Friction Testing Machine Research Articles

Study on the tribological and rheological properties of magnetorheological fluids based on different base oils

Abstract Base oil has great influence on the tribological and rheological properties of magnetorheological fluid. In this paper, four types of magnetorheological fluid are prepared respectively by silicone oil, mineral oil, synthetic oil (PAO) and castor oil, and their tribological and rheological properties are investigated. Firstly, the viscosity of the magnetorheological fluid is measured by a viscometer. Then the friction coefficient and wear scar diameter of the magnetorheological fluid is measured by a four ball friction testing machine. Next, the sedimentation rate of the magnetorheological fluids is calculated by the observation method. Finally, the shear yield stress of the magnetorheological fluid is measured by a rheometer. By analyzing the experimental data, it is concluded that the magnetorheological fluid prepared by white mineral oil and castor oil has excellent wear resistance. The magnetorheological fluid prepared by castor oil has better sedimentation stability and higher shear yield stress. Consequently, the magnetorheological fluid prepared by castor oil has better comprehensive properties.

Effect of time-varying friction coefficient on self-excited vibration of floating spline-rotor system

Different lubrication states seriously affect the stability and safety of the aviation power transmission system. This study investigates how time-varying friction coefficients impact the stability of an aviation spline-rotor system using a spline-rotor model that considers uneven stress distribution on the tooth surface. Experimental tests with a high-frequency friction and wear test machine yield time-varying friction coefficients for splines with different lubrication, surface roughness, and materials. A sharp change of friction coefficient for the sample occurs under wear debris lubrication. The average friction coefficient for the sample with roughness 1.6 is lower than those with roughness 0.8 and 3.2. Under the same lubrication conditions, the friction coefficient of Resin matrix composites is smaller than that of metallic materials. Dynamic simulation of the spline-rotor model considering time-varying friction coefficients shows rich self-excited vibration behaviors influenced by lubrication, surface roughness, and materials.

Investigation on microstructure and high-temperature wear properties of high-speed laser cladding Inconel 625 alloy

Inconel 625 alloy cladding layer was prepared by high-speed laser cladding (HLC) on Q245R steel substrate to improve the service performance of the structural components in the power industry in this work. A comprehensive study on the HLC Inconel 625 coating with different scanning speeds was conducted utilizing Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Laser Scanning Confocal Microscope (LSCM), X-Ray Diffraction (XRD), a microhardness tester, and an SRV-4 high-temperature friction and wear testing machine. The results show that the cladding layer's thickness and surface roughness decrease with the scanning speed increase. The cladding layers with different scanning speeds contain different microstructures. The phases mainly consist of γ-Ni and NbC. The microhardness of HLC coatings is generally higher than that of substrate, but decreased as the scanning speed increased. After the friction wear test at 500 °C, the cladding layer at the scanning speed of 2 m/min showed the best high-temperature wear resistance. The grain boundary area increases due to the formation of small-sized equiaxed dendrites, which resists dislocation slip and crack propagation, thereby enhancing high-temperature wear resistance. For the cladding layers at the higher scanning speed, the abrasive wear and the fatigue wear occur due to the precipitation of solid soluble elements such as Nb and Mo and the columnar crystal structures prone to deformation.

Repair feasibility and performance enhancement analysis of Fe-based alloy coating on ductile iron surface by high-speed laser cladding

In this paper, high-speed laser cladding technology with a scanning speed of 40 mm/s was used to clad the ductile iron surface with the Fe-based alloy coating. The coatings' microstructure, element distribution, crystallographic structure, wear resistance, and corrosion resistance were investigated by using an optical microscope, SEM, XRD, friction and wear testing machine, super depth-of-field microscope, and electrochemical workstation. The results show that the microstructure of the coating is mainly γ-Fe solid solution and carbide eutectic structure. The phases of the coating are FCC phase (γ-Fe dominated), BCC phase, and carbide. The elemental distribution of the coating cross-section elements is uniform, and no quality obvious defects such as large gas pores and cracks are found. The coating mass loss was 60.0% and 47.1% of the substrate for different friction parameters and the more significant coating oxide build-up phenomenon with increased loading force. The self-corrosion rate of the coating was 0.006 g/m2·h, and the substrate was 0.042 g/m2·h; the maximum impedance value of the coating (1.34×104 Ω·cm2) was increased 20 times based on the substrate (619.2 Ω·cm2). In summary, Fe-based coatings with these process parameters can repair failed ductile iron parts and significantly extend their service life.

