Rehbinder Effect Research Articles

Water-induced surface ordering facilitating the microcutting of ductile metals

Metal cutting is a crucial process in modern manufacturing. Enhancing the machinability of metals can significantly improve their production efficiency and surface integrity. Coating surface-active media (SAM) on the free surface of the metals before cutting is an easy method to improve machinability, which usually pertains to the category of the renowned Rehbinder effect. However, the existing SAM is usually hazardous and complex materials. Besides, the effect of SAM on the local structure of the metal surface remains unclear. In this study, water is employed as a simple yet often overlooked SAM in the microcutting of copper. Using water as SAM also allows the employment of X-ray absorption fine structure spectroscopy (XAFS) to study the local structure of copper with and without water coating. Results show that water coating on the free surface of copper can significantly reduce the cutting force and chip thickness, and improve the surface finish. Interestingly, removing the water coating enables the recovery of the cutting force, demonstrating a reversible effect. Based on the XAFS results and molecular dynamics simulation, a water-induced surface ordering mechanism is proposed to explain the findings from the microcutting experiments. This mechanism suggests that water molecules can induce surface ordering in copper, resulting in reduced surface energy and fracture toughness of copper, thus enhancing machinability. This work provides valuable insights into the comprehension of the Rehbinder effect and shows that picometer-scale modifications of the surface atom arrangement can considerably alter the deformation mode of metals, paving the way for the development of new manufacturing processes.

Effect of Shear Loading Conditions on the Measured Strength of Ice Adhesion to Superhydrophobic Surfaces

Despite the significant interest of researchers, icing of aircraft, vehicles, ships, and equipment of offshore oil structures remains to be an urgent problem. This paper considers the factors that promote a decrease in the strength of the contact between ice and surfaces under an applied shear load. The main attention is focused on studying the influence of the rate of shear loading on the fracture of the interfacial contact between ice and superhydrophobic coatings. The strength of the adhesive contact under the conditions of controlled variations in the applied load is measured using a technique based on the detachment of ice from a surface under the influence of centrifugal force. The study is carried out for large ensembles of samples in the temperature range from −5 to −20°C, thereby making it possible to evaluate the influence of the quasi-liquid layer and the Rehbinder effect on a decrease in the shear adhesive strength. The results obtained indicate that the contact between ice and a superhydrophobic coating is fractured through a mixed viscous–brittle mechanism. In this case, a decrease in temperature or an increase in the loading rate causes a transition from the viscous to the brittle fracture. These results indicate a potential acceleration of ice shedding with an increase in the growth rate of the shear stress.

Preparation of fullerene-containing nanocomposite materials based on high-density polyethylene via environmental crazing and their performance

This work offers a new concept relying on the Rehbinder effect in polymers for the preparation of fullerene-containing nanocomposite materials with added functionality. Tensile drawing of high-density polyethylene (HDPE) films in the solutions of 1,2–dichlorobenzene containing С60-С70 fullerenes (FL) proceeds via the environmental crazing according in the presence of surface active liquids (the Rehbinder effect). Environmental crazing provides the development of a highly developed surface and a mesoporous structure with a uniform distribution of monomeric FL within the HDPE matrix. The content of FL in the FL/HDPE nanocomposite materials can be varied from 1 to 8 wt%. Performance of the FL/HDPE nanocomposite materials (optical properties, thermal stability, mechanical characteristics) was studied by different physicochemical methods (TGA, UV- spectroscopy, tensile tests, etc.). Introduction of FL to HDPE is shown to increase the temperature of thermal degradation onset of HDPE by 30 °C. Rolling as the additional stage off post-treatment allows preparation of the FL/HDPE nanocomposite materials with high mechanical properties. This process can be upscaled using the existing technological equipment for the orientational drawing of polymers. The FL/HDPE nanocomposites with improved thermal resistance and good mechanical properties can be used as innovative optoelectronic materials within a broad temperature interval.

