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Lubricants, Volume 11, Issue 6 (June 2023) – 36 articles

Cover Story (view full-size image): Rotary shaft seals are used in many automotive and industrial applications. The associated challenges increase continuously. Hence, in-depth knowledge of structural mechanics is essential for the design and optimization of such sealing systems. High complexity results are gathered here from the multiscale interactions in the tribological system rotary shaft seal. Both numerical and experimental methods serve to study these effects. Multiscale finite element models allow the simulation of the macroscopic deformations of the sealing ring and the microscopic deformations in the sealing contact. Special test rigs provide visual in situ analyses of the sealing contact in operation. This yields a solid and profound understanding of the multiscale structural mechanics of rotary shaft seals. View this paper
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Article
Classification of Lubricating Oil Types Using Mid-Infrared Spectroscopy Combined with Linear Discriminant Analysis–Support Vector Machine Algorithm
Lubricants 2023, 11(6), 268; https://doi.org/10.3390/lubricants11060268 - 20 Jun 2023
Viewed by 653
Abstract
To realize the classification of lubricating oil types using mid-infrared (MIR) spectroscopy, linear discriminant analysis (LDA) was used for the dimensionality reduction of spectrum data, and the classification model was established based on the support vector machine (SVM). The spectra of the samples [...] Read more.
To realize the classification of lubricating oil types using mid-infrared (MIR) spectroscopy, linear discriminant analysis (LDA) was used for the dimensionality reduction of spectrum data, and the classification model was established based on the support vector machine (SVM). The spectra of the samples were pre-processed by interval selection, Savitzky–Golay smoothing, multiple scattering correction, and normalization. The Kennard–Stone algorithm (K/S) was used to construct the calibration and validation sets. The percentage of correct classification (%CC) was used to evaluate the model. This study compared the results obtained with several chemometric methods: PLS-DA, LDA, principal component analysis (PCA)-SVM, and LDA-SVM in MIR spectroscopy applications. In both calibration and verification sets, the LDA-SVM model achieved 100% favorable results. The PLS-DA analysis performed poorly. The cyclic resistance ratio (CRR) of the calibration set was classified via the LDA and PCA-SVM analysis as 100%, but the CRR of the verification set was not as good. The LDA-SVM model was superior to the other three models; it exhibited good robustness and strong generalization ability, providing a new method for the classification of lubricating oil types by MIR spectroscopy. Full article
(This article belongs to the Special Issue Recent Advances in Machine Learning in Tribology)
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Article
Investigation of the Static Performance of Hydrostatic Thrust Bearings Considering Non-Gaussian Surface Topography
Lubricants 2023, 11(6), 267; https://doi.org/10.3390/lubricants11060267 - 20 Jun 2023
Viewed by 482
Abstract
The dynamic and static characteristics of hydrostatic thrust bearings are significantly affected by the bearing surface topography. Previous studies on hydrostatic thrust bearings have focused on Gaussian distribution models of bearing surface topography. However, based on actual measurements, the non-Gaussianity of the distribution [...] Read more.
The dynamic and static characteristics of hydrostatic thrust bearings are significantly affected by the bearing surface topography. Previous studies on hydrostatic thrust bearings have focused on Gaussian distribution models of bearing surface topography. However, based on actual measurements, the non-Gaussianity of the distribution characteristics of bearing surface topography is clear. To accurately characterize the non-Gaussian distribution of bearing surface topography, the traditional probability density function of Gaussian distribution was modified by introducing Edgeworth expansion. The non-Gaussian surface was then reflected by two parameters: kurtosis and skewness. This had an effect on the static characteristics of hydrostatic thrust bearings with both circumferential and radial surface topographies. The comparison between the Gaussian distribution results and those of the non-Gaussian model showed that errors between the two models could reach more than 10%. Therefore, it is important to take into account the non-Gaussianity of bearing surface when discussing static characteristics of hydrostatic thrust bearings considering the surface topography. Full article
(This article belongs to the Special Issue Hydrodynamic Lubrication of Textured Surfaces)
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Article
Application of Load-Sharing Concept to Mechanical Seals
Lubricants 2023, 11(6), 266; https://doi.org/10.3390/lubricants11060266 - 17 Jun 2023
Viewed by 678
Abstract
Mechanical seals are mechanisms that are used to prevent fluid leakage. Since the seal surfaces are in contact with one another, hydrodynamic and contact forces are functions of surface roughness. Additionally, since the lubrication regime under specific operating conditions such as low speed [...] Read more.
Mechanical seals are mechanisms that are used to prevent fluid leakage. Since the seal surfaces are in contact with one another, hydrodynamic and contact forces are functions of surface roughness. Additionally, since the lubrication regime under specific operating conditions such as low speed or high load causes the seal to operate in the mixed lubrication regime, thus the contact of asperities plays an important role. The primary purpose of this paper is to apply the load-sharing concept to study the behavior of a mechanical seal in a mixed lubrication regime. The predicted results are compared to the published data from the literature, showing acceptable accuracy. The model presented in this paper can predict the performance of the mechanical seal system in a short execution time while providing acceptable accuracy by considering the surface roughness effect. Full article
(This article belongs to the Special Issue Tribological Properties and Failure Prediction in Mechanical Elements)
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Article
Wear and Subsurface Stress Evolution in a Half-Space under Cyclic Flat-Punch Indentation
Lubricants 2023, 11(6), 265; https://doi.org/10.3390/lubricants11060265 - 17 Jun 2023
Viewed by 642
Abstract
Wear is a tremendously important phenomenon, which takes place on the surfaces of two solids in contact under cyclic loads and constitutes one of the most-significant ways of failure for mechanical elements. However, it is not the only source of failure in contacting [...] Read more.
