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  • The Lubricating Properties of Spark Plasma Sintered (SPS) Ti3SiC2 MAX Phase Compound and Composite
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-14
    Carl Magnus; Joanne Sharp; William M. Rainforth

    MAX phase composites Ti3SiC2–TiCx and Ti3SiC2–(TiCx + TiC) were synthesized and consolidated via a powder metallurgy spark plasma sintering (SPS) technique. The bulk compositions and microstructural evolution of the resulting SPS discs were analyzed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM) paired with an energy-dispersive spectroscopy (EDS) system. The tribological behavior of the synthesized discs was investigated at room temperature under dry sliding conditions using an Al2O3 ball by employing a ball-on-disc tribometer configuration. Postmortem analyses of the worn surfaces showed that the Ti3SiC2 MAX phase exhibited intrinsic self-lubricating behavior due to the evolution of easily sheared graphitic carbon at the sliding surface. The addition of stoichiometric TiC delayed the oxidation kinetics of Ti3SiC2, which favors the evolution of graphitic carbon in lieu of rutile and oxycarbide films. Thus, this work shows comprehensively the existence of an intrinsic self-lubricating behavior of Ti3SiC2 and the important role of secondary-phase TiC in the Ti3SiC2 matrix in its tribological behavior. The wear mechanisms in both composites are dominated by tribo-oxidation triggered by frictional heating. This is then followed by deformation-induced wear upon friction transition.

    更新日期:2020-02-18
  • Effect of Expanded Graphite on the Tribological Behavior of Tin–Bronze Fiber Brushes Sliding against Brass
    Tribol. Trans. (IF 1.759) Pub Date : 2019-11-05
    Bo Luo; Chengshan Liu; Xinli Liu; Lei Zhang

    Fiber brushes with expanded graphite (EG) as a lubricant were successfully prepared. Compression properties of brushes filled with unbent fibers and bent fibers with different packing fractions were compared. Moreover, the friction and wear behaviors of the brushes with the same fiber packing fractions (17.5 vol%) but different EG volume contents were investigated. The effect of EG content on the tribological behavior of the fiber brush was analyzed according to the microstructure, debris, and worn surface of the brush and counterface disc. Results showed that both the elastic constant and compression strength of the brushes filled with bent fibers increased with an increase in packing fraction. Brushes filled with 17.5 vol% bent fibers had similar compression strength (2.69 MPa) but a lower elastic constant (150 N/mm) compared to the brush filled with 17.5 vol% unbent fibers (2.62 MPa and 425 N/mm). The friction coefficients and wear rates of the brushes decreased from 1.02 and 1.6 × 10−5 mm3/Nm to 0.25 and 0.28 × 10−5 mm3/Nm as the EG increased to a critical value (23.7 vol%). The worn surface and wear debris demonstrate that the wear mechanism of tin–bronze fiber brushes with EG sliding against brass discs transforms from adhesive wear to abrasive wear due to the formation of an EG lubricating film.

    更新日期:2020-02-03
  • The Contribution of Topography Formed by Fine Particle Peening Process in Reducing Friction Coefficient of Gear Steel
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-12
    Wei Li; Liantao Lu; Dongfang Zeng

    Fine particle peening (FPP) is a peening process using fine shots with an average diameter of less than 200 µm. Pairs of twin-disc specimens made of carburized and quenched 18CrNiMo7-6 gear steel were subjected to two different FPP processes and conventional shot peening (CSP) using big shots with an average diameter of 600 µm. Rolling–sliding tribology tests were carried out under oil lubrication, and comparisons of the friction coefficient were made between untreated, FPP-treated, and CSP-treated twin-disc specimens. To characterize the relationship between surface topography and friction coefficient, 3D surface parameters, including root mean square roughness (Sq), skewness (Ssk), kurtosis (Sku), core roughness depth (Sk), reduced peak height (Spk), and reduced valley depth (Svk) were measured before and after tribology tests. A linear regression method was applied to analyze the correlations between the surface parameters and the friction coefficient. It was found that FPP is effective in decreasing the friction coefficient during the lubricated rolling–sliding contact compared to untreated specimens. The friction coefficient has a higher correlation with Ssk and the ratio RSvk, which is defined as the ratio of Svk to the sum of Sk, Spk, and Svk. A lower friction coefficient was obtained when the topography had a more negative Ssk and a higher RSvk in the rolling–sliding condition. However, there was a weak linear correlation between the friction coefficient and surface parameters Sq, Sku, Sk, Spk, and Svk, and the relationship between the trend of friction coefficient and those surface parameters is not obvious.

    更新日期:2020-02-03
  • Concentrated Polymer Brush as Reciprocating Seal Material for Low Leakage and Low Friction
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-29
    Chiharu Tadokoro; Kosuke Sato; Takuo Nagamine; Ken Nakano; Shinya Sasaki; Takaya Sato; Keita Sakakibara; Yoshinobu Tsujii

    Abstract Recently, concentrated polymer brushes (CPBs) have attracted much attention as potential tribomaterials showing an ultralow friction coefficient (e.g., 10−4 in a microtribological analysis). In this study, a homemade apparatus modeling reciprocating seals was developed, which consisted of an inner steel rod and an outer steel ring with a narrow clearance less than several tens of micrometers. A few-micrometer-thick CPB film of poly(methyl methacrylate) well-swollen with an ionic liquid was prepared on each steel surface, and the impact of applying the CPB film to the clearance of reciprocating seals was examined by measuring the leakage rate of a fluid and the friction coefficient in reciprocating motion. The results showed that the CPB film narrowed the clearance between the two steel surfaces, which improved its sealing performance. In addition, the CPB film yielded a quite low friction coefficient (e.g., 10−3), which assured its smooth motion with small energy loss.

