.ItiSlt,e ()rl~'e that o f the clmsl, lL,tiPllL phases IS kll<)Wt'l, (li) t,o un~lerst,al~d ( w h e n simple superl_.)Sl t,lorl is inadequate) any athllt, lonal nleehanlsmS Stlc'h as slippage and dPc~dleSl~Ul at, the inter fa('en between the I'l.)Ililli~ll(-'ll{,S, an(I iiOll ll.,('al in l(-,ral'Lions ~o{,h IrellLIIle the use-' o f SOl.)hlsllCale~l star, is t,ics, itl paJ"L, t,i~ delllleal, e rnacronel)plcally "{hli'{,lle" beliLivlor ['r('ml b,q'o,%; fral'tLire Et,uh~lng Ill icruslrHt.'IHr~,s T h e classlcul, amI very nu~'eessful, al~l_mmch o r iflWslca] met,allurgy has I)een [,o ~lesrrlbP, in separuL~ disciplines, t,l~e mlcrost, rtleUJre and its r~mt.rol IW thermr)mecl~alllCa] [,leatiIlrlellt, Oll {.he one halltI, allcl l.he relallOll Llel.weell all anLabllshe(l i'liil'rl.l!~I, rul'{,i.iI'eLind n~a4'ros('(q,i~' i_)ropertles on II~e olhe~. A rnaI()r shorh'ommI~, of th~s aIflwoa~'h has L.,en sh~w Im.)~.O'Pss in t.he area WIlerP niii'rtlsl,i'ui'{,iire ('ll,'IIll.~e~ aii(I nle ('l~anlcal (tel'ornlat, l~)n hal_)pen Slmlllt,alle~HISIy. While t.lleet'l'el't, ~{' ;IIIal_)idle(l nt.le~.;s()II {.rLlllS t'urlnat, l~mS has been a m p l y I~westigat,e~t, t h~ et'i'ecL of u n g u m g lran,~l'c~rmahuus d u r i n g plastic ll~w alld l'ra~'tllr~, has I'eCelVe(I IlI.t.IP at, t ellt, lOl~ ~lmnlarlv, t,l~e I.)l'mrlornenorl of tlylloIIIl¢.' rPt'r.v,slullh:allc)l; allq| asso('tat,vct t w i n n i n g I:; o n l y begml~UH~, t~ h~, un~tPrst, o~)d tam'ha n iSl,l~'ally. HIgl~ {,elllllelLthJl'e erler,e,y techlloh.~la, le,'.; l'ellllU"ea Ilew e l n l d l a si n o1~ research Iii [llt,S~-, cl'it, ie~d aIPas.
(' ('hmnicol mu,."umm,nl,~ Aggressive ellVll(_)llll'lelll,n piny an u.zuzr.,'~ce ctmlted r~fle m n~w ml~rgy t erhnoh.)gi~s, t ranncmldmg, nn inany ways, l he classwal t'lehln (.)t' i'(.)llq.)~l(.)ll al~l sl, renn CmT()si()n crurkung. At I~lgh t,~mperutllres, m:lny Sl~ecnes q'an dtl'l'use I.,hrougll t.ll~, entur~ section, entller Into ~t' (.)Lit c)l' tilt-' mat,erlal, and LllLIS H~enge c~mlp~stlu.m amJ mtcrunlrtlcltn'P NPighl...)rln~, t'tel(Is in rout,el mls ncmm'e nilouhl mvestJga[,e, with hq~,hest prlorll,y, st.l~'h cl~al'lgeS Ill rPaltst te itlat,erlals, mid Illt, erll~'t, Wlt, h t,he mm.'l~anucal Um)l.)eMleS c(.)lnlnUlllt,y if Ile_W l,yl.leS ()[' ITII(.'II) st ru~'LLn~e s h o u M lip I'oui~l. At low Lmnl~eraU~res, o n l y u l'Pw element,s can dift'ul~-, Ion~g (lnnt,am'en ( h y d | ' l . ) g e n and s u l f u r being ~ul.,st,aIl(llng eXCPl_d,nons), m~)re (.'()mrrlolllV, t,he el'fPct.s (~1' i'henlll'al eiwIrOll rnents ate resl, rict,ed t,o near sin'/ace rt'gl¢911,~ Here, eVell the mont, I)u~.;l(' chmaci,et izal, iOll ol"
136
" e n v t r o n r n e n U ' , and t,he (Id'ferenL ways It, can affect, propert, leS, seems t,o be la,.'klng. Even cry,.,gen ie gases are "aggressive" in t,heu" effect, o n polymer q~razlng, and aqueous environ ment,s have a p r o f o u n d el'feet, on strain IocaJtzaLioll In fat, lgue. It, was a gener',.d e o n H u s i o n o f t,hls workshop t,hat, envi_ronmenLal effecLs on me(:hmli ~"al propert, ies, especially at, high t,emperat, ures, have not, beell t,reat, ed wlt, h nea.rly t,he maine sophist, l,:at, lon as 'all or,her aspeet,s ,.,f t.he i.wobleln, m rag,t,, reprodui'lhlllt.y of experi rrleilt, aJ ohservat, lons has only raJ'ely been at, t,ained. S o m e o f t,he I.winclpal deficiencies leading t,o Lhis impasse are t,he dtffwult, ies Inw.)lved I)ot, h ill det,eet, lng and t,ra<:lng l,he progress o f small quant, lt,les (1t' t,he m't, lve en vi_ronment, al species, and in est,ablishillg t.he effect, o f t,hese SlJe~'ies on lattt('e or mterlbc~, dt,coh~'stott The former problem ~'an be pazl.lally addressed I)y appealing Lu t.he wide variet, y of Leehniqtles now avadable for sur I'ace and bulk analysis. However, innovat.tve t,e,'hniques m'e required for many Ill' Lhe ('rlt, lcal I.woblems, and t,hus t,he st,rong [}~ll t,iclpat, lon o f surface physi~'lst,s is an essent, lal eonsl,~l, uent, In a viable st,udy. A cnt, leal issue ts t,he effect, on d e e o h e s i o n o f variotls act, ire specws; a prtort a p p r o a c h e s for caJ,zulat, ll~g t,hese efl'e('t,s are not, apl.,arm~t, Nevert,heless, some prols'q'ess will inevitably be aehteved If t,he prolflem is addressed hy the pert, lnent, physlcs/H~emlst,I.'y dlSellflines and su~'l~ a pm't, lelpaLIon IS strongly urged.
D Surl'aces and inter[aces T h e propert, ies o f int,erfaces have a ,'rlt, ical inq.mct, on mechanieaJ propert, leS Ill many areas and appear t,o be ripe for a major advance Ill underst.andlng. A bas," research proi.~lem o f g-teat, sibmlficance and general relevance Lo rraeLure p h e n o m e n a , is an u n d e r st,anding o r what, allows (or causes) an int,erface I,o be capable o f developinv, a crock. This IS a Nindament,al aspecl, o1' ~luct, de rract, ure nu,'leaLion (iJa.rt, lele-mat, rlx inl,erfaer,d failure), o f t e m p e r embrlt, t,lement In st,eels, o f h y d r o g e n assist,ed cracking, o f fraet, ure in ceramics, o f creep-rulM.ure eavtt, y nu('leat, lon, et, c. T h e area calls for basic w~)rk in the solidst,at,e physics and t,herm~)dynamles r.)l' inLer races (including segregant, adsorpLt~)n of impurlt.tes and consequent, alt,erat.ions or cohesion), ill laLt,iee dynamtcs, disl(.)eat, lOn
t,hPory, and ~)t,hert, ylJes of rnicrosLruct, ural nl~)dellng, and in relevant, t,eehmques of Lhe experlmerlLal and quanLiLaLive chemical allaJysls or in[,el'['aue.'4. The elTletem'y of hq'uin boumlaries as stn/,'s and sources for IJC)ln{ dere~.'i,s In dil'fLISWe flow, and Lhe assc.'laLed prol)lems o f gq'aln boun~lary sliding (or gratn botmdary dtsloca tu)n motu.)tt) need furLher illtlrninaLion. Esl.mcr,dly iiI .'eramli.'s, [.tlese i.)roi'esses can be rat,e.limlt, lng (as ~'ompared wlLh dirfuslon). T h e iil[]uence of sHr/'aces alld surl'ace /'rims iS recelVlllg renewed al, t,ent.lon alld is f)[ espe,'lal concern for energy sysLems: neat sur[a,'e behavic)r v.~ iml.,orLanL in er,.)Sl,.,n an,t wear, in faLigue ,-rack nucleation and, in some eases, ill Lhe general.ion ,)f plasLw flow (,.,r tt,s ,.',.,rl,'ei'lt,raLiort mt,o ImrsisLent, slip ban, is), which may have effe~'t,s on I~tllk behavior. This fiehl ('ould receive a slgnlfieallt, new InlpeLus I'nlm moderii e~permwnlal tech ntques applied Lo aet.tlally iml..)rt.ant, environ menLs, us well as from sophist, lcat,ed Itllet' alomi(' poh, ottal caleuluttons ( provided t,hese can Iw well mat, ehe~l t,o t,tle macroscopic rJlic)i.lert, ies relevanL li'1 t,hiS ease). Int.eraeLions heLweell i.)eople orlenLed In the direcLion of meehani~'aJ iJ|'opert, ies and surface scient, ist,s, as well as solitl st,at,e t,he,,'lst, s, would be mandat,~ry.
E. h'radtatu.m el'fi'cts The energeUc irradla[,ion ellvlronmenL in fission and fusion reacLors al'fecLs mechanwal hehavlor dlreeHy Lhrough t,he int, roducLton el' a~h li Lional defect,s, de reel t,h tst,ers, d islocat Ion loops, w)i(Is, and gas eOllt,aining bubbles; and mdireet, ly LhroLigh radial, ion.induced segre~a t,ion t,o surfaces or int,erfaees, changes in Lhe i.wet'it.fit,aLe st,|'LICLure, and possibly t.lle forma t,l~m or nonequlld)rn.lm phases. Recent, advances In our undersi,arldlng o1' t,he klrlet, lt's (.ff t.hese rnlt'rost.rucLur~ changes make a clef.ailed sLudy of mechanical erre,.t.s a, urgent, need. Pr(.)baLdy Lhe mosL mll3ortanL one of Lhese IS a loss In duct.lilLy, for exmnple, by severe slip h...'allzat,.m due Lo mwrost,lue t,ural mst,ablltt,y, or by t,he growt.h of macro scopic w.),ls or bubbles. R.elmhle predict, lens o1' l.omponenL life, so tmport.,ant, Lo {,he nuclear t.echllology, requtre a far bet.t.er under sLandmg of Lhese phenomena Lhan is currenLly available.