Wear is a tremendously important phenomenon, which takes place on the surfaces of two solids in contact under cyclic loads and constitutes one of the most-significant ways of failure for mechanical elements. However, it is not the only source of failure in contacting solids. The subsurface stresses should also be considered, due to the fatigue and crack initiation problems. Nevertheless, these stresses (i.e., their maximum values and distributions) evolve with the solids’ surface wear (i.e., with the load cycles) and also depend on the friction intensity. Therefore, their evolution should be properly computed to predict failures in mechanical elements under wear conditions. This work focused on the study of the evolution of the surface wear and the subsurface stress distributions generated—in an elastic half-space—by a cylindrical flat-ended punch, under cyclic indentation loading (i.e., radial fretting wear conditions). Based on a numerical scheme recently presented by the authors, this is the first time that, for this contact problem, the surface wear and subsurface stress distribution (i.e., maximum value and its location)—and its evolution—were simultaneously analyzed when orthotropic friction and fretting wear conditions were considered. The studies presented in this work were developed for purely elastic contact assumptions. Full article
(This article belongs to the Special Issue Advances in Wear Predictive Models)
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Article
Tribological, Oxidation and Thermal Analysis of Advanced Microwave–Hydrothermal Synthesised Ti3C2Tx MXene as Additives in Outboard Engine Oil
Lubricants 2023, 11(6), 264; https://doi.org/10.3390/lubricants11060264 - 16 Jun 2023
Viewed by 665
Abstract
In today’s fast, globalised world, lubrication has become essential in enhancing engine efficiency, including in the marine sector. While the number of fishing vessels increased, so did the environmental pollution issues, due to inefficient engines. An outboard engine oil’s tribological, oxidation and thermal [...] Read more.
In today’s fast, globalised world, lubrication has become essential in enhancing engine efficiency, including in the marine sector. While the number of fishing vessels increased, so did the environmental pollution issues, due to inefficient engines. An outboard engine oil’s tribological, oxidation and thermal conductivity behaviour play a crucial role in improving the quality of an outboard engine’s life. In this research, Ti3C2Tx MXene nanoparticles with different interlayer spacing were synthesised via an advanced microwave–hydrothermal approach. Later, the nanoparticles were dispersed in TC-W outboard engine oil to formulate the Ti3C2Tx MXene nanolubricant with different concentrations. The results show that nanolubricant with a 0.01 wt.% Ti3C2Tx MXene concentration with higher interlayer spacing reduced the coefficient of friction, and the average wear scar diameter by 14.5% and 6.3%, respectively, compared to the base oil. Furthermore, the nanolubricant with a 0.01 wt.% concentration of the Ti3C2Tx MXene nanoparticle showed an improvement of 54.8% in oxidation induction time compared to the base oil. In addition, MXene nanolubricant established a more than 50% improvement in thermal conductivity compared to the base oil. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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Article
Experimental Investigation of Tribology-Related Topography Parameters of Hard-Turned and Ground 16MnCr5 Surfaces
Lubricants 2023, 11(6), 263; https://doi.org/10.3390/lubricants11060263 - 16 Jun 2023
Viewed by 565
Abstract
Several surface topography parameters are available for the quantification of tribological properties of machined surfaces. Although these parameters and their influences are widely studied, there are contradictory findings due to the nature of the topography parameters, i.e., the behavior of different materials and [...] Read more.
Several surface topography parameters are available for the quantification of tribological properties of machined surfaces. Although these parameters and their influences are widely studied, there are contradictory findings due to the nature of the topography parameters, i.e., the behavior of different materials and cutting tool interactions lead to relatively varying numerical results. A comprehensive study of these interactions can contribute to more exact industrial machining applications. In this study, tribology-related 3D topography parameters of hard-machined (hard-turned and ground) surfaces were analyzed. The machining experiments were carried out based on a detailed design of the experiment; the analyzed material was case-hardened low-carbon content steel, which is widely used for automotive, industrial components such as bearings or gears. From the topography data, response function, correlation, and relative deviation analyses were carried out for the analyzed topography parameters, and tribology maps were created to support the selection of optimal cutting parameter values. Full article
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Article
A Mixed Lubrication Deterministic Model of an Elastic Support Water-Lubricated Tilting Pad Thrust Bearing
Lubricants 2023, 11(6), 262; https://doi.org/10.3390/lubricants11060262 - 15 Jun 2023
Viewed by 533
Abstract
In order to study the effect of surface roughness on lubrication performance of an elastic support water-lubricated tilting pad thrust bearing, a mixed lubrication (ML) deterministic model is hereby presented based on a unified Reynolds equation model. This very model incorporates the elastic–plastic [...] Read more.
In order to study the effect of surface roughness on lubrication performance of an elastic support water-lubricated tilting pad thrust bearing, a mixed lubrication (ML) deterministic model is hereby presented based on a unified Reynolds equation model. This very model incorporates the elastic–plastic deformation of asperities and polymer matrix of the thrust pad, as well as the elastic deformation of the rubber support. The randomly distributed surface roughness of the thrust pad is generated by a mathematical model and shares the same distribution characteristics as the measured surface roughness. The Greenwood and Williamson asperity contact model and thin plate deformation model are combined to solve the asperities contact stress and deformation. Meanwhile, the bearing ML performance is compared with the results calculated by a thermohydrodynamic (THD) lubrication model and a thermo-elasto-hydrodynamic (TEHD) lubrication model, while the film thickness is also compared with measurements. The results show that the water film thickness calculated by the ML model is smaller than that by the THD model and the TEHD model, but the water film temperature is higher. The roughness has a great influence on the contact area ratio and the lubrication state, but little effect on the average film thickness. A higher roughness indicates a higher rotational speed required for the bearing to achieve full hydrodynamic lubrication. The film thickness calculated by the mixed lubrication model is closer to the measured results. Overall, it is proved that the mixed lubrication model can more accurately predict the lubrication performance of bearings. Compared to the thin plate deformation model, the elastic deformation simulation based on the half-infinite space model severely overestimates the elastic deformation of the pad surface, making it unsuitable for calculating the elastic deformation of the polymer matrix of the thrust pad under contact force or water film pressure. This ML deterministic model provides an effective means for high-precision prediction of the lubrication performance of the elastic supported water-lubricated thrust bearings coupled with multi-layer soft materials. Full article
(This article belongs to the Special Issue Marine Tribology)
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Article
Prediction of Wear Rate in Al/SiC Metal Matrix Composites Using a Neurosymbolic Artificial Intelligence (NSAI)-Based Algorithm
Lubricants 2023, 11(6), 261; https://doi.org/10.3390/lubricants11060261 - 14 Jun 2023
Viewed by 542
Abstract
This research paper delves into an innovative utilization of neurosymbolic programming for forecasting wear rates in aluminum-silicon carbide (Al/SiC) metal matrix composites (MMCs). The study scrutinizes compositional transformations in MMCs with various weight percentages of SiC (0%, 3%, and 5%), employing comprehensive spectroscopic [...] Read more.