    更新日期:2020-02-03
  • Tilt Angle of Hydrostatic Spindle Influenced by Microscale Effects
    Tribol. Trans. (IF 1.759) Pub Date : 2019-09-11
    Dongju Chen; Xue Gao; Chunqing Zha; Ri Pan; Jinwei Fan

    Machining error in machining processes arises due to several factors. The tilt angle of the spindle of the machine tool is one of the important factors that directly affect the shape error, surface quality, and roughness of the machined part. In order to better analyze the effect of microscale effects on the tilt angle of a hydrostatic spindle, a fluid control model at the microscale is introduced into the traditional Reynolds equation. The static performance characteristics of hydrostatic bearings with four and eight pads under the influence of velocity slip are obtained. The results show that the existence of velocity slip improves the stiffness of the bearing. However, the influence of velocity slip on the tilt angle is obvious, and the tilt angle decreases as the increase of velocity slip. The experimental results verify the existence of velocity slip at the microscale indirectly and provide a theoretical basis for the study of the performance of liquid hydrostatic bearings at the microscale.

    更新日期:2020-02-03
  • The Thermal Unbalance Effect Induced by a Journal Bearing in Rigid and Flexible Rotors: Experimental Analysis
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-14
    Thibaud Plantegenet; Mihai Arghir; Mohamed-Amine Hassini; Pascal Jolly

    The present work presents the experimental analyses of a rigid (short) and a flexible (long) rotor subject to thermal unbalance effects. The rotors are supported by a ball bearing and by a cylindrical journal bearing. The differential heating generated in the journal bearing is responsible for the thermal unbalance. The results obtained with the short rotor at 7 krpm showed an increase in the synchronous amplitudes but slight phase changes before stabilization. The pronounced hysteresis of the synchronous amplitudes obtained during coast-down proved that the amplitude increase is due to the thermal unbalance. The results obtained for the long rotor at 6.6 krpm showed the same stabilized response when start-up was performed in 180 s. However, an instability leading to journal bearing contact was triggered when the start-up time was decreased to 80 s. The presented experimental results are the synchronous amplitudes and phases, the mean temperatures, and the maximum temperature differences of the journal and of the bearing and the phase lags between the high spot and the hot spot.

    更新日期:2020-02-03
  • Stability, Thermal Conductivity, Viscosity, and Tribological Characterization of Zirconia Nanofluids as a Function of Nanoparticle Concentration
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-14
    Steven J. Thrush; Allen S. Comfort; James S. Dusenbury; Yuzan Xiong; Hongwei Qu; Xue Han; J. David Schall; Gary C. Barber; Xia Wang

    Commercially prepared spherical zirconia (ZrO2) nanoparticles with an average particle diameter of 5 nm and functionalized with a hydrocarbon ligand were dispersed in a polyalphaolefin (PAO) base oil, producing a 10-nm stabilized zirconia nanofluid. The resulting nanofluid’s properties were characterized, including thermal conductivity and viscosity. A preliminary study of the nanofluid’s ability to generate protective tribofilms was conducted. Long-term stability was verified using dynamic light scattering (DLS) and average particle size was quantified as a function of time. A 10 wt% ZrO2 nanofluid maintained a 10-nm average particle size over 25 months, with no signs of agglomeration or sedimentation, and redispersion was not necessary before analysis. The tribological performance of several concentrations of ZrO2 nanofluids wasdisc characterized with a ball-on-disc tribometer. Tribofilm growth over time was collected via optical interference imaging. Friction data collected over time are also reported. Nanoparticle concentration was varied to understand its effect on tribofilm growth. The ZrO2 tribofilm morphology and chemistry were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM).

    更新日期:2020-02-03
  • Studies of Friction in Grease-Lubricated Rolling Bearings Using Ball-on-Disc and Full Bearing Tests
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-25
    Yuta Kanazawa; Nicola De Laurentis; Amir Kadiric

    Abstract This article evaluates the frictional performance of different bearing grease formulations in full rolling bearings and a ball-on-disc rig and subsequently assesses whether the ball-on-disc test results can be used to predict the grease performance in actual bearings. A selection of custom-made greases with systematically varied formulations as well as their base oils were tested. Bearing torque was measured in two different cylindrical roller thrust bearings and a thrust ball bearing. The same lubricants were tested with ball-on-disc tribometers, a mini traction machine (MTM) to measure friction and an optical elastohydrodynamic (EHD) rig to measure film thickness. Both lithium complex and diurea greases were observed to produce lower friction than their base oils within the low speed, low nominal lambda ratio region, whereas the greases and oils had the same friction at high nominal lambda ratio values. These relative trends were the same in full bearing and single-contact MTM tests. The reduction in friction was seen to be related to the level of film thickness enhancement provided by greases at lower speeds, which leads to an increase in the effective lambda ratio and hence reduced friction. By extracting the sliding torque component from the overall measured bearing torque, a plot of the friction coefficient against the effective lambda ratio was produced encompassing all bearing and single-contact tests and all lubricants and test conditions. This plot was seen to follow a general shape of a master Stribeck curve, indicating that the numerical values of the friction coefficient from ball-on-disc and full bearing tests overlap and can be related to each other using this approach over the range of conditions employed here. Thus, single-contact ball-on-disc tests can provide a fast and economical way of establishing the frictional performance of bearing greases in full bearings in terms of both relative performance rankings and quantitative values of bearing frictional power losses.

