which a s t ress is applied, in 1971 Academician of the Academy of Sciences of the Ukrainian SSR Karpenko was awarded the E. O. Patch Prize.

The sociopolitical activity of Karpenko, a member of the Communist Par ty of the Soviet Union since 1939, was muttifaceted and fruitful. He was a deputy of the Higher Council of the Ukrainian SSR at the sixth and seventh meetings and he was repeatedly elected a deputy of the L'vov city and the regional councils of workers deputies. He was elected amember of the Z'vov city and regional committees of the Communist Party of the Ukraine, and a member of the Par ty committee of the institute. He frequently lectured before the work- ers of L'vov and the region, on the radio, on television, in newspapers, and in popular magazines.

In 1960 he was awarded the honorary title of honored scientific worker of the Ukrainian SSR. In Decem- ber , 1967, he was elected an active member of the Academy of Sciences of the Ukrainian SSR. In 1970-1971, Academician Karpenko became a member of the Presidium of the Academy of Sciences of the Ukrainian SSR.

The multifaceted scientific, pedagogical, and social activity of Karpenko was highly valued by the Commu- n i s tP a r t y and the Soviet government. He was awarded the Order of the Red Banner of Labor (1954), the Order of Lenin (1967), and other state awards.

The scientific direction - the physicochemical mechanics of materials - which Karpenko helped establish and the journal Fiziko-Khimicheskaya Mekhanika Materialov (Soviet Materials Scienee),which he founded and was permanent editor-in-chief of until the end of his life, will continue to promote the scientific and technical progress of the country and the development of the material base of Communism.

S E V E N T H A L L - U N I O N C O N F E R E N C E ON C O L L O I D C H E M I S T R Y

AND P H Y S I C O C H E M I C A L M E C H A N I C S

The Seventh All-Union Conference on Colloid Chemistry and Physieochemical Mechanics was held in Minsk October 11-13, 1977. More than 400 people took part in the conference, representing scient i f ic-research estab [ishments, further education colleges, planning and design organizations, and industrial organizations from various cities of the Soviet Union, including Moscow, Kiev, Minsk, L'vov, Zaporozh', Leningrad, Togliatti, Uffi, Tbilisi, Gor'kii, Khar'kov, Donets, Erevan, and other cities.

The conference was opened by the President of the Organizing Committee B. V. Deryagin, Corresponding Member of the Academy of Sciences of the USSR. In his greeting from the Central Committee of the Communist Par tyof Belorussia, I. M. Glazkov, Vice-President of the Soviet of Ministers of the Belorussian SSR, emphasized the practical importance of scientific developments in the field of colloid chemistry and physicochemical mech- anics in oil extraction and refinement, in discovering new materials and by-products from the dressing of natural raw materials and by-products from the dressing of natural raw materials , and also in powder metal lur-

gY.

-Atthe f i rs t plenary session, several papers were read dealing not only with the achievements but also the problems in colloid chemistry and physicoehemieal mechanics. The development of colloid chemistry over the 60 years of Soviet rule was dealt with in contributions from Academician F. D. Ovcharenko (Ukrainian Academy of Sciences, Klev) and G. I. Fuks (Moscow). B .V.Deryagin , Corresponding Member of the Academy of Sciences of the USSR (Moscow}, dwelt on the problems of the stability of colloidal systems. An analysis of the main prin- ciples involved in the Rebinder effect and the application of this to dispersion and stabilization in systems con- tabling solid phases was given by E. A. Shchukin (Moscow}. By using several methods which made it possible to make an approximate analysis of elementary acts of interaction between a deformed solid and the surround- ing medium, concepts have been developed relating to the molecular mechanism of the Rebinder effect as an easing of the thermally activated processes of the rupture and restructuring of interatomic bonds in the pre- sence of specified surface-active atoms (molecules) with migrational mobility.