This research paper delves into an innovative utilization of neurosymbolic programming for forecasting wear rates in aluminum-silicon carbide (Al/SiC) metal matrix composites (MMCs). The study scrutinizes compositional transformations in MMCs with various weight percentages of SiC (0%, 3%, and 5%), employing comprehensive spectroscopic analysis. The effect of SiC integration on the compositional distribution and ratio of elements within the composite is meticulously examined. In a novel move for this field of research, the study introduces and applies neurosymbolic programming as a novel computational modeling approach. The performance of this cutting-edge methodology is compared to a traditional simple artificial neural network (ANN). The neurosymbolic algorithm exhibits superior performance, providing lower mean squared error (MSE) values and higher R-squared (R2) values across both training and validation datasets. This highlights its potential for delivering more precise and resilient predictions, marking a significant development in the field. Despite the promising results, the study recognizes that the performance of the model might vary based on specific characteristics of the composite material and operational conditions. Thus, it encourages future studies to authenticate and expand these innovative findings across a wider spectrum of materials and conditions. This research represents a substantial advancement towards a more profound understanding of wear rates in Al/SiC MMCs and emphasizes the potential of the novel neurosymbolic programming in predictive modeling of complex material systems. Full article
(This article belongs to the Special Issue Friction and Wear of Alloys)
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Article
The Enhancement of Overall Performance of Lubricating Grease by Adding Layered Double Hydroxides
Lubricants 2023, 11(6), 260; https://doi.org/10.3390/lubricants11060260 - 13 Jun 2023
Viewed by 814
Abstract
In this work, MgAl-layered double hydroxides (LDH) were synthesized by co-precipitation method using a colloid mill and characterized by XRD and SEM. It was found that the environmentally friendly LDHs had greater performance than the traditional antioxidant. By adding LDHs into large electric [...] Read more.
In this work, MgAl-layered double hydroxides (LDH) were synthesized by co-precipitation method using a colloid mill and characterized by XRD and SEM. It was found that the environmentally friendly LDHs had greater performance than the traditional antioxidant. By adding LDHs into large electric shovel grease (GRK-A) in open-pit coal mine, the service lifetime of grease was extended by 20%. With the increase in LDH addition, the grease sample attains greater activation energy, and the thermal oxidation and decomposition resistance become stronger. Comparing the energy storage modulus and flow transition index at different temperatures, adding the right amount of LDHs needs close attention for the system oxidation resistance and viscoelasticity. For the electric shovel grease, the best oxidation resistance and rheological properties can be achieved by adding 2% of LDHs. The rheological viscosity–temperature curves show that the grease samples with different ratios of solid LDHs have better low-temperature properties than the mine grease. This work outlines a simple method for creating an environmentally sustainable lubricant additive with the use of LDH. LDH serves as a novel inorganic antioxidant additive that is optimal for open gear lubrication and sliding friction. Full article
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Article
Tribological Behavior of WS2 Nanoparticles as Additives in Calcium Sulfonate Complex–Polyurea Grease
Lubricants 2023, 11(6), 259; https://doi.org/10.3390/lubricants11060259 - 12 Jun 2023
Cited by 1 | Viewed by 613
Abstract
In order to improve the tribological properties of calcium sulfonate complex–polyurea grease, WS2 nanoparticles were used as additives to prepare WS2 calcium sulfonate complex–polyurea grease. The tribological behavior of WS2 grease on the GCr15 surface was systematically studied. The results [...] Read more.
In order to improve the tribological properties of calcium sulfonate complex–polyurea grease, WS2 nanoparticles were used as additives to prepare WS2 calcium sulfonate complex–polyurea grease. The tribological behavior of WS2 grease on the GCr15 surface was systematically studied. The results indicate that WS2 nanoparticles can significantly improve the extreme pressure performance of calcium sulfonate complex–polyurea grease. When the concentration of WS2 nanoparticles is 2 wt.%, the friction coefficient decreases by 14.94%, and the maximum nonseizure load PB increases by 31.41%. As the temperature increases, the friction coefficient and wear rate of WS2 grease first decrease and then increase. This is mainly attributed to the adsorption and frictional chemical reaction between WS2 nanoparticles and the matrix. Full article
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Article
High-Temperature Superlubricity Performance of h-BN Coating on the Textured Inconel X750 Alloy
Lubricants 2023, 11(6), 258; https://doi.org/10.3390/lubricants11060258 - 10 Jun 2023
Cited by 1 | Viewed by 702
Abstract
The high-temperature superlubricity performances of h-BN coatings on the nontextured and textured surface of an Inconel X750 alloy is reported in the present paper. The hardness and bond strength of the h-BN coating and alloy were investigated. The tribological properties of the X750 [...] Read more.
The high-temperature superlubricity performances of h-BN coatings on the nontextured and textured surface of an Inconel X750 alloy is reported in the present paper. The hardness and bond strength of the h-BN coating and alloy were investigated. The tribological properties of the X750 alloy and coatings on the X750 alloy substrate were investigated at different temperatures. The surface texture was manufactured on the surface of the X750 alloy, and then coatings were deposited on the textured surface to reduce the cracking of the coating and enhance the stability of the antifriction behaviors of the h-BN coatings. The tribotest results showed that the texture is helpful to enhance the interface thermal compatibility of the coating and substrate and store the wear debris generated during sliding. Therefore, a stable superlubricity was achieved at high temperatures, and a super low friction mechanism is also discussed. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World 2023)
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Review
Surface Properties and Tribological Behavior of Additively Manufactured Components: A Systematic Review
Lubricants 2023, 11(6), 257; https://doi.org/10.3390/lubricants11060257 - 10 Jun 2023
Cited by 1 | Viewed by 1023
Abstract
Innovative additive manufacturing processes for resilient and sustainable production will become even more important in the upcoming years. Due to the targeted and flexible use of materials, additive manufacturing allows for conserving resources and lightweight design enabling energy-efficient systems. While additive manufacturing processes [...] Read more.
