Rehbinder Effect Research Articles

COMPARATIVE CHARACTERISTICS OF MECHANICAL AND ADSORPTION PROPERTIES OF ACTIVATED CHARCOALS APPLIED FOR ADSORBERS OF NPP AIR DISCHARGE SYSTEMS

This paper presents the results of studies on the strength and adsorption characteristics of granular activated charcoals of the brand ISQ DON GW4, С40/4 EXTRA KJ, and Norit RKJ4. The ultimate strength of samples was measured in different states: initial (H2O vapor saturation as a result of long-term storage), dehydrated, I2 vapor saturated and H2O + I2 vapor saturated. A significant (25…40%) decrease in the activated charcoal fracture stress due to the iodine vapor saturation, concerned with a Rehbinder effect, was observed. The degree of the adsorption decrease in the sorbent mechanical stability should be taken into account when selecting sorbents for filters of NPP air discharge purification systems (ventilation systems).

Novel Unexpected Reconstructions of (100) and (111) Surfaces of NaCl: Theoretical Prediction

We have predicted stable reconstructions of the (100) and (111) surfaces of NaCl using the global optimization algorithm USPEX. Several new reconstructions, together with the previously reported ones, are found. For the cleaved bare (100) surface, pure Na and pure Cl are the only stable surface phases. Our study of the (111) surface shows that a newly predicted Na3Cl-(1 × 1) reconstruction is thermodynamically stable in a wide range of chlorine chemical potentials. It has a sawtooth-like profile where each facet reproduces the (100) surface of rock-salt NaCl, hinting on the preferred growth of the (100) surface. We used Bader charge analysis to explain the preferable formation of this sawtooth-like Na3Cl-(1 × 1) reconstruction of the (111) surface of NaCl. We find that at a very high chemical potential of Na, the polar (and normally absent) (111) surface becomes part of the equilibrium crystal morphology. At both very high and very low chemical potentials of Cl, we predict a large decrease of surface energy and fracture toughness (the Rehbinder effect).

Physico-mathematical model for bellows expansion joint efficiency by different manufacturing technologies

Increasing the reliability and improving of the technical characteristics of bellows and bellows expansion joints widely used in various fields of technology is a recent issue today. To solve this issue, a physico-mathematical model of functioning and measuring the reliability performance of bellows expansion joints is developed. The model includes two mechanisms of fatigue breakdown and wear: the Rehbinder effect and fretting. The developed model allows for calculating cyclic operation life for different bellows expansion joints. The model describes bellows expansion joints by three parameters: growth rate of a microcrack due to the Rehbinder effect, speed of fretting wear, and value of reversible period of microcracks formation. One can experimentally measure these parameters for different constructions and technologies of manufacturing of bellows expansion joints. Today, there are various technologies of bellows expansion joints manufacturing, including promising technologies of modification using fluoro-organic surfactants. The developed model is applied for assessment of different manufacturing technologies. Based on the analysis of the physico-mathematical model, the requirements for technologies are defined that lead to increasing of reliability of bellows expansion joints. The technologies of modification using fluoro-organic surfactants are theoretically proved to lead to increasing of the reliability performance of bellows expansion joints.

Phenomena of crystal splitting during growth as a result of the Sternberg-Punin and Rebinder effects

The causes of growth blocking, splitting, twisting of crystals are considered. These phenomena are the result of the combined effect of the Punin effect (total autodeformation due to intersectorial heterometry, appearing when impurities are unequally captured by different faces or their parts) and the Rehbinder effect (a sharp decrease in the strength of the surface layer of a growing crystal several times covered by a film of mother solution containing active substances).

Studying the Machinability of Tin-Bearing Free-Cutting Steel

The machinability of 0.2% Sn free-cutting steel produced by vacuum melting and hot shaping under pressure using the method of hammer forging has been studied. The distribution of elements (Sn, S, Mn) in the steel has been investigated by secondary ion mass spectrometry (SIMS). It has been established that the doping with tin appreciably increases the machinability index of the free-cutting steel to kv = 1.72. The effect of S and Mn segregation with the formation of manganese sulfide MnS precipitates has been revealed. Tin in the form of fine particles is uniformly distributed in crystalline grains and along their boundaries and segregates on MnS particles. In the process of cutting, low-melting tin particles are melted to initiate the Rehbinder effect (liquid-metal embrittlement), thus embrittling the steel. Moreover, tin has a lubricating effect at the point of contact between the cutter and the machined surface. All these effects improve the machinability of tin-bearing free-cutting steel.