Corresponding Member of the Ukrainian Academy of Sciences V.V. Panasyuk (L'vov) in his paper indi- cated the main lines of the development of research on the physicochemical mechanics of brit t le destruction in constructionsl materials. One of the most important tasks is to develop methods of evaluating the working ca- pacity of materials in a s tructure where there are sharp s t ress concentrators, in particular, defects of

Translated from Flziko-Khimicheskaya Mekhanika Materialov, Vo[. 14, No. 1, pp. 8-11, January-Febru-

ary, 1978.

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the c rack type and where, in addition to intense fields, the physicochemical pa ramete r s of the working medium also have an effect.

There are two ways in which the problems can be solved. The f i r s t ~lcludes the development of methods for determining the physicochemical cha rac te r i s t i c s of s trength, in par t icu lar the toughness of the mater ia ls raking into account the effect on the mater ia l of var ious liquid and gas media; and also to develop methods of predie t ingthe durabil i ty on this bas is . The second line of attack is to find ways of developing mater ia l s with a high toughness, to study the use of active media for the efficient technological t rea tment of machinery details, and to increase the strength of the mate r ia l s .

His paper also repor ted some of the successes and disc losed some of the t rends for the future develop- ment of r e sea rch in the f i rs t of the lines of attack indicated above. He also indicated some new approaches to the task of determining the toughness and gave an analysis of the phenomenon of the development of fatigue cracks when the mater ia l is acted upon by loads and is in working media.

The work of the conference was conducted in six sect ions: "Surface phenomena and the stability of colloid sys temsn; NObtaining and stabilizing dispersed sys temsn; ~Structure-formation in d ispersed sys tems~; nNa- rural d ispersed s y s t e m s " ; Colloid chemis t ry of po lymers" ; and the nPhysicochemical mechanics of mate r ia l s . "

,4 total of 48 papers were read at the sess ions of the Physicochemieal Mechanics Section, dealing with various aspects of the physicochemical mechanics of mater ia l s . It should be pointed out that there were sev - e ra l key-note papers which determined the scientific direct ion of the sess ions . In his paper dealing with some of the problems of the physicoehemical mechanics of mater ia ls and elements in aviation design, A. V. Karla- shov (Kiev) repor ted some resul t s f rom a study of fatigue, cor ros ion-fa t igue s trength, and the co r ros ion r e - s is tance of design mate r ia l s made f rom aluminum alloys as a function of the thickness of their cladding layer and also some methods and reg imes for forming an anodic oxide film. It was shown that the mos t effective method of increasing the protect iveness of an anodic film is to add a sur face-ac t ive mater ia l to the electrolyte which fo rms the film. These mate r ia l s , such as thiocarbamide and potassium sodium ta r t r a te , significantly increase the cor ros ion- fa t igue strength and the cor ros ion res i s tance of the anodized mater ia ls .

The field of application of s t r e s s concentrat ion fac tor (SCF) for descr ib ing the subcr i t ica l growth of c racks during the action of a medium was the theme of a paper read by S. Ya. Yarema (L'vov). It was shown that a detailed descript ion is, to some extent, ambiguous and provisional since it cannot allow for those changes in the environment of the apex of a c rack which are caused by the p rocesses of interaction with the medium. The kinetics of c rack growth in the transi t ional period depend not only on the initial and current values of the s t r e s s pa r ame te r s but also on the rate of interaction between the mater ia l and the medium. The lat ter , in addition to its ambiguity, and the inadequacy of the determinat ion of the s t r e ss field using the normal SCF, p r o - duces a noninvariance of the destruct ion d iagrams and to avoid this it is suggested that they be determined f rom the establ ished velocities of c rack growth.

