Interfacial Friction Research Articles

Improvement of energy conversion efficiency in traveling wave rotary ultrasonic motor by increasing friction coefficient

This article introduces a method of enhancing the energy conversion efficiency of a traveling wave rotary ultrasonic motor with a flexible rotor by increasing the friction coefficient at the stator–rotor interface. The increased friction coefficient leads to improvements in energy conversion efficiency by increasing the output power and reducing friction loss power. Experimental verification showed that the friction coefficient in the interface increased from 0.21 to 0.32, the maximum energy conversion efficiency increased from 36.8% to 46.3%, and the interface friction loss was reduced.

Tribological and Mechanochemical Properties of Nanoparticle-Filled Polytetrafluoroethylene Composites under Different Loads.

For the tribological properties of nanoparticle-modified PTFE, a more comprehensive study has been conducted, but there is still some room for research on tribology behavior, tribofilm formation and structure evolution of polytetrafluoroethylene (PTFE) filled with α-Al2O3 and SiO2 nanoparticles during sliding against steel counterparts under different loads. At the same time, it establishes the linkage and mechanism between the maintenance of mechanical strength and the tribological application of polymers in service and provides corresponding scientific data and theoretical guidance for the long-lasting application of polymer lubrication materials. It is found that both composites exhibit good wear resistance across the pressure of 1 MPa to 10 MPa, with the α-Al2O3/PTFE composite demonstrating better performance stability compared to the SiO2/PTFE composite. The high wear resistance is attributed to the formation of tribofilms at the friction interface. For the α-Al2O3/PTFE, an island-like tribofilm is formed with a thickness ranging from 100 to 200 nm, while the tribofilm of the SiO2/PTFE composite is thinner, measuring approximately 50 to 100 nm, and manifests a striped pattern. The chemical composition, both at the surface and subsurface levels, as well as the morphology of the tribofilms, were studied using FTIR spectrometry, X-ray photoelectron spectroscopy (XPS), and FIB-TEM. It is found that the difference in thickness and microstructure of the tribofilms for the two composites is mainly due to the tribochemistry of the nanoparticles. The α-Al2O3 nanoparticle plays a "cohesion" role during the formation of the tribofilm, which facilitates the formation of a thicker, more uniform, and stronger adhered tribofilm on the metallic counterpart, making it more robust against higher shear stress.

Analyses of the Suction Anchor–Sandy Soil Interactions under Slidable Pulling Action Using DEM-FEM Coupling Method: The Interface Friction Effect

The microscale mechanisms underlying the suction anchor–sandy soil interaction under slidable pulling actions of mooring lines remain poorly understood. This technical note addresses this knowledge gap by investigating the suction anchor–sandy soil interaction from micro to macro, with a particular emphasis on the effect of interface friction. The discrete element method (DEM) was utilized to simulate the sandy soil, while the finite element method (FEM) was employed to model the suction anchors. The peak pulling forces in numerical simulations were verified by centrifuge test results. The research findings highlight the significant influence of interface friction on the pulling force–displacement curves, as it affects the patterns of suction anchor–sandy soil interactions. Furthermore, clear relationships were established between the magnitude of interface friction, rotation angle, and pullout displacement of suction anchors. By examining the macro-to-micro behaviors of suction anchor–sandy soil interactions, this study concludes with a comprehensive understanding of failure patterns and their key characteristics under different interface friction conditions. The findings proved that the interface friction not only influences the anti-pullout capacity but also changes the failure patterns of suction anchor–soil interactions in marine engineering.

