Adhesion Friction Research Articles

A REVIEW OF DIRECT SHEAR AND INCLINED PLANE TESTS RESULTS FOR DIFFERENT INTERFACES IN LANDFILL CAPPING

One of the crucial aspects in design of a landfill capping is the interface behavior between the different layers of the cover system, from levelling layer above waste up to the topsoil. Design guidelines and international codes require a geotechnical stability analysis to be performed along every interface. The critical interface is the one which gives the minimum shear resistance, in terms of friction angle and adhesion. Evaluation of the correct values to be used is then essential. Shear resistance at the interface between different geosynthetics or between a geosynthetic and a soil can be measured through laboratory tests. Testing methods are EN ISO 12957-1 and ASTM D5321 (for direct shear test) and EN ISO 12957-2 (for inclined plane). The paper briefly describes direct shear and inclined plane testing methods and enhances pros and cons. In the last 25 years the authors have coordinated a great number of the above tests with different types of geosynthetics and soils. The main results of these tests are reported in the paper, summarizing the values obtained with contact interface between different products belonging to the same families. The purpose of this work is to validate the already big database of interface strength measured with direct shear tests and to evaluate the differences with the results obtained for the different types of tests. This can give to designers the chance to have a critical approach toward the most suitable testing method to be used according to the specific needs of a project.

Experimental Investigation of the Tribological Contact between Ti6Al4V-EBM Pin and UHMWPE Rotating Sheet for Prosthetic Applications

This work is aimed at studying the tribological contact between a titanium–aluminum–vanadium alloy pin (Ti6Al4V), produced by Electron Beam Melting (EBM), and a sheet of ultra high molecular weight polyethylene (UHMWPE), which are widely utilized materials for prosthetic applications. Using a “pin on disc” system, tribometric tests of different duration (up to 240 min) were carried out in order to trace the trend of the polymer mass loss as a function of test time. In this way it was possible to identify the stationary phase of adhesive friction, at which the specific wear rate, which characterizes the tribological system under different lubrication conditions, was obtained. As for the pin, no weight losses were measured, while the optical observations on the tip showed a compressive effect after the entire test campaign.

Friction behaviors of rice husk silica-reinforced elastomer composites in contact with rough self-affine surfaces

This study presents rice husk silica-reinforced elastomer composites fabricated by wet compounding, exhibiting 10% higher dynamic friction coefficients than the reference composites made by conventional dry compounding. Depending on the fabrication method, the filler micro-dispersion was characterized to correlate the measured friction coefficients with the viscoelastic properties with respect to sliding velocity and substrate lubrication. The effect of viscoelastic properties of the elastomer composites on the adhesion and hysteresis friction coefficients was investigated based on the elastomer friction theory. It was found that the constructed friction master curves showed a reasonable correlation with the theory. This study demonstrates that the rice husk silica can be used as a reinforcing filler for sustainable tires. More importantly, the well-dispersed filler microstructures can ensure the higher friction coefficients of the elastomer composites on rough surfaces, improving the tire performances (e.g., wet traction, cornering, and acceleration) of the ever-growing electric vehicles and future mobility.

An experimental study on the effects of friction modifiers on wheel–rail dynamic interactions with various angles of attack

By modifying friction to the desired level, the application of friction modifiers (FMs) has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration, energy consumption, vibration and noise. Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice, which has, however, not been well explained. This study experimentally investigates the effects of two types of top-of-rail FM, i.e. FM-A and FM-B, and their application dosages on wheel–rail dynamic interactions with a range of angles of attack (AoAs) using an innovative well-controlled V-track test rig. The tested FMs have been used to provide intermediate friction for wear and noise reduction. The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration (ABA). This study provides the following new insights into the study of FM: the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive; stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B, depending on the dosage of the FMs applied; the negative friction characteristic is not a must for stick–slip; the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

Measuring the Frictional Behavior and Adhesion of PET Bottles

Polyethylene terephthalate (PET), due to its excellent physical and chemical properties, has become a widely used packaging material for liquids across many consumer market segments. However, one of the most common problems met in bottle manufacturing is the pile-up of bottles during conveying, due to static electrification caused by localized friction. To minimize such phenomena, a thin lubricant layer is applied onto the bottles. The absence of a thin lubricant layer increases the risk of localized sticking phenomena and pileups. In this work, an attempt is made to study the frictional behavior of commercially available PET bottles, with and without lubrication by using a high precision and light load technique. By analyzing the complete tribological pattern of the tangential force and not just averaged values, localized sticking events can be identified. In addition, by performing indentation-retraction measurements the electrostatic forces in a bottle-to-bottle contact can be measured. By combining light load friction and adhesion methods, a better understanding of PET sticking phenomena can be achieved which then can be translated in optimizing (minimizing) the amount of lubricant to be used.