Innovative additive manufacturing processes for resilient and sustainable production will become even more important in the upcoming years. Due to the targeted and flexible use of materials, additive manufacturing allows for conserving resources and lightweight design enabling energy-efficient systems. While additive manufacturing processes were used in the past several decades mainly for high-priced individualized components and prototypes, the focus is now increasingly shifting to near-net-shape series production and the production of spare parts, whereby surface properties and the tribological behavior of the manufactured parts is becoming more and more important. Therefore, the present review provides a comprehensive overview of research in tribology to date in the field of additively manufactured components. Basic research still remains the main focus of the analyzed 165 papers. However, due to the potential of additive manufacturing processes in the area of individualized components, a certain trend toward medical technology applications can be identified for the moment. Regarding materials, the focus of previous studies has been on metals, with stainless steel and titanium alloys being the most frequently investigated materials. On the processing side, powder bed processes are mainly used. Based on the present literature research, the expected future trends in the field of tribology of additively manufactured components can be identified. In addition to further basic research, these include, above all, aspects of process optimization, function integration, coating, and post-treatment of the surfaces. Full article
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Article
A New Type of Misaligned Journal Bearing with Flexible Structure
Lubricants 2023, 11(6), 256; https://doi.org/10.3390/lubricants11060256 - 10 Jun 2023
Viewed by 547
Abstract
A flexible structure is applied to improve the lubrication performance of a misaligned journal bearing. The journal bearing is a representative sliding bearing, and there is damage due to metal-to-metal contact as a result of misalignment. Since misalignment is an unavoidable phenomenon, a [...] Read more.
A flexible structure is applied to improve the lubrication performance of a misaligned journal bearing. The journal bearing is a representative sliding bearing, and there is damage due to metal-to-metal contact as a result of misalignment. Since misalignment is an unavoidable phenomenon, a journal bearing with a flexible structure was proposed as a way to improve it. The lubrication characteristics of the bearing were evaluated numerically under a steady-state condition. EHL (elastohydrodynamic lubrication) analysis considering elastic deformation was performed. The lubrication performance was compared in accordance with variation of the geometry of the flexible structure and evaluated based on the minimum film thickness. Moreover, the results of the journal bearing with a flexible structure were compared with those of the journal bearing without the flexible structure. The flexible structure was then applied in the form of a groove to the area supporting high load on the journal bearing; it was elastically deformed by the generated oil film pressure, which helps obscure a larger oil film. Through numerical analysis, it was found that the journal bearing with a flexible structure can improve the lubrication performance in the misaligned condition. Full article
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Article
Dynamic Responses of the Planetary Gear Mechanism Considering Dynamic Wear Effects
Lubricants 2023, 11(6), 255; https://doi.org/10.3390/lubricants11060255 - 09 Jun 2023
Viewed by 620
Abstract
Gear wear is unavoidable and results in vibrations and decreased performance in a planetary gear system. In this work, the wear phenomenon of the gear teeth surface and the dynamic responses of the planetary gear mechanism are investigated through a computational methodology. Dynamic [...] Read more.
Gear wear is unavoidable and results in vibrations and decreased performance in a planetary gear system. In this work, the wear phenomenon of the gear teeth surface and the dynamic responses of the planetary gear mechanism are investigated through a computational methodology. Dynamic responses are presented by considering the dynamic wear effects. First, the model of the planetary gear mechanism dynamics is established by considering the nonlinear stiffness and friction of gear surfaces. The dynamic wear model of the gear is then established based on Archard’s wear model. Further, the coupling between the dynamics and wear characteristics of the planetary gear mechanism is presented by considering the dynamic wear effects. Finally, a numerical investigation is conducted. The simulation results reveal severe wear between the sun and planet gears. The wear depth and meshing vibration responses exhibit prominent nonlinear characteristics. The low-order resonance of the meshing frequency becomes more marked as the mesh times and wear increase. Full article
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Article
Machine Learning Composite-Nanoparticle-Enriched Lubricant Oil Development for Improved Frictional Performance—An Experiment
Lubricants 2023, 11(6), 254; https://doi.org/10.3390/lubricants11060254 - 09 Jun 2023
Viewed by 703
Abstract
Improving the frictional response of a functional surface interface has been a significant research concern. During the last couple of decades, lubricant oils have been enriched with several additives to obtain formulations that can meet the requirements of different lubricating regimes from boundary [...] Read more.
Improving the frictional response of a functional surface interface has been a significant research concern. During the last couple of decades, lubricant oils have been enriched with several additives to obtain formulations that can meet the requirements of different lubricating regimes from boundary to full-film hydrodynamic lubrication. The possibility to improve the tribological performance of lubricating oils using various types of nanoparticles has been investigated. In this study, we proposed a data-driven approach that utilizes machine learning (ML) techniques to optimize the composition of a hybrid oil by adding ceramic and carbon-based nanoparticles in varying concentrations to the base oil. Supervised-learning-based regression methods including support vector machines, random forest trees, and artificial neural network (ANN) models are developed to capture the inherent non-linear behavior of the nano lubricants. The ANN hyperparameters were fine-tuned with Bayesian optimization. The regression performance is evaluated with multiple assessment metrics such as the root mean square error (RMSE), mean squared error (MSE), mean absolute error (MAE), and coefficient of determination (R2). The ANN showed the best prediction performance among all ML models, with 2.22 × 10−3 RMSE, 4.92 × 10−6 MSE, 2.1 × 10−3 MAE, and 0.99 R2. The computational models’ performance curves for the different nanoparticles and how the composition affects the interface were investigated. The results show that the composition of the optimized hybrid oil was highly dependent on the lubrication regime and that the coefficient of friction was significantly reduced when optimal concentrations of ceramic and carbon-based nanoparticles are added to the base oil. The proposed research work has potential applications in designing hybrid nano lubricants to achieve optimized tribological performance in changing lubrication regimes. Full article
(This article belongs to the Special Issue Recent Advances in Machine Learning in Tribology)
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Review
Review of the Modeling Methods of Bucket Tooth Wear for Construction Machinery
Lubricants 2023, 11(6), 253; https://doi.org/10.3390/lubricants11060253 - 08 Jun 2023
Cited by 1 | Viewed by 739
Abstract
Construction machinery, which is widely used in infrastructure construction, is growing rapidly all over the word. However, the complex working conditions of construction machinery lead to serious wear, particularly the wear of the bucket teeth on construction machinery. To control the wear procedure, [...] Read more.