Thermal-sprayed ceramic/fluoropolymer coatings with tight bond and self-lubrication: Microstructure, tribological properties, and lubrication mechanism

Ceramic/fluoropolymer composite coatings capable of controlling friction and wear have attracted the attention of numerous researchers. However, their practical applications are significantly limited by the complex fabrication process and weak interfacial bonding between ceramics and fluoropolymers. Herein, the robustly bonded Al2O3/Polytetrafluoroethylene (PFA) composite coatings were fabricated via a straightforward technology, and a comprehensive investigation was conducted to scrutinize their microstructure, tribological behaviors, and lubrication mechanism. Results show that forming an interdiffusion layer between Al2O3 and PFA splats could be responsible for robust interfacial bonding. The generation of a well-covered unique lubricant film at the frictional interface enables the coefficient of friction to be reduced by 83.7 % to 0.13, and the specific wear rate correspondingly diminished from 2.69 × 10−4 mm3 N−1 m−1 to 4.93 × 10−6 mm3 N−1 m−1. The lubricant film is composed of numerous spherical structures and a layer of amorphous material. The development of the hybrid coating with a simple and efficient preparation method, strong bonding, and excellent tribological properties offers significant potential for applications in the field of tribology.

Hydro‐mechanically coupled CEL analyses with effective contact stresses

AbstractThe coupled Eulerian–Lagrangian (CEL) method implemented in Abaqus is an established tool for modelling large deformations in numerical geomechanics. As shown in previous work, it can be extended to a hydro‐mechanically coupled scheme by exploiting the similarity of the heat balance equation to the mass balance equation of fluids. However, the distinction between effective and total contact stresses has not been possible in this approach, which hinders its application to problems with interface friction as frictional stresses are calculated based on total normal contact stress. An approach to circumvent this problem is presented in this work. Its relevance is demonstrated by the simulation of vibratory pile driving model tests in water‐saturated sand. The implementation by means of user‐subroutines is available and works for any total‐stress analysis.

Low-frequency vibration assisted self-pierce riveting (LV-SPR) of carbon fiber reinforced composite and aluminum alloy

Self-pierce riveting (SPR) has been widely applied to join carbon fiber-reinforced polymer (CFRP) composites and high-strength metallic plates in the automotive and aerospace fields. However, the CFRP is often damaged by rivet piercing owing to its brittleness as well as the relatively small interlocking that forms between the rivet leg and high-strength plate owing to the hard deformation characteristics. Therefore, in this study, a novel low-frequency vibration-assisted self-pierce riveting (LV-SPR) technology is proposed, which utilizes the vibration effect in softening the metal and reducing interfacial friction at room temperature. In riveting experiments involving CFRP and 5052 aluminum alloy utilizing 37Cr4 semi-hollow rivets, LV-SPR exhibited a significant reduction of 68.2% in the riveting force compared to the traditional SPR process. The decreased riveting pressure in LV-SPR effectively mitigated the CFRP damage by 36.2%, which was caused by a reduction in the interfacial friction force between the rivet and CFRP laminate. Moreover, owing to the improved deformation capacity of the rivet and alloy plate by the vibration softening effect, the lateral expansion of the rivet leg in the aluminum alloy was enlarged by 36.4% compared to that using the traditional self-piercing riveting (T-SPR) process. Microscopic characterization revealed that vibrations notably promoted grain refinement and enlarged the subgrain structures of the rivets and alloy plates. Finally, by superposing oscillations, the shear strength of the connection joint increased by 13.5% compared to the T-SPR joint. The proposed LV-SPR was validated as an effective technique to increase the connection strength of high-performance plates, which can efficiently improve the structural safety and promote the widespread application of CFRP/alloys in automobiles and aircrafts.

Tribological and corrosive behavior under HCl corrosive environment of diamond-like carbon films with doped H, Cr and WC

Diamond-like carbon films exhibit low friction and strong wear resistance under various conditions. In order to evaluate tribological and corrosion resistant performance of different types of diamond-like carbon films in hydrochloric acid (HCl) environment, DLC, Cr/DLC, H/DLC and WC/DLC films were prepared by unbalanced magnetron sputtering technology. Their microstructure, mechanical properties, tribological properties and corrosion resistance were characterized and studied. The results show that the prepared DLC film exhibits the lowest wear rate in 1 M HCl solution. H/DLC film has an obvious corrosion resistance due to its high sp3 C bond and dense structure. Cr/DLC and WC/DLC films show a lower friction coefficient. In general, tribological failure of DLC film is mainly due to ordinary mechanical wear; while that of Cr/DLC film is mainly attributed to abrasive wear caused by, for example, hard particles and wear products; adhesive wear is found to be responsible for H/DLC film, which is caused by transformation of CH bond to oxygen group at the friction interface. The WC/DLC film is experienced with both local degradation and low resistance to elastic/plastic changes (H/E and H3/E2), and therefore both granular and chemical failures occurred. This study provides a complete and comprehensive understanding of tribological and anti-corrosive performance of diamond-like carbon films in hydrochloric acid environment, and can be used further as a reference for industrial applications.

