Contact Surface Friction Research Articles

Analysis and optimization of repetitive positioning precision for kinematic couplings of opto-mechanical components considering uncertainty

Kinematic coupling, as an efficient form of connection, is frequently employed for the repeated assembly and accurate positioning of replaceable opto-mechanical assemblies within high-power solid-state laser systems. During the kinematic coupling process, uncertainties in the mechanical behavior within the contact region often hinder the attainment of consistent positioning precision, potentially leading to an inability to meet operational requirements. This study aims to enhance the repetitive positioning precision of kinematic couplings. A predictive model for repetitive positioning precision is established, accounting for uncertainties in contact region forces. Based on this model, an optimization design of kinematic couplings is conducted to mitigate these challenges. Initially, accounting for uncertainties in mechanical parameters within the contact region, we formulate a static analysis computational model to elucidate the probabilistic distribution of these parameters. Subsequently, employing Hertz contact theory and Holm-Archard wear theory, we quantify the elastic deformation and equivalent wear for each contact region through the calculation of normal pressures. Building upon this foundation, we establish a predictive model for repetitive positioning precision. Finally, optimization design is carried out on the friction coefficient of contact surfaces and the structural dimensions of positioning elements. The proposed optimization design is validated through experimental verification. The findings demonstrate that optimization of structural dimensions and contact surface friction coefficients resulted in enhanced repetitive positioning precision of 35.9 %, effectively ameliorating the assembly quality. This study contributes a quantifiable analytical approach to the prediction and optimization design of repetitive positioning precision in kinematic couplings.

Reliability modeling of pre-stressed composite structures subject to interlayer slip failure under multi-axial random impact and vibration loads

A time-dependent reliability model for pre-stressed metal/polymer/metal composite structures subject to interlayer slip failure is developed in this study, allowing for predicting the probability of failure of the whole structure under multi-axial random multi-peak impact loads and transport vibration. A multi-Gaussian envelope model with uniform modulations is proposed to model random multi-peak impact loads, and the inverse sampling method is employed to model random transport vibration. An interlayer slip physics model is developed based on the contact surface friction mechanism under multi-axial vibration load and the stress-relaxation constitutive model. By implementing the interlayer slip physics model in the finite element method framework via the user-material routine, the geometry effect of the structure can be dealt with, and the reliabilities at an arbitrary location of the structure can be obtained. The proposed method is demonstrated using engineering examples. The results show that the proposed reliability assessment method provides a viable and systematical procedure of computing the time-dependent reliability of composite structures as a whole under multi-axial impact loads and vibrations.

Influence of Nanoparticles in Lubricant on Sliding Contact of Atomic Rough Surfaces—A Molecular Dynamics Study

In this work, large-scale molecular dynamics (MD) computational simulations were performed in order to explore the sliding contact responses of rough surfaces with hexadecane lubricant and added nanoparticles. Simulation results revealed that the frictional state was dependent on the fluid, nanoparticle, and surface roughness. Three lubricating conditions were compared based on considerations of different amounts of fluid molecules. The lubricant was not able to separate the frictional contact surfaces if the quantity of lubricant molecules was insufficient. Particularly, there were no lubricating contributions when the amount of lubricant was too low, and the lubricant therefore only filled the pits in the surface roughness. Thus, the normal load was primarily supported by the contact between the two surfaces and nanoparticles, leading to significant surface morphology changes. In contrast, the frictional contact surfaces were able to be completely separated by the lubricant when there was a sufficient amount of fluid, and a very good lubricating effect could thus be achieved, resulting in a smaller friction force. In addition, the changes in surface morphology, contact area, and RMS are discussed in this paper, in order to reveal the dynamic frictional process.

