Friction Research Articles

Nitsche-based material point method for large deformation frictional contact problems

Nitsche-based material point method for large deformation frictional contact problems

Enhanced Tribological Performance of UHMWPE Composites Reinforced With Wollastonite: Biocompatibility and Wear Behavior

Abstract Ultra-high molecular weight polyethylene (UHMWPE) is often limited by poor tribological properties in artificial joints, leading to high wear-rates compared to metals and ceramics. This study explores the use of wollastonite, a natural mineral, as a filler to enhance the tribological performance of UHMWPE composites. X-ray diffraction (XRD) analysis revealed that wollastonite content and particle size inversely affected the crystallinity of the composite due to heterogeneous nucleation and stress concentration. The incorporation of wollastonite significantly improved the tribological performance, with wear-rate reductions of 71%, 69.81%, and 50.73% under dry friction, normal saline (NS) lubricant, and new-born calf serum (NBCS) lubricant conditions, respectively. The wear mechanisms in the composite were predominantly slight fatigue and abrasive wear, contrasting with the extrusion deformation and severe fatigue wear observed in neat UHMWPE. Additionally, simulated body fluid (SBF) immersion tests demonstrated the composite's ability to form a surface apatite-like deposition. These findings suggest that wollastonite reinforcement effectively enhances both mechanical and tribological properties of UHMWPE.

Energy Loss in Frictional Hertzian Contact Subjected to Two-Dimensional Cyclic Loadings

We investigate the effect of three different harmonically varying loads as a function of the friction coefficient on energy loss in a three-dimensional discrete uncoupled frictional contact problem. Three loading cases include (1) a normal force is constant and a tangential force varies, (2) normal and tangential forces both vary, but the loading and unloading curves are identical, and (3) normal and tangential forces both vary, but the loading and unloading curves are different. For a higher coefficient of friction, three loading cases show different characteristics. If a normal force is constant and a tangential force varies, there is always some slip, but dissipation tends asymptotically to zero at large coefficient of friction. If normal and tangential forces both vary, but the loading and unloading curves are identical, there is no slip and no dissipation above a critical coefficient of friction. If the loading and unloading curves are different, dissipation occurs for all values of the coefficient of friction, and we expect that the dissipation is asymptotic to the relaxation damping value as the coefficient of friction approaches infinity. For lowering coefficient of friction, the three loading cases show similar behavior. Dissipation increases and reaches a maximum just before a state where gross slip is possible.

Impact of Wetting and Drying Cycles on the Hydromechanical Properties of Soil and Implications on Slope Stability

The soil-based infrastructure is the backbone of the global economy, connecting people, enhancing quality of life, and promoting health and safety. However, its vulnerabilities are becoming apparent due to climate change, mainly through frequent wetting and drying (wd) cycles. Despite few studies in the past, research showing the stability of flood embankments in the long term, incorporating the impact of wetting and drying cycles on the hydromechanical characteristics of soil, is scarce. This study aimed to assess the impact of controlled wd cycles on the hydromechanical properties of clay and silty sand soils and its implications for the stability of a typical flood embankment. Volumetric changes were monitored during the wd cycles. The soil water characteristic curve (SWCC), saturated hydraulic conductivity (ksat), effective cohesion (c′), and effective angle of internal friction (ϕ′) were measured at 1 and 10 wd cycles. The results indicated that the 10 wd cycles decreased the saturated moisture content and resulted in a flatter SWCC compared to the 1 wd cycle for clayey soil. The ksat value was also significantly higher at 10 wd cycles than 1 wd cycle for clayey soil. An insignificant difference was found in both the SWCC and ksat at 1 and 10 wd cycles for silty sand soil. The ϕ′ value for the clayey soil decreased from 28.5 to 20.1 as the wd cycles increased from 1 to 10, while c′ remained unchanged at 10 kN/m2. On the other hand, for the silty sand soil, ϕ′ increased from 34.6 to 37.5 with an increase in wd cycles from 1 to 10, and c′ remained constant at 1 kN/m2. Numerical modelling of transient water flow coupled with a slope stability analysis revealed that the stability of a flood embankment depends on the evolution of soil hydromechanical properties due to wd cycles and the duration of flooding. These findings underscore the need for proactive measures to mitigate landslide risks in regions prone to frequent wd cycles, thereby ensuring the safety and resilience of slopes and associated infrastructure.