Effect of interphase layer on matrix cracking in fiber reinforced ceramic matrix composites

The onset of matrix steady-state cracking stands as a pivotal mechanical characteristic in fiber reinforced ceramic matrix composites (FRCMCs), garnering substantial attention and investigations. Experimentally, it has been demonstrated that increasing interphase layer thickness may cause non-monotonic changes in matrix cracking stress. However, the existing models can hardly elucidate this phenomenon thoroughly due to the neglect of interphase thickness. This paper presents a comprehensive analytical model for the matrix cracking incorporating interphase, the Poisson effect, Coulomb friction, fiber asperities, residual thermal stress (RTS), and their coupling effects, along with a modified criterion for interfacial debonding that accounts for the presence of the axial RTS. Based on the proposed model, three distinct cracking domains, i.e., perfectly bonded, debonding with and without interfacial separation, have been identified with the critical conditions deduced analytically. Thereby the mechanism of the non-monotonic influence of interphase thickness is thoroughly revealed as the transition of cracking modes. Meanwhile, the role of interphase on the matrix cracking is systematically studied, and the results indicate that interphase has a notable effect through relieving axial RTS, adjusting interfacial friction, altering interfacial shear modulus, and influencing debonding toughness. The outcomes of this study offer valuable guidance for the interphase design of FRCMCs.

Multilayer coatings of periodically co-deposited graphene and ag substrate: Improving the electrified friction interface by modifying the strength-ductility combination

Multifunctional and highly adaptable multilayer coatings are considered the future development trend in the field of protective coating design. To enhance wear resistance when subjected to an electric current and to reduce internal stresses, we developed a multilayer structure in which graphene nanoplatelets (GNPs) were deposited within pure silver using a dual electrolyte alternating deposition technique, resulting in the creation of Ag-Ag/GNP multilayer coatings. In this multilayer coating design, the continuous conductive silver layer enhances the overall electrical properties of the coating, and the soft silver layers absorb part of the internal stress in the coating. The deposited GNPs provide crucial structural reinforcement to the coating, thereby improving its mechanical and tribological properties. These coatings were characterized with respect to their structure and mechanical properties using X-ray diffraction, hardness testing, and electronic tensile testing, and their current-carrying tribological performance was studied. Experiments revealed that the crystal structure of single-layer composite coatings changed with increasing GNP content, whereas the multilayer coatings exhibited improved strength and toughness. In current-carrying tribological tests, the multilayer coatings demonstrated significant adaptability to increasing wear depth and current. The wear mechanism of multilayer coatings transitioned from adhesive to abrasive wear. The results indicate that the multilayer coating design effectively enhances friction stability, reduces electrical contact resistance, and decreases wear volume. The findings of this study provide new insights for the design of multilayer structured coatings and will help reduce the loss of rare metals in electrified friction applications.

Wedge-shaped lyophilic pattern on superlyophobic surface for unidirectional liquid guidance and lubrication enhancement

Effective maintenance of lubricants within the frictional interface is of great importance for the long-life operation of mechanical components. This paper proposes a wedge-shaped lyophilic groove with secondary structures on superlyophobic surfaces to achieve unidirectional guidance of liquid droplets. The experimental studies demonstrate its rapid and long-distance unidirectional self-driven spreading on water and oil droplets. Then, wedge-shaped lyophilic grooves were designed on non-contact area of friction pair to guide lubricant. Relatively lower and more stable friction coefficients were achieved. Further analysis reveals that wedge-shaped grooves restrict the drainage of liquid lubricants. The results of bearing experiments show that designing lyophilic wedge-shaped grooves in the non-contact area of the rolling bearing can effectively reduce the temperature rise of the outer ring.

