Smooth Friction Research Articles

An improved immersed boundary method for turbulent flow simulations on Cartesian grids: extension of a global geometric approach for thin boundary layers and strong flow incidence

This paper presents further improvements to the immersed boundary method introduced in [1]. The proposed developments take place during the pre- and post-processing stages of the simulation workflow and aim to further increase the accuracy of the approach for steady-state simulations of high Reynolds number turbulent flows around aerodynamic geometries facing strong incidence. To this end, the location of the forcing points is further optimized prior to simulation, with an adaptive and local modeling height that accounts for the evolution of the turbulent boundary layer thickness, especially at the leading edge. In addition, the direct extrapolation of the pressure solution at the wall is replaced by first- and second-order reconstructions using the normal pressure gradients interpolated at a new set of image points. This second approach is used only in post-processing, after the simulation, and prevents the degradation of the wall pressure in the presence of strong curvatures or thin boundary layers. These developments have been validated by simulating subsonic turbulent flows around the NACA0012 profile, 2D multi-element airfoil (2DMEA), and HL-CRM half-plane at significant angles of attack. Smooth and accurate skin pressure and friction coefficients are observed, in excellent agreement with body fitted wall-resolved solutions, even for coarser Cartesian meshes. Better drag and lift coefficients calculated by direct near-field integrations are obtained, along with accurate predictions of the near-wall flow physics throughout the turbulent boundary layer.

A novel cohesive interlayer model considering friction

To understand the influence of friction on the shear-slip behavior of heterogeneous brittle composites, a novel cohesive interlayer model that can effectively capture the friction effect was proposed based on the classical Park-Paulino-Roesler model. Meanwhile, the unified potential energy function governing the interface tangential and normal behaviors was introduced to realize the mechanical interaction between Mode I fracture and Mode II fracture, and a smooth friction growth function was added in the elastic deformation stage for calculating the accurate contact pressure and friction force. Furthermore, the capability of the proposed model in addressing unloading and reloading was improved, and the fracture energy can vary accordingly during cyclic loading. To verify the effectiveness of the proposed model, it was examined by modelling the shear behavior of a masonry wallette. The results show that the relative error of the proposed model is 14.92% which is much lower than those of the other three pre-existing models when calculating the displacement corresponding to peak shear stress. Meanwhile, in terms of peak shear stress and initial displacement at residual stage, the relative errors of the proposed model are only 1.82% and 5.04%, respectively, indicating the high accuracy. Besides, the tangent stiffness determined by the second-order integration of the potential energy function is also continuous and smooth, which ensures the effective convergence of the proposed cohesive model.

Research on the Influence of Surface Texture on the Friction Performance of Continuous Rotary Motor Friction Pairs

To study the effect of surface texture on the friction performance of continuous rotary motor friction pairs, a simplified model of the clearance flow field between the motor blades and stator friction pairs was first established. Single factor experimental plans and orthogonal experimental plans were designed with the maximum positive pressure of the oil film as the optimization objective. Then, simulation calculations were conducted on the texture fluid models under different morphologies and geometric parameters using FLUENT software to analyze the maximum positive pressure of the oil film The relationship between bearing capacity and friction coefficient is compared to obtain the surface texture applied to the friction pairs of motor blades and stator; Finally, the optimal texture obtained based on simulation calculations is processed on the specimen and friction tests are conducted. By comparing the friction coefficients of the friction surface between the textured surface and the smooth surface friction pair at different speeds and loads, the influence of surface texture on the friction performance of the friction pair is analyzed. The results indicate that the surface texture designed in this article can effectively improve the friction performance of motor friction pairs.

Effect of Multi-rough Element Combination on Hypersonic Boundary Layer

In this paper, the influence of multi-rough element combination controlled by cubic polynomial on the flow field of hypersonic blunt wedge is studied by direct numerical simulation. The influence mechanism of six continuous rough element combinations on the flow parameters in the boundary layer is analyzed in depth, and compared with the influence of double rough elements. It is concluded that the first rough element of the continuous rough element combination has a great influence on the flow field pressure, and the influence of the latter rough element decreases in turn. The combination of six continuous rough elements on the wall can better suppress the incoming flow heating and reduce the wall friction compared with the double rough elements. Compared with smooth wall, wall friction and incoming flow heating are reduced by 25.23 % and 2.69 %, respectively.