Construction machinery, which is widely used in infrastructure construction, is growing rapidly all over the word. However, the complex working conditions of construction machinery lead to serious wear, particularly the wear of the bucket teeth on construction machinery. To control the wear procedure, it is essential to understand the wear mechanism and identify the wear form under variable working conditions. The modeling methods of bucket tooth wear with different wear mechanisms were reviewed. The modeling methods were divided into the analytical method and the numerical simulation method. The numerical simulation method included the discrete element method, finite element method, SPH method, and so on, which were used to simulate the bucket digging process and analyze the interaction between the material and bucket teeth during the working process. This enabled a force analysis of the bucket digging process and the identification of the location of maximum wear. By establishing a wear model, it is possible to better understand and address the wear problem in construction machinery. This article aims to summarize research methods concerning the wear of wear parts in construction machinery. It provides a theoretical foundation for future investigations in this area and aims to address challenges such as lengthy wear life testing, numerous interfering factors, and the difficulty of data collection pertaining to wear parts. Full article
(This article belongs to the Special Issue Tribological Properties and Failure Prediction in Mechanical Elements)
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Article
Rotordynamic Analysis and Operating Test of an Externally Pressurized Gas Bearing Turbo Expander for Cryogenic Applications
Lubricants 2023, 11(6), 252; https://doi.org/10.3390/lubricants11060252 - 08 Jun 2023
Viewed by 875
Abstract
This study designed an externally pressurized bearing and analyzed the rotordynamics of a turbo expander for a hydrogen liquefaction plant. The turbo expander, comprising a turbine and compressor wheel assembled to a shaft, lowered the temperature of the helium refrigerant. Its rated speed [...] Read more.
This study designed an externally pressurized bearing and analyzed the rotordynamics of a turbo expander for a hydrogen liquefaction plant. The turbo expander, comprising a turbine and compressor wheel assembled to a shaft, lowered the temperature of the helium refrigerant. Its rated speed was 75,000 rpm, and an externally pressurized gas bearing was selected to support the rotor. Pressurized helium was used as the lubricant for the bearing operation. To design the rotor–bearing system, we conducted a bearing performance analysis and rotordynamic characteristic prediction using the developed numerical model. We calculated the bearing stiffness and flow rate of the bearing gas for various feed parameters and selected the appropriate orifice diameter for maximum stiffness. The predicted Campbell diagram showed that the system had a sufficient separation margin with the critical speed, and the predicted critical speed correlated well with the nonlinear orbit simulation. A successful operation was achieved with the manufactured turbo expander within the rated speed. The shaft vibration was monitored during the operation test, and the test results revealed two critical speeds below the rated speed, as predicted by the analytical model. In addition, the shaft vibration was maintained at <3 μm. Full article
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Article
Bearing Non-Uniform Loading Condition Monitoring Based on Dual-Channel Fusion Improved DenseNet Network
Lubricants 2023, 11(6), 251; https://doi.org/10.3390/lubricants11060251 - 07 Jun 2023
Viewed by 617
Abstract
Misalignment or unbalanced loading of machine tool spindle bearings often results in skewed bearing operation, which makes the spindle more susceptible to failure. In addition, due to the weak impact signal of the bearing in skewed operation, a single feature information cannot accurately [...] Read more.
Misalignment or unbalanced loading of machine tool spindle bearings often results in skewed bearing operation, which makes the spindle more susceptible to failure. In addition, due to the weak impact signal of the bearing in skewed operation, a single feature information cannot accurately characterize the operation status of the bearing. To address the above problems, this paper proposes a method to monitor the uneven running state of bearing load based on a dual-channel fusion improved dense connection (DenseNet) network. First, the original signal is pre-processed by overlapping sampling method, and the dual-channel experimental data are obtained by frequency-domain and time-frequency-domain algorithms; then the processed data are input into the improved 1D-DenseNet and 2D-DenseNet models respectively for feature extraction; then the frequency-domain and time-frequency-domain features are fused by concat splicing operation, and the output belongs to each category The probability distribution is used to characterize the operating state of the bearings. Finally, the validity of the algorithm model is verified by using the Case Western Reserve University public rolling bearing data set, and an experimental bench is designed and built for experimental verification of the uneven bearing load operation. The comparative analysis of the experimental results in this paper shows that the algorithm can extract the features of the input signal more comprehensively and finally achieve 100% recognition accuracy. Full article
(This article belongs to the Special Issue Advances in Bearing Lubrication and Thermodynamics 2023)
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Article
Comparative Cutting Fluid Study on Optimum Grinding Parameters of Ti-6Al-4V Alloy Using Flood, Minimum Quantity Lubrication (MQL), and Nanofluid MQL (NMQL)
Lubricants 2023, 11(6), 250; https://doi.org/10.3390/lubricants11060250 - 06 Jun 2023
Cited by 1 | Viewed by 804
Abstract
Titanium alloys have been of paramount interest to the aerospace industry due to their attractive characteristics. However, these alloys are difficult to machine and require grinding post-processes for quality assurance of the products. Conventional grinding takes a long time and uses a flood [...] Read more.