Interface frictional anisotropy of dilative sand.

Understanding direction-dependent friction anisotropy is necessary to optimize interface shear resistance across soil-structure. Previous studies estimated interface frictional anisotropy quantitatively using contractive sands. However, no studies have explored how sand with a high dilative tendency around the structural surface affects the interface shear response. In this study, a series of interface direct shear tests are conducted with selected French standard sand and snakeskin-inspired surfaces under three vertical stresses (50, 100, and 200kPa) and two shearing directions (cranial → caudal or caudal → cranial). First, the sand-sand test observes a higher dilative response, and a significant difference between the peak and residual friction angles (ϕpeak - ϕres = 8°) is obtained at even a lower initial relative density Dr = 40%. In addition, the interface test results show that (1) shearing against the scales (cranial shearing) mobilizes a larger shear resistance and produces a dilative response than shearing along the scales (caudal shearing), (2) a higher scale height or shorter scale length exhibits a higher dilative tendency and produces a higher interface friction angle, and (3) the interface anisotropy response is more pronounced during cranial shearing in all cases. Further analysis reveals that the interface friction angle and dilation angle are decreased with the scale geometry ratio (L/H). For L/H values between 16.67 and 60, the interface dilation angle varies between 9° and 4° for cranial first shearing and 3.9°-2.6° for caudal first shearing. However, the difference in dilation angle within the same shearing direction is less than 1°.

Temperature dependence of the dynamics and interfacial width in nanoconfined polymers via atomistic simulations.

We present a detailed computational study on the temperature effect of the dynamics and the interfacial width of unentangled cis-1,4 polybutadiene linear chains confined between strongly attractive alumina layers via long, several μs, atomistic molecular dynamics simulations for a wide range of temperatures (143-473 K). We examine the spatial gradient of the translational segmental dynamics and of an effective local glass temperature (TgL). The latter is found to be much higher than the bulk Tg for the adsorbed layer. It gradually reduces to the bulk Tg at about 2nm away from the substrate. For distant regions (more than ≈1.2nm), a bulk-like behavior is observed; relaxation times follow a typical Vogel-Fulcher-Tammann dependence for temperatures higher than Tg and an Arrhenius dependence for temperatures below the bulk Tg. On the contrary, the polymer chains at the vicinity of the substrate follow piecewise Arrhenius processes. For temperatures below about the adsorbed layer's TgL, the translational dynamics follows a bulk-like (same activation energy) Arrhenius process. At higher temperatures, there is a low activation energy Arrhenius process, caused by high interfacial friction forces. Finally, we compute the interfacial width, based on both structural and dynamical definitions, as a function of temperature. The absolute value of the interfacial width depends on the actual definition, but, regardless, the qualitative behavior is consistent. The interfacial width peaks around the bulk Tg and contracts for lower and higher temperatures. At bulk Tg, the estimated length of the interfacial width, computed via the various definitions, ranges between 1.0 and 2.7nm.

Numerical Analysis of Ground Surcharge Effects on Deformation Characteristics in Shield Tunnel Linings

To investigate the deformation characteristics of shield tunnel linings under ground surcharge, finite element software was employed to create a detailed three-dimensional model of the staggered assembly of the shield tunnel lining. This model includes components such as precast concrete segments, reinforcements, and joints (comprising bent bolts, washers, and bolt sleeves). Additionally, the model accounts for interface frictions between segments and the interactions between different rings. The reliability of the numerical model was verified based on the results of a full-scale model test. Additionally, the model accounts for interface frictions between segments and the interactions between different rings. Changes in tunnel convergence, joint tensioning, bolt stresses, reinforcement stresses, and concrete crack development were systematically analyzed. The results indicate the following: (1) the deformation mode of the lining structure under ground surcharge resembles a “transverse ellipse”. Joints located near the haunch opened along the outer arc, while those near the vault and bottom opened along the inner arc. The restraining effect of the bolts on joints opening in the inner arc was greater than that on the outer arc. Notably, when the opening of the inner arc reached 4.9 mm, the bolt stress escalated to the yield strength of 640 Mpa. (2) Under larger loads, the lining structure’s joints are susceptible to greater deformation, resulting in the tensile yielding of local reinforcement within these joints. (3) Cracks predominantly occur near the haunch, vault, and bottom of the lining structure, with the central angle of crack distribution ranging between 70° and 85°.