Eect of acid corrosion on physico-mechanical parameters and energy dissipation of granite

In deep underground engineering, it is inevitable that portions of the rock mass will be subjected to the erosion and chemical corrosion of infiltrating water. A comprehensive study of the physical, mechanical, and energetic properties of rocks after hydrochemical corrosion is crucial for ensuring the stability of the rock mass. The novelty of this research lies in the detailed investigation of the macroscopic and microscopic morphologies of rocks exposed to various corrosive solutions, as well as the changes in various physical and mechanical parameters. Utilizing the weighting method, a scientific comprehensive evaluation system for deep rocks after hydrochemical corrosion has been established. The results indicate a pronounced sensitivity of the macroscopic and microscopic morphologies to pH values. The longitudinal wave velocity of the corroded rock decreases obviously, with the maximum decrease being 13.46%. As the pH value decreases (from 7 to 3), the compressive strength, elastic modulus, cohesion, and internal friction angle of the rocks all decrease significantly. The acidity of the solution significantly aects the changes in the three types of strain energy of the rocks, with higher acidity leading to weaker energy storage capability. Among the factors influencing the characteristics of strain energy variation in rocks, confining pressure has a higher priority than pH value. This study precisely evaluates the impact of hydrochemical corrosion on rock damage using a percentage-based scoring system, and found that granite’s score dropped from 81 to 16. The research findings provide valuable insights for the evaluation of rock mass stability under hydrochemical corrosion conditions.

Floor Heave Mechanism and Control Technique of Water‐Rich Soft‐Rock Roadway in Thick Coal Seam

ABSTRACTThe severe deformation of the surrounding rock of the coal floor in Shanghaimiao mining area is affecting the safe, efficient production of mine wells in this region. In this study, the heave mechanism and control of the roadway floor were investigated through laboratory experiments, field research, theoretical analysis, numerical simulation, and on‐site testing. The results showed that the main reason for the serious damage to the roadway floor was the low strength of the surrounding rock of the roadway floor, and floor damage was exacerbated by the low support strength, hydraulic effects, and mining impact. A mechanical model of the asymmetric floor heave was established, and it was found that the stability of the roadway floor was positively correlated with the floor rock type, the stress concentration coefficients on the two sides of the roadway, and the burial depth, whereas it was negatively correlated with the cohesive force and internal friction angle of the floor rock mass. Expressions for the upward resultant force R of the roadway floor and the stress concentration coefficients K and K′ on both sides of the roadway were derived. The results of a FLAC3D numerical simulation analysis showed that the stress peak in front of the working face was 36 MPa, with a stress concentration factor of 3.7. After the floor support was reinforced, the floor heave was remarkably reduced, with a maximum value of approximately 600 mm, and the floor deformation became somewhat asymmetric. Finally, a double‐seal floor‐reinforcing “inverted arch” control technique was proposed and tested on‐site. The new system could efficiently and stably support the surrounding rock of the roadway.