Effect of surface-active media on chip formation in micromachining

Conventionally metal working fluids are employed to reduce tool wear and energy consumption in the metal cutting process. This paper presents a new method to achieve the same purpose by reducing chip thickness and cutting forces through introducing the mechanochemical effect, also referred to as Rehbinder effect, by applying the surface-active media on the workpiece surface before machining. Orthogonal cutting tests were conducted on the copper samples to understand the underlying mechanism of material deformation in the presence of surface-active media. Theoretical explanations for the mechanochemical phenomenon have also been provided. Moreover, the studies were extended to the face turning operation to examine the effectiveness of surface-active medium in a more general case study. It was found that the effectiveness of surface-active media is diminished with decrease in feed rate and enhanced with decrease in cutting velocity. A maximum of 60% reduction in cutting force can be achieved at the critical feed rate of 50 mm/min with low cutting speeds in face turning. This paper not only advances the understanding of the mechanochemical effect in micromachining but also for the first time correlates the surface effect with machining parameters and tool geometry. As validated, the significant reduction in cutting forces open new avenues for further development of new surface-active media for applications in machining processes.

On the Conditions of Change in the Type of the Dependence Curve of the Rehbinder Effect Value on Adsorbate Concentration with an S-Type Isotherm

On the Conditions of Change in the Type of the Dependence Curve of the Rehbinder Effect Value on Adsorbate Concentration with an S-Type Isotherm

Determining the Boundaries of the Concentration Area of Action of the Rehbinder Effect for an S-shaped Adsorption Isotherm

This paper continues a study of the magnitude of thermodynamic estimation of the Rehbinder effect as a function of volume concentration in a liquid solution of a surface-active substance (surfactant) in the case of an S-shaped adsorption isotherm on an undeformed and uncharged surface. A generally piecewise linear approximation of the isotherm is used. The conditions of existence of a bounded concentration action area of the Rehbinder effect, such that the area does not fall outside the bounds of defining data from the adsorption isotherm, are derived analytically in terms of theory parameters. The width of this area is compared to the data in the literature on the Rehbinder effect for quartz and granite obtained during dodecyltrimethylammonium bromide adsorption.

Rehbinder effect in ultraprecision machining of ductile materials

Abstract Rehbinder effect on ductile materials is observed when surfactant is applied on the material surface, which reduces the strength of material due to reduction in surface energy. Application of Rehbinder effect in conventional machining of ductile materials was studied previously which resulted in significant reduction in chip thickness and cutting forces. In this paper, the Rehbinder effect on ultraprecision microcutting of ductile materials is presented. Microcutting experiments were conducted on annealed copper, hardened copper, aluminium alloys AA-6061-T6 and RSA-6061 of different grain sizes at varying uncut chip thickness and cutting speed. Permanent metal marker ink was used as a surfactant to induce Rehbinder effect. As a result, cutting and thrust forces were reduced by 50% for pure copper whereas a 30% reduction was observed on aluminium alloys along with a reduction in chip thickness for the sections where ink was applied. It is also evident that the Rehbinder effect contributes towards an improvement in surface roughness. The underlying mechanism responsible for the reduction in cutting forces and chip thickness is explained in relation to a dislocation density model and explored further by a finite element method simulation. Positive results of Rehbinder effect on microcutting demand further studies to characterise the effect on other surfactant-material pairs for the applications in ultraprecision machining.

Investigation of the impact of Rehbinder effect, electrical erosion and wire tension on wire breakages during WEDM

The paper provides an analysis of the influence of the Rehbinder effect, electrical erosion and wire tension on breakages during wire electrical discharge machining (EDM) of steel 36CrNiMo4 (the analogue of AISI 9840) by the SODICK VZ300L machine. A classification of wire breakages (explicit and implicit) is proposed and the reasons for both breakage types are considered.The methods of optical microscopy, scanning electronic microscopy, fractography, and tensile testing of the wire in the air atmosphere, as well as pure and impure deionised water, are used to demonstrate that the Rehbinder effect and microdamage caused by electro-discharge do not have a substantial influence on implicit brass wire breakages. The experimentally determined average value of the amorphous zone width (8.4 μm) of an eroded wire was used during its stressed-state simulation, resulting from the non-uniformity of the temperature distribution throughout the wire depth.To estimate the influence of thermal stresses on implicit wire breakages, the internal thermal stresses calculation algorithm, based on the generalised Hooke’s law in a differential form and the consideration of stresses caused by thermal wire expansion, is proposed. Considering the wire pre-tension acting along the longitudinal wire axis (365 MPa) caused by rollers, and the maximum axial thermal stresses (167 MPa) obtained by simulation, the total tension of an eroded wire is 532 MPa, which is significantly lower than the tensile strength of the eroded wire (891 MPa) determined experimentally.The most probable reason for implicit wire breakages is violation of the continuity wire machine feedback following random large EDM debris sticking to the wire and workpiece. The investigation leads to the conclusion that the most probable cause of explicit breakages is short circuits.