Wear of the 3D Printed Polylactic Acid Elements Sliding against the Synthetic Resins at the Higher Speed Friction

Since the requirement of high dust-free levels, it is necessary to develop the technologies with anti-wear and low dust generation for drive elements that can be quickly printed. Polylactic acid and synthetic resins are often paired with each other for the 3D printed driven elements. To achieve "smooth friction", the adhesion wear under dry friction conditions should be reduced. To achieve a "high dust-free level", the anti-wear of the paired elements under higher speed friction should be improved to reduce the generation of abrasive dust. Therefore, wear of the 3D printed polylactic acid elements sliding against the synthetic resins at the high speed friction are investigated in this paper.

Mechanical behavior, tribological properties, and thermal stability of (AlCrNbSiTiVZr)N high entropy alloy nitride coatings and their application to Inconel 718 milling

(AlCrNbSiTiVZr)N high entropy alloy nitride coatings were deposited on silicon wafers and WC substrates using a radio-frequency magnetron sputtering system with nitrogen flow rates of 0, 10, 15, and 20 sccm (coating codes: N0, N10, N15, and N20, respectively). The coatings were subsequently annealed in a vacuum at 950 °C for 1 h (coating codes: HN0, HN10, HN15, and HN20). The effects of the nitrogen flow rate on the composition, microstructure, mechanical properties, and tribological properties of the coatings were systematically examined. The N0 and N10 coatings had amorphous structures, whereas the N15 and N20 coatings had FCC structures. Among the as-deposited coatings, the N20 coating exhibited excellent mechanical properties and a superior tribological performance. All the annealed coatings showed an FCC structure and formed a V2O5 solid lubricant layer in ball-on-disk sliding tests. The lubricant layer reduced the coefficient of friction and led to a smooth friction curve. The annealed coatings additionally showed a high hardness, good adhesion strength, and excellent thermal stability. The mechanical and tribological properties of the HN20 coating were particularly impressive. In Inconel 718 milling trials, the N20-coated cutter showed an excellent machining performance, with significantly reduced flank wear, notch wear, and built-up edge adhesion.

Study on tool wear mechanism and chip morphology during turning of Inconel 713C by textured inserts

The present study aims to analyze the tool wear mechanism and chip morphology during dry (D) and graphene solid-lubricant (S), turning of Inconel 713C with a new novel textured (honeycomb (T2) and rectangular(T3)) and further compare with the textured dimple tool (T1). In addition, the performances were compared with the untextured tool (T0). The machining tests for all conditions were carried out at different levels of cutting speeds (75 m/min and 150 m/min), feed rate (0.1 mm/rev and 0.2 mm/rev), and a constant level of depth of cut (0.5 mm). Honeycomb-textured cutting tools performed better. Improvements of 33.3 % (T1D), 50 % (T3D), and 75 % (T2D) without graphene and 66.6 %(T1S), 75 % (T3S), and 100 %(T2S) with graphene are observed compared to T0. The primary mechanism for the better performance of T2S was the reduced tool chip contact length (8–50 %), chip width (30.4 %), friction coefficient (57.4 %), chip thickness (17.8 %), and higher shear angle (14.2 %) compared to dry textured and untextured tools at the end of tool life. Additionally, the T2S (solid lubricant-impregnated honeycomb) demonstrates a decrease in equivalent chip thickness (19.8 %) and an increase in shrinkage factor (17.2 %) at worn-out tool life conditions at high cutting speed and feed rate. Under the same conditions, T2S has 27.3 % lower cutting force and 36.2 % lower surface roughness of machined workpieces compared to the untextured tool at the end of tool life. The chip micrograph reveals the chips are shorter, and the chip radius is lower for T2S tools with smooth friction tracks and fine deformed lamella on the free surface of the chip. Under SEM, flank wear, adhesion materials, abrasion, micro-chipping coating peeling, and BUE were dominant wear mechanisms. However, T2S tools effectively reduce Ni elements' diffusion and suppress the built-up edge's adhesion by improving friction characteristics at the tool-chip interface region. Lastly, the outcomes of experimental results suggest that the honeycomb texture for dry machining of Inconel 713C.