Effect of Co Addition on the Microstructure and Mechanical Properties of Sn-11Sb-6Cu Babbitt Alloy

A Babbitt alloy SnSb11Cu6 with 0–2.0 wt.% Co was synthesized using the induction melting process. This study examined the effect of cobalt (Co) on the microstructure, tensile properties, compressive properties, Brinell hardness, and wear properties of SnSb11Cu6 using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), a universal tensile testing machine, a Brinell hardness tester, and a wear testing machine. The results indicate that the optimal quantity of Co can enhance the microstructure of the Babbitt alloy and promote microstructure uniformity, with presence of Co3Sn2 in the matrix. With the increase in Co content, the tensile and compressive strength of the Babbitt alloy first increased and then decreased, and the Brinell hardness gradually increased with the increase in Co content. The presence of trace Co has a minimal effect on the dry friction coefficient of the Babbitt alloy. When the Co content exceeds 1.5 wt.%, the friction properties of the Babbitt alloy deteriorate significantly. The optimized Babbitt alloy SnSb11Cu6-1.5Co was subsequently fabricated into wires, followed by conducting cold metal transfer (CMT) surfacing experiments. The Co element can promote the growth of interfacial compounds. The microstructure at the interface of the Babbitt alloy/steel is dense, and there is element diffusion between it. The metallurgical bonding is good, and there are serrated compounds relying on the diffusion layer to extend to the direction of the additive layer with serrated compounds extending and growing from the diffusion layer to the additive layer. Overall, Babbitt alloys such as SnSb11Cu6 exhibit improved comprehensive properties when containing 1.5 wt.% Co.

Experimental Study on Mechanical Properties of Artificial Cores Saturated With Ice: An Analogical Simulation to Natural Gas Hydrate Bearing Sediments

ABSTRACTThis work takes the natural gas hydrate (NGH) reservoir in the Shenhu area at the South China Sea as the target. Using the quartz sand, calcite grains, and illite powder as the main mineral composites, and Portland cement as the bonding material, the host skeleton with similar porosity and mechanical properties to the target reservoir were prepared. Ice was used to simulate natural gas hydrates for their high similarity in mechanical properties and distributions within porous host. The ice saturation in the host skeleton is quantitatively controlled by the quality method. As an analogical simulation, artificial samples with different ice saturations were tested by uniaxial compression measurements and the Brazilian tensile tests, aiming to reveal the mechanical behavior of NGH sediments. The results indicated that the plasticity of the artificial sample increases and its damage form transitions from brittleness to ductility as the ice saturation increases. The effects of free water and ice on the strength of saturated samples are quite different. The free water tends to reduce the strength of the sample due to illite hydration and change of internal friction. The bonding effect of ice tends to increase the strength of the sample, while the ice could also reduce the internal friction. When the ice saturation is larger than 30%, the compressive and tensile strengths of the sample increase with ice saturation, which could be regressed as yc = 2.2628S + 0.8322, and yt = 0.411S + 0.0273, respectively. The constitutive model was developed based on the equivalent medium theory and the D‐P criterion, which could describe the experiment data well with deviations less than 10%.

A Correlation Relating the Residual Strength Parameters to the Proportions of Clay Fractions and Plasticity Characteristics of Overburden Sediments from the Open-Pit Mine Drmno

One of the prerequisites for the safe exploitation of surface mines is the stability of the working and final slopes of the mine. In order to ensure this, it is necessary to carry out detailed field and laboratory geomechanical tests of the soil and, based on the obtained results, make calculations related to stability analyses. The results obtained in this way are used for dimensioning the slope of exploitation slopes (excavation). Landslides occur when the ultimate shear strength is reached, and therefore, the adequate definition of shear strength parameters is one of the essential prerequisites for successfully solving the stability problem. Unlike earlier tests in Serbia, when the residual shear strength parameters were determined based on the usual conventional methods (direct shear apparatus, triaxial apparatus), this time, in addition to the direct shear apparatus, a ring shear apparatus was also chosen for testing. The paper shows the method of determining the residual shear strength parameters of high plasticity gray clays and siltstones of roof sediments from open pit mine Drmno, using direct and ring shear apparatus. The results show that the residual angle of internal friction for gray clays obtained with the ring shear apparatus is 9.9–10.8°, and for the siltstone, it is 11.8–12.9°, both of which are lower than the values obtained with the direct shear apparatus. In addition, correlations between the residual parameters of soil shear resistance and some physical indicators (plasticity index, clay content) are provided, showing high correlation coefficients. The proposed correlations should be used only when time and financial constraints prevent the execution of actual tests to determine residual shear strength, as concrete experimental procedures provide a much more reliable assessment of the residual strength properties of the soil.