    更新日期:2020-02-03
  • Effect of CuO and ZnO Nano-Additives on the Tribological Performance of Paraffin Oil–Based Lithium Grease
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-14
    Sooraj Singh Rawat; A. P. Harsha; Santanu Das; Agarwal Pratik Deepak

    The present study investigates the effect on the tribological behavior of paraffin grease incorporated with ZnO and CuO nanoparticles. ZnO nanoparticles of ∼32 nm were synthesized with a precipitation method. X-ray diffraction (XRD), Fourier transform infrared (FTIR), high-resolution scanning electron microscopy (HR-SEM), and energy-dispersive spectroscopy (EDS) were used to characterize the nanoparticles. The grease was formulated with lithium soap (lithium salt of 12-hydroxy stearate) and paraffin oil. The CuO and ZnO nano-additives were blended separately in the paraffin grease in the range between 0.2 to 1.0% w/w. The extreme pressure and antiwear behavior of the CuO and ZnO nano-additive-doped greases were evaluated as per ASTM D2596 and D 2266 respectively using a four-ball tester. Various physical properties of grease samples—for example, drop point, consistency, evaporation loss, water washout, and leakage tendency—were also examined as per ASTM D566, D1403, D1263, D1264, and D972, respectively. The antiwear test results showed that the maximum reduction in mean wear volume (MWV) was obtained (∼36 and ∼56%) with the incorporation of 0.2% w/w of CuO and ZnO nano-additives in the paraffin grease, respectively. At the same concentration, ∼31 and ∼28% decreases in energy consumption were also achieved by the dispersion of ZnO and CuO nano-additives in the paraffin grease. The worn surfaces of the test balls were studied with various analytical tools to determine the wear mechanisms.

    更新日期:2020-02-03
  • Nonlinear Dynamic Characteristics of Rub-Impact Process at High Circumferential Velocities in No-Load Multiplate Wet Clutch
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-23
    Lin Zhang; Chao Wei; Jibin Hu; Qi Hu

    Drag torque is common in wet clutches, and the mechanism of drag torque at high circumferential velocities is not yet well understood. In this article, fluid action, rub-impact action, and rotary moments, as well as the coupling motion relationship between the friction plate and steel plate in 3 degrees of freedom, are taken into consideration to establish the fluid–solid coupling dynamic model of the friction pairs. In addition, a theoretical model of the rub-impact drag torque in a multiplate wet clutch is proposed based on the dynamic contact impact theory. Due to the significant influence of the dynamic behaviors of the friction pairs on drag torque, the nonlinear motion characteristics of the friction pairs are analyzed. From an energy balance point of view, the impact mechanism of the friction pairs is revealed. Through this research, it can be found that the motion of the friction pairs becomes unstable and chaotic with an increase in rotating speed, and at approximately 2,300 rpm contact between the friction pairs occurs because a large amount of air enters and the fluid does positive work on the friction pairs.

    更新日期:2020-02-03
  • A 3D Approach for THD Lubrication in Tilting Pad Journal Bearing—Theory and Experiment
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-14
    L. Bizarre; T. B. Andersen; G. B. Daniel; I. F. Santos; K. L. Cavalca

    The study of rotating machines stands out in the context of systems and structures due to the significant number of typical phenomena that may be present during the operation of such equipment. Rotating systems play an important role in industrial environments, with a wide range of application, namely, pumps, turbines, generators and compressors, and turbochargers, among others. Given this context, tilting pad journal bearings (TPJBs) can offer considerable stability to the rotor system due to its damping and stiffness characteristics, especially under high rotation speeds, whereas journal bearings with a fixed geometry may be subjected to fluid-induced instability. Consequently, thermal effects are significant in rotating machines to evaluate the behavior of hydrodynamic bearings due to the increase in shear effects in the lubricant caused by the rotation speed, leading to excessive temperature increase under specific operational conditions and, therefore, significant changes in lubricant viscosity. These effects may influence the dynamic characteristics of bearings, affecting the dynamic response of the entire system. From this perspective, a specific test rig was designed to perform the characteristic uncoupled motion of the shaft when supported by this kind of bearing. Experimental tests were directly compared with numerical models, showing promising results. In addition, the thermohydrodynamic (THD) lubrication was numerically solved by a finite volume method, considering an approach for a 3D THD model and the pivot flexibility.

    更新日期:2020-02-03
  • Effect of Gradient Nanostructure on Plasma Sulfonitrocarburizing of 42MnCr52 Steel
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-14
    X. H. Zhao; Y. Q. Zhao; D. S. Xu; C. H. Hu

    A nanocrystalline layer was fabricated on the surface of 42MnCr52 steel by ultrasonic surface rolling processing (USRP). Plasma sulfonitrocarburizing (PSNC) was performed on the untreated surface and nanostructure surface to obtain a composite layer composed of the solid lubrication layer (FeS) and nitrocarburized subsurface layer. The effect of the nanocrystalline layer on PSNC was investigated using phase analysis, microstructural analysis, element analysis, hardness analysis, and wear property analysis. The results are as follows: The average grain size of the gradient nanostructure surface was about 40 nm. A more compact and homogeneous sulfide composite layer was formed on the surface of the USRP + PSNC specimen, and the sulfide composite layer was mainly composed of an FeS phase with excellent solid lubrication properties. The thickness of the nitrocarburized layer was increased by 130% on average and its homogeneity also improved after USRP. The hardness value of the subsurface (nitrocarburized layer) of the USRP + PSNC specimen was higher than that of the PSNC specimen. The wear volume and frictional coefficient of the USRP + PSNC specimen were obviously lower than those of the PSNC specimen. The USRP + PSNC specimen exhibited strong wear resistance.

    更新日期:2020-02-03
  • Effect of LaCl3 Surface-Modified Carbon Nanotubes on Tribological Properties and Thermal Stability of Carbon Nanotube–Reinforced Epoxy Resin Composites
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-22
    M. R. Jiang; Ying Xu; X. H. Cheng

    In this article, rare earth (RE)-modified carbon nanotubes (CNTs) were obtained by surface modification of multiwalled carbon nanotubes (MWCNTs) with rare earth LaCl3, and composite materials were prepared by using epoxy (EP) resin as the matrix. The modified CNTs were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The tribological properties and thermal stability of the composites were tested using a multifunctional tribological tester and TGA. The surface wear morphology of the composite and the dispersion of the CNTs in the composite were characterized by scanning electron microscopy. Studies have shown that RE-modified CNTs can indirectly improve the initial decomposition temperature of the composites, which is beneficial to the thermal properties of the composites. Moreover, the modified CNTs can obviously improve the tribological properties of the composites, in particular, they can reduce the wear rate (WR). Compared to pure EP, the coefficient of friction (COF) and WR of the composites were reduced by over 19 and 90%, respectively.