Thermomechanical response of kaolin clay–concrete interface in the context of energy geostructures

The analysis and design of energy geostructures are mainly characterised by the mechanical behaviour of the soil–structure interface in non-isothermal conditions. In this study, direct shear tests are conducted to investigate the shear behaviour of soil and soil–structure interface in the practical temperature range of energy geostructures (i.e., 8–45 °C). The interface in this study is formed of kaolin in contact with concrete specimens with different roughness. Tests are performed on normally consolidated and overconsolidated interfaces following the unloading/reloading paths to better understand the impact of thermal strain on the interface behaviour. The volumetric response of the interface is observed to be highly influenced by the thermal strains experienced during heating/cooling. The soil stress level and the most recent soil stress history are identified as the primary determinants of thermally induced changes in interface shear strength. For normally consolidated interfaces, the temperature increase led to higher adhesion and slightly lower friction angle, whereas higher adhesion and identical friction angles were found for tests conducted on cooled specimens. Temperature does not seem to affect the shear strength of overconsolidated interfaces. Finally, a conceptual understanding of the temperature effect on interface shear behaviour is provided by analysing data from the literature.

Discrete element simulation of powder flow in revolution powder analyser: Effects of shape factor, friction and adhesion

Through discrete element method (DEM) simulations in Revolution Powder Analyser (RPA), we found a strong correlation between the static powder bed packing density and the avalanche flow. A wider powder size distribution and a higher fraction of non-spherical powders caused larger misfits in the static packing of powders, and thereby enhanced the powder mobility during revolution, leading to an earlier avalanche. It performs a gradual avalanche under low friction, and an abrupt avalanche under high friction. The rolling motion of non-spherical powders was found to cause an instantaneous disturbance to the flow of neighbouring powders. It was also found that other factors, such as the filling degree, drum rotation speed and inter-powder adhesion, can also influence the measurement results and hence they must be controlled or standardized in order to achieve reliable and consistent measurements. Furthermore, based on the experimental measurements of avalanche angle and packing fraction, we extracted the intrinsic powder friction coefficient and adhesion energy. • DEM powder flow models with realistic powder size and shape distributions. • Performed DEM simulations to study powder flow profiles and avalanche phenomena. • Examined and identified the effects of system factors for reliable RPA measurements. • Extracted the rolling COF and adhesion energy by including powder non-sphericity.

Nanoscale contact mechanics of the interactions at monolayer MoS2 interfaces with Au and Si

Molybdenum disulfide (MoS2) is a two-dimensional material that exhibits unique interfacial interactions with gold (Au) and silicon (Si). These interfaces have gained attention due to their potential to be integrated into a broad range of applications, where they involve direct contact that affects their performance. Here we investigate the nanoscale mechanical contact interaction of MoS2 monolayers with Au and Si, using adhesion measurements and friction force microscopy. MoS2-Au contact exhibits pronounced adhesive interaction, manifested by higher adhesion pull-off forces and energies, compared to MoS2-Si. Influenced by the adhesive contacts, the friction forces recorded demonstrate stronger lateral interactions and stronger interfacial shear strength between MoS2 and Au. Analysis with the Prandtl–Tomlinson model reveals that the MoS2-Au direct interaction is also stiffer, suggesting higher elastic energy at the contact. This information on the mechanistic nature of MoS2-Au and MoS2-Si contacts under shear and normal loads is of potential importance in applications where such interfaces are utilized, such as in the design of coatings, sensors and mechanoelectrical devices.

Study of adhesive self-degrading gel for wellbore sealing

In this study, a self-degrading gel with high adhesion was synthesized by acrylamide, acrylic acid and an unstable cross-linker. It was used for the pressurized operation of oil and gas wells. The degradation time, adhesion and plugging performance of the gel were investigated by degradation experiments, adhesion experiments and plugging experiments. To a certain extent, it was found that the concentration of the reactants had different effects on the degradation time and adhesion friction of the gels. In addition, the adhesion friction varies due to compressional deformation of the gel by compression. The blocking ability of the gels was mainly related to the adhesion friction. The blocking capacity of high-strength horizontal gels is linearly related to the adhesion friction. The sealing capacity of low strength horizontal gel is non-linearly related to the adhesion friction. Compared with conventional gel blocking operation, the gel breaking operation at the end of gel blocking operation does not require additional injection of gel breaking agent due to the introduction of unstable crosslinker. The gel degradation time can be controlled by designing the formulation to achieve rapid gel breakage and rejection. It saves time cost and economic cost. The highly viscous self-degrading gel can be used as a wellbore pressure packer for oil and gas wells under pressure.