Novel Wood-Based Functional Material with Vibration and Noise Reduction.

As a kind of typical green material, natural materials tend to exhibit excellent performance in the engineering field because of their structure and special functions. The homogeneous vessels of red willow (RW) are potentially unique structures to store lubricants or reinforcing agents to present special functions for engineering applications. A series of novel red willow wood-based composites, which were infused with nano-MoS2 and then reinforced by the epoxy, were developed. Their self-lubricating, mechanical vibration and noise reduction performances were investigated, and the friction, vibration, and noise reduction mechanisms were disclosed. The infusion MoS2 treatment was very beneficial for improving the tribological properties of MoS2-curing epoxy/red willow (MCW), and the coefficient of friction (COF) was reduced by 65.8% under water-lubricated friction after infusing 24 times. Meanwhile, the mechanical performances of MCW were obviously enhanced through the curing treatment of the epoxy. The synergistic effects of the infusion and curing treatments significantly decreased the wear phenomena on the friction surfaces of MCW and weakened the COF and its fluctuation amplitudes, which resulted in the presented excellent vibration and noise reduction performance. The knowledge gained herein could not only develop a novel wood-based composite with low COF and good vibration reduction properties in the engineering field but also provide a new methodology for the design of artificial porous materials with stable and smooth friction processes.

Ultra‐low Friction and High Load‐Bearing Hydrogel with Tubular Structure Based on Controllable Light‐Induced Dissociation†

Comprehensive SummaryWith high water content, excellent biocompatibility and lubricating properties, and a microstructure similar to that of the extracellular matrix, hydrogel is becoming one of the most promising materials as a substitute for articular cartilage. However, it is a challenge for hydrogel materials to simultaneously satisfy high loading and low friction. Most hydrogels are brittle, with fracture energies of around 10 J·m−2, as compared with ∼1000 J·m−2 for cartilage. A great deal of effort has been devoted to the synthesis of hydrogels with improved mechanical properties, such as increasing the compactness of the polymer network, introducing dynamic non‐covalent bonds, and increasing the hydrophobicity of the polymer, all at the expense of the lubricating properties of the hydrogel. Herein, we develop a hydrogel material with anisotropic tubular structures where the compactness gradually decreases and eventually disappears from the surface to the subsurface, achieving a balance between lubrication and load‐bearing. The porous layer with hydrophilic carboxyl groups on the surface exhibits extremely low friction (coefficient of friction (COF) ∼0.003, 1 N; COF ∼0.08, 20 N) against the hard steel ball, while the bottom layer acts as an excellent load‐bearing function. What is more, the gradual transition of the tubular structures between the surface and the subsurface ensures the uniform distribution of friction stress between a lubricating and bearing layers, which endows the material with long‐lasting and smooth friction properties. The extraordinary lubricious performance of the hydrogels with anisotropic tubular structure has potential applications in tissue engineering and medical devices.

Effect of CrYN/TiBN coating on friction performance and corrosion resistance of 316 stainless steel in artificial seawater

CrYN, TiBN, and CrYN/TiBN coatings were successfully deposited on 316 stainless steel substrates via multi-arc ion plating techniques to improve their wear and corrosion resistance properties in marine environments. The morphology, microstructure, friction performance, and corrosion resistance of the three coatings in artificial seawater were systematically studied. X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy investigations confirmed a dominant face-centered cubic CrN structure, accompanied by hexagonal TiB2 and amorphous BN in CrYN/TiBN coatings. The SEM cross-section shows that the TiBN and CrYN/TiBN coatings have a more compact cross-sectional structure than the CrYN monolayer coating. The CrYN/TiBN coatings exhibited the lowest smooth friction coefficient in artificial seawater, and the wear rate was ranked as TiBN < CrYN/TiBN < CrYN. Surface morphological studies performed after tribocorrosion revealed that the protection ability of all three coatings remained acceptable. The electrochemical test showed that the corrosion tendency was CrYN/TiBN < TiBN < CrYN, and the CrYN/TiBN coating had the best performance in the AC impedance spectrum and polarization curve.