    更新日期:2020-02-03
  • Theoretical and Experimental Study of Transient Behavior of Spiral-Groove Thrust Bearings during Start-Up
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-25
    Yang Hu; Yonggang Meng

    In this study, a transient mixed lubrication model that considers mass-conserving cavitation and deterministic asperity contacts is established to study the evolution of the tribological behavior of spiral-groove thrust bearings during start-up. To overcome oil film thickness discontinuity at the edges and the complicated boundary shape of spiral grooves, a boundary-fitted coordinate system transformation is adopted. The evolution of the tribological behavior, including the asperity contact force, load-carrying capacity, minimum oil film thickness, and friction torque during start-up, is presented using the current model. To illustrate more clearly, the evolution of hydrodynamic pressure and cavitation fraction is also displayed. Experiments are performed to verify the proposed theoretical model. The results demonstrate that this model is able to capture the evolution of the tribological behavior of spiral-groove thrust bearings during start-up. To improve start-up performance, a parametric analysis is conducted to identify the effects of the main design parameters (groove depth, groove width ratio, and spiral angle) on the lift-off speed.

    更新日期:2020-02-03
  • State Evolution of Dry Gas Seal during Repeated Start–Stop Operation Using Acoustic Emission Method
    Tribol. Trans. (IF 1.759) Pub Date : 2019-11-19
    Wenjing Fan; Weifeng Huang; Ying Liu; Yuan Yin; Xiangfeng Liu; Yuming Wang

    Seal failure is a common phenomenon that occurs when using a dry gas seal. Many seal failures occur during the start-up process of the seal. In this study, the state evolution of a dry gas seal during repeated start–stop operations was investigated using an acoustic emission (AE) method and a modified empirical mode decomposition using masking signals (MS-EMD). It was evident that the liftoff speed and root mean square (RMS) of the full-speed period changed in stages. According to the change in these parameters, the state evolution of the dry gas seal during the experiment occurred in four stages: the running-in stage, normal working stage, transition stage, and abnormal stage. During the normal working stage, the RMS curve of the late liftoff period oscillated, but its wave trough was flattened due to misalignment of the seal face. After entering the transition stage, the period flattened at the wave trough disappeared and was replaced by a period of slow decline, which is attributed to the existence of abrasive particles between the seal faces. The unsteady accumulation of abrasive particles caused the liftoff speed to fluctuate significantly. By monitoring the liftoff speed of the seal and the RMS of the full-speed period, seal operators may assess the state of the seal and take intervention measures. This has great engineering value for the safe operation and life management of the seal.

    更新日期:2020-02-03
  • Numerical Modeling of Churning Power Loss of Gear System Based on Moving Particle Method
    Tribol. Trans. (IF 1.759) Pub Date : 2019-11-19
    Dong Guo; Fangchao Chen; Jiao Liu; Yawen Wang; Xi Wang

    Churning power losses are an important portion of transmission load-independent power losses, especially in high-speed condition and dip-lubricated gearboxes with high immersion depth. Generally, it is difficult to calculate the churning power losses due to the parameters of stirring oil and many other operating conditions. In this article, a method is proposed to determine the factors that influence churning power losses in gearboxes. Firstly, based on the moving particle semi-implicit (MPS) method, a numerical model of single-stage gears stirring oil is established. Then the accuracy of the established model is validated experimentally. Finally, the orthogonal simulation analysis is carried out to analyze the influence of gear rotation speed, tooth width, helix angle, immersion depth, and oil temperature on the churning power losses.

    更新日期:2020-02-03
  • Correction
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-16

    (2020). Correction. Tribology Transactions: Vol. 63, No. 1, pp. 194-195.

    更新日期:2020-02-03
  • Enhancing Film Stiffness of Spiral Groove Dry Gas Seal via Shape Modification at Low Speed: Numerical Results and Experiment
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-09
    Jinbo Jiang; Xudong Peng; Cong Zong; Wenjing Zhao; Yuan Chen; Jiyun Li

    The film stiffness of dry gas seal must be sufficient to keep gas film stable at high and low speed. A generalized geometric model based on triangles is proposed to characterize spiral grooves. A mathematical model is established and solved using the finite-difference method to obtain steady performance. The optimum spiral grooves for maximum opening force and film stiffness are obtained at low speed, and their steady performance is compared with conventional spiral grooves numerically and experimentally. The pressure and flow field of optimum spiral grooves and conventional spiral grooves are simulated to reveal the mechanism of the performance difference. Results show that through-combined spiral grooves outperform the other derived spiral grooves. Their film stiffness is up to 15% larger than that of conventional spiral grooves at low speed.

    更新日期:2020-01-04
  • Synthesis and investigation of halogen-free phosphonium-based ionic liquids for lubrication applications
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-21
    Lili Zhu; Jun Dong; Ying Ma; Yulong Jia; Cheng Peng; Weimin Li; Ming Zhang; Kuiliang Gong; Xiaobo Wang

    In the present work, three kinds of halogen-free ionic liquids (ILs) incorporating long-chain quaternary phosphonium as cations and dioctylsulfosuccinate (DOSS) as the anion were synthesized and characterized and the tribological properties of phosphonium ionic liquids were investigated as neat lubricants for steel ball–steel disc friction pairs at room temperature (RT) and elevated temperature (100 °C). The ILs were found to be noncorrosive and highly thermally stable and showed better antiwear and friction reduction performance than commercially available synthetic lube base oil poly-α-olefin (PAO10) and conventionally used IL 1-methyl-3-hexylimidazolium hexafluorophosphate (L-P106). Scanning electron microscopy (SEM) and energy-dispersive spectroscopic (EDS) analysis of the worn-out surfaces of the steel discs was performed and the results revealed that physical adsorption and tribochemical reactions occurred and formed a protective boundary film on the worn steel surface to prevent direct steel–steel contact between rubbing surfaces.