137 (.',reel_}
3 DEFOR M ATI(_)N Illereaslng Pnlpllasls has I_)Perl I)la,'ed in le('en{, all
A 8h'+',~lh+',mg ++++'+'IPa+++s+++s Sigliil'h'aiiL a d v a m ' e s h:.IVe beell llltlde Ill l,he la;st de<'ailP IiI Ollr undel'S{all
B Euul, t,.m ,,[ s,hsh'u('tm'e a , d de/vet .~l rllt't ll l'e 'File high t emllerat.Lire I)W<.gJel't.iPs ,)t" rnat.P rl'd..Is .'ire st, rollp, ly irlt'luence(I by deveh.)l.)lTlerlLs ill [.he (llsh.u'aLiorl and subbqaln s[.rtll'I.l.lIH t h n )ugh delc,'ma I/c ~/t arid rec'c ~uer.v I m.n_'esses. 'T'hls IS an LLIIeLI lagging I_lehlild low I.Prtll)erat.llrp s{rPllgIihl-'11111g 111Pchi.IlliSm,'.; i11 Ulldersl,Llnllll1~, ImL is <~iiP ill w l l w h ~'tlrreut (lewhq_mlmiL is i.'iplil llILe|'a~'{,Ion l)et, weerl lllVl-,S[,l~tJJ.ors tlSlllp, dIl'l'erei~t, classes oI' inat.erlals has l~eell v m y l'rLIItl'tIl, f<)r <-,×ample, a l_mrallelu.+rn lJPt,ween t,he l)Pllavlor cdu.+erved in l.+,eoloEI<'al rnuLmmls aml in metals llas been ('oun~l. 'T'he prlll~'ll_vd.I nle<'ll;misms t,hat trlLIst, I~e lill
eli.'1~latlon
<~I' l_.+~tI~'uIl~'
l_u'ol)leln <'a.+es
(2 ('+.mst/t,l/tp+, /'e/ul/o,s MzH'rosc.c~pu' d<-'l',)rnlut.u.,n must. evellt.uully lu-'
13H
param(-,l,ers - and as few o f t,hese as possible. T h i s IS anot,her area Ill whl(.'h all int,eg'rat, ion (:)l' ),he l.)h(-,nomen(.)logical and physical ap p r o a c h e s t,o rne(:hantcal pr(.-)pertaes has reeent, ly led t,o significant, advances and is expeel,e(t t,o I.)rovtde useful resLiIt, s in the I'c)reseeable I'ut, ure. T h e r(.)rmulat, i o n m t,erms o1' state parameters, raLher t,han hlsL<)ry vaxmbles, is i.)hysically well I'()un(ted and ('on nect, ed t,(.) ),he n(.)t, ion(.)t' ('(.)nLrol (.)1' pr<_)[+el't,ies I.)y )nl<.'r()st, ru('t, ure, it, shouht lead t,<:) a signlt'i ('ant, redu('t, ton m ),he n u m b e r ()f t,esLs t,hat, must, be l.~erl'onue~l t,o
rnat, ermls ('lasses s h u w m g great p r o m is<-, for enerls.W r<-,lat.ed a ppl,.'at, ic)ns. l)(.)stl,(-'s -
D D y n a m w el'l'eets For most, n()rmal (t(-,mgn applleat, i<.)ns, an underst, a n d m g (-)r small st, ram def(.)rmat,,:)n an(l o r ),he mit, mt,)<.)n (_)f failure is sufl','ient,. On ),he or, her h a n d , ir t,he eons(-,qtten(.'(-,s ()r failure must, he assessed )n (let,aft, elt, her bl a<'('ident, sit, u a t i o n s (r(-,a('t,or a('('ident,s, safet, y, as In ('oilt,ainment, (.)f l'ragmenl,s f r o m t,urbine rl.)t,(.)r <.)r Hywh(-'el failure, el, e l (.)r in l'(.)rmmg, l.)ro ('essmg, (')r h r e a k a g e (high.en(-,rls.wrate rl.)rrning, rock l.)reakage, et,c.), )t, is o f t e n ne('essary t,o have (:()nst, it,ut, ive relat, i(')ns f(.)r large def(.)rmat, i o n ( usu=d ly nonrad)al), and fl:)r p o s t / ' , d a r e heha+,ior, t.hat, is, for rnat.(-,)'ials ,'ont.ainmg c r a c k s (.)rot, her clamage. In rnany appl)('at,,:)ns, very high rates are involved. q"hm is a pr<.)l)lem (.)f htgh e(.)mplexit.y (tin. h:)<'at, il.)n an(I ),win nt,:leat, t()n, ir)ert, tal I.)an')er pen(-,t, rat, i<.)n, d m l o e a t , . : ) n - p h o n o n int,eract,ions, et,('., ()(.'('ur simult,aneously. All esl_)eelally seri(:)us and lil, t,le undt-,rst, o o d l:)robh-'m is all observe
1 ;;9
elect, Iron inl('rosl'c)pit.' t,e('hrllqLle8 su<'h as weak i.)ea111 ineLho(Is aim lat, t,i<'e m m g m g Anr)Lh<-,l,' l,n<)sl, iml...)rt,ant, area w h e r e I11(|I vulu'aJ dish.Jeat, i<.ms deI, e r M l l l e maeros('<.)pi<.' b e h a v l o r Js t,hat, oi" plast, i<: del'orl,nut, ion .i small t,oluln+' +'lPllletl,l,~t SLI('h aS i."ral'k t, llJ nelghb~Jrhoo
nLillll)ett', al+',.J.Jy{,l('al <-,lel'Lrl_)ll ml('r<.)s('()py. Elu,+lk' atttsolropy, w h u ' h is sul)st.ant, tal eVell III, III<_)SLSln+l.de metals, ulld very iml.)Or rant in low symlnet, ry l,nat.erials, ent,ers t.he mauruscot.nu st.renN.h by way o r dlshwut.lon p~(qJert.leS. SIgntl'lcant a<.tvun,q'es In t.he has,: Iin
f? S / s i n Ioeahzat;¢m I:'last, ictt,y resean'h is ustr.J.lly un(tert,aken under ~=nirorm defl,'maL~un u(md=t,,Jns. Yet,, one o1' t,he most, in+port,ant,, and pot,ent, rally (lallgel,'(.)us [.)hel,lOlTlel+a IS t,he Sl)(.)I1t,uneous h..'alIzat, lol,+ o r sLraii+ ()vel,' p+a.rt,lcular l~art,s (.)r the C,l'()ss se~_'l,lorl, or ll+t,i.) Int, ense b a n d s or sheaf,'. Suuh h..'aJlzat, i<.m cal,+ }+ave a n u m b e r ()I' dirrerel+t causes, it, rnay I)e a geOlrlet,l'ic' msLabdit,y, tt, may origmal,e I.)et,w(-,el,+ prevJ (,Jsly t'()rmed v<.),Js, or it, may be due t,u I'l]l(.'l'(.Is('(.)[_)l<' st,ram s(.)ft,enull;.J, pro('esses sucll us dish.'at, u.+n c h a n n e l m g and iJl,'e('ir.nLut,e rPsulu t,ion. Fmally+ a parLwularly fl'equent, mode of st, ram h.)('aligat, ion is t,he ['ormaLion o1" " p e r sist,ent, slip ban(is" (lurll+g (.'yeli,'
,1 F'R AC'"PI I R E SLuittes or rra<.'Lul,'e are eoni.'erned wit, h t,he preflR'{,ic)n <-)1' I'allur<-,. In ('(.)r+seLlUel+('i-' , I'ra
A Mt('rc~('rut'/t IIIIL'IeutI(+HI, grlHtp/It ottd <'oal+'s ~.'('IH.'P T h e I'ormaHon ol'a rnacrocra(.'k involves t,he nu<.'lea|,lon, growl, h, and c(~alescem'e c)l" rnl('n)
141)
rl'a~'ks. 'l'h,e inuiles n f mwroeraeh' tlllt'll'alloII are many anll va.rled. SeveraJ modes have already been (teserll~ed; f()ur addit, il)nal mechanisms of sul.)st,ant, iaJ pra(,t, lcal sil~nit'l. ~'anee al,'o dm~'ussed below. I n hl,lllll~ , matertal.s, rnicrocracks [ie nt,'leat, od at, st, ross L'(lll('ell,t, ratll(.)tlS i.)r()tltl('ed Ily elas[l(' (Jr [,hormal mlsmat,c'h a[ grahls rl,r second phase I.varti~'les. T h e cra('k forl,nalion IS st, tI(ll,l,gly Illl']l.lenll'ed by the s i z e dlst, rll)titllOnl o f "lWecLirsor" defe('ts at, Int, erfaeos, t,he st,eel.I st, ross t.,q'a(tlent,s, and t,he h..:al m i c r a l'ract, ure t,ouglhness (ill" [the mat,erlal. "l"he solttLi(m t,o t,hm pruhlerrn, as In aJl el, her rni~'ro cra('k rormat,.m I.)r()l.}lPms, den~ands lilt,OIl,SIre ('oojlora[.lOll IIet, weell resea.rl'Jlel'S In s(;!,Jll| nl,eehaiiws, sl,al, i,,.;Lies, an~l rnal,erlals st'tahoe. "rhls t"oopel,'aLiotl, has already begun. Ml('l,'l.)erLll?kS alld VOIDS ('all, also {'(.)rm dLIrllll2, Cl'ee[_l. S[l('h nll('rl.)(Taeks I're(itlon, t.ly derive from t,he st, ross (.'oneenl, rallCm sol, up by Ll(.)Llnltiary sliding. "['tie I'()rma{l()i1 prf)('ess is t,hils del)enlden{, 1)11 {,lie ('hli,Lra('[,or (.)l" [,lle st,l,'eSS singLilarlty pr(~(.Itwo(I by sit(ling, {,11odl['['tlSlVe or plast, lC st,ross relu.xat, iun, and t,ho operat, lve nucleut, i(.)nl ('ril,oriol~. ']"lie I'lrs[, {w~l aspoeLs (~[" t,he I_ii,'ol)lem Call LIe ad(lrosse(l by a me('hanlleS/ mal,eriuls SLLI(ly, hu{, {,lie last is an Ii1[,el,'l'at'e deeuhesion prul)lenn l,hmt, requires several adtlfl, ional PalenLs. Sirrnilarly, t,he ntleleaLion, of vat, Is at, s e c o n d phase pa.rl, l('les nee(Is I'urt, hel, t,ransd iscipllnary SLtldy. A t,hird m a d e o f crack t'urmat, l~m o('eurs (luring eyelw &,lbrmolton, Fatlil.,n.=e rlli('llll ('rm'ks t,yl.m'ally origmat,e wit, bin persist,ent, slip I.mnds or lueallzed bands or intense s h o a l In hel,erugeneous mat,el,'luls, t,his t u n lie a con SeqLlell,t'~ o1' S[I'eSs (Tm('e~l,[ra{l~mS genera[,ed incur kq'ain houlndarms, ()r mt, erphase inl,er I'a~'es In h u m o g e n e o u s mat,erials, cracks may ol,'iglnat,o in Iwrstst, ent, slip hands no~u' ['rue StlllraeeB, bUtl al.~u at, al.~t.)a.rent, ly r a n d u m hwa t,lons wit,hm ban(Is (~I" eon(:ent, raLell shear, Hie nucloat.i(m mechanisnl,s are, here, especially p o o r l y un, tlel,'st,ood, nor has lhe role of the mlerust, ruet, Lire been elea.rly est,ublishe~l. ']"he resulut, ion ul" t,ho prul)lem ro(luU'os a sLrtmg tllil, lal ernl.)haSlS on ol)setwal, iollS ()f rril~,'ro (.'rat'k I'ornlat, i(.Hi, t'()llowed by a ('~H)rlitil,at,ed rneehanit, slst, al, lst,i(:s-rrlat, erlals sl, u d y . In polyl,ncrw matertals, t,he p r e c u r s o l s t,o nl,a('r(~t'racks alle ( ' r a z e s . T h e tmt)rl.fll,()h.~gy o1' crazes and t,he dependorrwe o f t,hetr I'ormat~(.m o n mat,orial prr'opol,'t, ios, e g., l,noleetlltu' weight,,
are reasunahly well c o m p r e h e n d o d Huwever, st u(IIos Lo e x a m i n e t,he sLa/,isl, leS oi' craze fc)r mal, i~m in t,erms oI" material het,erogeneity and o f the efreet,s of urient, a[lun are needed. The propagalltm a n d / o r euales~'em'e or nlieru('raeks at'(-' t,he llOX{, st,ages (.)[' mael'ueraek I'(nlnlat, l o n T h e in'Ul.,agat.l,m o[" mlcr~wl'a~'ks IS Llese[, by all 'l' f t,ho I.lroblelllS asSoelat,o(t Wltlh mm'rucrack propagahtm, wIl,h l,he addd, ional c'(m11~lex p r u h l e m u f mI('ru('rm'k prulJagat, iun acr()ss t-_re(In botlntlaries. The s~)lut, lon t,o t,his prubleiTi is impeded by t,he presenl, in[,rat'[LIblll[,y ot' t,hl'ee (llttlerislon,'d st, ross alvaJyses l'()r " a n g l e d " cracks. S a m e iml..,~rt,allt, insights re(gilt, be ()hi,allied using n u m e r i c a l s(flultuns fur (.tu.erully seleet,ed analugies, ur I~y semi emptrl('al/(limonsiulml t,echniques. T h e c'ualosq'enee ()1' mier(H.'racks is det, e r m i n e d I~y t,he st,ross (st, rain)int,ellslftcat, tOll bet,WOOl1 alq.n'~.)a('hlllg nlte|'()era('ks an(I t,he erit,erlun I'()r i'oaJesL'en('e NOlllhel I aspect, is well L'Olll I.wehen(le(I hw t,hreecllnlenslonaJ :u'range nlellt, s u[' mlt'k(~c'raeks. ,_qume pllOgTeSS has beell a~'hieveil In bril, t,le mat, ormls - where t,he e u a l o s c ' e l ] e e i'l'ltlorioll (Imsod Oll l,he st, ross Illt,ellslt, y fact,or at o n e u f the m l c r o e r a e k s e × e o e d l n g a crit,.'al value) is relat, lvely st, ratghtl'urward - using a t,wudlmerl,slonal m o d e l . St, at,(st, loS ',dsu play an Iml_..~rt,an, t, rule II1 tlhe ovalllat, icm of t'oa.lesuenee, t,hl,l¢lugh tlhe spatllaJ dist, ribtlt, ltm ()[' sit,as ['()r intt, ial nll('ro cl,'aek t'cwmat,,.m. A closely ctHWdlnat,e(I mechmlll('s/mat, erials st, u~ly shouhl again prove I'rUitlftll [~n' t,h e evall.lat, lC)ll, o f Llle etl,ales('ol,lce iJruc'oss. When exI.OllSlVe nlll'rol'raL'{,ure precedes I.ilt.llTla{,e faliul,'e, as i[. does iil tl,o{,erogeno(Ju8 l,'na{.orials such as rut'ks, ('~)ul, arid control,o, or anlsl.lLl'opie mat, erlals SLIi.'il as kn'uphite and wil(ll,d, rrl,i(:ro['ra('t, ure ('all enl2,on(ler StlbS[,anll, lal nuillin, oarit, ies in load respunse T h l s " d e t e r mat, I()ii" ol'{,en needs t.o he l.)ledtet,al.)le, arl,(l eonshtuhve equatu'ms aJ'e re(iLib'etl fi.)r t,hls pt~rl..)se. The "defi.)rmat, lUl,i" t,hat ot'~'urs under t,onsile h~adul,g t'ail be addtlessed by {,he same mt('rt)l'l,'at't, ul,'e anYa.lyses described above. l.ll,ltler ('uml.}ressive h.mdmg, addit, i~mal mocha. nlsrns pert, ain, ÷'g, crack slidil,l,g undel,' t,he nmp~)sod shear sl, resses resisl,ed by surl'aee asl.lerll, lOSl Furl,her st, udles o f tlhe l,'neehanles (211'tlheSe ~)lIIi)tleSSOS ~I'P needed, 111 (,'ol,ijUl,ll'[,l(:m wit,h st,atlSt, lcal st,u(Iies o f mwroera,.'k dis t,riL)ul, tons, arld r'nicros('ul.)tc sJ,udles (_~1" t,he ac'tut'd er'aek o p e i i m g and slidtl,lg rnechunlsms