Influence Mechanism of Rubber Thermal Oxygen Aging on Dynamic Stiffness and Loss Factor of Rubber Isolation Pad

The influence mechanism of thermal oxygen aging on the dynamic characteristic of the rubber isolation pad (RIP) is usually ignored in studies. However, the ambient temperature of the RIP could reach up to 70°C in general, and even 108°C under some extreme conditions, which will lead to accelerated thermal oxygen aging and a decline in the mechanical performance for the RIP. In the meantime, the thermal oxygen aging will result in excessive vibration and even a damaged external air conditioner. Therefore, the research on the influence mechanism of rubber thermal oxygen aging on the dynamic performances of the RIP is crucial to the mechanical characteristic matching of the RIP. Considering the effect of the thermal oxygen aging on the dynamic characteristic, a novel model of thermal oxygen aging-dynamic characteristic of the RIP is established by adopting the Peck model, the hyperelastic model, the fractional derivative model, and the smooth Coulomb friction model (SCFM) in this paper. A test rig of the static and dynamic characteristics of the RIP is built, and an identification method of model parameters is developed based on the MTS831 elastomer test system as well which of the thermal oxygen aging-dynamic characteristic model is verified by the experimental data. The result is shown that the maximum growth rate of the static stiffness and the dynamic stiffness is 20.7% and 4.5%, respectively, and the maximum decrease rate of the loss factor is 10.6% as the thermal oxygen aging hardness of the RIP increases by 5HA. The amplitude-dependent, frequency-dependent, and thermal oxygen aging-dependent performances of the RIP are effectively characterized by the thermal oxygen aging-dynamic characteristic model. Moreover, a theoretical foundation is provided for the evolution law of the dynamic characteristic of the RIP after the service with the thermal oxygen aging condition in this research.

A Simplified Model for Numerical Investigation of Bump-Type Foil Bearings Based on Contact Nonlinearity

Abstract The paper introduces a simplified structural model for the numerical investigation of bump-type foil bearings. This analytical model is based on an efficient nonlinear contact procedure with consideration of friction, small deformations, and elasticity. The bump foil is modeled with a truss structure, while the top foil uses two-dimensional (2D) beam elements. In this present model, the normal and tangential contact forces between the bump foil and the bearing sleeve and between the foils are dealt with the penalty method. Even for a simple loading, the contact state might change between separation, stick, and slip. To avoid convergence problems caused by discontinuity, the regularized smooth friction model is used instead of the Coulomb friction model. In addition, due to contact problems that depend on time are accompanied by nonlinear evolution, the solution of the system equation using the incremental iterative method and the Newton–Raphson method is presented. The deflection of the top foil is added to the film controlled by the Reynolds equation (RE) to obtain the air pressure distribution. The theoretical predictions of the rotor push-pull tests agree well with results from the literature, which verifies the validity of the model. Using this present model, the quasi-static behaviors of the foil structure are mainly discussed, and parametric studies concerning environmental pressure and radial clearance are also conducted.

Friction reduction behavior of oil-infused natural wood

Natural materials tend to exhibit excellent performance in the engineering field because of their structure and special functions. A natural red willow, called natural porous wood material (NPWM), was found, and wear tests were conducted to determine its potential as an oil-impregnated material by utilizing its special porous structure. Fluorination treatment was adopted to improve the NPWM properties for absorbing and storing lubricating oil. The different contributions of soaking and fluorination-soaking treatments on the tribological properties of NPWMs and their respective mechanism of effect were revealed. The results showed that the fluorination-soaking treatment helped absorb and store sufficient lubricating oil in the NPWM porous structure; therefore, more lubricating oil would be squeezed out and function as a tribol-film between contacting surfaces during the friction process, thus ultimately contributing to stable and smooth wear responses even under prolong friction. However, the formation of an oil-in-water emulsion, caused by the buoyancy effect, destroyed the oil films on the worn NPWM surface in a water environment, resulting in higher coefficients of friction (COFs) under water conditions than under dry friction, even after the fluorination-soaking treatment. The knowledge gained herein could not only verify the potential of NPWM as an excellent oil-impregnated material in the engineering field but also provide a new methodology for the design of artificial porous materials with stable and smooth friction processes.