    更新日期:2020-01-04
  • Friction and Wear Behavior of 1-Octyl-3-methylimidazolium Lactate Ionic Liquid as Lubricant in Steel–Steel Contacts
    Tribol. Trans. (IF 1.759) Pub Date : 2019-07-18
    Changchao Sheng; Hui Chen; Jingjie Zhang; Zhaoqiang Chen; Mingdong Yi; Guangchun Xiao; Chonghai Xu

    The friction and wear behavior of 1-octyl-3-methylimidazolium lactate ionic liquid (L-L108) between steel surfaces was investigated in ball-on-disc sliding friction tests. At an applied load of 5 N and rotating speed of 200 rpm, the friction coefficient of L-L108 was measured as 0.023, which is about one third and one fifth the values of ionic liquid L-P108 (0.068) and SAE 10W-40 engine oil (0.107), respectively. Studies on wear surfaces show that the wear morphology improved when lubricated with L-L108. In addition, the anticorrosion property of L-L108 is better than that of L-P108. Possible mechanisms behind these encouraging performances of L-L108 are discussed and it was found that the interactions between L-L108 and steel surfaces are possible reasons for the reduction in friction coefficient and the improved wear morphology.

    更新日期:2020-01-04
  • Tribological Property of Selective Laser Melting–Processed 316L Stainless Steel against Filled PEEK under Water Lubrication
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-13
    Yinshui Liu; Xiaomin Zhai; Yipan Deng; Defa Wu

    As a 3D printing technology, selective laser melting has remarkable advantages such as high processing flexibility, high material utilization, and short production cycle. The applications of selective laser melting technology in industry have become quite extensive. There are many tribological studies on selective laser melting materials, but few based on water lubrication (Zhu, et al., Journal of Zhejiang University-Science A, 19(2), pp 95–110). In this article, the tribological properties of 316L stainless steel processed by selective laser melting and traditional methods have been studied under water lubrication. Polyether ether ketone (PEEK) filled with carbon fiber (CF)/polytetrafluoroethylene (PTFE)/graphite was selected as the counterpart. 316L stainless steel and PEEK are a tribopair commonly used in water hydraulics. This study is of great significance to the application of selective laser melting material of tribopairs in water hydraulics. Friction and wear tests were carried out on a pin-on-disc contact test apparatus under different operating conditions. The friction coefficient, specific wear coefficient, scanning electron microscopy (SEM) of the worn surface, and energy-dispersive spectroscopy (EDS) of the surface adhesions of the three tribopairs were measured and compared. The results revealed that the friction coefficient of the selective laser melting (SLM) 316L stainless steel was significantly higher than that of traditionally processed (TP) 316L stainless steel, which might be caused by the pores on the surface of SLM 316L stainless steel. Adhesion and cutting on the surface of SLM 316L stainless steel were also more serious, resulting in a higher specific wear coefficient of its counterpart PEEK composite compared to PEEK composite against TP 316L stainless steel.

    更新日期:2020-01-04
  • Effect of Matrix Microstructure on Abrasive Wear Resistance of Fe–2 wt% B Alloy
    Tribol. Trans. (IF 1.759) Pub Date : 2019-07-30
    Yanliang Yi; Jiandong Xing; Wei Li; Yangzhen Liu; Baochao Zheng

    Two-body abrasive wear tests of Fe-B alloys with various matrix microstructures were performed using a pin-on-disc tribometer at a normal load of 3 N. The wear behavior was analyzed using scanning electron microscopy (SEM) and color 3D laser scanning microscopy. The results show that the Fe–2 wt% B alloy is mainly composed of a metallic matrix, M2B and M23(C, B)6. A pure pearlitic matrix occurs at a cooling rate of 0.05 °C/s, and a pure martensitic matrix forms at a cooling rate above 0.3 °C/s. Compared to the pearlitic matrix, the martensitic matrix can better support the M2B against fracture and provides higher abrasion resistance for the Fe–2 wt% B alloy. Moreover, with an increase in sliding distance, the abrasion resistance of Fe–2 wt% B alloy decreases slightly at first and then decreases rapidly. To be exact, the M2B is steadily scraped off until the critical sliding distance of 6.06 m is reached, after which the neighboring M2B fractures, leading to high material removal.

    更新日期:2020-01-04
  • An Approach to Determine and Analyze the Wear Rates at Cage Pocket Contacts in Solid-Lubricated Rolling Bearings
    Tribol. Trans. (IF 1.759) Pub Date : 2019-07-30
    Rahul Dahiwal; Sascha Pörsch; Markus Löwenstein; Bernd Sauer

    Solid-lubricated rolling bearings are widely known in many technical systems where conventional lubrication, such as oil or grease, fails due to critical conditions like vacuum or high temperatures. Polymeric cages (e.g., polyimide) endowed with molybdenum disulfide (MoS2) particles and silver (Ag) coating on the bearing components have proven themselves as dry lubricants that could significantly increase the service life of solid-lubricated rolling bearings. It has been demonstrated that during the bearing operation, material particles of the cage are transferred onto the raceways and lubricate the bearing. Thereby, the energy dissipates due to the momentary sliding at the ball–cage pocket interface. As a result of this behavior, the cage experiences wear apart from serving as a lubrication reservoir. In order to describe the lubrication transfer amount or the wear volume at the cage pocket, it is essential to estimate the material-specific wear rate. This contribution introduces an approach to determine and analyze the wear rates at the ball–cage pocket interface. In this article, only one example of lubrication coatings with specific operating conditions are shown, but the approach applies to other cases as well. This analysis has been achieved by performing bearing experiments under high vacuum conditions together with the combination of computational modeling. As an outcome, there are two aspects considered. The present contribution provides insight into the procedure to estimate material-specific wear rates. Additionally, it shows how wear rate data distribution can be analyzed. The future scope of this work is the input for the development of the model to predict and optimize the service life of such bearings to some extent.