Перспективы применения эффекта Ребиндера в бурении

Перспективы применения эффекта Ребиндера в бурении

Thermodynamic Evaluation of the Rehbinder Effect during Adsorption According to an S-Shaped Isotherm

A liquid solution–solid surface system with a single-component adsorption of surfactant is considered. The case in which the surfactant is represented by dodecyltrimethylammonium bromide (DTAB), while the solid surface is silica, is considered. Based on the previously developed thermodynamic theory of adsorption on the solid surface assuming its deformation, the dependence of the thermodynamic evaluation of the Rehbinder effect on the bulk concentration of surfactant in solution is investigated analytically. In calculations, a clear S-shaped experimental adsorption isotherm of DTAB on the nondeformed surface is employed. Using this isotherm, a piecewise approximating function is plotted, which yields the necessary concentration dependence and conditions of its dome shape in terms of the parameters of the theory. Experimental characteristics (rate of drilling) on granite, quartz, and microcline are compared with the theory represented by the dependence of the thermodynamic evaluation of the Rehbinder effect on the concentration of DTAB.

Effect of technological parameters on the mutual penetration of copper and iron in laser cladding of steel with a copper–nickel alloy

A copper–nickel alloy was deposited on steel using a powerful fibre laser. Beads of different height and width were produced by varying the process parameters. The results of metallographic examination show that at optimum cladding conditions there are areas of unmelted steel. In areas where the steel is melted the penetration depth, the width of the transition zone from steel to copper, the depth of penetration of the cracks caused by the Rehbinder effect and the content of the iron phase in the copper layer are lower than in other conditions.

Thermodynamic estimation of the Rehbinder effect in the case of adsorption according to the Frumkin isotherm

The adsorption Rehbinder effect is determined using an earlier-suggested thermodynamical adsorption theory on a solid surface taking into account its deformation. Single-component adsorption is considered for the case in which the adsorption isotherm on an undeformed surface is the Frumkin isotherm. The dependence of the value of the effect on the adsorbate-bulk concentration and the effect of the attraction constant on The Frumkin isotherm on it are analyzed. The concentration selectivity of the adsorption effect and the condition of the dome shape of the dependence of this value on the bulk concentration are explained in terms of isotherm parameters.

ОБ ОСОБЕННОСТЯХ РОСТА ТРЕЩИН В ВЯЗКО-УПРУГОЙ СРЕДЕ С РАЗВИТОЙ ИЕРАРХИЧЕСКОЙ СТРУКТУРОЙ

The study of physical mechanisms of rock materials destruction allows obtaining the information necessary for the development of new technologies for mining and processing of minerals. Furthermore, such knowledge makes it possible to assess in real-life conditions the influence of external factors, for example, water, on the strength characteristics of mine workings and constructions, including the underground ones. The authors study the deformation behavior and special aspects of the destruction of small-sized specimens cut from the model viscoelastic materials – rock materials (carbonaceous quartzite, serpentinite, and artificial sandstone) under the diametrical compression – indirect stretching. Laboratory studies and subsequent modeling of the structure and properties of rock materials performed on small-sized specimens make it possible to solve the task not attracting the expensive test equipment and without violating the integrity of the specimens. During the study, small-sized specimens in the form of cylinders were produced from model viscoelastic materials. The mechanical properties of carbonaceous quartzite, serpentinite, and artificial sandstone specimens were estimated in the initial state and after a 24-hour water soak test. The study showed the influence of water on the change of a type of the specimens’ deformation behavior. The authors mapped the specimens’ side surfaces and created the topograms of the working surfaces before and after the tests. Based on them, the metallographic analysis of the geometric characteristics of cracks was performed at the macro- and microscopic levels. It was suggested that the change of a type of deformation behavior of rock materials, as well as the decrease in the strength properties of test rock materials specimens under the influence of water, are explained by the Rehbinder effect mechanisms.