Susceptibility of Poly–Alpha Olefin and Diisooctyl Sebacate Base Oils With Different Polarities to Oleic Acid Surface–Capped Ultra‐Small Cerium Oxide Nanoparticle

ABSTRACTA key issue for nano‐additive to effectively exert tribological function is to ensure its entrance to and adhesion on the frictional contact surfaces. But the adhesion of nano‐additive on the rubbed surfaces under oil lubrication faces the challenge of the competitive adsorption of lubricant base oil thereon. In this study, oleic acid–modified ultra‐small cerium oxide (OA‐CeO2) nanoparticle was synthesised by one‐pot liquid‐phase surface‐modification method in the presence of OA as the surface modifier. The susceptibility of non‐polar poly–alpha olefin 6 (PAO6) and polar diisooctyl sebacate (DIOS) base oils to the as‐prepared OA‐CeO2 nano‐additive was investigated, and the effect of the OA‐CeO2 nano‐additive on the friction‐reducing and anti‐wear abilities of the two kinds of base oils towards a steel–steel sliding contact was investigated with four‐ball friction and wear tester. Furthermore, the tribological mechanism of the adsorption and deposition of the OA‐CeO2 nano‐additive on the surface of friction steel and the competitive adsorption of base oil were discussed. Characterisations by scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy demonstrate that the as‐prepared OA‐CeO2 nanoparticle is of a spherical shape and has an ultra‐small average size of 1.2 nm. As the lubricant additive in PAO6 and DIOS base oils, the OA‐CeO2 nano‐additive exhibits different tribological properties, which is attributed to the difference in the base oils' polarity. Namely, the CeO2 nanoparticle in the non‐polar PAO6 base oil is more easily adsorbed on the rubbed surface of the steel–steel sliding contact, thereby forming the CeO2 deposition film to improve the tribological properties of the base oil. However, the CeO2 nanoparticle added in polar DIOS base oil is difficult to form the CeO2 deposition film, because of the competitive and preferential adsorption of the polar base oil on the rubbed steel surface. Therefore, it is imperative to select the base oils with proper polarity to better exert the friction‐reducing and anti‐wear functions of the OA‐CeO2 nano‐additive.

Synergistic effect of in-situ synthetic GE@Cu particles as additives for enhancement in lubrication performances

Graphene-encased copper particles (GE@Cu) with fluctuating particle sizes ranging from 3 to 15 nm, 80-210 nm, 270-530 nm, and 1.2–3.5 μm are prepared by metal-organic chemical vapor deposition using cupric tartrate and cupric acetylacetonate as precursors.The reaction temperature has been found a significant effect on the decomposition of the organocopper compounds, the coalescence of Cu/C clusters, and the morphology evolution of GE@Cu particles. Thus, the size of copper particles and thickness of the graphene cladding layer (few-layer and multi-layer) can be strictly controlled by modulating the pyrolysis temperatures of the organocopper compounds. The optimized GE@Cu particles with 0.5 wt% mass ratio in lubricants exhibit the reduction of wear track depths and coefficient of friction comparing with the pure lubricants. The corresponding wear rate for the 0.5 wt% few-layer graphene@Cu (FLGE@Cu) and 0.5 wt% multi-layer graphene@Cu (MLGE@Cu) decreases by 60.3 % and 62.5 %, respectively. Additionally, Raman spectroscopy illustrates the formation of a self-lubricating graphene layer on the wearing surface during the friction with GE@Cu as the lubricant additives. The hybridized structure of this nanoadditive introduces synergistic lubrication effects, involving sliding friction (graphene) and rolling friction (copper particles) at the friction contact surface, leading to enhanced lubrication performance. The comprehensive encapsulation of copper particles by GE established the suitability of this lubricant additive for enduring prolonged and intricate environments. In conclusion, GE@Cu lubricant additives hold great promise across the fields of mechanical equipment, bearings, and engines.