Effect of material composition on the action of surface active medium in ultra-precision microcutting

Ultra-precision diamond turning (UPDT) is an extensively adopted technology in optical applications owing to the nanometric surface finish and excellent form tolerance guaranteed on metallic materials. Coolants such as kerosene, isoparaffin etc. are broadly used in UPDT to reduce the friction at tool-workpiece interface for ultimately ensuring optical quality parts. However, the greater emphasis on sustainable manufacturing nowadays demand alternate approaches for minimizing cutting forces and improving the surface finish. The application of a surface active medium (SAM) over the workpiece surface prior to UPDT can be a befitting choice as it can induce Rehbinder effect on materials thereby minimizing cutting forces. Nevertheless, the performance of SAM in UPDT process with reference to material specific properties has not been widely explored in literature. The present study investigates the role of Rehbinder effect in controlling the material surface energy during UPDT of ductile materials. The surface integrity and force analysis indicate that the SAM action is significantly different for the parent metal (Cu) and alloy (Brass) under consideration. Moreover, the chip morphology inspection highlighted that SAM facilitates easier crack initiation and fracture in Cu unlike Brass. The results were further confirmed by conducting experiments on pure Zinc. Thus, the present study establishes the varying effectiveness of SAM towards material specific elemental composition.

The effect of cutting fluid on high strain rate dynamic mechanical property and cutting force of ultra-high-strength steel

Due to the different composition of cutting fluid will affect the failure stress of the material in the shear deformation area, so the rational use of cutting fluid can optimize the cutting force and the surface integrity of parts. Four kinds of hat-shaped samples with shear band widths were designed. The effects of different cutting fluids on mechanical properties of ultrahigh strength steel at different shear strain rates were studied in this paper by SHPB, and verified by cutting experiments. The stress–strain curve, shear failure stress, fracture morphology and cutting force were studied systematically. Experimental results show that the stress remains stable for a period of time with the increases of strain after strain hardening at γs= 10.03 × 104 1/s. All shear fracture is ductile fracture and at γs<1 0.03 ×104 1/s, the dimple will be elongated with the increase of the strain rate. When the shear bandwidth is reduced from 100 μm to 50 μm, size effect occurs, and the failure stress is increased by nearly 30%. The Rehbinder effect of TRIM E709 is more significant, the shear failure stress is the smallest, Fx, Fy and Fz decreases by 23.93%, 33.08% and 50.29% compared with HY-103. This research can guide the high-quality machining of ultra-high strength steel and may also evaluate and develop new cutting fluids to improve cutting performance.

The Rehbinder Effect in Testing Saturated Carbonate Geomaterials.

Carbonate geomaterial samples were tested for uniaxial compressive strength and tensile strength under air-dried and distilled-water-wet conditions. When tested for uniaxial compression, samples saturated with distilled water showed 20% lower average strength than that of air-dried samples. In the indirect tensile (Brazilian) test, samples saturated with distilled water showed 25% lower average strength than that of dry samples. In comparison with air-dried conditions, when the geomaterial is saturated with water, the ratio of the tensile strength to the compressive strength is decreased, mainly due to the decrease in the tensile strength caused by the Rehbinder effect.

Investigations of the structure of welded joints of polymers using the Rehbinder effect

Investigations of the structure of welded joints of polymers using the Rehbinder effect

Дослідження структури зварних з’єднань полімерів з використанням ефекту Ребіндера

Дослідження структури зварних з’єднань полімерів з використанням ефекту Ребіндера

The effects of cryogenic cooling on tool wear and chip morphology in turning of tantalum-tungsten alloys Ta-2.5W

Tantalum‑tungsten alloy is particularly difficult to cut due to its high plasticity. Environmentally friendly liquid nitrogen cooling and hybrid minimum quantity of lubricant-low temperature CO2 (MQL + CO2) technology can improve the machinability of ductile materials. In this paper, the experimental and numerical turning of tantalum‑tungsten alloy Ta-2.5W were carried out under cryogenic cooling conditions. The effects of liquid nitrogen cooling and MQL + CO2 cooling on the wear mechanism of cutting tools and the formation mechanism of chips were studied. The Rehbinder effect induced by the surfactant in MQL + CO2 system was analyzed. The results show that the cutting tool life can be effectively improved by 50 % in turning of Ta-2.5W under both cryogenic cooling conditions. Different from the flank wear dominated by adhesive wear under water-based emulsified cutting fluid, the tool failure was mainly caused by the notch wear under cryogenic cooling conditions. The chips in turning of high plastic Ta-2.5W showed a “pomelo-meat shaped” morphology with non-uniformed and non-periodic folds. Rehbinder effect was induced by the surfactant in MQL + CO2 system, which transformed the “pomelo-meat shaped” chips into “layered-rock shaped” chips. Under this effect, the machinability of tantalum‑tungsten alloy was effectively improved with a reduction of chip thickness and increment of the tool life.