Анализ зоны контакта железнодорожного колеса и рельса

Purpose: Investigation of stresses on contact surface during interaction of a railway wheel and rail from normal pressure and tangential forces in the presence of adhesion and sliding zones of different sizes. Methods: Formulas for equivalent and tangential stresses for plane deformation and plane stress state are given and used for calculations. Special attention is paid to the study of stress state at contact boundary points of cylinders, which parameters are calculated for at contact surface points at boundary between sliding and adhesion zones. Results: The study of the distribution of equivalent stresses in the zone of their maximal values is carried out, the dependence from friction coefficients is established. The distribution of stresses on contact surface of a drive cylinder from normal pressure and from contact tangential forces in the presence of adhesion and slippage zones for different ratios between them is shown. The obtained results revealed the increase in stresses at the boundaries of sliding and adhesion sections, the effect of absence of tangential forces or presence of complete slippage. Practical importance: The data make it possible to predict more accurately a decrease in the contact-fatigue durability of samples and can be useful in studying the appearance of microcracks of a wheel or rail during their interaction. Physical modeling of the interaction of rolling elements, such as a rail and a wheel, which is performed at actual work loads, interaction speeds, various friction coefficients, at sliding or adhesion recreates with certain reliability actual conditions of interaction of a wheel and a rail, and the results help to predict the reliability of a wheel-rail pair in railway transport.

Effect of cryogenic pretreatments on the microstructure and mechanical performance of diamond-like carbon coatings for high-speed alloys

Hydrogenated diamond-like carbon coatings (DLCs) with Cr/WC + C interlayers were deposited using a plasma-enhanced chemical vapor deposition (PECVD) method onto the surface of M35 high-speed alloys suffered by various pre-treatments including annealing and deep cryogenic cooling. Scanning electronic microscopy, transition electronic microscopy, X-ray diffractometry, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the microstructure, and hardness indentation, scratch testing, and friction testing were used to measure the mechanical performance of the DLCs. The results showed that different pretreatments led to variations in the microstructure of the M35 alloy, which influenced the coating growth process. Although all the pretreatments resulted in the same fraction of carbon-hybrid structures of the top DLC layer, the best combination of adhesion strength, hardness, friction, and wear resistance was found when the alloy was tempered at 525 °C for 1 h, followed by cryogenic treatment at −180 °C for 6 h. In contrast with the DLC deposited onto M35 alloy substrate pretreated by only 525 °C for 1 h tempering, the above pretreatment could improve adhesion force by 20 %, hardness by 15 %, and wear resistance by approximately 50 %.

Tribological mechanism of micro/meso/macroscopic textured surfaces under different normal forces, relative velocities, and sliding directions

Friction behavior under different operating conditions, such as normal forces, relative velocities, and length scales of the textured surfaces, is a crucial topic in tribology. In this study, different tribology mechanisms of micro/meso/macroscopic textured surfaces were investigated, considering the effects of asperities and operating conditions. A prediction model of the friction coefficient was proposed and validated for polished and microscopic, mesoscopic, and macroscopic textured surfaces. Subsequently, reciprocating sliding friction experiments (sphere-on-plate) were carried out to estimate the friction coefficients of the specimens in contact with an aluminum sphere (Al 99.9). The results indicate that a larger normal force, relative velocity, and length scale produce more wear debris, which transforms the friction mode from adhesive friction to abrasive friction.

Tribological and mechanical analysis of hybrid epoxy based polymer composites with different in situ liquid lubricants (silicone oil, PAO and SN150 base oil)

This study compares the tribological, thermal and mechanical properties of epoxy-based composites with solid fillers (ultrahigh molecular weight polyethylene, molybdenum disulphide), and different in situ liquid lubricants in different volume proportions. Liquid lubricants used in this paper are three types of silicon oil with different viscosities, base oil and polyalphaolefins (PAO). The base oil-epoxy composite showed superior tribological performance among the three. The coefficient of friction of 0.1 and specific wear rate in the range of 10−7 mm3/Nm were obtained at an apparent pressure of 0.611 MPa. Transfer film formation with oil pockets on both the tribo-pair surfaces was identified as the main friction and wear reduction mechanisms. The surface of epoxy became hydrophobic, reducing adhesive interaction and friction.