The critical role of c and φ in ensuring stability: A study on rockfill dams

Abstract Slope stability analysis is an important part of rockfill dam design, and the uncertainty of rock and soil physical and mechanical parameters has a significant impact on slope stability. In this article, based on physical and mechanical parameters c and φ, simplified Bishop’s method and mean clustering method are adopted to study the influence of parameter cohesion c and internal friction Angle φ on slope safety factor k of composite geomembrane rockfill dam, and the key and non-critical areas of the dam are preliminarily differentiated according to the different influences of the changes in different sections of the dam body on slope safety factor c and φ. The research results show that whether c and φ change ±5 and ±10% simultaneously with single parameter or double parameter, it shows that cohesion force c has little influence on slope stability, while internal friction Angle φ is the most sensitive factor in slope stability calculation, and its numerical accuracy has a great influence on the calculation result of safety factor. In addition, the influence of c and φ in key areas on the stability of the dam body is more significant. Therefore, in the construction of a composite geofilm rockfill dam, a relatively accurate φ value is required when selecting parameters, especially in key areas. This study not only has a certain guiding significance for the property requirements of the selected soil, engineering safety, and engineering optimization design, but also puts forward some new methods and ideas for optimizing the design scheme and improving the safety of the dam.

Inertial Active Matter with Coulomb Friction

Inertial Active Matter with Coulomb Friction

Theoretical model construction and static performance analysis of multi-leaf journal foil bearings

Abstract Multi-leaf journal foil bearing (MLJFB) structures are complex, making performance prediction challenging, and the accurate prediction of gas film thickness and pressure distributions is crucial. In this study, COMSOL finite-element software was used to establish an initial foil assembly and structural deformation simulation model for an MLJFB with bump foils. Using MATLAB, a compressible gas lubrication model was established and solved using the finite volume method (FVM). Real-time data transfer between COMSOL and MATLAB enabled a fully coupled fluid-structure interaction simulation. This model meticulously accounts for the pre-tension force in the multi-leaf bearing assembly, contact friction between adjacent foils, and the interaction between the top foil and gas film pressure. The effects of journal movement distance, direction, and top foil overlapping ratio on the bearing capacity as well as the effects of different external load directions on the journal equilibrium position were analyzed based on this model. The results indicate that increasing the top foil overlapping ratio enhances the bearing capacity of the MLJFB. Furthermore, compared to the direction of the top foil overlap position, external loads applied in the direction of the top foil midpoint are more beneficial for bearing operational stability.

Application of a regularised Coulomb sliding law to Jakobshavn Isbræ, western Greenland

Abstract. Reliable projections of future sea level rise from the polar ice sheets depend on the ability of ice sheet models to accurately reproduce flow dynamics in an evolving ice sheet system. Ice sheet models are sensitive to the choice of the basal sliding law, which remains a significant source of uncertainty. In this study we apply a range of sliding laws to a hindcast model of Jakobshavn Isbræ, western Greenland, from 2009 to 2018. We demonstrate that a linear viscous sliding law requires the assimilation of regular velocity observations into the model in order to reproduce the observed large seasonal and inter-annual variations in flow speed. This requirement introduces a major limitation for producing accurate future projections. A regularised Coulomb friction law, in which basal traction has an upper limit, is able to more accurately reproduce the range of speeds from 2012 to 2015, the period of peak flow and maximal retreat, without the requirement for assimilating regular observations. Additionally, we find evidence that the speed at which sliding transitions between power-law and Coulomb regimes may vary spatially and temporally. These results point towards the possible form of an ideal sliding parameterisation for accurately modelling fast-flowing glaciers and ice streams, although determining this is beyond the scope of this study.