Some Features of Cleavage Cracks in Rocks and Metals

The cracking of some rocks, namely granite, serpentinite and sandstone under tensile stress is examined in details. Brazilian testing or diametral compression, three points bending and explosion testing are used as the loading schemes in air at room temperature. Morphology of cracks in the model rocks are compared with cracks in silicon crystals, as the standard of a brittle crack, with cleavage cracks in iridium single crystals and with cracks in gallium-covered aluminum single crystals. The comparison of cracks between themselves has shown that there is additional channel for stress accommodation in the model rocks. This channel does not lead to transformation of a rock into a macroscopically ductile material, but it causes the arrest of the dangerous crack in it under tensile stress. Its influence causes transition from the brittle crack to the pore-like crack on the microscopic scale. The most probable mechanism of this transition is the dislocation emission from crack, which becomes possible in such a natural covalent solid as a rock due to Rehbinder's effect.

The Rehbinder Effect in Fracturing of Metals and Rocks

The Rehbinder Effect in Fracturing of Metals and Rocks

Investigation on the influences of CO2 adsorption on the mechanical properties of anthracite by Brazilian splitting test

To understand CO2 sequestration in coal seam, the Brazilian splitting test is adopted to examine the effect of CO2 saturation pressure on anthracite mechanical properties, and the variations in the internal structure of coal are analyzed using X-ray diffraction and low-pressure N2 adsorption methods. The results show that as the CO2 adsorption pressure increases, the Brazilian splitting strength, Brazilian splitting modulus, absorbed energy, and Brittleness index of anthracite decrease by 11.5%–49.2%, 11.0%–44.2%, 17%–42.3%, and 6.7%–49.3%, respectively, while the BET-SSA, DFT and BJH pore volumes increase by 60.3%–225.1%, 11.6%–61.3% and 10.1%–42.7%, respectively. Moreover, the influence of supercritical CO2 on coal pore structure and mechanical property is more prominent than that of subcritical CO2. The mineral dissolution, organic matter extraction and molecular structure rearrangement caused by CO2 intrusion develop the pore structure of anthracite, which resultes in the degradation of coal mechanical properties. In addition, the swelling, plasticity, and ‘Rehbinder effect’ caused by CO2 adsorption contribute to the mechanical damage of anthracite. Due to the remarkable impact of high-pressure CO2 on the pore structure and mechanical properties of coal, the critical point pressure of CO2 should be used in the storage process to ensure enhanced CO2 storage capacity while reducing storage risks.

Environment- and Surface-Sensitive Effects on Mechanical Properties and Machinability of Solid Material : Part 1―Rehbinder Effect and the Others―

Environment- and Surface-Sensitive Effects on Mechanical Properties and Machinability of Solid Material : Part 1―Rehbinder Effect and the Others―

Effect of cutting fluid on high strain rate dynamic mechanical property and cutting performance of nickel based superalloy

Cutting fluids are essential for the machining of difficult-to-cut materials in production. In addition to four basic functions including cooling, lubrication, cleaning, and antirust, cutting fluids also have an effect on the reduction of hardness and ductility of materials. Focused on the effect of cutting fluid composition in the material deformation processes, the influence of two universal cutting fluids (denoted as Blasocut and E709) on high strain rate dynamic mechanical properties of Ni-based superalloy was experimentally investigated and verified by cutting process. The shear stress-shear strain curve, maximum shear stress and shear failure stress, milling force as well as chip formation were systematically investigated. It is indicated that the results from Split Hopkinson Pressure Bar tests are consistent with those from cutting experiments. The Rehbinder effect for the samples under E709 conditions is more significant and the stress fluctuation is the largest, which is up to 14%. Brittle fracture exists under a narrow shear bandwidth 100 μm with high strain rate 10 × 104 s−1, while ductile fracture occurs under a wide shear bandwidth 400 μm with low strain rate 3 × 104 s−1. The cutting force amplitude under E709 is larger than that of Blasocut. The chip burrs under E709 and water are more severe than those under Blasocut. This research reveal significant connection between the cutting fluids and the dynamic mechanical properties or the cutting performance of the metal, which is also helpful to the control of mechanical properties and fatigue resistance of the machined surface.