    更新日期:2020-01-04
  • Numerical and Experimental Analysis of the Honing Texture on the Lubrication Performance of Piston Ring–Cylinder Liner Tribosystem
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-05
    Tongyang Li; Xiqun Lu; Xuan Ma; Hanzhang Xu; Bowen Jiao; Dequan Zou

    A lubrication model of the piston ring–cylinder liner tribosystem taking account of the honing texture was established in this study. The impact of honing texture parameter, which was characterized by its crossing angle α, groove depth dp, and groove density de, was investigated experimentally and numerically to evaluate the lubrication performance of this tribosystem. The experiment was performed on a reciprocating workbench involving piston ring and cylinder liner segments to verify this model, and the calculated average friction coefficient was in good agreement with the measured data. The numerical analysis of the instantaneous friction coefficient (IFC), minimum oil film thickness (MOFT), and load-carrying capacity of oil (LCCO) were applied to analyze the effect of different honing texture parameters using single-factor analysis. Furthermore, the friction force at the dead center was optimized by multiple-factor analysis and reached the minimum value when α = 40°, dp = 3 μm, and de = 1.5 mm−1. Finally, analysis of parameter sensitivity showed that honing density has the most significant influence on lubrication performance.

    更新日期:2020-01-04
  • Fabrication, Characterization, and Evaluation of Monolithic NiTi Nanolaminate Coatings
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-08
    Nicole Cameron; Zoheir Farhat

    Nickel and titanium are common elements in coatings. When Ni and Ti are combined they offer promising characteristics; specifically, the NiTi intermetallic phase. NiTi is a shape memory alloy possessing a stress-induced reversible martensitic transformation. NiTi alloys are used in a variety of industrial applications and are prevalent in the automotive, aerospace, and medical sectors. The problem with using NiTi is its poor machinability and formability. Applying NiTi as a surface coating will provide an alternate manufacturing method that will require limited machining. The objective of this study is to produce a superelastic NiTi surface coating that still possesses excellent wear and dent resistance while reducing forming and machining processes. A full and comprehensive understanding of the formation of the superelastic NiTi phase during coating development is nonexistent. Fabrication of this intermetallic phase is formed through the annealing of sputter-deposited Ti and Ni layers in a coating. Crystalline phases and residual stresses of the coating were established through X-ray diffraction (XRD). The behavior of the coatings was studied through scratch and Hertzian-type indentation testing. XRD and residual stress analysis suggest that intermetallic Ni and Ti phases precipitated at elevated temperatures, which resulted in excellent dent and scratch resistance compared to as-deposited Ni/Ti nanolaminate coating. This indicates that superelastic NiTi can form while annealing nanolaminates, further suggesting that dent- and wear-resistant coatings have the potential to be produced through annealing layers of Ni and Ti to form superelastic NiTi.

    更新日期:2020-01-04
  • Effects of Typical Physical Properties on Tribological Behaviors of Three Kinds of Polymer Materials for Water-Lubricated Bearings
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-06
    Yuhang Wu; Xiuqin Bai; Chengqing Yuan; Conglin Dong; Liyuan Zhang; Shutian Liu

    The stretching, shearing, deformation, peeling, and temperature rise phenomena at the micro–nano contact interface have a great influence on its tribological properties and significantly affect the service life of key moving parts made of polymers. The physical properties of the three typical polymer materials used for ship bearing polymer materials (ultra-high-molecular-weight polyethylene, synthetic rubber, and polypropylene) were examined to investigate their effects on the wear behaviors. The results showed that synthetic rubber has good wear resistance because of its excellent shear strength, tensile strength, and high initial thermoplastic deformation temperature. Low initial thermoplastic deformation temperature resulted in great wear to the polypropylene material under dry friction, whereas its good wettability resulted in good wear resistance under water-lubricated condition. The ultra-high-molecular-weight polyethylene had the poorest wear resistance under water-lubricated condition because it had the poorest shear strength and tensile strength. The knowledge gained herein provides a better understanding of the relationships between the physical behaviors of polymer materials and their friction and wear mechanisms, along with guidance for selecting and designing polymer friction pairs for ship bearings.

    更新日期:2020-01-04
  • Porosity Effect of Sintered Steel on the Frictional Performance of Conformal and Nonconformal Lubricated Contacts
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-08
    G. Boidi; I. S. Tertuliano; L. G. B. S. Lima; F. J. Profito; I. F. Machado

    The effect of surface topography on lubricated systems plays a crucial role in terms of friction performance, because surface micro-irregularities can improve the load-carrying capacity of mechanical parts in lubricated conformal and nonconformal contacts. Sintered materials, which can be applied to manufacturing several mechanical components such as gears, axial thrust bearings, and disc brake pads, are interesting candidates, because they present pores that could be somewhat compared to microcavities produced by surface texturing techniques. This work aims at studying the influence of surface pores originated from the sintering process on the frictional performance of lubricated contacts under different lubrication regimes and slide-to-roll ratios (SRR). The research contributes to understanding how random micro-irregularities could change lubrication conditions and promote effects similar to those of more expensive and precise surface features produced by texturing techniques. The experimental results showed that a decrease in porosity led to a reduction in the coefficient of friction. Furthermore, less porous samples promoted friction reduction compared to nonporous materials due to the probable additional load support caused by small-scale surface pores. Therefore, in addition to the traditional appeal of the use of sintered materials to reduce production costs, the present contribution reveals that this type of material could also be used to reduce friction in contacting mechanical components operating under certain tribological conditions.