Friction Characteristics of Open Graded Asphalt Friction Courses with BOF and EAF Steel Slag Aggregates

Friction properties of open graded asphalt friction course (OGAFC) mixtures play an essential role in ensuring traffic safety, especially under wet weather conditions. This study evaluated the friction characteristics of basic oxygen furnace (BOF) and electric-arc furnace (EAF) steel slag aggregate incorporated OGAFC mixes. Nine sets of OGAFC mixes were fabricated using five percentage replacements (0%, 25%, 50%, 75%, and 100%) of the coarse natural aggregate fraction by BOF and EAF steel slags. The effect of modified binder type (polymer and crumb-rubber modified) on the frictional characteristics of OGAFC mixes was also examined. The principal friction test devices used were the British pendulum tester and dynamic friction tester. Multiple friction performance aspects were studied: (1) effect of surface condition (dry, wet, and ponding) on the measured friction coefficient; (2) separate evaluation of adhesion and hysteresis friction components; (3) variation of friction coefficient with varying slip speeds, and (4) friction performance later in the OGAFC service life using artificially polished aggregates, and comparison of the performance with unpolished aggregates. Results revealed that the use of steel slags in OGAFC mixes considerably enhanced the frictional characteristics and that the skid resistance of OGAFC-BOF mixes was better than that of OGAFC-EAF mixes. Frictional resistance of the mixes was found to increase with an increase in steel slag content. OGAFC mixes comprising polished steel slag aggregates also showed promising results with the increment in steel slag content. The findings also indicated that OGAFC-CRMB mixes perform better than OGAFC-PMB mixes.

Tribological study on the surface modification of metal-on-polymer bioimplants

The tribological performance of artificial joints is regarded as the main factor of the lifespan of implanted prostheses. The relationship between surface roughness and coefficient of friction (COF) under dry and lubricated conditions is studied. Results show that under dry test, friction coefficient is not reduced all the time with a decrease in surface roughness. On the contrary, a threshold of roughness value is observed, and frictional force increases again below this value. This critical value lies between 40 and 100 nm in Sa (roughness). This phenomenon is due to the transfer of friction mechanisms from abrasion to adhesion. Under wet test, COF always decreases with reduction in surface roughness. This result is mainly attributed to the existence of a thin layer of lubricant film that prevents the intimate contact of two articulating surfaces, thus greatly alleviating adhesion friction. Furthermore, surface texturing technology is successful in improving the corresponding tribological performance by decreasing friction force and mitigating surface deterioration. The even-distribution mode of texturing patterns is most suitable for artificial joints. By obtaining the optimal surface roughness and applying texturing technology, the tribological performance of polymer-based bioimplants can be greatly enhanced.

Controllable high adhesion and low friction coefficient in TiAlCN coatings by tuning the C/N ratio

The cutting temperature will be significantly increased while cutting high reactive titanium alloy due to the large friction coefficient of the traditional TiAlN coated tools. The tool could also easily appear adhesive wear and thereby reduce the service life. In this work, TiAlCN coatings with high adhesion and low friction coefficient were deposited by changing the C2H2 and N2 flow rates and using medium-frequency magnetron sputtering. Compared with the TiAlN coating, the hardness of the TiAlCN coating increases up to the value of 20.36 GPa, the toughness is improved by about 230%, the adhesion reaches the value of 156 N. However, the friction coefficient is only 0.231. This performance improvement is attributed to the special structure of (Ti,Al)(C,N) nano-crystalline wrapped by a C-related amorphous phase that is formed in the coating. The structure can be formed by adjusting the C/N ratio to make the C atom content exceed the solid solubility but the C/N ratio does not reach saturation. This kind of TiAlCN coating reduces the wear and inhibits the adhesive wear during the high-speed cutting process of titanium alloy. The cutting distance is also increased by 50% compared with the TiAlN coating.