Coherent Acoustic Phonons in Plasmonic Nanoparticles: Elastic Properties and Dissipation at Low Temperatures.

We studied the frequency and quality factor of mechanical plasmonic nanoresonators as a function of temperature, ranging from ambient to 4 K. Our investigation focused on individual gold nanorods and nanodisks of various sizes. We observed that oscillation frequencies increase linearly as temperature decreases until saturation is reached at cryogenic temperatures. This behavior is explained by the temperature dependence of the elastic modulus, with a Debye temperature compatible with reported bulk values for gold. To describe the behavior of the quality factor, we developed a model considering the nanostructures as anelastic solids, identifying a dissipation peak around 150 K due to a thermally activated process, likely of the Niblett-Wilks mechanism type. Importantly, our findings suggest that external dissipation factors are more critical to improving quality factors than internal friction, which can be increased by modifying the nanoresonator's environment. Our results enable the future design of structures with high vibration frequencies and quality factors by effectively controlling external losses.

Construction and Mechanism of Janus Nano-Graphite Reinforced Foam Gel System for Plugging Steam in Heavy Oil Reservoirs

High-temperature steam injection is a primary method for viscosity reduction and recovery in heavy oil reservoirs. However, due to the high mobility of steam, channeling often occurs within the reservoir, leading to reduced thermal efficiency and challenges in enhancing oil production. Foam fluids, with their dual advantages of selective plugging and efficient oil displacement, are widely used in steam-injection heavy oil recovery. Nonetheless, conventional foams tend to destabilize under high-temperature conditions, resulting in poor stability and suboptimal plugging performance, which hampers the efficient development of heavy oil resources. To address these technical challenges, this study introduces a foam system reinforced with Janus nano-graphite, a high-temperature stabilizer characterized by its small particle size and thermal resistance. The foaming agents used in the system are sodium α-olefin sulfonate (AOS), an anionic surfactant, and octadecyl hydroxylpropyl sulfobetaine (OHSB), a zwitterionic surfactant. Under conditions of 250 °C and 5 MPa, the foam system achieved a half-life of 47.8 min, 3.4 times longer than conventional foams. Janus nano-graphite forms a multidimensional network structure in the liquid phase, increasing internal friction and enhancing shear viscosity by 1.2 to 1.8 times that of conventional foams. Furthermore, the foam gel system demonstrated effective steam-channeling control in heterogeneous heavy oil reservoirs, particularly in reservoirs with permeability differentials ranging from 3 to 9. These findings suggest that the Janus nano-graphite reinforced foam system holds significant potential for steam-channeling mitigation in heavy oil reservoirs.

Experimental study on the maximum static friction coefficient of fiber winding based on semi‐geodesic method

Experimental study on the maximum static friction coefficient of fiber winding based on semi‐geodesic method

Effect of Liquid Properties on the Non-Newtonian Rheology of Concentrated Silica Suspensions: Discontinuous Shear Thickening, Shear Jamming, and Shock Absorbance.

Concentrated particle suspensions exhibit rheological behavior, such as discontinuous shear thickening (DST) and dynamic shear jamming (SJ), which affect applications such as soft armors. Although the origin of this behavior in shear-activated particle-particle interactions has been identified, the effect of chemical factors, especially the role of liquids, on this behavior remains unexplored. Hydrogen bonding in suspensions has been proposed to be essential for frictional contacts between particles, and therefore, most studies on DST and SJ have focused on aqueous and protic organic media with a definite hydrogen bonding ability. To identify an alternative molecular mechanism, this study explored the effects of liquid polarity and an aprotic nature on the rheological behavior of concentrated suspensions of silica microparticles. Owing to their excellent particle dispersion, the DST behavior of polar liquids was observed, independent of protic and aprotic liquids. In contrast, nonpolar liquids formed particle agglomerates because of the particle-particle attraction and became a paste at a high particle fraction. The SJ behavior was confirmed for three aprotic organic liquids (propylene carbonate, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethylpropyleneurea), suggesting the hydrogen bonding ability of these aprotic liquids. The diverse mechanisms of shear-activated interactions between particles present material design possibilities for the non-Newtonian rheology of concentrated particle suspensions.