Prob lems of the physicochemical mechanics of deformed construct ion mater ia l s were the subject of the paper by G. G. Maksimovich, V. S. Pavlina, and E. M. Lyutyi (L'vov). They have elucidated some of the pr in- ciples involved in the changes in the physicomeehanical proper t ies and s t ruc ture of d ispers ion-hardened alloys as a function of the size of the s t r e s s e s and the duration and temperature of the tes ts , including the t empera- t u r e - t i m e inversion of the effect of the deformation strengthening of steels. Data were given on the effect of su r face -ac t ive media on the dislocation s t ructure of deformed steel a t room tempera ture and above. The equa- tions charac ter iz ing the laws of summation of damage in the case of strengthened mater ia ls allowing for the effect of the s t r e s s level of the pre l iminary loading and the subsequent tests under conditions of cyclic and stat ic loading were compared.

It was pointed out that the studies of deformed metals and alloys should make it possible to estab_~.n the optimum conditions of use and the optimum conditions of use and the optimum t rea tment and can be used as the basis for predicting proper t ies (in par t icular , on a long- te rm basis); to develop methods of strengthening ma- ter ia ls ; and to c rea te some elements of a theory relating to the deformation and destruct ion of design mater ia l s under the action of working media.

In their contribution O. N. Romaniv, G. N. Nikfforchin, and A. V. Slinehisin (L'vov) dealt with questions relat ing to the l inear mechanics of destruct ion and engineering methods of evaluating reliability. Up-to-date ideas based on the fundamental theories of linear mechanics of co r ros ion destruct ion on the suberi t ieal growth of c racks with the action of aqueous solutions and of alcohols were developed. They came to the conclusion that the rate of subcri t ical c rack growth is not determined by an unequivocal p a r a m e t e r K 1 but depends also on the

initial conditions created by the size of the initial s t ress . The effect of the initial conditions is associated with the development during subcritical crack growth of a microbranching process. The concepts of macro- and mi- crobranching of cracks is introduced as is the concept of microbranching of a single and multiple type which occurs both along the boundaries of an austenite grain and bundles of martensite crystals and also along the slip lines.

Microbranching is considered as a competing process of the low-energy dissemination of a crack and an effective relaxation of s t resses at the mouth of the crack and in the predestruction region. An evaluation is given of the energy losses associated with the slowing down of the starting rate of crack growth as a result of the microbranching.

An analysis is made of the possibility of controlling the kinetic retardation of crazing based on the regula- tion of the branching process by means of changing the structure of the steels and their impurity compositions; inhibiting the media; and also using relaxation treatments to ensure a lowering of the structural micros t resses which ar ise during the martens ire transformation.

The use of the Rebinder effect to intensify the mechanical treatment of solids and materials was discussed in the contribution by L. S. Bryukhanova, Yu. V. Goryunov, N. V. Pertsov, and E. D. Shchukin (Moscow). The optimum scientifically based combination of physicochemical and mechanical conditions for the emergence of the Rebinder effect - the absorption-facilitation of deformation, fracture, and dispers ion of solids under the effect of the surrounding m e d i u m - can be used to intensify various processes of mechanical treatment (turning, drilling, milling, grinding, etc.) of high-strength and almost unworkable materials.

In the special processes of surface treatment (mechanical, mechanoultrasonic, friction-strengthening, laser, electrohydropulse, etc.) of details made of quenched steels and various grades of cast iron, structure- formation of the so-called ,,unetched white layers" occurs. Various aspects of this problem were discussed in the paper given by Yu. I. Babel (L'vov). Suitable physicomechanical, electrochemical properties and the struc- ture of the white layers and also the presence in the layers of residual compressive stresses have a good effect on the resistance of the steel to corrosive and mechanical destruction. The normal corrosion and low-cycle fatigue of steel details with a white layer in fresh, salt, or well water increases 3-12 fold; the resistance to corrosion crazing in sulfuric acid solutions, 2-3 fold; the resistance to fretting corrosion (fatigue in a ~ solu- tion of NaCI of specimens with pressed-on collars), 1.5-2 fold; and the resistance to wear, 2-3 fold.