I,-I B (Tru(,t., propogult~m W h e n InlLial v|'a(:k growt, h IJ|'e(.'edes stgntfi cat|t m m l u w a r i t , y in t,he h.lad/deflevt, tOl~ response, |,lie ol'ack ext.,elision ('all be e[l'eu Lively ~'h,rQ('terlz~'d hy the i.lerJ, lllen{, s[ress III[,PIISII,V ['a('t,or, K 'T'e('|IIII(_ILIPN for eva.lua[,Ing K are als(.) relat, lvely we,ll eMabllshed, alt,h(~ugi~ ,~ome ad(llt, l(irla.I e['I'(3l~, live(IS {,O lie (_tevuted t,lJ very hlgl~ {,emi.lerat, tlrP {,v('llllll.ll.leS lot' SLl'UVl, llrLll ('PralTtil's, all(I to t,et'hnlqLle,~ t'(ir evahlalln~2, K IJ;.l.ralnPters j)erLillvnI [o wPhl IllPII(,S, joint,s, el,('. P, tr rrai'k ext,ellSll)li pt'v(.'e(led lly ill)r1 lillVaJ'l[,leS ill t,he load response (e.~, m l h l steels), {|lP Inlti:ll bq'(Iwt,II (.'or1 I.iv c'IlaJ'a('t,el'lZ, ed Ily t,he rr'at'k i.Ilil-,lli|'lg dIslllav.enlent, ((3(_)I-)}, iir [,he path In(iPi_lVll(ierl{, int,egt'al, ,I T h e Lest, rlle{ih(illt~i r(.)|. ()bt,allllll~ t,hese j.)aJ'arllet,ers ate alNo rea,~Ollahly well dPl'lnP(I. H o w e v e r . {,lip sul_l,~iPqUPrl{, ,,.;t,ahie growl,h o r {,he uiat'k, whl('h I)I'iPI1 allows a sul.lsLalltial Inr|'vase m hlad JiPl'orP ,'l|{,alning irist ablllLv, is IPs,,-; well vlla.I ul'[,erlZ(.e(J, an(I has IP(I t,o h i g h l y ('l.)llSPrl/at, lVe (IeSl!_Ul,'-; alllI ineJ't'li'iPn[, nlaLerlaJs usage. It IS i.iI'PSllrrle(I t,haL Lhe sLable vt';.tvk ex|,PnSlOll In st, Ill I i n l q u e l y (let,Prrntne(I lly ,I, alt,hoLigh i n u r e e×t,~n,~ive ,lUstlt'k'at, lon ( i n c l u d i n g m| eXl_)llrlt, inrot'l.i~li'ut, iol| ill' rat,e el'l'ert,s) ~s r ~ q u l r e d ; but, t,l~e instal_lllltV IS Sl.leVllllen (syst,eln) d e p e n ( I e n t OIHI IS, ;.iS yet,, inadecluaLely rharacl,PrlZed. Furt,ller exl_)ei'lnlellt,',.LI sLu(JIPs, voOrdlnat,e(I w i t h iliiiTiPril'al (aliaJyl, ll'al) soJu[,ll)ns |'(it" i.lUaSl sLaLir rl'avk ~q'clwLh, are ileedPd t,o d e v e l o p g,'n,,rolh.'#d tn,,~tebdtt.v ¢'t'llt'rle ThP teSl,~Lall,',_, to vt'a('k ~_Xt'owt.l, can be st,|'~mgly Inl'luelwell by mwr¢~strttrt~tr,, T h e pert lt|e,llt. |'el:dlunsltIps L)et,ween crack growt, h L'Illd ml('rliM, ructui'e are rive(Je(I to (|PSII:,Tll ma terlah~ Wl[,|l Ol_lt,lnll.lm [,ougllrle~s and M,al.llP ('|al'k ~q,'owt,h t en(lenl'lP,~. III fully hriLLle Illat, e|'lals, SLich as ,~lvlll'lltrGI ('Pl'~Jiiili's, ('l'a('k ~2,|'~)wt,h IH:I'LI|',~ II.V {I|P IIIJ"Pl't t-'×{,PI1SI(H1 ol' |,he_ J.)rllllal."~ crack,, anll ii,~uaJIv hlvolves ;.1 I)ond |Lii){.ure jli'(H'e,'-;s. "rile i'rark g r o w [ h resIs[,alICe |','In t,hI.l~ JIP Pllllall('P(I Lly el'I'Pc't, lrlg ('hallj~Ps near t,hP r r a u k t H_i Lhai" re(lure t,i~e u|'ack LIp (lisl_ila~'emPnL { o r K) 'T'h|'~e p r i m a r y t,oLighen Ing nlerha|ii,~ms o f |his t y p e have t,hus Jar lleen ident, ll'lP(I st, tess a('twat,e(I st,uble rl'llL'l'i) i'|at'kllll:? , (t,~ , Ill AI,,(_):~ alh.)ys), st|'Pss IrI(JLIc'P(J phase t,|'unst'(~rrnaLions (~'.g , 111 Zrl.) 2 ',/.1.1J(.)yS), an~l t'lt.mm~.~ ~rain " p u l l out," (~.'~ , in ~I:~N 4 alh lys). H i , w e r e | ' , i'oo|'d inaLe(I sl, ress analy~Ps all(I en|llEiraJ studies are lleP(IPIt t,l_) (.iLlarlt, ll'y
1
and opt, imlzP t,h~ t,o u g h n P s s , and addlt,tonM t,oughenlng mecIl,'llltStllS (¢ g., I)aSP(I Oil large inl,ernal sh'auls) sh~mhl lie e×ph)red For po/ynleric meleriol,~, craZlrl~ IS n l.lr(-,(.'ursor {,o ('rack ext,ensIoll. Henl'e, aklrl to st,able nllc'r(.10ravkllll~ Iii hrit, t,le mat,Prr,.lJs, aJ'iUys o f nonl.lropagat, lng ('i'a'z.,es (."al'l lie LISe(I t,O al'llleve high t,OllghnP,'-;,'~. (-)he" al_lpl'OUcll [o| I~,(Jnera[,lllp, ,'-;ur|l ('OllLl'(.lllP(I craT_,e arrays is {,o uLiIl'ze sPl'(lll~.i phase i.)art h'lPs. S{,tl(lleS t,o irlvPs{,igat,e the I'e~l_le'l_'tlve I'olPI,i o{" IJaJ't,wle shaI_l(--', d IsIJer SlOll, rcmM, iLuLiorl, allll int,ert'ave ('ha.ravt,eris Ll('S un vraze development,, shoul(I be mst, i {ut,e(I in ()r(h-,r (,o |(lent, sly ol.)[,Imunl al_l p|'llu('ilPs for polyrne|' t ougllenmp, In /nelel ,~ystems, where siihst, allt, laJ ri'ack Lip (tel'ilt'rlrla Lion i'an i.)|'eceile rlac'k exLelIsillll, t,he deLalls t hut, pert, aln to s|Je(.'ifl(: syst, ems a|'e (:orr|l.dex, all(I sorl'let, irnes e.(ltllV(.)('aJ. T h e r e are t w o r)rllllary nl(.)des i)f eXt,PtISlOll rleavoge, Urld h(fle I~m_lwt,h, o ( ' c i l r r l n g separaLely (Jr, m o r e usually, In r(l|'nl.)inat, il)n The t,uughr'lVSS t'I)I' bot,h modes IS dlvtaLed I.)rimaJ'tly hy t,he ma('|'o~cupw st,res,'.;/st, raln rhararLerlst, lV of t,he mat,erial, t,hruLigh it,~ et'l'erL on eit, h e r t,he st, i'ess amlJllt, u(le i|1 t,he plart, w zone, lit' on |,he re,,.;t,raln[ itlll.,.)sed by t,he ~lllrLlle IlgamerlLs. H o w e v e r , t,('ltlghi-'lllll~, ('all lie erl'e(,t,ed wit, llout, Val?Jllg Lile fh)w s{,I'ellg_-,d.h.These L,i)u[~,ilPlllrl[2, el'l'e('t,s u|'e realized Liy Siil_Ipresslng vh-'uvuge r|'u('k or h(fle I'o|'nmLion a n d / o r ll.y prevent, ing l.)re|nal, u|'e slip h..'alizaLion, (i|' fly mLi'odu(ung ('|auk I.lut, h t,l.lrt, u~lslt, y. T h e most, Import,anL s{,rLl('t, ural ['ea[,ures that, (llg{,~lt,V |,lie t,OLl~hellLn~ at ('onst.ant. st.|'engt, h alipear t.l~ lle i.i|'e('ll.)it, at,e,,,; and imlmrlt.les F'(J|' e x a m p l e , mult.lple r.lrertptt.at.e an'ays m slevls lead t.o sLihst, allt.raJ {.oughelllng Lly SUpl_l|'eSSlng holP l'~)rmat.lon or slip hwallzat.llm; Wt, lmansLat.LeI| I.)rerll_)tLaLes In 'T't a.lloys pr, l(.luce t.oughenlng by iJ~(tLl('lng t,o|'t,u {.)st t,y, w hl-' reas t rn Ibu I"It,.y seb"Tega t,lO i1 c"a.ll enrclurage ('lPavage anLI t.hLIS (lel.,q'a(le t.he t.(lughl|eSs. These el'l'ert.s a'e (rely (_lualtt.ntwely underst.ood A slll_)st.anLlal m ( . l e l i n g effort. I:,l) qLInnl, l t'y t.oLIgh(-,lllng processes is rtLiclal [or sy~.~t,ematll.' a l l o y (teSIgql ,~tudles SI.II'II al'l el'fort, r a n o n l y i.m.tgq'ess sut, isl'n(:t,~lrtly t[', hi addil, l(in {,o t,he rnat,(-,rials sviellLISL, t,here is al| art, we p:~rt, lVilmtlcln f r o m sevPi'al disrlpllneS, e g , niPrhanl('S (t() (Je[lliV the stre,'.;,'-; I'lelds d u e [,o rnBvrosl'orJll' and hlcallzvd (Jel'ormn{l()|l), surt'a(.'e p h y s w s { t o an'3dZe ImllUrlLd cl~s LrllJuLl(m, e s p e r i u l l y at, int,vrt'ace,~), st,aList, w,~ (Lo c h ~ a v t , e r l z e size and ,~paLlal d~s{~ ibutlon,~
142
or precll.)lt.at,es, et,c.), anti solid st.at,e I.,hysl,'s (t,o det, ermlne int.erface cohesion chara,.' t.erist, ics). (? Sic)u, crack growth There are t,hree IJrlmary modes or slow crack growt.h' envb'onment.ally assisted, cyclic, azld viscous; I,tley can UCCltr separat, ely, ill pm'allel, or Irl seqllem'e. SubsLarlt.iaJ pl'o~q'Pss in l.hP coml.)rehPr~SlOll ol' t,hPse pr(., cesses has been realized in recent, years, hut, m a n y irnl.,:)rt.anL deficiencies remau~. The efl'ect.s of ctwtrunmenls are relat,ed prlmardy t,o t.he~r role in lat, t,we or mt,erface decoheston t.hruugh hole a n d / o r cleavage crack formal, ion 'ahead of t,he l.,rtma .ry crack: a p o o r l y u n d e r s t o o d p h e n u m e n o n . T h e el'feet, o f t,he m I c r o s l , ruct, urP as It, u11"]LIerl('es t,he craPk l.mt,h, and l,he mode o f crack exLenmon (e.g., hole roiTnatJon or cleavage ['ract, ure) in t,he presence o f t,he enwronment,, is clearly irnportant, and requires detailed st,tidy. St, ress dist, rihut, iuns in t,he plast, ic zone require I'urt.her qLlant, ll'~catior~ t.hrough pert, inent, numet'icaJ anaJysPs. Cychc cracl; growth (t'at.igue) has m a n y of t,he n~icroscolJic I'eat,ures (such as slip Ioc',dtza t.ton) assoctat,ed wlt.h cycltc microcrack inlt, ia t.ton. These dmnage accumulat, ion processes are o1' i.)art,tcular irnporLalwe at, t,he fat, lg'ue t,hreshold, and t,heu' comprehension should bP aCt,lvely pursued. In addlt, ion, t,he det, alls of Lhe sl,ress or d~splucement, variat, ion in t,he plast, ie zone are of crucral tmportanee. For example, crack closure can dlct, al,e t,he effec Live stress int,enslt.y ract,or or ('rack opening experienced by t,he crack during each cycle; t,he closure process must,, t,herefore, be account, able b~ t.erms of t,he elast, ic/plast, ic pn)perttes o f t,l'~e mat,erial; l,!he underst.and Irlg ol' how t,l'~e n(.)n rei'overable mcremertt, in t.he crack-.opening displacement, is con vert,ed int,o a ~'rack ext.ension m LPt'ms or mwruscoplc mechanisms (including t,he role of st,at, to fract,ure processes) is incomplet,e. A conLil~uut,ion of recent, mat, erlals/mechar~ics studies should see advances in t,hese areas. Viscous tract: growth (creep rupt, ure) inw.~lves t,he nucleat, lun ,Jr microcracks in a zone ahead or t.he primary crack (or t,he nudeat.ion or grain I,.~Linda.ry cavit.ies), t.heir prupagat, turt, and finally t,heu" c(.)ales~.'en('e (especially wit, h t,he prtma=."y crack ur void). In most, inst,ances, t,he propagat,,.m ts diffu
sion cant.rolled, a process that, has heen widely st,u(Jl~l in t,he last, decade; celt,am ambtg'ult, les remain, however, and furl,her st,udms are l,o be encouraged. "the coalescence i.~hellornenun is ilrlore um'ert,ain, largely be ('ause a ~(.iqlel'aill'~,ed ('l'a('k t'oaile~t'e, llOP e r l [ , e r i o n
has no)t, been es[,abllshe~l. AnuUler import.ant, aspect, or slow crack p|lol,agat, ion IS Ills charttch, rtzation in terms ul" crack growt.h rat.es. Again, difflcult, leS are en (.'ount,PrPd irl /he presence or ext.enslve plas t,icll,y. Schemes based on l,tle crack pal, h mt,ebn'al, AJ (l'at, llsme), ~r it,s tame dependent, equtvalenl, (~' (creep), have Iteen i.~roposed. Huwever, t,hey are nut, expect, ed t,o be general, an~l their limit, a l i o n s should l~e det,er'mmed e x p e r i m e n L a l l y . Alsu, oI" course, more generaJ ,'haracLerizat, iun uPl:m.~aches musl. be sought,. D Dynamw crack propttgol/t)tt and arr~,st In a n u m b e r u f mat,erlal sysLPms it, is impor. t,ant t,o be uhle t,o predict, t,he ext,ent, or rapid crack I.~r~q~agat,ion I~eyond crit, icalit, y. For examl)le, in rluclear pressure vessels, crack an'est, must. occur before t,he crack ext,ends t,hrul@"~ t,h,~ t,hi,.'kness and causes leakage. A pert.inent, crack arrest, criterion is I,hus an essent, ml requiremt-,r~t,. When t.he cracks are small relat.lve t.o t,he (timenSlOnS of t,he c a m poner~t., crack arrest. IS essent, ially dPrn'~ed by a rnat,erlal del.~enderlt, stress mt,ensit.y I'm't,or, K,. (equ',d t.u K.. I',)r (errant(s, but, usually . K,. for met,als und polymers). However, when t,he crack length becurnes comparuhle t,o, or larger t,haJl, t.he smallest, component, dimension, t,he arq.,arent, st,russ mt,enslt,y fact,or at, arrest, is K,, (except. when the medium surr,.)un(ling t,he component, has a relat, ively large acoust.ic irtlpe(Jant'e, whereuporl atTeSt, cart oet'ur at, K :: K,,). The addihun',d ext,ension o1' t,he crack derives from t.he klnet, lc energy deveh.)ped I~y the mat,erml around t,he separat, ing crack and I'rom st,ress waves |'erlect,ed at, t.he coml..:menL hc)undartes. The mat,erial mot, ion and t,he st,ress waves car'~ augrnent, t,he apparent, stress mt,enslf,.'at, ton at, t.he crack t,ip, and ext,enslort will proceed utltll t.he erI'ect.tw st,tess int, enslt, y fact,or diminishes t.(~ K.,. A crack arrest, condtt, ion t,hat, accounts for I,he IncremPIll,s Irl crack lengt,h caused hy kmet, lc et't'ect,s has been cumput,ed for simple geomet, ltes. Hq~wever, a gcm,rahzed cracl; arrvsl cmterlon needs t,o he developed. "['his w o u h l inw.)lve e×lJermlent,al st,udies o1' (:rack
1,4 3
arrPst,, (.'tlordinat,ed wit,t~ lll.lmerli-&l ( ~ , g , t'init,e ,tit't't-'i',-'i'l,',-') si,ress ana.lyses ,~f r a p i d c r a c k I_li'(il.lUgU t, il ill.