Quantitative Test and Engineering Application of Wear Resistance of a Kind of Mine-Filled Composite Pipeline

Wear resistance is one of the most important performance indicators of filling pipelines, but there are few studies on its quantitative test and life prediction. In this paper, an experimental device and its application method for testing the wear resistance of the pipeline are proposed, and the device is used to test the wear resistance of the self-developed lining composite pipeline, the traditional 16 Mn steel pipeline and the ordinary carbon structural steel pipeline. The results show that the wear resistance of the composite lining material is 12.35 times of that of 16 Mn steel and 7.32 times of that of ordinary carbon structural steel. The wear resistance mechanism is analyzed from the perspective of the material composition of the composite liner, mainly because the composite liner material uses fused alumina grain sand, silicon carbide and other extremely wear-resistant materials with high hardness as aggregate, and the aggregates are spherical or nearly spherical particles, with smooth surface and small friction resistance. Finally, through a comparison engineering application of a certain iron ore concentrate transportation. Compared with the traditional 16 Mn steel pipeline, the composite lined pipeline has been used for more than 5 years without any problems, while the traditional 16 Mn steel pipeline is worn through within 1 year. Engineering application shows that the composite lined pipeline has good wear resistance, and it also confirms the reliability of the detection method proposed in this paper.

Study on Lubrication and Friction Reduction Properties of ZIF-8 Nanoparticles as Si3N4 Ceramic Water Lubrication Additives.

Ceramics can achieve superlubricity under water lubrication; however, their running-in period is long and application is rather limited by wear limit. Thus, zeolite imidazole ester skeleton (ZIF), an important branch of metal organic framework materials (MOFs), is expected to improve the tribological properties of lubricants and associated additives. As such, it has broad application prospects within the field. In this paper, ZIF-8 nanoparticles of varying concentrations were prepared and linked with amino functional groups. Specimens were used in silicon nitride self-matching pairs and their tribological properties were observed. After the experiment, friction surfaces were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and Fourier transform infrared radiation (FTIR). The experimental results have shown that ZIF-8 nanoparticles greatly reduced both friction and wear. Comprehensively considering running-in time, average COF during the whole process and smooth friction period COF, optimal performance was obtained for the ZIF-8 nanoparticle solution concentration of 1wt%. Furthermore, it was concluded that the lubrication properties of amino-modified ZIF-8 nanoparticles are significantly better compared to that of the unmodified ZIF-8. The anti-friction mechanism of ZIF-8 as a ceramic water lubrication additive was mainly through the filling and forming of nanoparticle film on the ceramic surface.

Dry sliding behavior of copper based composite materials prepared using conventional compaction and sintering technique and spark plasma sintering

The study aimed to investigate the dry sliding properties of as received copper based composite materials, with varying silica and copper content, and produced through two different techniques: conventional compaction and sintering and spark plasma sintering (SPS). The SPS process induced pronounced densification and hardness of the materials and a better distribution of constituents when compared to conventionally sintered specimens. The SPS specimens observed the presence of a C layer of varying thickness on their surfaces, transferred from the graphite die used for their production. The thickness and adhesion of the C layer was influenced by the silica content in the specimens. Specimens containing low silica content showed a significant C layer on the pin surface. This C layer was not removed during dry sliding pin on disc testing, thus resulting in very low COF (coefficient of friction) and pin wear. Specimens containing high silica content led to the formation of a sparse C layer on their surfaces due to the low chemical interactions of silica with other atoms or compounds, leading to easy removal during tests and elevated COF magnitude. However, high silica content also led to low adhesion between the friction layer and the worn surfaces, resulting in instability and higher pin wear. The specimens containing moderate silica content were identified as the best composition due to their ability to easily shed the C layer during testing, maintain smooth, compact, and continuous friction layer without any detachment/adherence issues, and demonstrate permissible COF and pin wear in the mild range.

Vibration energy flow transmission in systems with Coulomb friction

This study focusses on the vibration transmission and energy flow characteristics of low dimensional models of dynamical systems with Coulomb friction. The Karnopp friction model and smooth Coulomb friction models are employed to estimate the dry friction force. The steady-state responses of the system are determined by the harmonic balance (HB) approximations with numerical continuations and a time-marching method. The level of vibration transmission and energy dissipation within the system are assessed by the force transmissibility and power flow variables. For a single degree-of-freedom oscillator system, in the low- and high-frequency ranges away from the resonance, it is found that the dry frictional contact can suppress the vibration response and effectively dissipate vibrational energy. For the coupled system, the existence of frictional contact at the interface can lead to a significant growth in the force transmissibility and energy transfer from the force-excited subsystem to the secondary system, especially at the high excitation frequencies. The interfacial frictional contact can also result in a large amount of energy dissipation at the interface. The studies show that vibration transmission and energy dissipation in a dynamic system with contacting subsystems can be tailored by adjusting the properties of the frictional contact. Design strategies can be developed using frictional contacts for vibration suppression by minimizing vibration energy transmission or maximizing energy dissipation.