Titanium alloys have been of paramount interest to the aerospace industry due to their attractive characteristics. However, these alloys are difficult to machine and require grinding post-processes for quality assurance of the products. Conventional grinding takes a long time and uses a flood coolant-lubrication technique, which is not cost effective nor environmentally friendly. Several studies have been performed to prove the viability and benefit of using Minimum Quantity Lubrication (MQL) with vegetable or synthetic-ester fluids. This work aims to find the optimum grinding parameters of creep feed grinding Ti-6Al-4V with a green silicon carbide wheel, using a flood lubrication system with water-soluble synthetic oil, MQL with ester oil, and nano-MQL (NMQL) using alumina-nanopowder homogeneously dispersed within an ester oil. It is concluded that at 0.635 mm and 1.27 mm infeeds, the three lubrication methods performed similarly. At an infeed of 1.905 mm, MQL did not provide desirable quality, though NMQL and flood lubrication performed practically identically. At a cross feed of 0.254 mm, an infeed of 1.27 mm, and a table feed rate of 6.7 m/min, these grinding parameters provide a material removal rate of 2163 mm3/min with a surface roughness across (Ra) of 0.515 µm. These parameters provide the quickest material removal rate while still maintaining industrial quality. This conclusion is based on environmental, economic, and qualitative results. Full article
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Article
Multi-Objective Optimization Design of Micro-Texture Parameters of Tool for Cutting GH4169 during Spray Cooling
Lubricants 2023, 11(6), 249; https://doi.org/10.3390/lubricants11060249 - 06 Jun 2023
Cited by 1 | Viewed by 668
Abstract
This study explores the performance of micro-textured tools when cutting GH4169 during spray cooling. First, the morphologies of the micro-textures were selected according to the simulation and experiments. Secondly, cutting experiments were carried out during spray cooling. As appropriate for each experiment, regression [...] Read more.
This study explores the performance of micro-textured tools when cutting GH4169 during spray cooling. First, the morphologies of the micro-textures were selected according to the simulation and experiments. Secondly, cutting experiments were carried out during spray cooling. As appropriate for each experiment, regression models of cutting force, cutting temperature, or tool wear area were established, and variance analysis was conducted. The cutting force, cutting temperature, and tool wear area functions were obtained from the respective regression models. Based on these functions, the micro-texture parameters were optimized using the response surface method with the cutting force, cutting temperature, and rake face wear area as the objectives. Finally, a full factor experiment on the micro-texture parameters was designed using Minitab, and cutting experiments were conducted using micro-textured tools with these parameters. Taking a relatively low cutting force, cutting temperature, and tool wear as the objectives, a genetic algorithm multi-objective optimization model for the micro-texture parameters of the tools was established, and the model was solved using the NSGA-II algorithm to obtain a Pareto solution set and micro-texture parameters with a good, comprehensive cutting performance. The micro-texture morphology and parameters obtained in this study can also be used for cutting other high-temperature alloy materials with similar properties to GH4169. This research method can also be used to optimize micro-textured tools for cutting other materials. Full article
(This article belongs to the Special Issue Friction and Wear of Cutting Tools and Cutting Tool Materials)
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Article
Numerical Calculation Method of Multi-Lip Seal Wear under Mixed Thermal Elastohydrodynamic Lubrication
Lubricants 2023, 11(6), 248; https://doi.org/10.3390/lubricants11060248 - 06 Jun 2023
Viewed by 701
Abstract
The multi-lip combined seal has the advantages of multi-lip coupling, large supporting force, and can withstand high-pressure shocks. It is an irreplaceable structure for single-lip seals. However, most of the seal wear analysis focuses on the simulation method of the single-lip seal under [...] Read more.
The multi-lip combined seal has the advantages of multi-lip coupling, large supporting force, and can withstand high-pressure shocks. It is an irreplaceable structure for single-lip seals. However, most of the seal wear analysis focuses on the simulation method of the single-lip seal under the influence of macro factors, and very little involves the wear characteristics of multi-lip seals. In this paper, a micro numerical method is established, which combines the elastohydrodynamic lubrication theory with the modified Archard equation. The performance of a multi-lip combined seal under different working conditions is analyzed through simulation, including macro and micro factors. It is found that some of the characteristics of single-lip seals are also reflected in multi-lip seals, and there is a critical speed that makes the sealing behavior of each seal lip different. Full article
(This article belongs to the Special Issue Modelling in Tribology and Biotribology)
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Editorial
Rolling Contact Fatigue and White Etching Cracks of Bearings
Lubricants 2023, 11(6), 247; https://doi.org/10.3390/lubricants11060247 - 04 Jun 2023
Viewed by 724
Abstract
Lubricants have taken a leading role as drive- train system components in recent years, mainly attributed to their viscosity as a quality criterion [...] Full article
(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)
Article
Eccentric Rotor Drop Dynamics Study of Vertical Maglev Bearing System
Lubricants 2023, 11(6), 246; https://doi.org/10.3390/lubricants11060246 - 03 Jun 2023
Viewed by 648
Abstract
When considering the problem of a vertical magnetic levitation bearing system, the rotor eccentric fall is more likely to cause the failure of the protective bearing. In this paper, a rotor drop collision model and a protective bearing dynamics model are constructed. It [...] Read more.