Генезис структурно-функціональних порушень та гідростатична модель кісти Бейкера

Вступ. Колінний суглоб оточують різноманітні кістоподібні утворення (КПУ) — бурси, які у нормі клінічно не проявляються. Усі синовіальні порожнини, до яких, зокрема, належать колінний суглоб та бурси, які оточують колінний суглоб, містять синовіальну рідину. Синовіальна рідина є ультрафільтратом плазми крові і складається із білків та інтерстиціальної рідини. У літературі описані бурси, що оточують колінний суглоб, висвітлена ультразвукова класифікація кіст Бейкера залежно від стадії перебігу, яка запропонована І.М. Даниловою [10], та класифікація кістозного переродження меніска, але відсутня інформація щодо патофізіологічних та гістохімічних змін, які відбуваються у КПУ ділянки колінного суглоба, а також відсутня патофізіологічна модель КПУ ділянки колінного суглоба, яка б відображала природу даного захворювання з точки зору фізико-біохімічних процесів. Матеріали та методи. У травматологічному відділенні клініки ­ушкоджень Військово-медичного клінічного центру Північного регіону з початку 2016 року під спостереженням знаходилось 15 пацієнтів із клінічної картиною кістоподібного утворення ділянки колінного суглоба, що підтверджено інструментальними методами обстеженнями: ультразвуковим дослідженням (УЗД), магнітно-резонансною томографією (МРТ) та спіральною комп’ютерною артрографією (СКТА) колінного суглоба. Із них литково-напівперетинчастий бурсит спостерігався у 9 пацієнтів, кісти менісків — у 5 пацієнтів, бурсит переднього відділу колінного суглоба — в 1 пацієнта. Серед пацієнтів 11 чоловіків та 4 жінки. Середній вік пацієнтів становив 43,5 року. Об’єктом дослідження були кістоподібні утворення ділянки колінного суглоба. Усім хворим із КПУ проводили комплексне інструментальне обстеження, яке включало УЗД, СКТА, МРТ, вимірювання внутрішньосуглобового та внутрішньокістозного тисків за допомогою контактного манометра фірми Stryker та надалі — діагностично-лікувальної артроскопії. На основі отриманих даних УЗД проводився розподіл хворих на 4 групи, що базується на процентному відношенню внутрішньопросвітних нашарувань (включень) до загального просвіту КПУ, що дало можливість сформувати нову класифікацію КПУ ділянки колінного суглоба для вибору того чи іншого методу лікування. Результати та обговорення. Для формування та прогресування КПУ має значення підвищений тиск, який становить у середньому 29 мм рт.ст. у положенні згинання та до 58,4 мм рт.ст. у положенні розгинання. Виходячи із попередніх даних, на нашу думку, критичним показником тиску, при якому може настати розрив кісти Бейкера, є тиск більше 60 мм рт.ст. Зазвичай таке ускладнення виникає при тривалому існуванні кісти, коли тривала адсорбція білкових молекул на стінці кісти призводить до адсорбційного зниження міцності та зниження поверхневого натягу — ефект Ребіндера. Висновки. Враховуючи дані біохімічних процесів, УЗД та ендоскопії кіст Бейкера на різних стадіях, ми дослідили, що сама стінка кісти не потовщується, а відбувається пристінкове нашарування білкових молекул із формуванням глобул, які і формують так звану псевдостінку. У подальшому ці нашарування починають формувати перетинки між протилежними стінки, ущільнюватись, що призводить до камерності КПУ. На пізніх стадіях дані нашарування переважають над просвітом КПУ. Запропонована нами класифікація заснована на визначенні процентного відношення внутрішньопросвітних нашарувань до загального просвіту КПУ у двох зрізах та відображає основні морфологічні зміни, що дає можливість визначити оптимальний метод лікування даного кістоподібного утворення та широкого практичного використання у травматології та ортопедії.

The mechanisms of anti-icing properties degradation for slippery liquid-infused porous surfaces under shear stresses

HypothesisLoss of anti-icing properties of slippery liquid-infused porous surfaces (SLIPS) in conditions of repetitive shear stresses is the intrinsic process related to peculiarities of SLIPS structure. ExperimentsThe study of the evolution of the ice adhesion strength to superhydrophobic surfaces (SHS) and SLIPS during repetitive icing/de-icing cycles measured by a centrifugal method was supplemented with the estimation of change in capillary pressure inside the pores, and SEM analysis of the effect of multiple ice detachments on surface morphology. FindingsObtained data indicated that although for freshly prepared SLIPS, the ice shear adhesion strength at −25 °C was several times lower than for SHS, repetitive icing-deicing cycles resulted in dramatic SLIPS degradation. In contrast, SHS showed weak degradation at least during 50 cycles. Additional to the depletion of an impregnating oil layer, other mechanisms of SLIPS degradation were hypothesized and tested. It was shown that lower capillary pressure required to displace air by water from the surface texture for SLIPSs compared to SHSs resulted in deeper water/ice penetration inside the grooves. The accelerated destruction of the mechanical texture caused by the Rehbinder effect constitutes another mechanism of SLIPSs degradation.