E N{m d,.slr.clmt. ~,valualiun CiirrPnl. N D E LPehn,ques ('ouhl b(-, signifi ('aiit.ly ntilirovell by I.iet.t.Pr nlPi.hod,~ t.o i'hm'ul'. tei'lzP the size, shalle, an(I i.yl,-' o f d(-,fPeL'.; or ('i'n,'ks ii, strti,'t,liral I'(.llTli_ll.llll-'ll{,~ A I111.)~{, l'ruii, rul alilli'om'h w(lillcl I.iP a Si, Lilly l,hnt, ~'~i'rPlut,P,~ ni()(lei'il t~lt.iPi'li~li~ni,al mPt,h~,ts {)1" iliiani, iLativt~ dPt'ei'i, ('haru~'tm'rzat, h.in wit,h ei'ul'k lliP('li;.llll(',,4, lilil, lully, Slli'h :l Si, lldV Woill(t 14enei':tt, t~ rPhii, h.)ns l l i 4 w P P n t,hP I'allilre lll'l)ll;.llllllty (for ;;pi-'l'll'll' Ilt'e_i.irnes, e l l v i r o l l lileili,~, P×l~P~'i,e(.t sirt~ss llls{,iii'li~S el,l_' ) i.ln(t l hi ~ illt'PiTed (ll~fP~'t, (,tll.i_i'a(,l,l-,rl~,~i, ll',~. (_if eV~ll t~l't~,'l{,t-,i• inil_irlrt,:ini'e Wlillht tip i,he suhse(lUell{, itPier ininai, llUl c)r t,hi-, t_irliliOi'l, lCUl i.)l' pu.rt, s Lhat, :ire ;.li't,l.lallv s;Ji, lsl':l;'l,oi~, evl-,ll i,hou~h t,h+~v al'P I't~it~'tPit I_l.V a i_lartll'tlh.lr IllSl.lei'i, llin I_ii'(.ll_'el.lui'e. t_lase(t (in ;i Sl_lt~l'il'ie(I ulh'~wable [ u i l u r e lii'lll_)a bllli,y. PePilll;.li'k i,l.i t,ht~ i~nlllh.i.y~t rnet, hl.)il,~ (it' ~tPl'P,,l, ~'h~ll';JC{,i-,rlT.nt, illll alll.I (Tat'k mt-,l'linlill'S w ill iilent, il'y t,hPir (let'h'iencies, i.illlJ will i, llLIS t~itll_ltl;.lSl'Z,t~ thl)se a,~l.iel't,,~ ~)1' t,ht~ t':illurP l.lrt~llll.' t, llin l ll'l_l~'t~ss l,hat m~ ~st, a(twi'seI,v i_'oni, l'lljut,e t,ll l, he I'ejei't, lOll r;Jt,e. "rht ~ rorrnui, ll)n ;.llllt bq'owl, h o f t'rni.'k,~ ('an lie st, i'Oill~l.v Inl'lul~llt'PII b y rt,,,~ldl/al ,,#r'¢,,~s~.,,,i,w h l t ' h augrlrIPllt, t,ht ~ alJIJIled St,l'ess A llon(h~,sl, rlli'LlVl -' (t.ei,i~l'llililUt, lOli o1' t h e mal411ii, tlde oil' t,ht~se ,~ll'PSsPs, ~ , g , in wPhls, i1puJ Sl.ll't';.l('~s is iiii liurl,alli, f o r t~t't'ei'l, ivl ~ t':lllurt ~ t.lreltic't, ilm 'T'ectl nlllUt-,s t'lii' eSilitlai, lng IIIt,l~i'll'd.I St, i't~S~ ~'e. avail ulJIe, t,~ , X ruy itil'l'rui'i,h.in, ull, ru,~onh.' surt'm.'e wavi~s, Illli'a,~onl(' vt~h.icil, y dil'l't~i'~nl, iuls, tll.lt, t,liese t,el'hnlqiie,~ uri-, ill_it, sul'l'll'ient, ly itevlq i_ll_ll-'(t i,ll lie ililivi~i',~,'tllv allplll_,alJh ~ In rlal'l, li,U h.u', ,~f,rt~,,,;s 14r;.ldlents Ii1 I'eT, IOllS (.)t' lil'e~LIl,'li' la,i~l_illlt~t,i'V i'annot, lie e×l.llli'itly eva.luati~d. Flirt, h er deveh_ll.in~el~L~ In i,Pst t,el'hnlclUPS ai'p f hllS t,i) Ijl-, .enc'ouri.17,Pd. Cr;.il'k ~ r o w t h ill rt~sllllinl st, iPss t'iehls IS ,'lh,;ll p o o r l y i'h&r,'ll, t,Pi'lzed, H o w P v e l ' , ili.imerical t e { ' h n i q u e s [ o r e;,;t,atilislilll~ St,l'eS:~ Illiensii,y t'~i{'l,(_ii',~ Ill resldl.i'dJ st, iess l'lehJs ,'li't~ availablP, alid {,he~t ~ ~hiillht tie usi-,lt {,o i.)lrli,alll ~olui, ll.ln~ f o r [irol.ilPl'n,~ ill" l~art ll'ul&r Ill t,Pre,~t, b GENERAL
RECOMMEN[iA'T'I(')N
']"tip i)vt~rwh(--,lmlrlb ,, rl¢-,ed in (irdl:,.r t,h:it, |.13,Sl(' ri-',~t-'LLrch Ill rt"ii-,('l"il.ll'll(:,"ll llrOl.lt-,l"t,i(-,,s is al.ih:,, t.(.)
il}ll.la<-t, r,-,al i,l-,('hrloh_)gl('al pr<.)l.)h-,ms IS fo r cot,prehe,.,,ue r(-,s¢-,ar('h. Most. ut' t.l'le crit, ic'aJ p r o b l e n l s at, t,tli,s t,ime inw.)lve a m,ilt, ipli1'it, y i.)[' I.i,ri,tlllda.ry ('Oll(iltl,liirl,s, such aS mo l l i .)to l l i c ,'111(I ('.yl:ll(' Ioadlrlg u,u wt-,,ll as [,t-,nllJ(-'lrOt, l.lrl-' ¢'liar'itges, u rnult, ipItct|,y o f ,'.;imult,aneiiLtsly a,L'{,in~ ml-,(,h;.lrii,,4ms q)l" ili-~[()rllll.l|,i()f'l uiid [rai'turP, arid u rtiult, iplii'it.y o [ i-HwIIrl.)lllnt-h|l{,,t.J oJ' Liil[ir(-,cederlt,i-,d sevPrlt,y. W h i l e r(Jsi-i~j.rl_lh (ill lilitlVllluaJ i'OlnllOllPnts ol' i h~se [llolih~lilS is o f high Sl'li~ill, l[i(' inl,ere,~l, nlllt is ilePiJe(J t,o i.irovl(-h-, I_)uih.'ting llh.ii'ks t'lli' ally illort-, ('lllli I~lPt,e I, rl-'at, nli-'ll[,, ;.lily iliiliaCt, (ill alll_lJll'al, lons l','lll J_ll-, i'i~alist, ii'ally Pxj_iP('i,t-,d l)llJy ir t,h~ dlrl't-,ri~n{, liulhJlllT, I.ih.li'ks (','ill Ill ~ ilit, t~i'l'm'ed Wlt, h ,-,nt'h oLht-'r .'illil Sylli-,rglSt, l(' el'l't-'('t.s s t u d i e d "['lie lli'est~nt, st.at,e c)t" t.he art. tn Lht-, m~Hlanisktt' undPr,~Lan~itng ~1' m e c h a n i ( ' a l i')ropert.ies a p p e a r s Lo wurrali{. ~1 ma.l~r ~ iJt-,rillli.tlr~ ror such i'()n'l].iri-,he_llSlVl-, s t u d y a n d a u g u r fo r a r~asonal)le ~'halwe o[' 8tll'(.'ess. A i'P('omml-,ndutt~ln (_)r t.liis w~rkshot_l ts L.ha{. t.he ent.u'e s p e v t r . . t o r " l ) i ' ~ I x t m i l . y " bet.wPt-,n baste rt-,sl-,ut'~'h and ~'urrl-'nt.I y re~'lll.jnizl-'d t,P,_'ll noh~gi,_'al i.trol)lelns tip eill'itlli'agelt (.in ,'l (:lJll t, lllttillt~, liasiS, aRid i hul h o i h reseail'ht~r,~ arid i:,.ll~lllt~Pl',,,i lie. i-'lll_'Otll']l~Pd i,o lll;.Ik~ t,Plli,at, lVe LI~& (it' ri~sellrl'h i't~sult,s ill t,Pi,l'lilllhigl('al at_~l_)l,~,a t,;ons
PA R'T'IC I PA NTS
A S AiRim, MI'T'
I. M BPrns(.em, (."urni=l~W Mt4hm I lnnv (_I R BImkman, Oak Rtl"ll-_.;(,-'Nut.'l L:lb R M Cunn~m,Jr , MIT ,J R (2~,~1,, ERDA, Physical Re.~(~:Jreh "r B ("o~, ERE)A, Fo,'.~,ll Erl~uRy D R [)lPrck~, Aigonnl • Nut'l Lab A (] Evarui, Roi.'hwell Se,Pnl,t-, I?t-,nl.l-,l' 8 D Haiknt-,~,s, Argonne Nal'l Lab W Herrrnalm, Sandia Albuqul-,ique I.l F Koel,ts, Aigorlnl-, Nat'l Lab C Latrd, l.lnw of Pt-,nnsylvanm (? Y L,I, C'orn,-'ll I.hlivP|','.;It, v N H Maen',tllari, Piton Sl,,'t{.t-, LltllV M Ml-','.lhll, N¢.irf,hwl-,,~t,Prn I.IIiiv¢-,r.til|,V ,I W Morn,% ,Ir , B(-'rk,-,h-,v H (3 Nt.'h,i,.m, Arl,l~,~i Rl-',',, (~e'rl|.t-'r, N A S A E Pul~h, Oak RIIJF~e Nal,'l Lab ,I R Rl(.'l-', Brc)wrl Ilrllw'rsl|.y 'T' E Scott, ArnP!~ Lal)oral(iry 8. M. Woll', E RDA , Phv,'sm.",l REsearch M H Yoll, O;Jk Rldl~e Nal'l Lab
1.43
133
MECHANICAL PROPERTIES (.)r i.~an i'/.e r .~ I.I F' K<.'k,,,, ,,4~t.~,mm' N'~.~/~.md L,~JhlmJh~ V ,I R iY,~.;I, E/TDA, [ht,~:.mm <~/ ['hy;m'al h'e,~t,arch
A (_] Evum,;, /~',.'/,'wHI ,'+c.,m'e t~e.ter
ThP h i g h e s t I_~rli)rity shuuht he I.)la('ed on
St."( )PE "l"he MPchanlcal Prol.mtLIvs W(.)rksh,.)l.~ was asked t,o ~teM wtt, il all I.)r(~blems <)r d e f l ) r m a Lion and flrac't,Llrv, ex~'vpL wit, h t,llv folh.)wmg Sl.~Vi'tl'm areas w h m h were asstgnPd t,o i~t,her w,,rkshol.,S defornlaLli.,n IJro,'et.;sIIlg, w,-'hls and t.hI,'k sec'l.ll.ms, ,-,rosic, i~ and w,-'ar, Hie ,'< )rrosion :~Sl.,,-'cl,s o r st.r,-,ss ~.'orl'< ~SlOt'~ Cl'a('k iiiI.~, Irra, lmt.i,.m crePp, anll n,m-,le.st.ru,'Lwe evaluaLi,.)n
{,}IP t'(_~IIIpP'+'hf'IISIP~.'II(~S,~; <.)r rl+lPchurll('a] ]lt'Ul)er tiPS r~sPart?Jl, P i i c o L i r a g l l l ~ a('{,iv~ ~)v.~t'Ja[.) b(¢.{,weP|l (i,) rtllCr<_)s('i)j.H(- and mai'lrosi'(~pl~' al_)
pr( )at.'h vs', (11) MP('h:.llll<~al J.)l'oJ_).~rLll-~s reSVLli"('ll
a|l(J
u thl-'r d tsvq din(-.s, (Hal) inv.,st, alsatians orl dtlT,-,r(-,nt ('lass~.s of r~iu t,Vl'ia Is', (iv) thP s,'lent.~l'~' a n d th<-, l.P,'hn
'T'<.)F' f'R I( )R ITY M EC'H ANICAL F'RI.)PF_:F{'T'IES F',SE A RCH
1 I N'T'R (.) EII.II"T I0 N
A I1 irH'rl-,asPd u tll[vrst,al~d Irlg o f m i('r< )s('OlJl(' a n d illa('l'(.),~('(-)i_)l(: m ~ v h a n l l ' a l prr)liPrt, iPs IS
A Pm'spe('twe
('rit, i<'ally rlPP(|.~l| iii 'all PnPrgy Lvt:hnoh-)gleS. FtPsear<'h urPas wit, h a high pid,Pnt,~al impact and a high prohahdHy o/' s+tcc+,ss over b<.)t,ll t.h~' short.vr an<| I<.)ngvr t.i-,|'nl are (i) c'onst, lt, tlt, lV<-, ri-,l:~it.lOl++.+ al1(l llullla,g,e,_ ai' ~'u rntllal.lon lawn, (li) crlt.i-,l'Ja f o r t,lle h~i'aJlzut.irm o f llPl'or mat ion;
t,ur,;m~ point Whil,-' in the, ~)()'s and 6()'s [h,-,
( l l i ) [.) red l t' t, l <.)n <-)1' {'alJLirP ra{,es;
(IV) ma{Prlals dPslgn anlJ subst, lt, uLablll|,V Research ari~a,~ {,hal liPPit ill(,r'Ptl,~ed mnphus~,~ to (Ievehq_~ {,hP h,'lSl4' undel'S{,andlll~ irrl].lort,all{, J'l)r {,by s ( ) l t l [ l ( m o[' t'lrltlt'al prol_) lems at'<-, <'<.)licP.rlivd Wlt, h (I)
C'lr~lck IIl.l<'h-'a{llm ~'l'i{,Prla,
(11) rP](-'van{ sllrfa~.'e and in{,erl'a('P i)rol .) eft ivs
M~,4'hani<'M l.)rol..-'rt.les r,-,s~,an'h
is at a
MIL'rosI.'()pI(' ,'.1|11~ inLicr(.)s(,oi31(, alq_~tuach,-,s t u (lt-~forr(l:lt, l(.H1 an(t flia(:~,ur( -, (:?v(.)lv(~(I us i~ssPn
t,lally in(l~,per.lent dlSCll.llln.s, (,hP 7()'s haw' I.)rotlghL Ir.:'r(-,aslngly eft'eCt, lW mlerucl.m I.),t.we.Pn t.h~ two. ,.qilnult.ane()Lisly, t h , ~'on sidvrallh-, Irlt'l'easv Ii1 sOphl.,~tl£'Cttltm that, has I_'.-'rva~l,-'d all ill' mat.t-,rials sc'ivn<'v has ma
mPt-ilatllSnlS
0[' J)ot,h d v f c ) r m a t , i
and I'rac'Lure IS n(~w I)~lng vonslcl(-,red, an(| all II'l{,Pl,~ra{,IO|l c)vi-Jr ('omph-'x I(.)a(tmg lli,,-;t.orlPs (Stl('l'l ,'lS a]{,Prllat, lllg~ i'|'P~la all(J ['~[iLVtlP) IS
(iv) r e i ' l w v r y , lecryst,alllzaLion, and r)hasP t,ransf()rma{l~mS ooc'urrlng s~multanPouslv w it,h dPl'<)rmat i(.)11
J~PIn{2, a{,[,PITII)[,Pd 'T'h~ glaring vx('ept, lon t,(.i t,his i.)rogrvs:slng suphist, lcat, lon an
O0'Jb b4 If;/'Tali)(Kih 4)I 3;J%~ LPb
,,_~F:I,,i,~n~! Sl~q~siq,n,J.i..; A , L,du,,aririvlPrlnJ.Pd m ille '~{'l.i'ie|l,~ri{J,,
( I l l ) {,hP erJ'P('[l,; o f L'hPmll'aJ . ~ n v i r o n r I l e t l { , s ,
1 :} 4
Stl<'h a rapid ~levelopment, ul hot, h t,he breadt.h and delJt, h o1' ultderst,anding pt'ovldes exciting scten{.ll'l~' c'haJlenges, and i[+ portends a rapidly m~'reasing us+,[uhlf,ss of the results or such resean'lh. In some cases, t,he I1npa~'t 1311 Lo('hn<)h)gl('al a
mal+,rtals developments; ['or example, I11 t,he ..)pt,lmlzat, l
ehalll'P
(i) [1 SLIII'('eHS IS u n l ' e r t , a l l l .