Laser manufactured-liquid metal nanodroplets intercalated Mxene as oil-based lubricant additives for reducing friction and wear

Two-dimensional (2D) material MXene is a research hotspot in lubricating materials because of its unique layered structure, which provides weak interlayer interaction and easy shear ability. Herein, the liquid metal nanodroplets intercalated MXene were successfully prepared via pulsed laser treatment and self-assembly method. First, zero-dimensional (0D) nano gallium-based liquid metal (GLM) was synthesized by pulsed laser irradiation of bulk Ga80In20 in acetone. Then, the GLM nanodroplets were loaded onto 2D MXene nanosheets via the effect of electrostatic adsorption to prepare MXene@GLM composite material. The as-obtained GLM not only widens the interlayer distance between MXene nanosheets, making it more susceptible to interlayer shear, but also enhances its lipophilicity. The friction test results showed that the MXene@GLM has the best lubrication performance with 1.0 wt% additive. The coefficient of friction (COF) of base oil PAO-6 can decrease from 0.79 to 0.097, the wear volume is reduced by 90.3 %, and the maximum load sustained reaches 950 N. The good tribological properties are mainly owing to the synergistic lubrication of GLM and MXene, which can form a continuous and firm tribofilm on the friction contact surface and avoid the direct contact of the friction pair.

Redesign of a Disc-on-Disc Computer Numerical Control Tribometer for a Wide-Range and Shudder-Resistant Operation

The paper presents a redesign of the custom disc-on-disc-type tribometer intended for the experimental characterization of the friction and wear of automotive dry clutch friction lining. The redesign is aimed at expanding the operating range at which the machine is not sensitive to shudder vibrations. This is achieved through a set of hardware and software upgrade measures. First, the natural frequency of the normal load-generation linear axis of the machine is increased by enlarging its bending stiffness and reducing the suspended mass. The former is realized by replacing the single, two-axial force/torque piezoelectric sensor with a set of three three-axial piezoelectric force sensors, adding a set of stiff linear guides, and reducing the lengths of the cantilevers of lateral forces acting on the linear axis guide system. The latter is accomplished by reducing the overall dimensions of the cooling disc and redesigning the thermal insulation components. The shudder sensitivity resistance is further reduced through individual normal force-readings-based adjustment of parallelism between friction contact surfaces and the increase in the stiffness of eccentrically positioned water-cooling pipes. Finally, the stability of the coefficient of friction and, consequently, the wear process are boosted by adjusting the control routines to minimize the circumferential and/or radial temperature gradients. These adjustments include the introduction of a clutch lock-up interval at the end of the clutch closing cycle, a minimum cooling delay inserted between two closing cycles, and maximum normal force demand of the clutch torque controller. The performance gain of the upgraded tribometer is demonstrated through a study of the dry clutch friction plate static wear experimental characterization for a wide range of operating conditions.

Influence of contact curvature on frictional energy dissipation under varying tangential loads

This study investigates the effect of contact surface curvatures on the friction response under varying tangential loadings using a finite element (FE) model. The results showed that the geometry of the surface influences the contact force at the interface and reduces the friction effect through an unsteady distribution of the contact force. The relationship between the friction effect, excitation, and contact surface shape was also examined, revealing a linear inverse relationship between the friction and curvature. The findings provide a comprehensive understanding of the frictional interactions between elastic bodies and highlight the role of curvature as a design parameter for regulating the friction effect.

A semi-analytical matrix formalism for stress singularities in anisotropic multi-material corners with frictional boundary and interface conditions

A new general semi-analytic procedure for the characterisation of singular asymptotic elastic states in the vicinity of the apex of linearly elastic anisotropic multi-material corners, including frictional contact, is developed and tested. The corners can consist of any finite number of homogeneous wedges defined by polar sectors. The variability of configurations covered is enormous as frictional contact can be considered on one or more outer boundary surfaces or interfaces, in addition to a large variety of homogeneous boundary conditions and perfect bonding or frictionless sliding interface conditions between wedges in the corner. The Coulomb rate-independent and dry frictional contact law is assumed. One of the novelties is that, in addition to the singularity exponent λ, the angle ω of the friction tangential stress vector on each frictional contact surface is an a priory unknown to be determined by solving a nonlinear corner eigensystem. The procedure, which considers power-law stress singularities, is based on the Stroh formalism of anisotropic elasticity, assuming generalised plane strain (2.5D) conditions, and on the semi-analytic matrix formalism for wedge transfer-matrices and boundary and interface condition matrices. This makes it, firstly, very suitable for computational implementations, secondly, very efficient especially in cases with several perfectly bonded homogeneous wedges, and, thirdly, very accurate due to its fully semi-analytic nature. The code developed is tested by solving a large variety of examples, comparing the present results with those obtained by solving closed-form corner-eigenequations deduced by previous authors for specific useful practical configurations, confirming the extremely high accuracy of the present code in the computation of λ and ω. The differences observed in some cases with anisotropic materials are explained by the fact that some of the previous authors did not take the true 3D Coulomb friction law into account.

