Surface Phenomena in Solids During the Course of Their Deformation and Failure

Abstract

The fact that deformation and failure are facilitated by the reversible physico-chemical influence of the medium has been established by now for all types of solids: for metals (and also certain covalent crystals) in contact with liquid metals, for ionic crystals and inorganic glasses in the presence of molten salts, water, alcohol, or other polar media, and for molecular crystals of organic compounds in contact with nonpolar and low-polarity organic liquids. In general these phenomena facilitate the breaking and realignment of the interatomic bonds in the presence of certain foreign atoms or molecules (which have sufficient mobility to ensure their penetration into the bond-breaking zone) and can be described as a lowering of the free surface energy of the given solid under the influence of the surrounding medium. The main condition under which the medium exerts a strong influence on the mechanical properties of the body (in cases of reversible adsorption interaction not connected with dissolution, corrosion, or other chemical processes) is that the solid and the medium be of related nature, to make the surface energy low on the boundary between the solid and liquid phases. At the same time, the form and degree of manifestation of these effects depend in a complicated manner on the real structure of the body (defects) and on the deformation conditions (stresses, temperature, strain rate, time of contact, etc.) An optimal combination of these factors makes it possible to use the influence of the medium to facilitate dispersion and treatment, particularly of solid materials that are difficult to work. To the contrary, by eliminating individual factors that lower the strength by adsorption it becomes possible to protect against the influence of the medium. CONTENTS

The stress driven instability in elastic crystals: Mathematical models and physical manifestations

“…The processes of stress corrosion are especially spectacular under the action of the melts acting on nonhydrostatically stressed solids (see a review [39]). It is worthwhile to mention that our theory implies this as an immediate consequence because of the two following reasons: First, we emphasize that the most effective mechanism of rearranging the material particles in the vicinity of the boundary separating a nonhydrostatically stressed solid and its melt or vapor is not a surface diffusion of "atoms" (which is often limited by rather small values of the diffusion coefficient), but rather the local "melting-crystallization" or "absorp.tion-desorption" processes which are not bound by long-distance transportation and are therefore much faster.…”

Effect of radiation modification of wear-resistant polyvinylenfluoride under friction on metal in oil

“…Based on the above said, in the first case, the dif ference between the regularities of behavior of the radiation bonded PVDF during friction in oil and water (or in the air) can be explained by the Rebinder effect or the adsorptive and plasticizing effect of the grease (oil) on the solid body in the friction area [10]. This effect does not penetrate deeply and reduces the hardness of the surface layer.…”

Change in the deformation and strength properties of coal during interaction with surfactant solutions

“…The greatest crack concentration is observed under generalized shear conditions (curve i). This is explained by the fact that the generation and development of "equilibrium" cracks on the basis of local strain and stress concentration are gradually controlled by the progress of the plastic deformations, and therefore by the action of the shear stresses [9]. Moreover, under the effect of ~eneralized shear (volume compression plus shear), the global stress tensor components are less than under generalized tension (volume compression plus tension) for the identical values of the principal compressive stresses.…”

“…The processes of an increase in moistness and the formation of microfractures start to he developed simultaneously under the effect of an adsorption-actlve solution, but the process of increasing moistness predominates in the initial stage because of filling up of the pore ~'zo 9 …”

“…Filling of the sorption space of coal under complex stress state conditions will depend not only on the degree of molecular interaction between the adsorption-active medium and the microcrack surface but also on the kind of stress state and the magnitude of the strain energy [5][6][8][9], as well as on the conditions of stratum exposure [7].…”