Study on Friction and Wear Characteristics of Axial Piston Pump Valve Plate Pairs Modified with Different Surface Energies

To explore the friction and wear performance of the valve pair with different wetting combinations under various working conditions in hydraulic oil lubrication, a low surface energy modification method was adopted in this paper to improve the surface wettability of the upper sample composed of SAF2507 and the lower sample composed of CFRPEEK, and to prepare valve plate pairs with different wetting combinations. The MMU-5G friction and wear testing machine was used to investigate its friction and wear characteristics under hydraulic oil lubrication. The results show that the surface free energy of SAF2507 and CFRPEEK decreased significantly after the treatment with a low surface energy solution, and the surface free energy of the upper and lower samples decreased by 41.9% and 42.2%, respectively. The oil contact angle of samples remained lipophilic, but the oil contact angle increased significantly. Under the working condition of low speed (800 r/min), the surface wettability of the valve plate pair has a great influence on its friction and wear characteristics. When operating at high speed (1200 r/min), the surface wettability of the valve plate pair has little influence on its friction and wear characteristics.

Research on maintenance-free design and low friction characteristics of industrial robot sliding components

With the continuous progress of industrial automation, the application of industrial robots in various fields has become increasingly common, and ensuring their efficient and stable operation and reducing maintenance costs is crucial. This study used powder metallurgy technology, combined with multiple sintering-rolling processes and oil-immersed vacuum assistance, to successfully prepare Fe-Cu-Ni-Sn-graphite oil-immersed self-lubricating composite materials to meet this demand. In-depth microstructure and wear surface studies revealed that this porous oil-immersed self-lubricating composite material exhibits long-term low friction and high wear resistance and reduces the friction coefficient by 40% compared to untreated samples after a specific composite process. In addition, the material exhibits excellent friction performance in the high-temperature pin-on-disc friction and wear test machine. Even after continuous sliding for 24 hours, its friction coefficient remains low and stable. The study also found that its lubrication mechanism may be attributed to solid-liquid synergistic lubrication, thanks to the appearance of oil-graphite mixtures around the wear track. This design ensures high rigidity and reduced frictional loss, providing a strong reference for the design and optimization of sliding components of industrial robots, and is highly suitable for the widespread application of industrial robots.

Effect of Cryogenic Time on Wear Resistance of M2 High Speed Steel

The wear resistance, residual austenite volume and carbon content in martensite of M2 steel were studied by means of universal vertical friction and wear testing machine, X-ray diffractometer (XRD), scanning electron microscope (SEM) and digital Rockwell hardness tester. The results show that a large number of fine carbide particles in M2 steel martensite are precipitated by cryogenic treatment and distributed uniformly and diffusely in the structure. With the increase of cryogenic time, the residual Austenite volume of M2 steel gradually decreases, while the Martensite volume increases, resulting in the wear resistance and Rockwell hardness increasing first and then decreasing. After 24 hours of cryogenic treatment of M2 steel, its wear resistance increased by 310%, hardness increased by 3.6%. Therefore, 24 hours is confirmed as the best cryogenic treatment time for the wear resistance and hardness of M2 steel.