Numerical simulation of pressure relief stress distribution of diamond beaded rope saw cutting in low permeability coal seam

The diamond bead slit is a practical method for changing the stress distribution of low permeability coal seam and achieving pressure relief and reflection improvement. The stress distribution of coal seam in large scale is not clear due to the influence of diamond bead slit parameters and geological parameters, making it difficult to identify. In this paper, the finite element model with built-in Coulomb friction contact surface is used to simulate the stress distribution in coal with different angles, seam length, working face length, seam friction coefficient and different in-situ stress difference. This investigation is conducted to examine the stress distribution of parallel working face, vertical coal seam, and advance working face. The simulation results show that the mechanism of stress transfer in large scale diamond beaded rope saw cutting coal seam is mainly due to the tangential slip of coal body on both sides of seam surface, forming concentrative zone and pressure relief zone with axial distribution, center symmetry and phase. The pressure relief range and maximum pressure relief range of all three direction present a "single peak" distribution with the change of angel α between slit and maximum in-situ stress, i.e. when α = 45°, both of them are maximum. The slit length mainly affects the stress distribution in the advancing direction of the working face, and the length of working face mainly affects the stress distribution in the direction of parallel working face and vertical coal seam, both of which are positively correlated with the pressure relief range and the maximum pressure relief amplitude. The friction coefficient of seam surface and the difference of in-situ stress affect the relative dislocation of coal body on both sides of seam surface, and they inhibit and promote the pressure relief range and the maximum pressure relief amplitude respectively, and are greatly affected by α. The simulation results above suggest that it is reasonable to select fracture and geological parameters in practical engineering.

On a hierarchical adaptive and robust inverse dynamic control strategy with experiment for robot manipulators under uncertainties

This paper proposes a hierarchical robot manipulation control scheme for the manipulator pushing task. Considering the contact surface and the object mass parameters are generally unknown to the pushing task, a hierarchical control strategy is designed that enables the robot manipulator to perform the manipulation pushing task without any prior knowledge of the objects mass and friction. Specifically, we first present an adaptive controller to achieve the desired interaction force exerted on the end of the manipulator even without knowing the object mass and friction contact surface. We then introduce a unified robust adaptive controller that takes into account the desired interaction manipulation force in our robot manipulator dynamics. A robust inverse dynamic controller combining a barrier Lyapunov function is included to prevent constraint violation, which can effectively keep the object motion along the desired trajectory while regulating the interaction force between the robot manipulator and the object. Furthermore, an adaptive unit control gain is designed to make the manipulator adapt to follow the perturbation variations without being overestimated. An experiment has been performed to test the effectiveness and to demonstrate the guaranteed performance of the proposed methods.

Numerical Analysis of Fretting Wear Characteristics of Aluminum Cable Steel Reinforced Strands

In view of the concealment of the wind vibration of transmission lines and the technical problems that can easily lead to accidents caused by the wear of wires and fittings, overhead power lines are taken as a research object, and the contact and fretting wear characteristics of the transmission lines are studied. The important parameters such as stress during frictional contact, wear morphology and contact surface pressure during frictional wear are analyzed and appropriate conclusions are drawn from them. Taking the LGJ 150/8 transmission line as an example, through the theoretical analysis and calculation of the steel core-aluminum strand model, and according to the parameters of the power grid program, the contact mechanics model of the overhead line under the wind vibration is created using the three-dimensional modeling software. The change in the contact stress between the steel strand and the conductor layer, the change in the micro-displacement and the relationship between stress and vibration frequency are examined. The fretting properties of adjacent conductor contact points are calculated and analyzed, providing a mechanical basis for analyzing the mechanism of wear of overhead lines.