Effect of surface roughness on the interface behavior of clayey soils

Abstract This study investigates the effect of surface roughness on the interface behavior between clayey soils and structural materials, aiming to determine the necessary parameters for soil-structural interaction. The research site, located in one of Iraq’s seismically active regions, was selected for its significance. Experimental measurements were conducted using the SRT-6210 Digital Surface Roughness Tester to assess the roughness characteristics of steel and concrete samples. Four distinct roughness parameters were measured, and their correlation with shear parameters was analyzed. The shear behavior of clay-steel and clay-concrete interfaces was successfully described using the average roughness parameter (Ra), which exhibited the strongest correlation with shear parameters. Direct shear box and interface shear box tests were employed to identify soil’s shear strength parameters and evaluate interface shear strength parameters. The experimental findings highlight the significant influence of surface roughness on the shear strength parameters of clay-steel and clay-concrete interfaces. The interface shear strength, friction angle, and adhesion exhibited an increasing trend with roughness. Notably, shear strength increased by approximately 29.76% when concrete sample roughness was below 20 μm and by 32.8% when steel sample roughness was below 30 μm. Moreover, increasing surface roughness improved the interface friction angle of clay-steel and clay-concrete samples by about 37.95 and 36.3%, respectively. Additionally, an increase in roughness led to a rise in the adhesion of concrete and steel samples by approximately 26.24 and 32%, respectively. These findings emphasize the significance of surface roughness in optimizing the interface behavior between clayey soils and structural materials. The results have important implications for enhancing the design and performance of soil-structural systems.

Synergistic lubrication effects of Sn–Ag–Cu and MXene–Ti3C2 to improve tribological properties of M50 bearing steel with microporous channels

Purpose This paper aims to study the synergistic lubrication effects of Sn–Ag–Cu and MXene–Ti3C2 to improve the tribological properties of M50 bearing steel with microporous channels. Design/methodology/approach M50 matrix self-lubricating composites (MMSC) were designed and prepared by filling Sn–Ag–Cu and MXene–Ti3C2 in the microporous channels of M50 bearing steel. The tribology performance testing of as-prepared samples was executed with a multifunction tribometer. The optimum hole size and lubricant content, as well as self-lubricating mechanism of MMSC, were studied. Findings The tribological properties of MMSC are strongly dependent on the synergistic lubrication effect of MXene–Ti3C2 and Sn–Ag–Cu. When the hole size of microchannel is 1 mm and the content of MXene–Ti3C2 in mixed lubricant is 4 wt.%, MMSC shows the lowest friction coefficient and wear rate. The Sn–Ag–Cu and MXene–Ti3C2 are extruded from the microporous channels and spread to the friction interface, and a relatively complete lubricating film is formed at the friction interface. Meanwhile, the synergistic lubrication of Sn–Ag–Cu and MXene–Ti3C2 can improve the stability of the lubricating film, thus the excellent tribological property of MMSC is obtained. Originality/value The results help in deep understanding of the synergistic lubrication effects of Sn–Ag–Cu and MXene–Ti3C2 on the tribological properties of M50 bearing steel. This work also provides a useful reference for the tribological design of mechanical components by combining surface texture with solid lubrication. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2023-0381/

Role of Carbon Nanotube Wetting Transparency in Rapid Water Transport for a Nanopore Membrane.