Fin',.dly, t,hero are arras of mPchanl('aJ pr<)l'~ ert, leS research where Lhe Impact, of any rest.llt, s on te<'hnoh)gieal i.mfl.flerns w()ul
f~rmant'e <)r st,ru,'lural ,'oml.,.menl,s, t,hey will be highly seh-,<'tlW In terms or l,he alloys aiM <'omput, at, ional Lechnlques used. rl"he basic r e s e a r ( ' h IJl'OIb'q'aI11 18 nee
B. Outline, The main body c~l" t,he repm't summartzes out, stal;
M A T E R I A L S AND ENVIRf)NMEN'T'S
,4 Materials T o the h e n e r i t or met'Ironical properties research,
arl u1(.'reasJrlg L e n t l e n c y
can
he
1 3h
ol.lservm.I b.i integrut,e the un~lersLun~linl4 gall"md fl'(ml d i f f e r e n t kblds ot' mat.m'tals met.aJs and alloys, c e r a m i c s , s e m l c o n d u c L o r s allqI illlllelIL.IIN, I.i(.Ilylllel'S ailc.ILlm(ilri.ilic)I.iS nla l m'nals It, us u m e a s u r e ~)t' the Sol~hust, icat, non~ (~t' t,he t'iHd t h a t sm'h old t nme classul'ucaLu~ms llave hlst, Ill significance atilt m'e being re IJh_lce(I I.)y cah'gurle,'~ Sll('h aS {,WCI phase rl'lal,e rmls, mal,ermls w i t h a high F'eierls stress i)r a h~w i'leavage sl, rengl,h, aml the I~ke. II in t,hus m~L eXlJel'telt that Sl~ecufll' " n e w m u l e r i a l s " re, lUre' a redu'el'tlon or the ii~e(,hau~ul'uJ i_)rol.~rLues research el't'~)rt,, rut, her, they sl..mht t.-, ilwl.)rl)(_)ral,e(I ii~t,o (li'~g~)mg I)iOb.'~'arnn l i) Ira)aden t.he base ~)1' un~lerst,andnng. T h e (llst, inct, l~m I_)el.,Weell "acallemnl'" and "l'e:ll l i f e " materials is also I.lel:()mlrl~, I)hlrr'ed. Mal,erl;.lJs foi elec't,i'li'aI a n d rn;..l~a,l l e l l c al.)ldlca t, loIIS ill'e ot't,en plli'e nm{,als
(tt t,o derive alfl~ropriale SUlmrl.~SlLll)l~ laws [ih;.It ',.dlow ()lie t , I . ) i ' a h . ' u l a t e ( w h e n e v e r I,)nSll)le) tile InelanLie t_)eh,'lVlUr i)f [lie i'oln
I.ItiSlt,e ()rl~'e that o f the clmsl, lL,tiPllL phases IS kll<)Wt'l, (li) t,o un~lerst,al~d ( w h e n simple superl_.)Sl t,lorl is inadequate) any athllt, lonal nleehanlsmS Stlc'h as slippage and dPc~dleSl~Ul at, the inter fa('en between the I'l.)Ililli~ll(-'ll{,S, an(I iiOll ll.,('al in l(-,ral'Lions ~o{,h IrellLIIle the use-' o f SOl.)hlsllCale~l star, is t,ics, itl paJ"L, t,i~ delllleal, e rnacronel)plcally "{hli'{,lle" beliLivlor ['r('ml b,q'o,%; fral'tLire Et,uh~lng Ill icruslrHt.'IHr~,s T h e classlcul, amI very nu~'eessful, al~l_mmch o r iflWslca] met,allurgy has I)een [,o ~lesrrlbP, in separuL~ disciplines, t,l~e mlcrost, rtleUJre and its r~mt.rol IW thermr)mecl~alllCa] [,leatiIlrlellt, Oll {.he one halltI, allcl l.he relallOll Llel.weell all anLabllshe(l i'liil'rl.l!~I, rul'{,i.iI'eLind n~a4'ros('(q,i~' i_)ropertles on II~e olhe~. A rnaI()r shorh'ommI~, of th~s aIflwoa~'h has L.,en sh~w Im.)~.O'Pss in t.he area WIlerP niii'rtlsl,i'ui'{,iire ('ll,'IIll.~e~ aii(I nle ('l~anlcal (tel'ornlat, l~)n hal_)pen Slmlllt,alle~HISIy. While t.lleet'l'el't, ~{' ;IIIal_)idle(l nt.le~.;s()II {.rLlllS t'urlnat, l~mS has been a m p l y I~westigat,e~t, t h~ et'i'ecL of u n g u m g lran,~l'c~rmahuus d u r i n g plastic ll~w alld l'ra~'tllr~, has I'eCelVe(I IlI.t.IP at, t ellt, lOl~ ~lmnlarlv, t,l~e I.)l'mrlornenorl of tlylloIIIl¢.' rPt'r.v,slullh:allc)l; allq| asso('tat,vct t w i n n i n g I:; o n l y begml~UH~, t~ h~, un~tPrst, o~)d tam'ha n iSl,l~'ally. HIgl~ {,elllllelLthJl'e erler,e,y techlloh.~la, le,'.; l'ellllU"ea Ilew e l n l d l a si n o1~ research Iii [llt,S~-, cl'it, ie~d aIPas.
(' ('hmnicol mu,."umm,nl,~ Aggressive ellVll(_)llll'lelll,n piny an u.zuzr.,'~ce ctmlted r~fle m n~w ml~rgy t erhnoh.)gi~s, t ranncmldmg, nn inany ways, l he classwal t'lehln (.)t' i'(.)llq.)~l(.)ll al~l sl, renn CmT()si()n crurkung. At I~lgh t,~mperutllres, m:lny Sl~ecnes q'an dtl'l'use I.,hrougll t.ll~, entur~ section, entller Into ~t' (.)Lit c)l' tilt-' mat,erlal, and LllLIS H~enge c~mlp~stlu.m amJ mtcrunlrtlcltn'P NPighl...)rln~, t'tel(Is in rout,el mls ncmm'e nilouhl mvestJga[,e, with hq~,hest prlorll,y, st.l~'h cl~al'lgeS Ill rPaltst te itlat,erlals, mid Illt, erll~'t, Wlt, h t,he mm.'l~anucal Um)l.)eMleS c(.)lnlnUlllt,y if Ile_W l,yl.leS ()[' ITII(.'II) st ru~'LLn~e s h o u M lip I'oui~l. At low Lmnl~eraU~res, o n l y u l'Pw element,s can dift'ul~-, Ion~g (lnnt,am'en ( h y d | ' l . ) g e n and s u l f u r being ~ul.,st,aIl(llng eXCPl_d,nons), m~)re (.'()mrrlolllV, t,he el'fPct.s (~1' i'henlll'al eiwIrOll rnents ate resl, rict,ed t,o near sin'/ace rt'gl¢911,~ Here, eVell the mont, I)u~.;l(' chmaci,et izal, iOll ol"
136
" e n v t r o n r n e n U ' , and t,he (Id'ferenL ways It, can affect, propert, leS, seems t,o be la,.'klng. Even cry,.,gen ie gases are "aggressive" in t,heu" effect, o n polymer q~razlng, and aqueous environ ment,s have a p r o f o u n d el'feet, on strain IocaJtzaLioll In fat, lgue. It, was a gener',.d e o n H u s i o n o f t,hls workshop t,hat, envi_ronmenLal effecLs on me(:hmli ~"al propert, ies, especially at, high t,emperat, ures, have not, beell t,reat, ed wlt, h nea.rly t,he maine sophist, l,:at, lon as 'all or,her aspeet,s ,.,f t.he i.wobleln, m rag,t,, reprodui'lhlllt.y of experi rrleilt, aJ ohservat, lons has only raJ'ely been at, t,ained. S o m e o f t,he I.winclpal deficiencies leading t,o Lhis impasse are t,he dtffwult, ies Inw.)lved I)ot, h ill det,eet, lng and t,ra<:lng l,he progress o f small quant, lt,les (1t' t,he m't, lve en vi_ronment, al species, and in est,ablishillg t.he effect, o f t,hese SlJe~'ies on lattt('e or mterlbc~, dt,coh~'stott The former problem ~'an be pazl.lally addressed I)y appealing Lu t.he wide variet, y of Leehniqtles now avadable for sur I'ace and bulk analysis. However, innovat.tve t,e,'hniques m'e required for many Ill' Lhe ('rlt, lcal I.woblems, and t,hus t,he st,rong [}~ll t,iclpat, lon o f surface physi~'lst,s is an essent, lal eonsl,~l, uent, In a viable st,udy. A cnt, leal issue ts t,he effect, on d e e o h e s i o n o f variotls act, ire specws; a prtort a p p r o a c h e s for caJ,zulat, ll~g t,hese efl'e('t,s are not, apl.,arm~t, Nevert,heless, some prols'q'ess will inevitably be aehteved If t,he prolflem is addressed hy the pert, lnent, physlcs/H~emlst,I.'y dlSellflines and su~'l~ a pm't, lelpaLIon IS strongly urged.
D Surl'aces and inter[aces T h e propert, ies o f int,erfaces have a ,'rlt, ical inq.mct, on mechanieaJ propert, leS Ill many areas and appear t,o be ripe for a major advance Ill underst.andlng. A bas," research proi.~lem o f g-teat, sibmlficance and general relevance Lo rraeLure p h e n o m e n a , is an u n d e r st,anding o r what, allows (or causes) an int,erface I,o be capable o f developinv, a crock. This IS a Nindament,al aspecl, o1' ~luct, de rract, ure nu,'leaLion (iJa.rt, lele-mat, rlx inl,erfaer,d failure), o f t e m p e r embrlt, t,lement In st,eels, o f h y d r o g e n assist,ed cracking, o f fraet, ure in ceramics, o f creep-rulM.ure eavtt, y nu('leat, lon, et, c. T h e area calls for basic w~)rk in the solidst,at,e physics and t,herm~)dynamles r.)l' inLer races (including segregant, adsorpLt~)n of impurlt.tes and consequent, alt,erat.ions or cohesion), ill laLt,iee dynamtcs, disl(.)eat, lOn
t,hPory, and ~)t,hert, ylJes of rnicrosLruct, ural nl~)dellng, and in relevant, t,eehmques of Lhe experlmerlLal and quanLiLaLive chemical allaJysls or in[,el'['aue.'4. The elTletem'y of hq'uin boumlaries as stn/,'s and sources for IJC)ln{ dere~.'i,s In dil'fLISWe flow, and Lhe assc.'laLed prol)lems o f gq'aln boun~lary sliding (or gratn botmdary dtsloca tu)n motu.)tt) need furLher illtlrninaLion. Esl.mcr,dly iiI .'eramli.'s, [.tlese i.)roi'esses can be rat,e.limlt, lng (as ~'ompared wlLh dirfuslon). T h e iil[]uence of sHr/'aces alld surl'ace /'rims iS recelVlllg renewed al, t,ent.lon alld is f)[ espe,'lal concern for energy sysLems: neat sur[a,'e behavic)r v.~ iml.,orLanL in er,.)Sl,.,n an,t wear, in faLigue ,-rack nucleation and, in some eases, ill Lhe general.ion ,)f plasLw flow (,.,r tt,s ,.',.,rl,'ei'lt,raLiort mt,o ImrsisLent, slip ban, is), which may have effe~'t,s on I~tllk behavior. This fiehl ('ould receive a slgnlfieallt, new InlpeLus I'nlm moderii e~permwnlal tech ntques applied Lo aet.tlally iml..)rt.ant, environ menLs, us well as from sophist, lcat,ed Itllet' alomi(' poh, ottal caleuluttons ( provided t,hese can Iw well mat, ehe~l t,o t,tle macroscopic rJlic)i.lert, ies relevanL li'1 t,hiS ease). Int.eraeLions heLweell i.)eople orlenLed In the direcLion of meehani~'aJ iJ|'opert, ies and surface scient, ist,s, as well as solitl st,at,e t,he,,'lst, s, would be mandat,~ry.
E. h'radtatu.m el'fi'cts The energeUc irradla[,ion ellvlronmenL in fission and fusion reacLors al'fecLs mechanwal hehavlor dlreeHy Lhrough t,he int, roducLton el' a~h li Lional defect,s, de reel t,h tst,ers, d islocat Ion loops, w)i(Is, and gas eOllt,aining bubbles; and mdireet, ly LhroLigh radial, ion.induced segre~a t,ion t,o surfaces or int,erfaees, changes in Lhe i.wet'it.fit,aLe st,|'LICLure, and possibly t.lle forma t,l~m or nonequlld)rn.lm phases. Recent, advances In our undersi,arldlng o1' t,he klrlet, lt's (.ff t.hese rnlt'rost.rucLur~ changes make a clef.ailed sLudy of mechanical erre,.t.s a, urgent, need. Pr(.)baLdy Lhe mosL mll3ortanL one of Lhese IS a loss In duct.lilLy, for exmnple, by severe slip h...'allzat,.m due Lo mwrost,lue t,ural mst,ablltt,y, or by t,he growt.h of macro scopic w.),ls or bubbles. R.elmhle predict, lens o1' l.omponenL life, so tmport.,ant, Lo {,he nuclear t.echllology, requtre a far bet.t.er under sLandmg of Lhese phenomena Lhan is currenLly available.