FRICTION AND WEAR PERFORMANCE OF AN ELECTROSPARK-DEPOSITED Ta COATING ON CrNi3MoVA ST

A Ta coating was prepared on a CrNi3MoVA steel substrate by means of electrospark deposition (ESD) and its friction and wear performance was investigated. The nanomechanical properties and friction coefficient were tested by employing a nanoindenter and a friction and wear testing machine, respectively. Moreover, the phase structure was obtained using X-ray diffraction (XRD), and the morphology and composition were analysed before and after friction utilizing scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that the gradient Ta coating with nanocrystals is composed of -Ta and Fe-Ta intermetallics, and Ta2O5 and -Fe phases. The hardness of the Ta coating increased by 115 % compared to that of the CrNi3MoVA steel and its elasticity was reduced by 21 %. The friction coefficient of the Ta coating was reduced by 81 % compared to that of the CrNi3MoVA steel and its weight loss was reduced by 89 %. The wear mechanism of the Ta coating can be characterized as slight adherence, whilst that of the CrNi3MoVA steel includes severe adherence and fatigue.

Effects of methane concentration on tribological properties of diamond films prepared on different ceramic substrates

ABSTARCT Diamond films were prepared on silicon nitride and zirconia ceramic substrates using hot filament chemical vapor deposition (HFCVD). The surface morphology, friction, and wear properties of the diamond films prepared with different methane concentrations (2%, 4%, and 6%) were compared using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and friction and wear testing machines. The results showed that, with an increase in the methane concentration, the diamond particles gradually changed from micro- to nanodiamonds, and the grain size first increased and then decreased. The diamond films on silicon nitride substrates were of excellent quality, with good wear resistance, strong adhesion, and wear rates of 2.857 × 10−8 mm−3•m−1•N−1, 5.151 × 10−8 mm−3•m−1•N−1, and 1.334 × 10−7 mm−3•m−1•N−1, respectively. The diamond films on zirconia substrates had more impurities on the surface, higher internal stress, poorer wear resistance, and weaker adhesion, with wear rates of 3.789 × 10−8 mm−3•m−1•N−1, 5.899 × 10−8 mm−3•m−1•N−1, and 2.074 × 10−7 mm−3•m−1•N−1, respectively. Hence, the deposition of diamond films on ceramic substrates significantly reduced the friction coefficient, and the performance of diamond films on silicon nitride substrates was excellent.

Effect of irradiation modification above melting point on the wear resistance of polytetrafluoroethylene

AbstractThe cross‐linked polytetrafluoroethylene (PTFE) and PTFE/carbon fiber (CF) composites were synthesized through electron beam irradiation in the molten state of PTFE at a controlled temperature of 340 ± 3°C under an inert gas atmosphere for this study. The wear resistance of raw (raw‐PTFE), irradiated modified PTFE (RM‐PTFE), and CF‐reinforced PTFE composites were evaluated using a friction and wear testing machine. The testing was conducted under varying ambient temperatures and dynamic loads. After irradiation, the samples were sectioned into specific sizes for subsequent testing purposes. Under the test conditions of 4.64 MPa positive pressure, 800 rpm speed, and a duration of 300 s at 20°C, the wear amount of PTFE after irradiation modification is significantly reduced from 1.4103 mm to only 0.0233 mm, representing a remarkable reduction by a factor of 60. Similarly, under the test conditions of 4.64 MPa positive pressure, 200 rpm speed, and a duration of 300 s at 20°C, the friction coefficient of PTFE after irradiation modification is substantially decreased from an initial value of 0.13 to just 0.03. The observed improvement can be attributed to the transformation of PTFE's crystalline form into spherulite, accompanied by a significant enhancement in the degree of cross‐linking within its molecular chain. The PTFE was supplemented with 10% CF prior to irradiation. Under the test conditions of a positive pressure of 4.64 MPa, rotation speed of 800 rpm, and a duration time of 300 s at 20°C, the wear amount of the composite material measured only 0.0007 mm, representing a reduction by a factor of 2000 compared to that observed for pure PTFE. This improvement can be attributed to the CF filler's high wear resistance properties and the composite's enhanced thermal conductivity.