    更新日期:2020-01-04
  • Multi-Objective Optimization of Grooved Gas Journal Bearings for Robustness in Manufacturing Tolerances
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-22
    Eliott Guenat; Jürg Schiffmann

    A tolerancing method highlighting trade-offs against key design variables of mechanical systems is proposed and applied to herringbone-grooved gas journal bearings. Gas bearings typically suffer from a subsynchronous instability, demanding a very tight tolerance on the bearing clearance and groove depth. Classical optimization techniques look for the most stable design, which does not necessarily lead to most robust design against manufacturing deviations. The proposed method uses a normalized multidimensional lookup table of stability score (critical mass), covering a large design space of gas bearings. It then dimensionalizes the table for a specific rotor–bearing system, highlighting regions of the hyperspace where the system is stable. The hyperspace is sliced into 2D maps and a Monte Carlo method creates windows within the stable domain along the two most critical design variables regarding manufacturing: the bearing clearance and the groove depth. Width and length of the windows represent the manufacturing tolerance allowed for the two parameters to remain stable. A Pareto front of optimum windows in the entire hyperspace is then compiled. It displays the trade-off between the tolerance against deviation in clearance and groove depth, allowing the designer to select a nominal geometry tailored to the available manufacturing methods. A test rotor is analyzed with this method and the effects of pressure, speed, viscosity, radius, mass, and centrifugal growth on manufacturing tolerances are investigated, highlighting that the radius and viscosity have the greatest impact on the robustness.

    更新日期:2020-01-04
  • Tribological Performance Improvement of Polyamide against Steel Using Polymer Coating
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-12
    Kian Bashandeh; Pixiang Lan; Andreas A. Polycarpou

    Polyamide (PA) is used in industrial applications such as automotive, gears, bearings, and pipeline spacers. As a bearing material, PA can support high contact pressures under low sliding speeds. To achieve high-performing and durable contacts, it is necessary to have low friction, low vibration, and low wear between PA and steel contacts at different operating temperatures. This study proposes the use of an advanced polymer coating, namely, aromatic thermosetting copolyester (ATSP), on the steel surface and investigates the friction and wear properties between PA–ATSP coating and PA–steel at environmental temperatures of 25, 50, and 80 °C. The experiments were carried out using a pin-on-disc configuration under unlubricated sliding conditions. The results showed excellent performance of the coating on reducing the coefficient of friction (COF) by 80% and PA wear by 95% compared to bare steel. The ATSP coating worked as a predeposited transfer layer and showed nonmeasurable wear under moderate to high contact pressure conditions at all temperatures. The worn surfaces and the formation of transfer layers were further examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy.

    更新日期:2020-01-04
  • An Alternative Procedure to Quantify Soot in Engine Oil by Ultraviolet-Visible Spectroscopy
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-01
    Vicente Macián; Bernardo Tormos; Santiago Ruiz; Antonio García-Barberá

    Due to new pollutant emissions standards, internal combustion engines need several emission control strategies (and related procedures) such as exhaust gas recirculation, diesel/gasoline particulate filters, and selective catalyst reduction that allow them to comply with complete requirements defined on those standards. These strategies result in faster degradation of engine oil, one of the most relevant consequences of which is an increase in soot contamination level. All of these strategies facilitate soot generation. Consequently, soot is one of the most important contaminants present in engine oil. The main technique to measure the content of soot in oil is thermogravimetric analysis (TGA), but this technique has certain limitations. TGA requires a long and specific procedure and has limitations in measuring small concentrations of soot in oil. Therefore, the design of an alternative technique to quantify soot in oil is relevant. One alternative is Fourier transform infrared (FTIR) spectroscopy, but it also has limitations related to low concentrations of soot in oil. This work presents an alternative technique based on ultraviolet-visible (UV-Vis) spectroscopy that allows quantification of small soot contents in used engine oil samples and avoids potential interference from other typical contaminants or those related to measurement processes, such as sample cuvette material.

    更新日期:2020-01-04
  • The Synergistic Effect of Cr and CrFe Particles on the Braking Behavior of Cu-Based Powder Metallurgy Brake Pads
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-09
    Peng Zhang; Lin Zhang; Dongbin Wei; Peifang Wu; Jingwu Cao; Cairang Shijia; Xuanhui Qu; Kangxi Fu

    Different Cu-based brake pads applied in high-speed railway trains were fabricated by the co-addition of Cr and CrFe particles, and the influence of the Cr/CrFe ratio on the tribological behavior of the powder metallurgy brake pads were studied by a reduced scale testing apparatus with the pad-on-disc configuration under various braking speeds. The results indicated that the Cu-based brake pad containing 6 wt% Cr and 4 wt% CrFe exhibited the highest and the most stable friction coefficient as well as the lowest wear loss when the braking speed was higher than 300 km/h. Moreover, a new reasonable explanation is provided for the effect of Cr and CrFe particles during the braking process. The excellent braking properties are attributed to the synergistic effect of Cr and CrFe on promoting the formation and stabilization of a tribofilm. Cr particles, which have high reactivity with Fe and O, act as a steady source of fine oxides in the tribofilm, and CrFe particles bear the load and strengthen the subsurface in the position near the friction surface. It is clear that the application of an appropriate ratio between Cr and CrFe can develop Cu-based brake pads suitable for more serious braking conditions.

    更新日期:2020-01-04
  • Experimental Investigation on Temperature Field of a Double-Row Tapered Roller Bearing
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-21
    Xianwen Zhou; Qingyu Zhu; Baogang Wen; Guang Zhao; Qingkai Han

    Based on the structural features of a double-row tapered roller bearing (DTRB), a test rig for multipoint temperature measurement was built to investigate the temperature filed characteristics of DTRB under different operating conditions. Firstly, the composition of the test rig and the measuring instruments are described and the loading method is introduced. Secondly, a multipoint temperature measurement method for inner and outer rings of DTRBs is introduced, including the arrangement of the sensors and the signal transmission. Finally, the influence of rotational speed and external load on the circumferential, axial, and radial temperature rise and temperature distribution in a DTRB is studied. Results show that for the stationary bearing outer ring, the temperature rise in the load zone is significantly higher than that in the non-load zone. Under combined load, there are obvious temperature differences in the axial, circumferential, and radial directions of a DTRB.