137 (.',reel_}
3 DEFOR M ATI(_)N Illereaslng Pnlpllasls has I_)Perl I)la,'ed in le('en{, all
A 8h'+',~lh+',mg ++++'+'IPa+++s+++s Sigliil'h'aiiL a d v a m ' e s h:.IVe beell llltlde Ill l,he la;st de<'ailP IiI Ollr undel'S{all
B Euul, t,.m ,,[ s,hsh'u('tm'e a , d de/vet .~l rllt't ll l'e 'File high t emllerat.Lire I)W<.gJel't.iPs ,)t" rnat.P rl'd..Is .'ire st, rollp, ly irlt'luence(I by deveh.)l.)lTlerlLs ill [.he (llsh.u'aLiorl and subbqaln s[.rtll'I.l.lIH t h n )ugh delc,'ma I/c ~/t arid rec'c ~uer.v I m.n_'esses. 'T'hls IS an LLIIeLI lagging I_lehlild low I.Prtll)erat.llrp s{rPllgIihl-'11111g 111Pchi.IlliSm,'.; i11 Ulldersl,Llnllll1~, ImL is <~iiP ill w l l w h ~'tlrreut (lewhq_mlmiL is i.'iplil llILe|'a~'{,Ion l)et, weerl lllVl-,S[,l~tJJ.ors tlSlllp, dIl'l'erei~t, classes oI' inat.erlals has l~eell v m y l'rLIItl'tIl, f<)r <-,×ample, a l_mrallelu.+rn lJPt,ween t,he l)Pllavlor cdu.+erved in l.+,eoloEI<'al rnuLmmls aml in metals llas been ('oun~l. 'T'he prlll~'ll_vd.I nle<'ll;misms t,hat trlLIst, I~e lill
eli.'1~latlon
<~I' l_.+~tI~'uIl~'
l_u'ol)leln <'a.+es
(2 ('+.mst/t,l/tp+, /'e/ul/o,s MzH'rosc.c~pu' d<-'l',)rnlut.u.,n must. evellt.uully lu-'
13H
param(-,l,ers - and as few o f t,hese as possible. T h i s IS anot,her area Ill whl(.'h all int,eg'rat, ion (:)l' ),he l.)h(-,nomen(.)logical and physical ap p r o a c h e s t,o rne(:hantcal pr(.-)pertaes has reeent, ly led t,o significant, advances and is expeel,e(t t,o I.)rovtde useful resLiIt, s in the I'c)reseeable I'ut, ure. T h e r(.)rmulat, i o n m t,erms o1' state parameters, raLher t,han hlsL<)ry vaxmbles, is i.)hysically well I'()un(ted and ('on nect, ed t,(.) ),he n(.)t, ion(.)t' ('(.)nLrol (.)1' pr<_)[+el't,ies I.)y )nl<.'r()st, ru('t, ure, it, shouht lead t,<:) a signlt'i ('ant, redu('t, ton m ),he n u m b e r ()f t,esLs t,hat, must, be l.~erl'onue~l t,o
rnat, ermls ('lasses s h u w m g great p r o m is<-, for enerls.W r<-,lat.ed a ppl,.'at, ic)ns. l)(.)stl,(-'s -
D D y n a m w el'l'eets For most, n()rmal (t(-,mgn applleat, i<.)ns, an underst, a n d m g (-)r small st, ram def(.)rmat,,:)n an(l o r ),he mit, mt,)<.)n (_)f failure is sufl','ient,. On ),he or, her h a n d , ir t,he eons(-,qtten(.'(-,s ()r failure must, he assessed )n (let,aft, elt, her bl a<'('ident, sit, u a t i o n s (r(-,a('t,or a('('ident,s, safet, y, as In ('oilt,ainment, (.)f l'ragmenl,s f r o m t,urbine rl.)t,(.)r <.)r Hywh(-'el failure, el, e l (.)r in l'(.)rmmg, l.)ro ('essmg, (')r h r e a k a g e (high.en(-,rls.wrate rl.)rrning, rock l.)reakage, et,c.), )t, is o f t e n ne('essary t,o have (:()nst, it,ut, ive relat, i(')ns f(.)r large def(.)rmat, i o n ( usu=d ly nonrad)al), and fl:)r p o s t / ' , d a r e heha+,ior, t.hat, is, for rnat.(-,)'ials ,'ont.ainmg c r a c k s (.)rot, her clamage. In rnany appl)('at,,:)ns, very high rates are involved. q"hm is a pr<.)l)lem (.)f htgh e(.)mplexit.y (tin. h:)<'at, il.)n an(I ),win nt,:leat, t()n, ir)ert, tal I.)an')er pen(-,t, rat, i<.)n, d m l o e a t , . : ) n - p h o n o n int,eract,ions, et,('., ()(.'('ur simult,aneously. All esl_)eelally seri(:)us and lil, t,le undt-,rst, o o d l:)robh-'m is all observe
1 ;;9
elect, Iron inl('rosl'c)pit.' t,e('hrllqLle8 su<'h as weak i.)ea111 ineLho(Is aim lat, t,i<'e m m g m g Anr)Lh<-,l,' l,n<)sl, iml...)rt,ant, area w h e r e I11(|I vulu'aJ dish.Jeat, i<.ms deI, e r M l l l e maeros('<.)pi<.' b e h a v l o r Js t,hat, oi" plast, i<: del'orl,nut, ion .i small t,oluln+' +'lPllletl,l,~t SLI('h aS i."ral'k t, llJ nelghb~Jrhoo
nLillll)ett', al+',.J.Jy{,l('al <-,lel'Lrl_)ll ml('r<.)s('()py. Elu,+lk' atttsolropy, w h u ' h is sul)st.ant, tal eVell III, III<_)SLSln+l.de metals, ulld very iml.)Or rant in low symlnet, ry l,nat.erials, ent,ers t.he mauruscot.nu st.renN.h by way o r dlshwut.lon p~(qJert.leS. SIgntl'lcant a<.tvun,q'es In t.he has,: Iin
f? S / s i n Ioeahzat;¢m I:'last, ictt,y resean'h is ustr.J.lly un(tert,aken under ~=nirorm defl,'maL~un u(md=t,,Jns. Yet,, one o1' t,he most, in+port,ant,, and pot,ent, rally (lallgel,'(.)us [.)hel,lOlTlel+a IS t,he Sl)(.)I1t,uneous h..'alIzat, lol,+ o r sLraii+ ()vel,' p+a.rt,lcular l~art,s (.)r the C,l'()ss se~_'l,lorl, or ll+t,i.) Int, ense b a n d s or sheaf,'. Suuh h..'aJlzat, i<.m cal,+ }+ave a n u m b e r ()I' dirrerel+t causes, it, rnay I)e a geOlrlet,l'ic' msLabdit,y, tt, may origmal,e I.)et,w(-,el,+ prevJ (,Jsly t'()rmed v<.),Js, or it, may be due t,u I'l]l(.'l'(.Is('(.)[_)l<' st,ram s(.)ft,enull;.J, pro('esses sucll us dish.'at, u.+n c h a n n e l m g and iJl,'e('ir.nLut,e rPsulu t,ion. Fmally+ a parLwularly fl'equent, mode of st, ram h.)('aligat, ion is t,he ['ormaLion o1" " p e r sist,ent, slip ban(is" (lurll+g (.'yeli,'
,1 F'R AC'"PI I R E SLuittes or rra<.'Lul,'e are eoni.'erned wit, h t,he preflR'{,ic)n <-)1' I'allur<-,. In ('(.)r+seLlUel+('i-' , I'ra
A Mt('rc~('rut'/t IIIIL'IeutI(+HI, grlHtp/It ottd <'oal+'s ~.'('IH.'P T h e I'ormaHon ol'a rnacrocra(.'k involves t,he nu<.'lea|,lon, growl, h, and c(~alescem'e c)l" rnl('n)
141)
rl'a~'ks. 'l'h,e inuiles n f mwroeraeh' tlllt'll'alloII are many anll va.rled. SeveraJ modes have already been (teserll~ed; f()ur addit, il)nal mechanisms of sul.)st,ant, iaJ pra(,t, lcal sil~nit'l. ~'anee al,'o dm~'ussed below. I n hl,lllll~ , matertal.s, rnicrocracks [ie nt,'leat, od at, st, ross L'(lll('ell,t, ratll(.)tlS i.)r()tltl('ed Ily elas[l(' (Jr [,hormal mlsmat,c'h a[ grahls rl,r second phase I.varti~'les. T h e cra('k forl,nalion IS st, tI(ll,l,gly Illl']l.lenll'ed by the s i z e dlst, rll)titllOnl o f "lWecLirsor" defe('ts at, Int, erfaeos, t,he st,eel.I st, ross t.,q'a(tlent,s, and t,he h..:al m i c r a l'ract, ure t,ouglhness (ill" [the mat,erlal. "l"he solttLi(m t,o t,hm pruhlerrn, as In aJl el, her rni~'ro cra('k rormat,.m I.)r()l.}lPms, den~ands lilt,OIl,SIre ('oojlora[.lOll IIet, weell resea.rl'Jlel'S In s(;!,Jll| nl,eehaiiws, sl,al, i,,.;Lies, an~l rnal,erlals st'tahoe. "rhls t"oopel,'aLiotl, has already begun. Ml('l,'l.)erLll?kS alld VOIDS ('all, also {'(.)rm dLIrllll2, Cl'ee[_l. S[l('h nll('rl.)(Taeks I're(itlon, t.ly derive from t,he st, ross (.'oneenl, rallCm sol, up by Ll(.)Llnltiary sliding. "['tie I'()rma{l()i1 prf)('ess is t,hils del)enlden{, 1)11 {,lie ('hli,Lra('[,or (.)l" [,lle st,l,'eSS singLilarlty pr(~(.Itwo(I by sit(ling, {,11odl['['tlSlVe or plast, lC st,ross relu.xat, iun, and t,ho operat, lve nucleut, i(.)nl ('ril,oriol~. ']"lie I'lrs[, {w~l aspoeLs (~[" t,he I_ii,'ol)lem Call LIe ad(lrosse(l by a me('hanlleS/ mal,eriuls SLLI(ly, hu{, {,lie last is an Ii1[,el,'l'at'e deeuhesion prul)lenn l,hmt, requires several adtlfl, ional PalenLs. Sirrnilarly, t,he ntleleaLion, of vat, Is at, s e c o n d phase pa.rl, l('les nee(Is I'urt, hel, t,ransd iscipllnary SLtldy. A t,hird m a d e o f crack t'urmat, l~m o('eurs (luring eyelw &,lbrmolton, Fatlil.,n.=e rlli('llll ('rm'ks t,yl.m'ally origmat,e wit, bin persist,ent, slip I.mnds or lueallzed bands or intense s h o a l In hel,erugeneous mat,el,'luls, t,his t u n lie a con SeqLlell,t'~ o1' S[I'eSs (Tm('e~l,[ra{l~mS genera[,ed incur kq'ain houlndarms, ()r mt, erphase inl,er I'a~'es In h u m o g e n e o u s mat,erials, cracks may ol,'iglnat,o in Iwrstst, ent, slip hands no~u' ['rue StlllraeeB, bUtl al.~u at, al.~t.)a.rent, ly r a n d u m hwa t,lons wit,hm ban(Is (~I" eon(:ent, raLell shear, Hie nucloat.i(m mechanisnl,s are, here, especially p o o r l y un, tlel,'st,ood, nor has lhe role of the mlerust, ruet, Lire been elea.rly est,ublishe~l. ']"he resulut, ion ul" t,ho prul)lem ro(luU'os a sLrtmg tllil, lal ernl.)haSlS on ol)setwal, iollS ()f rril~,'ro (.'rat'k I'ornlat, i(.Hi, t'()llowed by a ('~H)rlitil,at,ed rneehanit, slst, al, lst,i(:s-rrlat, erlals sl, u d y . In polyl,ncrw matertals, t,he p r e c u r s o l s t,o nl,a('r(~t'racks alle ( ' r a z e s . T h e tmt)rl.fll,()h.~gy o1' crazes and t,he dependorrwe o f t,hetr I'ormat~(.m o n mat,orial prr'opol,'t, ios, e g., l,noleetlltu' weight,,
are reasunahly well c o m p r e h e n d o d Huwever, st u(IIos Lo e x a m i n e t,he sLa/,isl, leS oi' craze fc)r mal, i~m in t,erms oI" material het,erogeneity and o f the efreet,s of urient, a[lun are needed. The propagalltm a n d / o r euales~'em'e or nlieru('raeks at'(-' t,he llOX{, st,ages (.)[' mael'ueraek I'(nlnlat, l o n T h e in'Ul.,agat.l,m o[" mlcr~wl'a~'ks IS Llese[, by all 'l' f t,ho I.lroblelllS asSoelat,o(t Wltlh mm'rucrack propagahtm, wIl,h l,he addd, ional c'(m11~lex p r u h l e m u f mI('ru('rm'k prulJagat, iun acr()ss t-_re(In botlntlaries. The s~)lut, lon t,o t,his prubleiTi is impeded by t,he presenl, in[,rat'[LIblll[,y ot' t,hl'ee (llttlerislon,'d st, ross alvaJyses l'()r " a n g l e d " cracks. S a m e iml..,~rt,allt, insights re(gilt, be ()hi,allied using n u m e r i c a l s(flultuns fur (.tu.erully seleet,ed analugies, ur I~y semi emptrl('al/(limonsiulml t,echniques. T h e c'ualosq'enee ()1' mier(H.'racks is det, e r m i n e d I~y t,he st,ross (st, rain)int,ellslftcat, tOll bet,WOOl1 alq.n'~.)a('hlllg nlte|'()era('ks an(I t,he erit,erlun I'()r i'oaJesL'en('e NOlllhel I aspect, is well L'Olll I.wehen(le(I hw t,hreecllnlenslonaJ :u'range nlellt, s u[' mlt'k(~c'raeks. ,_qume pllOgTeSS has beell a~'hieveil In bril, t,le mat, ormls - where t,he e u a l o s c ' e l ] e e i'l'ltlorioll (Imsod Oll l,he st, ross Illt,ellslt, y fact,or at o n e u f the m l c r o e r a e k s e × e o e d l n g a crit,.'al value) is relat, lvely st, ratghtl'urward - using a t,wudlmerl,slonal m o d e l . St, at,(st, loS ',dsu play an Iml_..