Results of a study of the kinetics of corrosion-fatigue destruction of surface-strengthened steels were reported in the paper by V. I. Pokhmurskii T. N. Kalichak, Ya. L. Poberezhnyi, and A. M. Krokhmal'nyi (L'vov). The corrosion-fatigue studies of carbon and light steels after being diffusion-saturated with chromium and ti- 'tanium showed that, with respect to the character and intensity of the accumulation of inelastic deformations, the process of cyclic deformation and destruction of specimens can be provisionally divided into three periods. In the first period there is intense plastic flow in the surface layers. The second period corresponds to the accumulation of damage. In the third stage of corrosion fatigue, a macroscopic crack develops leading to the spontaneous destruction of the specimens. Some general principles of the accumulation of inelastic deforma- tions are established in the cases where the coating on the steel works in a cyclically softened (45 steel after annealing) and a cyclically stable (I~12NMBF steel) structural state.

"The reports heard at the sectional sessions dealt mainly with questions involved in the effect of surface- active media on the deformation of solids and the use of this effect in various production processes; the devel- opment of criteria for the evaluation of the destruction of material under the action of the workIng media; ways of increasing the strength and improving the fatigue resistance of the materials of details and design elements under user conditions; and the physicochemical phenomena appearing in the Interaction between structural ma-

terials and aggressive media.

The conference summed up the studies in the Soviet Union in the field of physicochemical mechanics over the period since the Sixth All-Union Conference. During that period several new corrosion-resistant design materials have been developed; new technological process for the purpose of improving the strength and relia- bility of machIne details and design elements have found wide applications; the quality of many products has been improved; and the consumption of energy in cutting, pressing, etc., treatments has been reduced.

It was emphasized that one important task in the physicochemical mechanics of materials is the further development of research on fundamental and applied aspects of the strength of design and other (highway con- struction and building) materials allowIng for the use conditions, in particular, a study of the mechanism involved in the Interaction in deformed-material - workIng-media systems and the deveiopment on this basis of methods of forming materials with specified use properties (strengthening technology, protective coatings, inhibiting) and

also methods of evaluating the durabi l i ty c h a r a c t e r i s t i c s of a ma te r i a l ; a study of the p r o c e s s e s of b r i t t l e de - s t ruc t ion of design m a t e r i a l s , pa r t i cu l a r l y under the action of su r face -ac t ive m a t e r i a l s , low t e m p e r a t u r e s , i r - radia t ion, and o ther actual use conditions.

An extended sess ion of the sc ient i f ic soviet on the p rob lem nPhys icochemica l mechan ic s of m a t e r i a l s u was held and a s u m m a r y of its work o v e r the recen t per iod was given.

In conclusion, the conference de legates e x p r e s s e d the i r be l ie f that the resu l t s of r e s e a r c h in colloid c h e m - i s t ry and the phys icochemica[ mechan ics of m a t e r i a l s will make a worthy contr ibution to the solution of urgent p rob l ems of industr ial 'and agr icu l tu ra l product ion, r a i s e the quality of products , and will help in eve ry way the successfu l fulfillment of the Tenth F i v e - Y e a r Plan.

U N L O A D I N G M E T H O D IN E X P E R I M E N T A L F R A C T U R E M E C H A N I C S

V . M. M a r k o c h e v a n d E . M. M o r o z o v UDC 620.171

The theore t ica l development of new mechan ica l c h a r a c t e r i s t i c s of a m a t e r i a l is typical of f r a c t u r e m e - chanics . They a re v i r tual ly all de te rmined exper imenta l ly on spec imens with a p r e f o r m e d (fatigue) c r ack and define the r e s i s t ance of the m a t e r i a l to m ov emen t and p r i n c i p a l - c r a c k propagat ion, including against a back - ground of l a rge p las t ic deformat ions .