The Rehbinder effect in tests of superalloys in contact with molten salts

The results of the Rehbinder effect manifestation during testing of superalloys in contact with corrosive media containing Na2SO4 + NaCl are discussed. We present the experimental study of the effect of salts containing chlorine and sulfur on the mechanical properties and long-term strength of single crystal and powder nickel-based superalloys at high temperatures. The practical value of the work is associated with the possible operation of gas turbine parts in conditions of ingress of the particles containing chlorine, sulfur and sodium into the flow path. A simplified (compared to a previously used) procedure of testing wrought alloys for long-term strength in molten salts is developed. A comparative study of the mechanical properties and long-term strength of a single crystal superalloy in the initial state (previously damaged by corrosion of different duration) and being in contact with salts during testing is carried out. Due to the large scatter of experimental data, the method of lower envelopes has been proposed and implemented to determine the guaranteed values of the long-term strength. It is shown that the guaranteed values of the long-term strength at different temperatures and test durations can decrease by 2.5 – 5.0 times in the presence of salts. Metallographic studies of the nature of damage and destruction of samples are carried out. The revealed decrease in the long-term strength of heat-resistant alloys in contact with salts is interpreted as the Rehbinder effect and not as a manifestation of the effect of stress corrosion cracking. A methodology for using the obtained test results with a duration of up to several thousand hours in highly aggressive environments is proposed to predict the long-term strength in relation to long-term operation (tens of thousands of hours) under conditions of relatively low salt loads.

Ultra-precision micro-cutting of maraging steel 3J33C under the influence of a surface-active medium

The excellent mechanical properties of maraging steel 3J33C make it desirable for a wide spectrum of high-strength applications, which would also mean that it is difficult to machine. The application of surface-active media onto the pre-machined surface is explored to improve the machinability of this high-strength material. This mechanochemical effect, named after its discoverer as the Rehbinder effect, was implemented using a marker ink to reduce machining forces and deformed chip thicknesses, and significantly improve the machined surface quality. Machined subsurface microstructure characterization reveals the occurrence of grain refinement with evenly distributed orientations and the microstructure texture components when cutting with the mechanochemical influence. This work also demonstrates with an analytical model the effectiveness of the Rehbinder effect when coupled with the tool-edge radius effect. Lastly, numerical simulations are developed for chip evolution and cutting forces in machining a polycrystalline workpiece material with the mechanochemical influence by modifying the fracture energy.

Microsclerometry as Applied to Studying Rehbinder Effect. Review

Works devoted to studying the effect of active environments on damageability of surfaces of solid bodies and materials upon contact actions (Rehbinder effect) have been briefly reviewed. A novel procedure, which combines microscratching and electrochemical reduction of an active component on a studied material surface, has been described. This procedure enables one to simulate and study the liquid-metal embrittlement of the material in the absence of a liquid metal phase on its surface.

Surface Texture Transformation in Micro-Cutting of AA6061-T6 with the Rehbinder Effect

The Rehbinder effect (R-effect) on microcutting has been successful to augment machinability of ductile metals; however, there is a lack in understanding of its influence on texture evolution in the machined surfaces. This study validates the R-effect on AA6061-T6 and characterises the influence of the R-effect on the texture transformation in the machined surface. Microhardness tests reveal that the R-effect produces softer surfaces (87–96 HV) as compared with the surfaces produced conventionally (96–108 HV), which is attributed to the differences in grain types. A large fraction of substructured grains (96.4%) exists in the surfactant-affected subsurface while a higher proportion of deformed grains (42.8%) forms during conventional microcutting. In addition, the main texture components of the conventionally produced surface are Cube, Goss and S textures, which differ from the dominant volumes of Copper and R textures under the R-effect. The differences are results of the stress states induced during microcutting, which is exemplified through numerical simulations that consider the reduction in fracture toughness of the material with the R-effect. The advanced understanding of the R-effect better positions the use of surfactants as a cleaner near-dry metalworking fluid.