Friction-reducing and anti-wear performance of SiO2-Coated TiN nanoparticles in gear oil

This article proposes modification of TiN nanoparticles via the sol-gel method and grafting reaction to prepare TiN@SiO2 nanocomposites (TiN@SiO2-RC), which was added into 85W90 gear oil as lubricant additive. The microstructure and oil dispersion stability of these nanocomposites were analyzed using transmission electron microscopy, potentiometer, infrared spectroscopy, and X-ray diffraction. Additionally, the tribological performance of these oils was evaluated using a four-ball friction and wear test machine. The 2D and 3D morphology, elemental composition, and chemical states of the worn surface on friction pair were comprehensively analyzed using scanning electron microscopy, 3D confocal microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy.Results show that the modified TiN nanoparticles exhibit considerably better dispersivity and stability than original TiN nanoparticles in 85W90 gear lubricating oil. At a mass concentration of 0.4 wt%, the 85W90 gear oil containing TiN@SiO2-RC achieved a substantial reduction of up to 14.6 % in the friction coefficient and a remarkable decrease of up to 23.2 % in the wear scar diameter. Notably, the nano-additives on the friction surface underwent chemical reactions to form reactive films, while the nonreactive nanoparticles mainly contributed to the formation of physical deposition films and acted as rolling bearing, improving the overall friction-reducing and antiwear properties.

Preparation and tribological properties of GO supported MoO3 composite nanomaterials

The MoO3/GO composites were synthesized via a hydrothermal method. The performance of these composites as lubricating oil additives was investigated by a multifunctional friction testing machine. And the lubrication mechanism of MoO3/GO in base oil was discussed based on SEM and EDS test data. The results demonstrate that MoO3/GO composites as additives exhibit excellent anti-friction and anti-wear properties. This is mainly due to the synergistic effect between the lubricating film formed by the composite material on the wear surface and the self-healing ability of nano-MoO3, which can effectively fill and repair wear scars while reducing friction and wear on the steel disc surface.

Numerical Simulation and Wear Resistance Property of Ni-Based Alloy Coating on the Surface of Ti-6Al-4V Substrate

Laser cladding is a new technology to improve the wear resistance or corrosion resistance properties of metal parts. A finite element model of laser cladding coating was established by numerical simulation technology. The temperature field distribution was studied and analyzed during the laser cladding process at three different scanning speeds and three different laser powers. A Ni-based coating was also fabricated on the substrate by a CO2 laser. The optimum parameters of the laser cladding were selected and compared with the melt pool depth and width of the Ni-based coating. Then, the cooling rate, temperature gradient, temperature and stress fields were calculated and analyzed. The growth mechanism of the crystal structure was analyzed by scanning electron microscope (SEM). The wear resistance of the Ni-based coating was measured by a friction and wear testing machine. The results showed that the optimal parameters were laser power 1600 W and scanning speed 3 mm/s. The temperature trends at different locations were similar. The calculated maximum residual stress was 0.157 GPa. The stress concentration appeared near the surface and both sides of the cladding layer. From the coating’s microstructure, it could be seen that it contained a large number of columnar dendrites, and the crystal size gradually decreased with the increase of cooling rate. The wear rates of the Ti-6Al-4V (TC4) substrate and the Ni-based coating were 6.98 mm3/(N·m) and 3.45 mm3/(N·m), respectively. The Ni-based layer had a low wear rate and good wear resistance, which is helpful to obtain good friction and wear resistance of TC4 substrates.

Optimization of current-carrying friction and wear properties of copper-carbon composite materials based on damage

This study investigated the friction and wear properties and current-carrying properties of copper-graphite composites paired with brass C28000 on a self-made current-carrying friction test machine. The results indicate that the current-carrying properties of the copper-graphite gradient composite materials are excellent, the core factor limiting its service properties is its wear rate. With the increase in the thickness of the Cu-5 wt% graphite layer, the unevenness of the damage improves. The composite material with a Cu-5 wt% graphite layer thickness of 8/5 mm exhibits friction and current-carrying properties close to that of the composite material with a Cu-5 wt% graphite layer thickness of 4 mm. It has a higher electrical conductivity by approximately 20 % and a higher hardness.