In this connection, e x p e r i m e n t e r s a re faced with p rob lems assoc ia ted with de te rmin ing opt imum methods of es tabl i sh ing des i r ed m a t e r i a l c h a r a c t e r i s t i c s . These methods have a bea r ing on analyt ical computat ions fo r appropr i a t e p a r a m e t e r s (for example , the K-ca l ib ra t ion for the s t r e s s - c o n c e n t r a t i o n fac tor , equations for c rack opening, the J - i n t e g r a l , etc.) . In expe r imen t , we cannot d i spense with specif ic inves t iga tory p rocedures . Among these p r o c e d u r e s , the "load P - d i s p l a c e m e n t A T d iag ram, which can be used to es t imate such mechanica l c h a r - a c t e r i s t i c s as K c, Kic, 5e, and J Ic , has come into the m o s t widespread use. A s i m i l a r d i ag ram (f rac ture d ia- g r am) es t ab l i shes the reac t ion between a solid and c r ack on the f o r c e effect .

F r a c t u r e d i a g r a m s are unusual in that any p a r a m e t e r es t imat ing the s tage of fa i lu re can be e x p r e s s e d in accordance with a speci f ic rule by the coordinates of any c h a r a c t e r i s t i c point on the d iagram. In addition to developing methods for cons t ruc t ing these d i a g r a m s , however , the need exis ts to isola te the effects that con t r i - bute to plas t ic deformat ion and c rack propagat ion. Both of these p r o c e s s e s can proceed s imul taneous ly under load and m a y f requent ly exe r t the same influence on the readings of the measu r ing device (for example , the c r a c k opening, which is m e a s u r e d by a d i sp lacement s enso r , is the sum of the d i sp lacements due to plas t ic de- fo rmat ion and c rack propagation).

On unloading the spec imen , the p rope r ty of r eve r s ib i l i t y of e las t ic deformat ions and the i r r e v e r s i b i l i t y of p las t ic de format ions (as well as the inability of the c r ack to c lose up) can be a s sumed on the bas i s of separa t ion of effects . The unloading method* that we have proposed in combinat ion with the yield method [1] always makes it poss ib le to sepa ra t e r e v e r s i b l e f r o m i r r e v e r s i b l e p r o c e s s e s .

Note that the unloading method can be used when in termedia te unloading (the remova l of a fo rce f rom the spec imen) and subsequent loading do not a l t e r the shape of the f r a c t u r e d i ag ram (a s i m i l a r l y known proper ty of the conventional s t ra in d iag ram during the tensor ing of a flat specimen) . It should be assumed , m o r e o v e r , that the p resence of p las t ic deformat ion dis t r ibuted over the ne t - sec t ion does not give r i se to a change J,~ the spec imen e las t ic pliabil i ty. Both of these posi t ions were conf i rmed exper imenta l ly ; in this case , it is c~ ~vered tha t in te rmedia te unloadings a r e not ref lec ted in the genera l configuration of the f r a c tu r e d iagram, while y ie ld- ing of a dense spec imen with a single la te ra l notch (radius of 1 m m at the tip), which is subjected to eccen t r i c tensioning, does not change until the points of force applicat ion exper ience a 4 - m m inelast ic d isplacement .

We can cite specif ic examples of de te rmina t ion of mechan ica l c h a r a c t e r i s t i c s by the unloading method.

*We f i r s t r epor t ed the unloading method at the All-Union Conference on "Evaluat ion of the Bear ing Capacity of Mate r i a l s and Welded Joints f rom Cr i t e r i a of F r a c t u r e Mechanics~ (Kiev, December 19-21,1972) .

Moscow Insti tute of Physica l Engineering. Trans la ted f rom F iz iko-Khimicheskaya Mekhanika Mater ia lov , Vol. 14, No. 1, pp. 12-22, J a n u a r y - F e b r u a r y , 1978. Original a r t i c l e submit ted April 2, 1977.

0038-5565/78/1401-0007507.50 �9 1978 Plenum Publishing Corpora t ion 7