Numerical solution of the adhesive rubber-solid contact problem and friction coefficients using a scale-splitting approach

We present a comprehensive investigation of the adhesive rubber-solid contact problem by analytical and numerical methods. Theories of rubber friction are reviewed and a new contact theory is developed. The adhesive contact problem is solved using the boundary element method. The introduction of adhesion leads to full coverage below a certain length scale. Friction coefficients are calculated from the spectral density of the rubber surface by splitting the numerical problem into two length scales. Adhesion is shown to increase friction at low velocities. The influence of filler is modeled by assuming that their size corresponds to a linear cross-over dimension separating the bulk elastomer from the composite. Finally, we discuss open problems and describe a simplified picture of rubber friction.

Mechanism and Internal Stability of Supportive Stone Constructions.

Natural stone constructions for the protection of slopes, banks and riverbeds are widely used in infrastructure engineering. These structures are made of stacked natural stones, which can be placed loosely on top of each other. Additionally, their bond behavior can be improved by using concrete mortar to fill the joints between the stones. Although such structures are now widely used, there is still a need for research concerning their inner stability and the structural design of such protective stone structures. In this study, experimentally, investigations were made to determine the force transmission and the interaction between rock and concrete mortar by deriving characteristic values of the adhesion strength and friction angle at different scales. A method for the determination of shear parameters from direct shear testing is used, considering the interaction between vertical and horizontal forces in the joint. In the course of these investigations, the roughness of the rock surface was recorded using conventional visual methods using the joint roughness coefficient (JRC) as well as via laser imaging. By applying laser scanning, a theoretical roughness factor could be derived. Furthermore, the properties of the rocks of the concrete mortar (fresh and hardened concrete mortar properties as well as a durability characteristic) were investigated in detail. It could be shown that different types of concrete mortar result in different bond strengths—expressed as tensile and shear strengths—when applied to a stone surface. The roughness of the stone surface has a positive influence on the tensile and shear strength between the stone and the mortar. Based on the test results, a failure description based on the Mohr–Coulomb fracture criterion could be determined, which can be used to calculate characteristic parameters for the design of stone support bodies. It was also shown that the stone’s compressive strength is being exceeded through load due to very punctual contact areas. Moreover, concrete mortar differs significantly from conventional concrete in terms of its mechanical properties due to the on-site installation conditions, which allow no dynamic compaction.

STATISTICAL FEATURES OF FIBRE FRICTION IN A ONE-DIMENSIONAL FIBROUS PRODUCT

The article considers a model of plastic deformation for one-dimensional fibrous products based on the ideas of the forces of adhesion and dry friction between the fibres on the surfaces of the areas where the fibres touch in the product. It is proposed to take into account in this model the statistical nature of such factors as the magnitude and direction of the normal pressure forces, the magnitude of the coefficient of friction, the direction of the contact surfaces in the product. The gamma distribution is chosen as the model distribution. The statistical modelling method shows that taking into account the statistical nature of the listed factors leads to a fundamentally new relationship between the rate of plastic deformation and the mechanical stress of forces arising in the product under the action of an external elongating load – the dependence is similar to those acting for viscous materials with Newton's law of viscous friction.

Ballistic performance of functionally graded boron carbide reinforced Al – Zn – Mg – Cu alloy

Functionally Graded Materials (FGM) with graded ceramic content offer significant protection against high-velocity ballistic impacts. The incorporation of ceramic reinforcements helps in increasing the hardness of individual layers, and the presence of a ceramic-rich top layer offers a better ballistic resistance with fewer layers. In the present study, Boron carbide reinforced Al–Zn–Mg–Cu matrix FGM is fabricated by hot pressure-assisted sintering. Three FGMs of five layers, each with power-law indices (N = 0.5,1 and 2.5), are fabricated. FGM N = 2.5 shows the highest hardness at the top ceramic-rich layer (70 vol% B4C) was 266.7 HV. The highest compressive strength of 597 ± 8.97 MPa was achieved in FGM N = 2.5, 35.99% and 44.90%, higher than the FGM N = 1 and FGMN = 0.5, respectively. The 70 vol% B4C aids in dissipating the kinetic energy of the projectile, and ballistic tests carried out at 700 m/s show that FGM N = 1 and N = 2.5 offer better ballistic resistance with a 36.27% and 26.89% improvement in the depth of penetration as compared to N = 0.5. Our results show that an adhesive and abrasive friction mechanism is responsible for slowing the projectile within the FGM. Analytical studies such as calculating the Ballistic Performance Index and stress wave analysis corroborate the experimental results. The fabricated FGM N = 1 and N = 2.5 offer significant protection against projectile 7.62 Χ 39 mm type III+ level threats for velocities up to 700 m/s and can be used as light-weight armours.