Development of multifunctional current-carrying friction and wear test machine based on LabVIEW

In order to study the effect of friction wear behavior on electrical signal transmission, a carrier friction wear test machine was developed which can be analyzed under different test conditions (load, speed and current). The testing machine builds a measurement and control system through LabVIEW platform to realize real-time acquisition and synchronous display of electrical signals, friction coefficient and temperature, and control of load size, and uses wavelet decomposition and arithmetic average to process data and PID control algorithm to revise load in real time. The experimental results show that the stability of the test machine and the accuracy of control system meet the test requirements.

Study on the Sliding Tribological Behavior of Oleic Acid-Modified MoS2 under Boundary Lubrication.

The effects of MoS2 and MoS2 modified by adding oleic acid (OA) on the friction properties of lithium-based grease under boundary lubrication conditions are studied by molecular dynamics (MD) simulation and experiment. A rough wall boundary lubrication MD model with peaks and grooves is established to simulate the mechanical properties and lubrication effects of three lubrication systems on rough walls for the relative shear velocity between the two solid walls of 5 m/s at 500 MPa. The stress, wear amount, friction force, normal pressure, and friction heat of the friction surface are quantitively calculated. Simultaneously, a Retc friction and wear testing machine is used to measure the friction coefficient under different concentrations of additives and different pressures. The results show that the grease added with MoS2 can reduce friction, wear, and the temperature between friction pairs. However, under high pressure and shear, MoS2 can easily agglomerate and accumulate in the pits, reducing the lubricating effect. At the same time, since OA-modified MoS2 can reduce agglomeration, the modified MoS2 is adsorbed on the metal wall surface, forming a stable lubricant film. The main contributions of this article can be found in combining MD simulation and experimentation, establishing the connection between micronano structures and macroscopic properties, exploring the mechanism of the influence of wall roughness and particle size on the friction performance of lubricating oil, and providing a theory for predicting and developing high-performance new lubricating grease.

Analysis of key brake pad parameters on brake system stability

PurposeThis study aims to explore the impact of key parameters of brake pads on the dynamic characteristics of the braking system.Design/methodology/approachThis study conducted experimental research based on a friction testing machine with a slider-disc structure. The experiment studied the impact of key parameters of brake pads (rotation speed, pressure, mass, braking radius, etc.) and the braking environment (dry friction, wetness, sand, etc.) on the stability of the braking system. At the same time, a dynamic model of the brake pad braking system was established and compared with experimental results using the mathematical tool of autocorrelation coefficient.FindingsThe key parameters of brake pads have a significant impact on the dynamic characteristics of the braking system; under different conditions of brake pad mass, tribological parameters, brake pad radius and braking environment, the chaotic characteristics of the braking friction force signal show a trend of expansion or contraction, which can be suppressed by adjusting the key parameters of brake pads.Originality/valueThis study can provide a reference for optimizing the braking strategy and reducing noise and vibration in brake pad systems.

Influence of Braking Speed on the Friction and Wear Characteristics of High-Speed Railway Braking Materials under High Ambient Humidity Conditions.

The friction and wear tests of high-speed railway braking materials for a variety of braking speeds (600, 400, and 200 rad/min) at 65% and 98% RH RH (RH: relative humidity) were carried out utilizing a friction-testing machine and humidity generator. The research results indicate that braking speeds and ambient humidity have a prominent influence on the friction and wear characteristics of high-speed railway braking materials. At 65% and 98% RH, the lower the braking speed, the lower the wear rate, and the better the wear resistance property of the braking material. Furthermore, at 600 rad/min, the wear rate of the braking material at 98% RH was smaller than that at 65% RH. However, at 200 rad/min, the wear rate of the braking material at 98% RH was greater compared to that at 65% RH. Concretely, at 600 rad/min, compared with 65% RH, the wear rate to the brake disc at 98% RH was reduced by about 9%, and the brake pin decreased by about 6%. However, at 200 rad/min, compared to 65% RH, the wear rate to the brake disc at 98% RH increased by about 39%, and the brake pin increased by about 37%.