A COMPARATIVE STUDY OF THE SURFACE OF FACTORY AND HAND-MADE LOOPS ON TITANIUM-MOLYBDENUM ORTHODONTIC ARCHWIRE

The most important part of the brackets, used in orthodontic treatment, is the archwire, which, when activated, generate light and long-lasting biomechanical forces that make the teeth move. Different manufacturers offer ready-made expensive solutions for orthodontists - archwire with loops along the length of the wire of different shape, which increases the cost of treatment. However, orthodontic practice is strictly individual, depending on the patient’s orthodontic problems, the stages and methods of treatment.Orthodontists often have to choose between expensive archwires with pre-made loops or using an archwire that they can manually bend in the right places depending on the patient’s individual characteristics and specific needs. In this case, the orthodontist’s decision depends on preserving the quality of the archwire surface. The surface roughness of the orthodontic archwire plays an important role in the bracket-archwire complex and is an essential factor that determines the effectiveness of the guided movement of the teeth along the arch. Surface roughness not only affects the efficiency of sliding mechanics, due to frictional effects, but also corrosion behaviour and aesthetics. A comparison of the surface characteristics of Ti-Mo archwire - with factory and hand-made loops is made. The surface of the archwire in the bending zones of the loops was investigated by SEM analysis and Surface roughness analysis. The analysis of the results shows that manual bending practically does not change the surface of the archwire, does not introduce additional defects that increase the contact friction, as well as create conditions for faster deterioration of properties and the undesirable breakage of the archwire. Research results give orthodontists confidence that the manual bending process does not degrade the quality of the archwire surface. The hand-bent archwire preserves the possibility of trouble-free movement in the braces when tightening or loosening during the different stages of treatment.

On the dynamics of transporting rolling cylinders

AbstractA common, yet hazardous, method of transporting cylindrical tanks used to carry compressed gas involves rolling both tanks at opposite angles of inclination to the vertical. By propelling one of the tanks while maintaining point contact between the tanks, both tanks can be moved such that their centers of mass move in a straight line. The purpose of this paper is to explore this locomotion mechanism. First, the problem of supporting an inclined cylinder in point contact with a rough surface is examined. The analysis shows that dependent on the geometry of the cylinder and the coefficient of static friction, a wide range of angles of inclination are feasible. The presence of non-integrable constraints on the motion of the rolling cylinder is explored using the concept of a holonomy. The problem of transporting two cylinders using the aforementioned mechanism is then analyzed with the help of Frobenius’ integrability criterion for constraints and numerical simulations. The results show the mechanical advantage of transporting a pair of cylinders, the range of possible angles of inclination, and the forces needed to sustain the motion.

Influence of Plasma Arc Current and Gas Flow on the Structural and Tribological Properties of TiN Coatings Obtained by Plasma Spraying

This study investigates the development of TiN-based coatings using plasma spraying technology, focusing on how plasma arc current and working gas flow rate affect the coatings’ structural-phase composition and mechanical–tribological properties. The research highlights the potential and effectiveness of plasma spraying for TiN coatings. Results from scanning electron microscopy and nanoindentation tests show that the TiN coatings have a dense microstructure with strong adhesion. Tribological testing demonstrated that coatings deposited at a 250 A arc current displayed the lowest coefficient of dry friction and the lowest porosity (2.13%) compared to those deposited at 350 A and 450 A arc currents, which exhibited higher porosity (up to 10.45%).