Effect of Frictional Contact Surface on Maximum Pressing Load during Equal Channel Angular Pressing Process

Effect of Frictional Contact Surface on Maximum Pressing Load during Equal Channel Angular Pressing Process

A novel equal channel angular pressing design to eliminate punch deflection and to reduce the pressing force

AbstractIn the present study a new design of the equal channel angular pressing die and punch is introduced. The new design eliminates the deflection of the punch and at the same time lowers the frictional forces by reducing the contact area. In order to show the capability of the new design, the Al‐7075 alloy samples were processed in two equal channel angular pressing dies. The measured data for the novel and conventional equal channel angular pressing processes were compared. The microstructure of the processed samples was examined with scanning electron microscopy and transmission electron microscopy. The results of the experimental study revealed that the novel die can fully eliminate the risk of the punch deflection and simultaneously reduce the maximum required pressing force by about 3.1 % to 9.8 % for 16 % to 40 % reduction in frictional contact surfaces. The analysis of experimental results showed that there is non‐linear relation between the frictional contact area and the pressing load. In addition, it is shown that despites high contact pressures and high temperatures the use of graphite as a lubricant between sliding surfaces can considerably reduce the pressing load.

Anti-loosening mechanism of pitch difference bolt nut connections based on Junker loosening test

Bolt nut connections are essential elements and widely used in industry. The authors have verified that introducing a slight pitch difference between the bolt and the nut may improve the anti-loosening performance and fatigue life of the bolt nut connections. Besides, the effect of residual torque of pitch difference bolt-nut connections on the loosening resistance performance was discussed. In this study, the Junker loosening test was investigated experimentally and analytically to confirm the anti-loosening performance of pitch difference bolt nut connections directly. The FEA results are in good agreement with the experiments. It is confirmed that, for pitch difference bolt nut connections, the threads contact status is different from the common bolt nut connections, and the torque between the thread contact surface friction is the main reason of anti-loosening performance improvement of the pitch difference bolt nut connections. In addition, the results showed that if the pitch difference is large enough, the nut loosening angle equals the tightening angle for each vibration, and nut loosening does not occur. If the pitch difference is relatively small but just large enough to provide a prevailing torque, with increasing of the vibrations number of the nut, the loosening speed decreases gradually and finally the clamping force remains steady, which means the bolt nut connections retain anti-loosening performance to some extent.

Tribological properties of Ni3Al matrix self-lubricating composites with a gradient composite structure prepared by laser melt deposition

As the contact part of metal-matrix self-lubricating composites during sliding friction, the friction interface layer directly affects the tribological performance of the material. However, the formation of the friction interface layer with outstanding tribological performance is limited by the friction conditions during sliding friction. To address this problem, based on the antifriction and wear resistance mechanisms of the in situ formed friction interface layer of Ni3Al matrix self-lubricating composites (NMSCs) with homogeneous solid lubricant, Ni3Al matrix self-lubricating composites with a gradient composite structure (Ni3Al-GCS) were prepared via laser melt deposition, in which each component layer contained different contents of Sn-Ag-Cu and Ti3SiC2. Dry sliding friction tests of Ni3Al-GCS against GCr15 steel balls were performed under different loading conditions. The results showed that the tribological performances of Ni3Al-GCS in the range of 4–16 N were less affected by the variation of the loading conditions than those of NMSCs. The gradient composite structure of Ni3Al-GCS could reduce the dependence of the tribological behavior on the friction conditions, resulting in excellent antifriction and wear resistance of Ni3Al-GCS in a wide load range. In addition, the gradient composite structure could reduce the sliding contact damage of the friction contact surface of Ni3Al-GCS, and contribute to the formation of friction interface layer rich in the lubrication phase and oxides, thus improving the tribological performance of Ni3Al-GCS during sliding friction. This study provides new approaches for the tribological design of metal-matrix self-lubricating composites in a wide load range.