A carbon nanotube (CNT) may facilitate near-frictionless water transport within it. In this work, we elucidate the slip flow characteristics for a CNT embedded in a silicon nitride matrix using the molecular dynamics (MD) method. We reveal that the wetting transparency of a CNT, the transmission of the membrane matrix wetting property over a CNT, cannot be ignored. Due to the effect of CNT wetting transparency, the orientation flip behavior of water molecules should be the primary cause of the entrance and exit losses, which is a dominant factor influencing the interfacial friction coefficient for the thin CNT membrane. The relationship between the friction coefficient and pore size follows a logarithmic function, which agrees well with the reported experimental data. Our findings bridge the gap between the MD prediction and experimental observation for water transport in a CNT membrane and provide a clear understanding of the mechanism behind its ultrafast flow performance.

Comparative Study of Air–Water and Air–Oil Frictional Pressure Drops in Horizontal Pipe Flow

Experimental data for frictional pressure drop using both air–water and air–oil mixtures are reported, compared and used to evaluate predictive methods. The data were gathered using the 2-inch (54.8 mm) flow loop of the multiphase flow facility at the National University of Singapore. Experiments were carried out over a wide range of flow conditions of superficial liquid and gas velocities that were varied from 0.05 to 1.5 m/s and 2 to 23 m/s, respectively. Pressure drops were measured using pressure transducers and a differential pressure (DP) cell. A hitherto unreported finding was achieved, as the pressure drop in air–oil flow can be lower than that in air–water flow for the higher range of flow conditions. Using flow visualization to explain this phenomenon, it was found that it is related to the higher liquid holdup that occurs in the case of air–oil around the annular flow transition and the resulting interfacial friction. This additional key finding can have applications in flow assurance to improve the efficiency of oil and gas transportation in pipelines. Models and correlations from the open literature were tested against the present data.

The unique failure behavior of Ni–Mo–Cr-Gd superalloy during hot compression at ultrahigh temperatures

The unique failure behavior of the Ni–Mo–Cr-Gd superalloy deformed at 0.01 s−1 and 0.5 strain with ultra-high temperatures has been investigated. The samples compressed at 0.01 s−1 and 0.5 strain are severely cracked at 1230 °C, and almost completely crushed at 1250 °C. The microstructure observations show that the divorced γ/Ni5Gd eutectic phase transforms into the lamellar γ/Ni5Gd eutectic phase, and the Ni5Gd phase disappears in the center of samples, especially at 1250 °C. Here, the eutectic transformation is attributed to the fact that the Ni5Gd phase melts and solidifies due to the temperature rise of local interface friction between the Ni5Gd phase and the γ matrix. Furthermore, the severe failure of samples and the unexpected disappearance of the Ni5Gd phases were ascribed to the interconnected localized melting regions of the Ni5Gd phase.

Nonlinear Dynamic Analysis for a Jeffcott Rotor Considering Varying Connection Stiffness of Bolted Joint

Bolted joints have been widely used in rotor assemblies of aircraft engines. A typical bolt joint is composed of two metal parts connected mechanically with pre-tensioned bolts. During operations, the bolting pretensions can vary with the changing contacting relationship between the parts, which makes the connection stiffness of the joint nonlinear on the macroscopic scale. The fundamental problems of the dynamical analysis for bolted joints are (1) to identify the transition of the change of the connection stiffness and properly model the overall connection stiffness and (2) to investigate the influence of such variable stiffness on the rotor vibration. In this paper, an analytical model is proposed considering the effect of bolted joints. The bolt of the joint is simplified as a two-node spring-like connection element considering different axial tension and compression stiffness, non-uniform preload of bolts and the contact interface friction described based on Coulomb friction. The dynamic equations of the rotor system are established based on the lumped mass modeling and the proposed connection element, and numerically solved through the Runge–Kutta method. The results indicate that the rotor system exhibits a variety of states, such as period-1 motion, multi-period motion, quasi-periodic motion and chaotic motion. The effects of friction coefficient and preload of the bolts on the nonlinear dynamic behaviors of the bolted rotor system are demonstrated in detail.

Modeling of Concrete Printing Process with Frictional Interface

Modeling of Concrete Printing Process with Frictional Interface