~rt,an, t, rule II1 tlhe ovalllat, icm of t'oa.lesuenee, t,hl,l¢lugh tlhe spatllaJ dist, ribtlt, ltm ()[' sit,as ['()r intt, ial nll('ro cl,'aek t'cwmat,,.m. A closely ctHWdlnat,e(I mechmlll('s/mat, erials st, u~ly shouhl again prove I'rUitlftll [~n' t,h e evall.lat, lC)ll, o f Llle etl,ales('ol,lce iJruc'oss. When exI.OllSlVe nlll'rol'raL'{,ure precedes I.ilt.llTla{,e faliul,'e, as i[. does iil tl,o{,erogeno(Ju8 l,'na{.orials such as rut'ks, ('~)ul, arid control,o, or anlsl.lLl'opie mat, erlals SLIi.'il as kn'uphite and wil(ll,d, rrl,i(:ro['ra('t, ure ('all enl2,on(ler StlbS[,anll, lal nuillin, oarit, ies in load respunse T h l s " d e t e r mat, I()ii" ol'{,en needs t.o he l.)ledtet,al.)le, arl,(l eonshtuhve equatu'ms aJ'e re(iLib'etl fi.)r t,hls pt~rl..)se. The "defi.)rmat, lUl,i" t,hat ot'~'urs under t,onsile h~adul,g t'ail be addtlessed by {,he same mt('rt)l'l,'at't, ul,'e anYa.lyses described above. l.ll,ltler ('uml.}ressive h.mdmg, addit, i~mal mocha. nlsrns pert, ain, ÷'g, crack slidil,l,g undel,' t,he nmp~)sod shear sl, resses resisl,ed by surl'aee asl.lerll, lOSl Furl,her st, udles o f tlhe l,'neehanles (211'tlheSe ~)lIIi)tleSSOS ~I'P needed, 111 (,'ol,ijUl,ll'[,l(:m wit,h st,atlSt, lcal st,u(Iies o f mwroera,.'k dis t,riL)ul, tons, arld r'nicros('ul.)tc sJ,udles (_~1" t,he ac'tut'd er'aek o p e i i m g and slidtl,lg rnechunlsms
I,-I B (Tru(,t., propogult~m W h e n InlLial v|'a(:k growt, h IJ|'e(.'edes stgntfi cat|t m m l u w a r i t , y in t,he h.lad/deflevt, tOl~ response, |,lie ol'ack ext.,elision ('all be e[l'eu Lively ~'h,rQ('terlz~'d hy the i.lerJ, lllen{, s[ress III[,PIISII,V ['a('t,or, K 'T'e('|IIII(_ILIPN for eva.lua[,Ing K are als(.) relat, lvely we,ll eMabllshed, alt,h(~ugi~ ,~ome ad(llt, l(irla.I e['I'(3l~, live(IS {,O lie (_tevuted t,lJ very hlgl~ {,emi.lerat, tlrP {,v('llllll.ll.leS lot' SLl'UVl, llrLll ('PralTtil's, all(I to t,et'hnlqLle,~ t'(ir evahlalln~2, K IJ;.l.ralnPters j)erLillvnI [o wPhl IllPII(,S, joint,s, el,('. P, tr rrai'k ext,ellSll)li pt'v(.'e(led lly ill)r1 lillVaJ'l[,leS ill t,he load response (e.~, m l h l steels), {|lP Inlti:ll bq'(Iwt,II (.'or1 I.iv c'IlaJ'a('t,el'lZ, ed Ily t,he rr'at'k i.Ilil-,lli|'lg dIslllav.enlent, ((3(_)I-)}, iir [,he path In(iPi_lVll(ierl{, int,egt'al, ,I T h e Lest, rlle{ih(illt~i r(.)|. ()bt,allllll~ t,hese j.)aJ'arllet,ers ate alNo rea,~Ollahly well dPl'lnP(I. H o w e v e r . {,lip sul_l,~iPqUPrl{, ,,.;t,ahie growl,h o r {,he uiat'k, whl('h I)I'iPI1 allows a sul.lsLalltial Inr|'vase m hlad JiPl'orP ,'l|{,alning irist ablllLv, is IPs,,-; well vlla.I ul'[,erlZ(.e(J, an(I has IP(I t,o h i g h l y ('l.)llSPrl/at, lVe (IeSl!_Ul,'-; alllI ineJ't'li'iPn[, nlaLerlaJs usage. It IS i.iI'PSllrrle(I t,haL Lhe sLable vt';.tvk ex|,PnSlOll In st, Ill I i n l q u e l y (let,Prrntne(I lly ,I, alt,hoLigh i n u r e e×t,~n,~ive ,lUstlt'k'at, lon ( i n c l u d i n g m| eXl_)llrlt, inrot'l.i~li'ut, iol| ill' rat,e el'l'ert,s) ~s r ~ q u l r e d ; but, t,l~e instal_lllltV IS Sl.leVllllen (syst,eln) d e p e n ( I e n t OIHI IS, ;.iS yet,, inadecluaLely rharacl,PrlZed. Furt,ller exl_)ei'lnlellt,',.LI sLu(JIPs, voOrdlnat,e(I w i t h iliiiTiPril'al (aliaJyl, ll'al) soJu[,ll)ns |'(it" i.lUaSl sLaLir rl'avk ~q'clwLh, are ileedPd t,o d e v e l o p g,'n,,rolh.'#d tn,,~tebdtt.v ¢'t'llt'rle ThP teSl,~Lall,',_, to vt'a('k ~_Xt'owt.l, can be st,|'~mgly Inl'luelwell by mwr¢~strttrt~tr,, T h e pert lt|e,llt. |'el:dlunsltIps L)et,ween crack growt, h L'Illd ml('rliM, ructui'e are rive(Je(I to (|PSII:,Tll ma terlah~ Wl[,|l Ol_lt,lnll.lm [,ougllrle~s and M,al.llP ('|al'k ~q,'owt,h t en(lenl'lP,~. III fully hriLLle Illat, e|'lals, SLich as ,~lvlll'lltrGI ('Pl'~Jiiili's, ('l'a('k ~2,|'~)wt,h IH:I'LI|',~ II.V {I|P IIIJ"Pl't t-'×{,PI1SI(H1 ol' |,he_ J.)rllllal."~ crack,, anll ii,~uaJIv hlvolves ;.1 I)ond |Lii){.ure jli'(H'e,'-;s. "rile i'rark g r o w [ h resIs[,alICe |','In t,hI.l~ JIP Pllllall('P(I Lly el'I'Pc't, lrlg ('hallj~Ps near t,hP r r a u k t H_i Lhai" re(lure t,i~e u|'ack LIp (lisl_ila~'emPnL { o r K) 'T'h|'~e p r i m a r y t,oLighen Ing nlerha|ii,~ms o f |his t y p e have t,hus Jar lleen ident, ll'lP(I st, tess a('twat,e(I st,uble rl'llL'l'i) i'|at'kllll:? , (t,~ , Ill AI,,(_):~ alh.)ys), st|'Pss IrI(JLIc'P(J phase t,|'unst'(~rrnaLions (~'.g , 111 Zrl.) 2 ',/.1.1J(.)yS), an~l t'lt.mm~.~ ~rain " p u l l out," (~.'~ , in ~I:~N 4 alh lys). H i , w e r e | ' , i'oo|'d inaLe(I sl, ress analy~Ps all(I en|llEiraJ studies are lleP(IPIt t,l_) (.iLlarlt, ll'y
1
and opt, imlzP t,h~ t,o u g h n P s s , and addlt,tonM t,oughenlng mecIl,'llltStllS (¢ g., I)aSP(I Oil large inl,ernal sh'auls) sh~mhl lie e×ph)red For po/ynleric meleriol,~, craZlrl~ IS n l.lr(-,(.'ursor {,o ('rack ext,ensIoll. Henl'e, aklrl to st,able nllc'r(.10ravkllll~ Iii hrit, t,le mat,Prr,.lJs, aJ'iUys o f nonl.lropagat, lng ('i'a'z.,es (."al'l lie LISe(I t,O al'llleve high t,OllghnP,'-;,'~. (-)he" al_lpl'OUcll [o| I~,(Jnera[,lllp, ,'-;ur|l ('OllLl'(.lllP(I craT_,e arrays is {,o uLiIl'ze sPl'(lll~.i phase i.)art h'lPs. S{,tl(lleS t,o irlvPs{,igat,e the I'e~l_le'l_'tlve I'olPI,i o{" IJaJ't,wle shaI_l(--', d IsIJer SlOll, rcmM, iLuLiorl, allll int,ert'ave ('ha.ravt,eris Ll('S un vraze development,, shoul(I be mst, i {ut,e(I in ()r(h-,r (,o |(lent, sly ol.)[,Imunl al_l p|'llu('ilPs for polyrne|' t ougllenmp, In /nelel ,~ystems, where siihst, allt, laJ ri'ack Lip (tel'ilt'rlrla Lion i'an i.)|'eceile rlac'k exLelIsillll, t,he deLalls t hut, pert, aln to s|Je(.'ifl(: syst, ems a|'e (:orr|l.dex, all(I sorl'let, irnes e.(ltllV(.)('aJ. T h e r e are t w o r)rllllary nl(.)des i)f eXt,PtISlOll rleavoge, Urld h(fle I~m_lwt,h, o ( ' c i l r r l n g separaLely (Jr, m o r e usually, In r(l|'nl.)inat, il)n The t,uughr'lVSS t'I)I' bot,h modes IS dlvtaLed I.)rimaJ'tly hy t,he ma('|'o~cupw st,res,'.;/st, raln rhararLerlst, lV of t,he mat,erial, t,hruLigh it,~ et'l'erL on eit, h e r t,he st, i'ess amlJllt, u(le i|1 t,he plart, w zone, lit' on |,he re,,.;t,raln[ itlll.,.)sed by t,he ~lllrLlle IlgamerlLs. H o w e v e r , t,('ltlghi-'lllll~, ('all lie erl'e(,t,ed wit, llout, Val?Jllg Lile fh)w s{,I'ellg_-,d.h.These L,i)u[~,ilPlllrl[2, el'l'e('t,s u|'e realized Liy Siil_Ipresslng vh-'uvuge r|'u('k or h(fle I'o|'nmLion a n d / o r ll.y prevent, ing l.)re|nal, u|'e slip h..'alizaLion, (i|' fly mLi'odu(ung ('|auk I.lut, h t,l.lrt, u~lslt, y. T h e most, Import,anL s{,rLl('t, ural ['ea[,ures that, (llg{,~lt,V |,lie t,OLl~hellLn~ at ('onst.ant. st.|'engt, h alipear t.l~ lle i.i|'e('ll.)it, at,e,,,; and imlmrlt.les F'(J|' e x a m p l e , mult.lple r.lrertptt.at.e an'ays m slevls lead t.o sLihst, allt.raJ {.oughelllng Lly SUpl_l|'eSSlng holP l'~)rmat.lon or slip hwallzat.llm; Wt, lmansLat.LeI| I.)rerll_)tLaLes In 'T't a.lloys pr, l(.luce t.oughenlng by iJ~(tLl('lng t,o|'t,u {.)st t,y, w hl-' reas t rn Ibu I"It,.y seb"Tega t,lO i1 c"a.ll enrclurage ('lPavage anLI t.hLIS (lel.,q'a(le t.he t.(lughl|eSs. These el'l'ert.s a'e (rely (_lualtt.ntwely underst.ood A slll_)st.anLlal m ( . l e l i n g effort. I:,l) qLInnl, l t'y t.oLIgh(-,lllng processes is rtLiclal [or sy~.~t,ematll.' a l l o y (teSIgql ,~tudles SI.II'II al'l el'fort, r a n o n l y i.m.tgq'ess sut, isl'n(:t,~lrtly t[', hi addil, l(in {,o t,he rnat,(-,rials sviellLISL, t,here is al| art, we p:~rt, lVilmtlcln f r o m sevPi'al disrlpllneS, e g , niPrhanl('S (t() (Je[lliV the stre,'.;,'-; I'lelds d u e [,o rnBvrosl'orJll' and hlcallzvd (Jel'ormn{l()|l), surt'a(.'e p h y s w s { t o an'3dZe ImllUrlLd cl~s LrllJuLl(m, e s p e r i u l l y at, int,vrt'ace,~), st,aList, w,~ (Lo c h ~ a v t , e r l z e size and ,~paLlal d~s{~ ibutlon,~
142
or precll.)lt.at,es, et,c.), anti solid st.at,e I.,hysl,'s (t,o det, ermlne int.erface cohesion chara,.' t.erist, ics). (? Sic)u, crack growth There are t,hree IJrlmary modes or slow crack growt.h' envb'onment.ally assisted, cyclic, azld viscous; I,tley can UCCltr separat, ely, ill pm'allel, or Irl seqllem'e. SubsLarlt.iaJ pl'o~q'Pss in l.hP coml.)rehPr~SlOll ol' t,hPse pr(., cesses has been realized in recent, years, hut, m a n y irnl.,:)rt.anL deficiencies remau~. The efl'ect.s of ctwtrunmenls are relat,ed prlmardy t,o t.he~r role in lat, t,we or mt,erface decoheston t.hruugh hole a n d / o r cleavage crack formal, ion 'ahead of t,he l.,rtma .ry crack: a p o o r l y u n d e r s t o o d p h e n u m e n o n . T h e el'feet, o f t,he m I c r o s l , ruct, urP as It, u11"]LIerl('es t,he craPk l.mt,h, and l,he mode o f crack exLenmon (e.g., hole roiTnatJon or cleavage ['ract, ure) in t,he presence o f t,he enwronment,, is clearly irnportant, and requires detailed st,tidy. St, ress dist, rihut, iuns in t,he plast, ic zone require I'urt.her qLlant, ll'~catior~ t.hrough pert, inent, numet'icaJ anaJysPs. Cychc cracl; growth (t'at.igue) has m a n y of t,he n~icroscolJic I'eat,ures (such as slip Ioc',dtza t.ton) assoctat,ed wlt.h cycltc microcrack inlt, ia t.ton. These dmnage accumulat, ion processes are o1' i.)art,tcular irnporLalwe at, t,he fat, lg'ue t,hreshold, and t,heu' comprehension should bP aCt,lvely pursued. In addlt, ion, t,he det, alls of Lhe sl,ress or d~splucement, variat, ion in t,he plast, ie zone are of crucral tmportanee. For example, crack closure can dlct, al,e t,he effec Live stress int,enslt.y ract,or or ('rack opening experienced by t,he crack during each cycle; t,he closure process must,, t,herefore, be account, able b~ t.erms of t,he elast, ic/plast, ic pn)perttes o f t,l'~e mat,erial; l,!he underst.and Irlg ol' how t,l'~e n(.)n rei'overable mcremertt, in t.he crack-.opening displacement, is con vert,ed int,o a ~'rack ext.ension m LPt'ms or mwruscoplc mechanisms (including t,he role of st,at, to fract,ure processes) is incomplet,e. A conLil~uut,ion of recent, mat, erlals/mechar~ics studies should see advances in t,hese areas. Viscous tract: growth (creep rupt, ure) inw.~lves t,he nucleat, lun ,Jr microcracks in a zone ahead or t.he primary crack (or t,he nudeat.ion or grain I,.~Linda.ry cavit.ies), t.heir prupagat, turt, and finally t,heu" c(.)ales~.'en('e (especially wit, h t,he prtma=."y crack ur void). In most, inst,ances, t,he propagat,,.m ts diffu