Thermodynamic Conditions of the Rehbinder Effect and Dependence of the Adsorption Effect on Electric Potential of a Solid Surface and Adsorbate Concentration

Thermodynamic conditions of the Rehbinder effect and the dependence of adsorption effect on the electric potential of the solid phase and volume concentration of adsorbate are analytically studied in the framework of the theory of single-component adsorption from a liquid on a solid surface in the presence of an electric charge on the surface and taking into account the surface deformation proposed earlier. These conditions and general dependences are supplemented with detailed analysis for the case of adsorption according to the Temkin isotherm.

Damage evolution in metals under the gigacycle fatigue loading due to the contact with surface-active liquid

The Rehbinder effect (adsorption strength reduction effect) consists in a qualitative change of the development of multi-scale damage kinetics in a deformed sample in the presence of surfactants (in our case, liquid gallium). Its influence on the fatigue life of pure iron under gigacycle loading conditions is associated with a qualitative change of the role of the surface. The property of the surface to serve as a high power "sink" for defects is significantly reduced due to similarity of the chemical potential of the solid and surfactant as a result of "filling" the incomplete atomic planes ,which provides the "adiabatic" character of the process of damage accumulation in the volume of material. Fatigue tests of pure iron were carried out on the ultrasonic resonant fatigue machine Shimadzu USF-2000 with frequency of 20 kHz in the gigacycle fatigue loading regime with very low stress amplitude, during which the material failure occurs after realization of 109 loading cycles. Fractured surfaces were analyzed by optical and electronic microscopes to identify the depth of penetration of liquid metal into the fracture area. It has been shown that the durability and strength of the material coming into contact with a surfactant are significantly reduced on the "adiabatic" surface and the region of localization of the defect density is shifted to the surface layer, which is characteristic of "embrittlement" materials being in contact with a surfactant. The Rehbinder effect radically changes the mechanism of crack initiation in gigacycle fatigue regime, which leads to the formation of cracks in the surface layer of the sample, rather than in the volume of the material, which is characteristic of this kind of fatigue failure.

On conditions of change of sign of the Rehbinder effect in the case of single-component adsorption according to the Frumkin isotherm

Thermodynamic criteria of the “positive” (a decrease in surface hardness) and “negative” (an increase in surface hardness) Rehbinder effect are studied in terms of an earlier-proposed theory of adsorption on a solid surface that takes into account its deformation. Single-component adsorption according to Frumkin isotherm is considered. The conditions for transition from surface stretching in the presence of a “positive” Rehbinder effect to its compression and appearance of the “negative” effect is considered numerically and analytically.

Water treeing in extruded cable insulation as Rehbinder electrical effect

The paper contains systematic comparison of signs and properties of the water treeing phenomenon (the basic mechanism of degradation of medium voltage electric cable extrudered insulation which develops under combined action of electric stress and water) and Rehbinder Effect – the reduction of mechanical strength of solids due to physical and chemical action of liquid medium.The analysis of the published data permits to distinguish 13 indications of the Rehbinder Effect. The authors show successively the direct analogy of the water treeing and the Rehbinder Effect using the above mentioned indications, including decrease of work of the development of new surfaces in the course of destruction, chemical specificity, role of material defects, two-stage destruction nature, etc. The analogy obtained is accepted as a working hypothesis which permits to bring certain order into theoretical and experimental studies of the water treeing.

Chemomechanical effects of self-assembled monolayers on gold films

Chemomechanical effects are technologically of great importance, but they have been highly controversial due to issues with reproducibility, environmental sensitivity and the fact that they only become dominant in the near-surface region. Using nanoindentation and the careful control of surface chemistry, we have isolated specific chemomechanical effects in nanoscale gold films. The Au was tested with and without alkanethiol self-assembled monolayers (SAMs) and the environmental conditions were carefully monitored throughout. For shallow nanoindentations, a well-formed SAM lowered the load–depth curves substantially and pile-up at the indent sides was slightly reduced. This can be attributed to the so-called “Rehbinder effect”, where changes in surface energy, in this case due to the SAM, affect plastic deformation. Interestingly, even at greater depths the SAM was still found to lower the load–depth curves, though it greatly increased the pile-up volume (+300%). This is likely due to a different effect where the presence of the SAM allows greater ductile flow and, hence, extrusion of the Au during the indentation. In all cases the plastic work of indentation was lowered by the SAM, indicating that it made plastic deformation easier than for uncoated Au films.