Comparison and Harmonization of the Locked-Wheel Skid Tester and the Sideway-Force Coefficient Routine Investigation Machine

Abstract Skid resistance is a characteristic of a pavement surface that is critical to pavement safety. Skid resistance can be measured with different types of equipment, but because of the differences in the system configurations and the testing methods (fixed slip, locked-wheel, sideway-force, and variable-slip), the measured friction characteristics are not the same. To compare the measurements, analysts have attempted to harmonize measurements to a common scale by integrating the effects of macrotexture and slip-speed on skid resistance. Examples of these efforts include the Penn State model, the Rado Model, the Permanent International Association of Road Congresses International Friction Index (IFI), and the Rolling Resistance, Skid Resistance, and Noise Emission (ROSANNE) Skid Resistance Index (SRI). In the United States, skid resistance is traditionally measured with a locked-wheel skid trailer (LWST), but there has been increasing interest in the use of continuous friction measurement equipment. This paper compares friction measured using a LWST ribbed tire and smooth tire with measurements collected with a Sideway-Force Routine Investigation Machine (SCRIM). The first objective is to evaluate the influence of macrotexture on the friction measured with both devices. The second objective is to compare the friction measurements using orthogonal regression (OR) and derive equations for interconversion between both devices. The findings in this paper establish that the LWST ribbed tire and the SCRIM shared similar sensitivity to changes in microtexture, whereas smooth tire was more sensitive to changes in microtexture. The direction of the OR of both devices produced a greater correlation for the SCRIM and ribbed tire than did the smooth tire. The correlation was increased when the measurements with the SCRIM and smooth tire were converted to 60 km/h using the IFI FR60 conversion. The higher correlation using FR60 conversion provides further support for the dependence of smooth tire friction on macrotexture measurements.

Hydrothermal synthesis and tribological properties of WS2 microspheres

In this work, WS2 microspheres were synthesized through a facile hydrothermal route. The as-synthesized samples were characterized by powder X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive spectroscopy and scanning electron microscopy (SEM). The XRD spectrum of the sample is indexed to hexagonal WS2. SEM graphics of the products reveal that the WS2 microspheres with diameters of about 2-8 μm were synthesized. The tribological properties of WS2 microspheres as oil additives were tested on a ball-disk tribometer. Under the given experimental conditions, the friction coefficient of the oil containing WS2 is lower than that of the base oil. The formation of rolling friction between the friction pairs and the smooth friction film on the wear surface are considered to be the reason for the good lubricating effect of WS2 microspheres as an additive.

Ventilator integrated triboelectric nanogenerator based on structure of centrifugal brake

Numerous studies have been conducted in the recent years for the practical application of triboelectric nanogenerators (TENGs). The underlying concept of TENG is to convert the inexhaustible kinetic energy obtained from natural sources into mechanical energy for triboelectricity. Among these energy sources, wind energy occurs freely throughout the world and can be easily transformed through mechanical motion. This study proposes a ventilator integrated TENG (VTENG) capable of continuous energy production using a ventilator that converts wind energy into rotational motion. The internal triboelectric generator structure of VTENG is based on the principle of the centrifugal brake to prevent friction at a low rotational speed, which prevents the ventilator from playing its original role due to the rotational disturbance at low speeds. Additionally, a micro/nano surface structure is adopted to prevent stoppage due to strong frictional force during which, both friction and smooth friction are observed. When the rotational speed reaches a certain level, the internal TENG produces friction due to the centrifugal force and generates electric energy. The amount of electric energy generated is measured and analyzed based on the rotational speed. The ventilator is an essential element for air circulation, and the VTENG proposed in this study can be applied to ventilators even in remote locations to generate electric energy. Therefore, it can be considered as an important discovery in identifying the practical application of the TENG.