Mechanisms of friction and wear reduction by nanosilver additives to base oil: Molecular dynamics simulation and experimental study

Although nanosilver particles are commonly used as oil lubrication additives, their mechanism for improving lubrication at the atomic scale remains unclear. This article explains how the performance of a pentaerythritol oleate lubrication system can be improved using silver nanoparticles through molecular dynamics simulation. Additionally, tribological tests were conducted using a reciprocating friction and wear testing machine. The relative concentrations and simulated shear conformation revealed that silver nanoparticles underwent deformation under shear stress and fractured at the interlayer slip. This resulted in the formation of a deposited film that spread over both the top and bottom Fe layers. We characterized the interaction between pentaerythritol oleate molecular chains and Fe layers by analyzing interfacial interaction energies, mean square displacements, and self-diffusion coefficients. Our findings indicate that the presence of silver nanoparticles improves both the adsorption of pentaerythritol oleate molecular chains onto the Fe layer and their diffusion behavior. The results of tribological tests indicate that adding silver nanoparticles significantly reduces friction coefficient and frictional wear across various lubrication conditions. The addition of silver nanoparticles at different loads and temperatures resulted in varying reductions in the coefficient of friction and wear. At a load of 20 N and a temperature of 298 K, the coefficient of friction decreased by 9%, and wear decreased by 31%. When the load was reduced to 2 N while maintaining a temperature of 298 K, the coefficient of friction decreased by 8% and wear decreased significantly by 84%. Finally, at a load of 20 N but with an increased temperature to 373 K, there was a larger reduction in the coefficient of friction (23%) compared to wear (50%). The film-formation mechanism of improved lubrication by silver nanoparticles was verified through tribological tests and simulations.

Effect of Cu Addition on Properties of an Al-La Alloy

The effect of copper content on the microstructure and properties of an aluminum copper alloy containing lanthanum was studied by adding 0.5 wt% lanthanum and different contents of copper to the 2A12 alloy. We used a universal testing machine, Brinell hardness tester, and friction and wear testing machine to test the mechanical properties of the alloy. The microstructure and phase composition of the alloy were analyzed using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The results show that, after adding La and Cu, the alloy grain is refined, and the fracture mode changes from dissociation fracture to quasi dissociation fracture. A new phase containing La accumulates at the grain boundary. If the amount of Cu added is too large, the tendency for hot cracking increases, which can easily lead to the formation of voids or even cracks. The tensile strength and hardness of the cast alloy significantly increase with the increase in Cu addition. In the range of adding 2 wt% to 5 wt% Cu, the tensile strength and hardness of the cast alloy increases by approximately 12% and 17.84%, respectively, compared with the original alloy. With the increase in Cu addition, the elongation of the alloy first increases and then decreases, reaching its maximum value when Cu addition is 3 wt%. Adding Cu is beneficial for improving the wear resistance of the alloy. When the addition of Cu is 3 wt%, the alloy has the best wear resistance and minimum wear amount. This is due to the enrichment of La and Cu at the grain boundaries, forming new La phases or other phases with higher hardness, which changes the properties of the alloy. It shows that the content of Cu in the 2A12 alloy can be increased to 7-8% with the increasing of additional rare-earth elements, and a new Al-Cu (7 wt% to 8 wt%)-Mg (1.2 wt% to 1.8 wt%)-Mn (0.3 wt% to 0.9 wt%)-La (0.5 wt%) alloy, in which tensile strength, hardness, and elongation of the alloy are increased by 8.1%, 16%, and 79.1%, respectively, can be formed. In addition, the wear resistance of Al-La alloys also improves significantly with the addition of copper content. The coefficient of friction is reduced by 68% compared with no copper addition.