    更新日期:2020-01-04
  • A Simulation Study on the Behavior of Magnetorheological Fluid on Herringbone-Grooved Hybrid Slot-Entry Bearing
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-21
    Krishnkant Sahu; Satish C. Sharma

    In recent years, extensive use of smart lubricants has been made in order to control the tribological performance of fluid film bearings. The grooved surfaces of the journal bearing greatly influence the performance of bearings. In the present work, various geometric shapes of herringbone grooves (rectangular, triangular, and parabolic) with groove angles (30° and 60°) have been considered to numerically simulate the performance of slot-entry bearings. The work reported in this article deals with the numerical simulation of magnetorheological (MR) fluid–lubricated slot-entry herringbone-grooved hybrid journal bearings. Dave equation, a constitutive relation of the Bingham model, was employed to simulate the flow behavior of MR fluid. Using the finite element method (FEM), the governing Reynolds equation for a hybrid slot-entry bearing model was solved. The result shows that the use of a herringbone-grooved surface and application of MR fluid in a slot-entry bearing offers better stability and higher fluid film stiffness and minimizes frictional torque.

    更新日期:2020-01-04
  • The Friction and Wear Properties of Metal-Doped DLC Films under Current-Carrying Condition
    Tribol. Trans. (IF 1.759) Pub Date : 2019-08-21
    Yunfeng Wang; Yan Wang; Xia Li; An Li; Zhibin Lu; Guangan Zhang; Zhiguo Wu

    In an effort to improve the surface properties of electrical contact materials in terms of high friction coefficient and wear rate, diamond-like carbon (DLC) films containing different metal elements were prepared on stainless steel substrates using an unbalanced magnetron sputtering system. In the present study, the effect of current-carrying on DLC film, Cu-doped DLC film (Cu/DLC), and Ti-doped DLC film (Ti/DLC) is reported. The structure and mechanical properties of the films were characterized systematically by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectra; these methods were also used to analyze the initial surface of the films. Moreover, the tribological behaviors of the films sliding against AISI 52100 steel with and without an electric current (1 A) applied were investigated using a tribometer with ball-on-disc configuration in an atmospheric environment. The results demonstrated that the friction coefficients of DLC and Cu/DLC under current-carrying condition were decreased, whereas Ti/DLC showed opposite experimental results. The wear rate of the films with a current was higher than that without a current. Therefore, this study is meaningful to understand the tribological behaviors of microelectromechanical systems.

    更新日期:2020-01-04
  • Life Model Enhancement for Hybrid Ball Bearings
    Tribol. Trans. (IF 1.759) Pub Date : 2019-09-11
    Pradeep K. Gupta; Erwin V. Zaretsky

    Based on experimental life data on silicon nitride balls, the stress-life exponent and life constant in the generalized ball life equation, developed earlier, are modified to better simulate the fatigue life of silicon nitride balls in hybrid ball bearings. The modified ball life equation is then integrated with generalized life equations for the outer and inner races to model the life of a complete hybrid ball bearing. It is found that in view of the relatively high stress-life exponent for silicon nitride balls, computation of hybrid bearing life with infinite ball life may not be unreasonable. Model predictions are in good agreement with limited available experimental life data on hybrid ball bearings.

    更新日期:2020-01-04
  • Deformation Analysis of Hydrostatic Guideways Based on the Cantilever Plate Bending Calculation Method
    Tribol. Trans. (IF 1.759) Pub Date : 2019-10-08
    Wanjiao Dong; Beizhi Li; Weicheng Guo; Qinzhi Zhou

    In this study, a novel analytical model considering practical oil pressure and a cantilever plate bending calculation method is proposed to calculate the deformation of a vertical hydrostatic guideway. Based on the governing equations of rectangular thin plates, the finite integral transformation theory and the series-by-item differential transformation theory are used to solve the bending deformation of the target guideway to avoid the errors caused by an artificially selected deflection function and Kirchhoff’s hypothesis. The deformation values obtained from finite element simulation and experiments are compared with those calculated from the model. The comparison results show that the proposed model is capable of providing deformation values that are in better agreement with the experimental values than simulation values and its computation time is much less than that of the finite element method. The quantitative relationship between the actual oil film thickness and the performance of the hydrostatic guideways considering the size effect of the oil film thickness is studied.

    更新日期:2020-01-04
  • Influence of Deposition Positions on Fretting Behaviors of DLC Coating on Ti-6Al-4V
    Tribol. Trans. (IF 1.759) Pub Date : 2019-09-11
    Hao-Hao Ding; Vincent Fridrici; Gaëtan Bouvard; Jean Geringer; Julien Fontaine; Philippe Kapsa

    The influence of diamond-like carbon (DLC) coating positions—coated flat, coated cylinder, and self-mated coated surface tribopairs—on the fretting behaviors of Ti-6Al-4V were investigated using a fretting wear test rig with a cylinder-on-flat contact. The results indicated that, for tests without coating (Ti-6Al-4V–Ti-6Al-4V contact), the friction (Qmax/P) was high (0.8–1.2), wear volumes were large (0.08–0.1 mm3) under a large displacement amplitude of ±40 µm and small (close to 0) under a small displacement amplitude of ±20 µm, and the wear debris was composed of Ti-6Al-4V flakes and oxidized particles. For tests with the DLC coating, under low load conditions, the DLC coating was not removed or was only partially removed, Qmax/P was low (≤0.2), and the wear volumes were small. Under high load conditions, the coating was entirely removed, Qmax/P was high (0.6–0.8), and the wear volumes were similar to those in tests without coating. The wear debris was composed of DLC particles, Ti-6Al-4V flakes, and oxidized particles. The DLC coating was damaged more severely when deposited on a flat surface than when deposited on a cylindrical surface. The DLC coating was damaged more severely when sliding against a DLC-coated countersurface than when sliding against the Ti-6Al-4V alloy.

    更新日期:2020-01-04
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