When considering the problem of a vertical magnetic levitation bearing system, the rotor eccentric fall is more likely to cause the failure of the protective bearing. In this paper, a rotor drop collision model and a protective bearing dynamics model are constructed. It compares and analyzes the evolution of collision force values of the rotor eccentric drop as well as the non-eccentric drop. Further, this paper discusses the law of influence of three factors, rotor quality, rotational speed, and axial protection clearance, on the collision characteristics of the protected bearing in eccentric and non-eccentric cases. It has also experimentally verified this characteristic of rotor speed. The results show that compared with the non-eccentric condition, the axial impact force and radial impact forces of the rotor in the eccentric condition increase by 14% and 114%, respectively. Compared with the non-eccentric condition, with the increase in rotor quality, the axial and radial impact force increase by 68% on average, and the axial depth amplitude of the rotor increases by 350%. With the increase of rotor speed, the axial impact force without an eccentric drop is basically unchanged; the axial impact force of an eccentric drop increases slightly, and the radial impact force increases by 110%. With the increase of axial protection clearance, the radial displacement vibration of the rotor axis increases; the average increase of the maximum axial force is 120 N, and the average increase of the maximum radial force is 100%. Full article
(This article belongs to the Special Issue Advances in Bearing Lubrication and Thermodynamics 2023)
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Article
Analysis of Tool Wear in GH4169 Material Milling Process
Lubricants 2023, 11(6), 245; https://doi.org/10.3390/lubricants11060245 - 01 Jun 2023
Viewed by 549
Abstract
Nickel-based superalloy GH4169 is a material with strong mechanical properties and is difficult to process. In order to reduce tool wear during material processing and improve the workpiece surface processing quality, based on the finite element simulation software DEFORM, the influence of n, [...] Read more.
Nickel-based superalloy GH4169 is a material with strong mechanical properties and is difficult to process. In order to reduce tool wear during material processing and improve the workpiece surface processing quality, based on the finite element simulation software DEFORM, the influence of n, ap, and fz parameters on tool wear during carbide tool milling GH4169 was studied, and a simulation of an orthogonal experimental model was established. The prediction model of tool wear was obtained. The ultrasonic vibration milling was compared with ordinary milling, and the improvement degree of different coating materials on carbide tool wear was explored. The results showed that the ultrasonic vibration signal is helpful to reduce tool wear, improve the surface quality of the workpiece, and improve the stability of the milling process. TiAlN/TiN (WC)-composite-coated tools have good cutting performance, help to reduce tool temperature, reduce tool wear, and improve tool life. Full article
(This article belongs to the Special Issue Friction and Wear of Cutting Tools and Cutting Tool Materials)
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Article
Synergistic Lubrication Mechanism of Nano-Fluid and Grinding Wheel Prepared by CNTs@T304 Nano-Capsules
Lubricants 2023, 11(6), 244; https://doi.org/10.3390/lubricants11060244 - 01 Jun 2023
Viewed by 635
Abstract
Grinding fluid often struggles to enter the grinding area and overcoming this challenge has been a major focus of research in recent years. Therefore, CNTs@T304 nano-capsules are prepared by filling the cavities of CNTs with a lubricant of T304. CNTs@T304 nano-capsules were used [...] Read more.
Grinding fluid often struggles to enter the grinding area and overcoming this challenge has been a major focus of research in recent years. Therefore, CNTs@T304 nano-capsules are prepared by filling the cavities of CNTs with a lubricant of T304. CNTs@T304 nano-capsules were used as an additive in this paper to prepare resin grinding wheels and nanofluids, respectively. The resin wheels filled with nano-capsules were used for grinding under the lubrication of nanofluids, and T304 could then be released to the grinding area to play a self-lubricating role during grinding. First, CNTs@T304 nano-capsules were characterized, and the properties of the prepared grinding wheels and nanofluids were tested. Second, the effects of the filling of nano-capsules and grinding speed on the grinding force, grinding temperature, surface roughness, and grinding ratio were studied. Finally, the lubrication mechanism of the nano-capsules was revealed through surface analysis of the workpiece. The results suggested that nano-capsules had good thermal stability and the nanofluid prepared from them exhibited good dispersion stability and thermal conductivity. The grinding wheel was found to satisfy the service conditions when the filling content was less than 15%. Compared with a common wheel, the grinding force and grinding temperature were reduced by 24% and 28%, respectively, and the surface roughness of the workpiece and the grinding ratio were increased by 18% and by 21%, respectively, when grinding GCr15 steel with the nano-capsule wheel. Lubrication with nanofluids could further reduce the grinding force, grinding temperature, and surface roughness values. During grinding, the self-lubrication film formed by the T304 released from the nano-capsules in the wheel served first and foremost as a lubricant. The intervention of the nanofluid enhanced the heat-exchange effect and lubrication efficiency in the grinding zone. Full article
(This article belongs to the Special Issue Science and Technology in Nanotribology)
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Article
Erosive Wear Behavior of Novel Hybrid Multicomponent Cast Alloys with Different C and B Contents
Lubricants 2023, 11(6), 243; https://doi.org/10.3390/lubricants11060243 - 31 May 2023
Viewed by 556
Abstract
Multicomponent and high-boron cast alloys have been recognized as materials with excellent wear resistance due to the formation of hard phases called carbides and borides. However, the wear performance of the combination of these two materials called hybrid multicomponent cast alloys (HMCAs) has [...] Read more.
Multicomponent and high-boron cast alloys have been recognized as materials with excellent wear resistance due to the formation of hard phases called carbides and borides. However, the wear performance of the combination of these two materials called hybrid multicomponent cast alloys (HMCAs) has not been comprehensively studied. Therefore, this study will evaluate the effect of C (0–0.9 wt.%) and B (1.5–3.5 wt.%) addition on the erosion wear behavior of an HMCA containing 2.5 wt.% Ti, 10 wt.% Cr, and 5 wt.% each of V, Mo, and W. Shot-blast erosion testing was used to evaluate the wear resistance of each alloy. The test was conducted for 3600 s using 2 kg of irregularly shaped steel sand as a scraper at impact angles of 30°, 60°, and 90°. The results showed that the highest wear rate in 0C and 0.45C with 1.5–3.5% B occurred at an impact angle of 60° due to gouging and indentation mechanisms occurring simultaneously. However, different results occurred in the case of 0.9C with the same amount of B where the wear rate increased with increasing impact angle due to brittleness. Based on the chemical composition, the wear resistance of the alloy increased with increasing C content due to higher hardness values. However, the reverse performance occurred when the addition of B exceeded the threshold (more than 1.5 wt.%) despite the higher hardness. This fact was due to the susceptibility to carbide cracking as the amount of B increased. Therefore, the alloy with the best erosion wear resistance was 0.9C–1.5B HMCA. Full article
(This article belongs to the Special Issue Frictional Behavior and Wear Performance of Cast Irons)
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Article
A Numerical Investigation of the Effects of Groove Texture on the Dynamics of a Water-Lubricated Bearing–Rotor System
Lubricants 2023, 11(6), 242; https://doi.org/10.3390/lubricants11060242 - 31 May 2023
Cited by 1 | Viewed by 627
Abstract
This paper aims to investigate the combined effects of working condition and structural parameters of groove texture on the dynamic characteristics, stability and unbalance response of a water-lubricated hydrodynamic bearing–rotor system to avoid instability and excessive vibration of the rotor. The Navier–Stokes equation, [...] Read more.