sion cant.rolled, a process that, has heen widely st,u(Jl~l in t,he last, decade; celt,am ambtg'ult, les remain, however, and furl,her st,udms are l,o be encouraged. "the coalescence i.~hellornenun is ilrlore um'ert,ain, largely be ('ause a ~(.iqlel'aill'~,ed ('l'a('k t'oaile~t'e, llOP e r l [ , e r i o n
has no)t, been es[,abllshe~l. AnuUler import.ant, aspect, or slow crack p|lol,agat, ion IS Ills charttch, rtzation in terms ul" crack growt.h rat.es. Again, difflcult, leS are en (.'ount,PrPd irl /he presence or ext.enslve plas t,icll,y. Schemes based on l,tle crack pal, h mt,ebn'al, AJ (l'at, llsme), ~r it,s tame dependent, equtvalenl, (~' (creep), have Iteen i.~roposed. Huwever, t,hey are nut, expect, ed t,o be general, an~l their limit, a l i o n s should l~e det,er'mmed e x p e r i m e n L a l l y . Alsu, oI" course, more generaJ ,'haracLerizat, iun uPl:m.~aches musl. be sought,. D Dynamw crack propttgol/t)tt and arr~,st In a n u m b e r u f mat,erlal sysLPms it, is impor. t,ant t,o be uhle t,o predict, t,he ext,ent, or rapid crack I.~r~q~agat,ion I~eyond crit, icalit, y. For examl)le, in rluclear pressure vessels, crack an'est, must. occur before t,he crack ext,ends t,hrul@"~ t,h,~ t,hi,.'kness and causes leakage. A pert.inent, crack arrest, criterion is I,hus an essent, ml requiremt-,r~t,. When t.he cracks are small relat.lve t.o t,he (timenSlOnS of t,he c a m poner~t., crack arrest. IS essent, ially dPrn'~ed by a rnat,erlal del.~enderlt, stress mt,ensit.y I'm't,or, K,. (equ',d t.u K.. I',)r (errant(s, but, usually . K,. for met,als und polymers). However, when t,he crack length becurnes comparuhle t,o, or larger t,haJl, t.he smallest, component, dimension, t,he arq.,arent, st,russ mt,enslt,y fact,or at, arrest, is K,, (except. when the medium surr,.)un(ling t,he component, has a relat, ively large acoust.ic irtlpe(Jant'e, whereuporl atTeSt, cart oet'ur at, K :: K,,). The addihun',d ext,ension o1' t,he crack derives from t.he klnet, lc energy deveh.)ped I~y the mat,erml around t,he separat, ing crack and I'rom st,ress waves |'erlect,ed at, t.he coml..:menL hc)undartes. The mat,erial mot, ion and t,he st,ress waves car'~ augrnent, t,he apparent, stress mt,enslf,.'at, ton at, t.he crack t,ip, and ext,enslort will proceed utltll t.he erI'ect.tw st,tess int, enslt, y fact,or diminishes t.(~ K.,. A crack arrest, condtt, ion t,hat, accounts for I,he IncremPIll,s Irl crack lengt,h caused hy kmet, lc et't'ect,s has been cumput,ed for simple geomet, ltes. Hq~wever, a gcm,rahzed cracl; arrvsl cmterlon needs t,o he developed. "['his w o u h l inw.)lve e×lJermlent,al st,udies o1' (:rack
1,4 3
arrPst,, (.'tlordinat,ed wit,t~ lll.lmerli-&l ( ~ , g , t'init,e ,tit't't-'i',-'i'l,',-') si,ress ana.lyses ,~f r a p i d c r a c k I_li'(il.lUgU t, il ill.
E N{m d,.slr.clmt. ~,valualiun CiirrPnl. N D E LPehn,ques ('ouhl b(-, signifi ('aiit.ly ntilirovell by I.iet.t.Pr nlPi.hod,~ t.o i'hm'ul'. tei'lzP the size, shalle, an(I i.yl,-' o f d(-,fPeL'.; or ('i'n,'ks ii, strti,'t,liral I'(.llTli_ll.llll-'ll{,~ A I111.)~{, l'ruii, rul alilli'om'h w(lillcl I.iP a Si, Lilly l,hnt, ~'~i'rPlut,P,~ ni()(lei'il t~lt.iPi'li~li~ni,al mPt,h~,ts {)1" iliiani, iLativt~ dPt'ei'i, ('haru~'tm'rzat, h.in wit,h ei'ul'k lliP('li;.llll(',,4, lilil, lully, Slli'h :l Si, lldV Woill(t 14enei':tt, t~ rPhii, h.)ns l l i 4 w P P n t,hP I'allilre lll'l)ll;.llllllty (for ;;pi-'l'll'll' Ilt'e_i.irnes, e l l v i r o l l lileili,~, P×l~P~'i,e(.t sirt~ss llls{,iii'li~S el,l_' ) i.ln(t l hi ~ illt'PiTed (ll~fP~'t, (,tll.i_i'a(,l,l-,rl~,~i, ll',~. (_if eV~ll t~l't~,'l{,t-,i• inil_irlrt,:ini'e Wlillht tip i,he suhse(lUell{, itPier ininai, llUl c)r t,hi-, t_irliliOi'l, lCUl i.)l' pu.rt, s Lhat, :ire ;.li't,l.lallv s;Ji, lsl':l;'l,oi~, evl-,ll i,hou~h t,h+~v al'P I't~it~'tPit I_l.V a i_lartll'tlh.lr IllSl.lei'i, llin I_ii'(.ll_'el.lui'e. t_lase(t (in ;i Sl_lt~l'il'ie(I ulh'~wable [ u i l u r e lii'lll_)a bllli,y. PePilll;.li'k i,l.i t,ht~ i~nlllh.i.y~t rnet, hl.)il,~ (it' ~tPl'P,,l, ~'h~ll';JC{,i-,rlT.nt, illll alll.I (Tat'k mt-,l'linlill'S w ill iilent, il'y t,hPir (let'h'iencies, i.illlJ will i, llLIS t~itll_ltl;.lSl'Z,t~ thl)se a,~l.iel't,,~ ~)1' t,ht~ t':illurP l.lrt~llll.' t, llin l ll'l_l~'t~ss l,hat m~ ~st, a(twi'seI,v i_'oni, l'lljut,e t,ll l, he I'ejei't, lOll r;Jt,e. "rht ~ rorrnui, ll)n ;.llllt bq'owl, h o f t'rni.'k,~ ('an lie st, i'Oill~l.v Inl'lul~llt'PII b y rt,,,~ldl/al ,,#r'¢,,~s~.,,,i,w h l t ' h augrlrIPllt, t,ht ~ alJIJIled St,l'ess A llon(h~,sl, rlli'LlVl -' (t.ei,i~l'llililUt, lOli o1' t h e mal411ii, tlde oil' t,ht~se ,~ll'PSsPs, ~ , g , in wPhls, i1puJ Sl.ll't';.l('~s is iiii liurl,alli, f o r t~t't'ei'l, ivl ~ t':lllurt ~ t.lreltic't, ilm 'T'ectl nlllUt-,s t'lii' eSilitlai, lng IIIt,l~i'll'd.I St, i't~S~ ~'e. avail ulJIe, t,~ , X ruy itil'l'rui'i,h.in, ull, ru,~onh.' surt'm.'e wavi~s, Illli'a,~onl(' vt~h.icil, y dil'l't~i'~nl, iuls, tll.lt, t,liese t,el'hnlqiie,~ uri-, ill_it, sul'l'll'ient, ly itevlq i_ll_ll-'(t i,ll lie ililivi~i',~,'tllv allplll_,alJh ~ In rlal'l, li,U h.u', ,~f,rt~,,,;s 14r;.ldlents Ii1 I'eT, IOllS (.)t' lil'e~LIl,'li' la,i~l_illlt~t,i'V i'annot, lie e×l.llli'itly eva.luati~d. Flirt, h er deveh_ll.in~el~L~ In i,Pst t,el'hnlclUPS ai'p f hllS t,i) Ijl-, .enc'ouri.17,Pd. Cr;.il'k ~ r o w t h ill rt~sllllinl st, iPss t'iehls IS ,'lh,;ll p o o r l y i'h&r,'ll, t,Pi'lzed, H o w P v e l ' , ili.imerical t e { ' h n i q u e s [ o r e;,;t,atilislilll~ St,l'eS:~ Illiensii,y t'~i{'l,(_ii',~ Ill resldl.i'dJ st, iess l'lehJs ,'li't~ availablP, alid {,he~t ~ ~hiillht tie usi-,lt {,o i.)lrli,alll ~olui, ll.ln~ f o r [irol.ilPl'n,~ ill" l~art ll'ul&r Ill t,Pre,~t, b GENERAL
RECOMMEN[iA'T'I(')N
']"tip i)vt~rwh(--,lmlrlb ,, rl¢-,ed in (irdl:,.r t,h:it, |.13,Sl(' ri-',~t-'LLrch Ill rt"ii-,('l"il.ll'll(:,"ll llrOl.lt-,l"t,i(-,,s is al.ih:,, t.(.)
il}ll.la<-t, r,-,al i,l-,('hrloh_)gl('al pr<.)l.)h-,ms IS fo r cot,prehe,.,,ue r(-,s¢-,ar('h. Most. ut' t.l'le crit, ic'aJ p r o b l e n l s at, t,tli,s t,ime inw.)lve a m,ilt, ipli1'it, y i.)[' I.i,ri,tlllda.ry ('Oll(iltl,liirl,s, such aS mo l l i .)to l l i c ,'111(I ('.yl:ll(' Ioadlrlg u,u wt-,,ll as [,t-,nllJ(-'lrOt, l.lrl-' ¢'liar'itges, u rnult, ipItct|,y o f ,'.;imult,aneiiLtsly a,L'{,in~ ml-,(,h;.lrii,,4ms q)l" ili-~[()rllll.l|,i()f'l uiid [rai'turP, arid u rtiult, iplii'it.y o [ i-HwIIrl.)lllnt-h|l{,,t.J oJ' Liil[ir(-,cederlt,i-,d sevPrlt,y. W h i l e r(Jsi-i~j.rl_lh (ill lilitlVllluaJ i'OlnllOllPnts ol' i h~se [llolih~lilS is o f high Sl'li~ill, l[i(' inl,ere,~l, nlllt is ilePiJe(J t,o i.irovl(-h-, I_)uih.'ting llh.ii'ks t'lli' ally illort-, ('lllli I~lPt,e I, rl-'at, nli-'ll[,, ;.lily iliiliaCt, (ill alll_lJll'al, lons l','lll J_ll-, i'i~alist, ii'ally Pxj_iP('i,t-,d l)llJy ir t,h~ dlrl't-,ri~n{, liulhJlllT, I.ih.li'ks (','ill Ill ~ ilit, t~i'l'm'ed Wlt, h ,-,nt'h oLht-'r .'illil Sylli-,rglSt, l(' el'l't-'('t.s s t u d i e d "['lie lli'est~nt, st.at,e c)t" t.he art. tn Lht-, m~Hlanisktt' undPr,~Lan~itng ~1' m e c h a n i ( ' a l i')ropert.ies a p p e a r s Lo wurrali{. ~1 ma.l~r ~ iJt-,rillli.tlr~ ror such i'()n'l].iri-,he_llSlVl-, s t u d y a n d a u g u r fo r a r~asonal)le ~'halwe o[' 8tll'(.'ess. A i'P('omml-,ndutt~ln (_)r t.liis w~rkshot_l ts L.ha{. t.he ent.u'e s p e v t r . . t o r " l ) i ' ~ I x t m i l . y " bet.wPt-,n baste rt-,sl-,ut'~'h and ~'urrl-'nt.I y re~'lll.jnizl-'d t,P,_'ll noh~gi,_'al i.trol)lelns tip eill'itlli'agelt (.in ,'l (:lJll t, lllttillt~, liasiS, aRid i hul h o i h reseail'ht~r,~ arid i:,.ll~lllt~Pl',,,i lie. i-'lll_'Otll']l~Pd i,o lll;.Ik~ t,Plli,at, lVe LI~& (it' ri~sellrl'h i't~sult,s ill t,Pi,l'lilllhigl('al at_~l_)l,~,a t,;ons
PA R'T'IC I PA NTS
A S AiRim, MI'T'
I. M BPrns(.em, (."urni=l~W Mt4hm I lnnv (_I R BImkman, Oak Rtl"ll-_.;(,-'Nut.'l L:lb R M Cunn~m,Jr , MIT ,J R (2~,~1,, ERDA, Physical Re.~(~:Jreh "r B ("o~, ERE)A, Fo,'.~,ll Erl~uRy D R [)lPrck~, Aigonnl • Nut'l Lab A (] Evarui, Roi.'hwell Se,Pnl,t-, I?t-,nl.l-,l' 8 D Haiknt-,~,s, Argonne Nal'l Lab W Herrrnalm, Sandia Albuqul-,ique I.l F Koel,ts, Aigorlnl-, Nat'l Lab C Latrd, l.lnw of Pt-,nnsylvanm (? Y L,I, C'orn,-'ll I.hlivP|','.;It, v N H Maen',tllari, Piton Sl,,'t{.t-, LltllV M Ml-','.lhll, N¢.irf,hwl-,,~t,Prn I.IIiiv¢-,r.til|,V ,I W Morn,% ,Ir , B(-'rk,-,h-,v H (3 Nt.'h,i,.m, Arl,l~,~i Rl-',',, (~e'rl|.t-'r, N A S A E Pul~h, Oak RIIJF~e Nal,'l Lab ,I R Rl(.'l-', Brc)wrl Ilrllw'rsl|.y 'T' E Scott, ArnP!~ Lal)oral(iry 8. M. Woll', E RDA , Phv,'sm.",l REsearch M H Yoll, O;Jk Rldl~e Nal'l Lab