Carbon brush wear calculation in marine environment based on temperature field analysis

In the marine environment, the working environment of the doubly fed wind generator carbon brush and slip-ring system is complicated, salt spray deposits and seawater erosion affect the temperature field and contact surface friction factor leading to carbon brush wear increase and shortened replacement cycle. The three-dimensional temperature field simulation model of the carbon brush and slip-ring system is established. The main factors affecting the carbon brush and slip-ring system temperature field are sliding velocity, load current, ambient temperature, contact surface condition and contact pressure applied to the brush. Wear capacity of carbon brushes is affected by contact surface temperature. An experimental platform combined with the salt spray test machine was built to carry out the contact current, contact pressure, salt spray concentration and experimental temperature experiment. The improved Coulomb-viscous friction force model was used for the wear prediction model. The sliding velocity, contact pressure, contact current, experimental temperature and salt spray concentration were introduced into the model. The experimental verification has shown that the prediction model can effectively predict the carbon brush wearing capacity under different conditions. This model can be applied to formulating the carbon brush wear amount and replacement cycle in the marine environment reducing operation and maintenance costs.

Microstructure and Wear Behavior of TC4 Laser Cladding Modified via SiC and MoS2

A TC4 composite coating reinforced by SiC ceramic phase and MoS2 self-lubricating phase was prepared on a muzzle brake by laser cladding to improve its wear resistance properties. In this study, we investigated the microstructure and wear behavior of the composite coating. The results show that the composite coating consisted of equiaxed grains with grain sizes ranging from 102.39 to 255.31 μm on the surface and columnar grains on the bottom. The grains with mesh basket microstructure were mainly with α-Ti and β-Ti phases. When wearing against H70 brass, the main wear mechanism of the composite coating at room temperature was adhesive wear, while the wear mechanism was dominated by adhesive wear, oxidation wear, and slight abrasive wear at high temperature. Compared with TC4 coating without SiC and MoS2, the wear rate of the composite coating was reduced by 15%–35% when the temperature was below 400 °C, and the wear rate was reduced by about 55% at 600 °C, resulting from the addition of SiC. Moreover, the friction coefficient of the composite coating was about 10%, which was 30% lower than that of the substrate and TC4 coating when the temperature was below 400 °C and at 600 °C due to the forming of the dense oxide film and the MoS2 friction transfer film on the friction contact surface of the titanium-based composite coating.

Modelling of Off-Road Truck Tire-Rim Slip Using Finite Element Analysis

<div class="section abstract"><div class="htmlview paragraph">Slip or relative rotation between the tire and rim is a significant concern for vehicle operation and wheel manufacturing since it leads to wheel imbalance and vibration as well as power losses. A slip situation typically occurs due to improper bead lubrication and mounting, irregularities in the bead seat, and extreme loading conditions with high torques and low tire pressures. Currently, there are relatively few published studies on the tire-rim interface, and they mainly focus on topics such as the mounting process, load transfer, and friction modelling. This leaves a gap to explore the measurement and variation of gross tire-rim slip under the dynamic conditions of a driven tire. In this paper, a previously developed and validated FEA truck tire model was modified to include a frictional contact surface between the tire and rim, and then the slip ratio between the tire and rim was measured under different operating conditions. The new model’s static behavior was compared to the previously validated model with the fixed tire-rim connection, then the model parameters such as vertical load, inflation pressure, drawbar load, longitudinal wheel speed, and tire-rim friction were varied and their effects on the tire-rim slip of the driven truck tire were investigated. It was discovered that factors affecting the torque transmitted through the wheel, including the tire-rim friction, vertical load, and inflation pressure, had the most significant effect, while the longitudinal wheel speed had a minimal effect on the tire-rim slip. The findings of this research work will be useful for determining the tire-rim slip under various operating conditions.</div></div>

Methods for increasing the wear resistance of heavy loaded metal-polymer tribosystems

Methods of increasing the wear resistance and reliability of friction units are generating considerable interest being a vital factor in transport, mechanical engineering, and other fields of technology. The solution of the given problem is impossible without the creation of self-regulating structures on the friction contact surfaces. We strongly believe that this problem can be solved by creating multicomponent functional layers (hereafter MFL) on tribocontact.