This paper aims to investigate the combined effects of working condition and structural parameters of groove texture on the dynamic characteristics, stability and unbalance response of a water-lubricated hydrodynamic bearing–rotor system to avoid instability and excessive vibration of the rotor. The Navier–Stokes equation, standard K-ε model with enhanced wall treatment and Zwart–Gerber–Belamri cavitation model are considered using the commercial software Fluent to calculate the stiffness and damping coefficients of a groove-textured, water-lubricated bearing based on the dynamic mesh method; the critical mass to express the stability and the unbalance response solved by the fourth order Runge–Kutta method of the rotor are calculated based on dynamic equations. The results indicate that shallower and longer groove textures can improve the direct stiffness along the load direction kyy, weaken the stiffness in the orthogonal direction kxx, improve stability and decrease the unbalance response amplitude of the water-lubricated bearing–rotor system at a greater rotational speed and smaller eccentricity ratio; however, the impact of grooves on damping parameters is not as great as it is on stiffness—there exists an optimum groove width to achieve a best dynamic performance. Full article
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Article
Degradation Effects of Base Oils after Thermal and Electrical Aging for EV Thermal Fluid Applications
Lubricants 2023, 11(6), 241; https://doi.org/10.3390/lubricants11060241 - 31 May 2023
Viewed by 848
Abstract
This study presents the experimental results of the effects on base oils after thermal and electrical aging to determine key parameters of next-generation fluids for thermal management in electric vehicles. The test fluids selected were a mineral base oil API G-III, an API [...] Read more.
This study presents the experimental results of the effects on base oils after thermal and electrical aging to determine key parameters of next-generation fluids for thermal management in electric vehicles. The test fluids selected were a mineral base oil API G-III, an API G-IV Polyalphaolefin (PAO), a diester, and a polyolester, all of which had similar kinematic viscosity (KV100 = 4 cSt). All were initially characterized with measurements of density, viscosity, thermal conductivity, specific heat capacity, breakdown voltage, resistivity, and dissipation factor. They underwent two separate aging processes, one thermal, heating the test fluid at 150 °C for 120 h with a copper strip as a catalyst; and the second one an electrical aging process, with the application of 1000 breakdown voltage discharges. The same properties were measured again after each aging process and compared to the initial ones. It was found that the thermal properties ranged with similar values and did not suffer major changes after the aging processes, unlike electrical properties, which vary between samples and after thermal and electrical stress. The insights gained from this study have implications for both the development of next-generation e-thermal fluids and the future standardization of these fluids for EV thermal management applications. The findings of this study underscore the significance of formulating and selecting a suitable dielectric fluid for EV thermal management. By leveraging the insights provided, researchers and engineers can advance in the development of efficient and reliable e-thermal fluids while working towards future standardization to enhance the performance and safety of EV battery systems. Full article
(This article belongs to the Special Issue Tribology in Mobility, Volume II)
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Article
A Fluid-Structure Interaction Method for the Elastohydrodynamic Lubrication Characteristics of Rubber-Plastic Double-Layer Water-Lubricated Journal Bearings
Lubricants 2023, 11(6), 240; https://doi.org/10.3390/lubricants11060240 - 28 May 2023
Viewed by 813
Abstract
This paper proposes a fluid-structure interaction (FSI) numerical calculation method for investigation of the elastohydrodynamic lubrication performance of the rubber-plastic double-layer water-lubricated journal bearings. The accuracy and rapidity of the FSI method are improved by studying the effect of mesh density and by [...] Read more.
This paper proposes a fluid-structure interaction (FSI) numerical calculation method for investigation of the elastohydrodynamic lubrication performance of the rubber-plastic double-layer water-lubricated journal bearings. The accuracy and rapidity of the FSI method are improved by studying the effect of mesh density and by comparing the calculation results with those in the literature. Based on the proposed method, a series of numerical simulations are carried out to reveal the influence of operating conditions and structural parameters on the lubrication performance of the rubber-plastic bearings. Numerical results show that the bush deformation of the rubber-plastic bearing is between that of the rubber bearing and the plastic bearing, and the deformation area is close to that of the rubber bearing. The bearing load carrying capacity increases significantly with the rotational speed, eccentricity ratio, bearing length, and decrease with the clearance. But the influences of the plastic layer elastic modulus and thickness on bearing load are unremarkable. The effect of bush deformation on bearing load is noticeable when the eccentricity ratio is more than 0.8. The results are expected to provide design references for the bearings. Full article
(This article belongs to the Special Issue Water-Lubricated Bearings)
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Article
Novel Process Modeling of Magnetic-Field Assisted Finishing (MAF) with Rheological Properties
Lubricants 2023, 11(6), 239; https://doi.org/10.3390/lubricants11060239 - 27 May 2023
Cited by 1 | Viewed by 734
Abstract
The performance of a magnetic-field-assisted finishing (MAF) process, an advanced surface finishing process, is severely affected by the rheological properties of an MAF brush. The yield stress and viscosity of the MAF brush, comprising iron particles and abrasives mixed in a liquid carrier [...] Read more.
The performance of a magnetic-field-assisted finishing (MAF) process, an advanced surface finishing process, is severely affected by the rheological properties of an MAF brush. The yield stress and viscosity of the MAF brush, comprising iron particles and abrasives mixed in a liquid carrier medium, change depending on the brush’s constituents and the applied magnetic field, which in turn affect the material removal mechanism and the corresponding final surface roughness after the MAF. A series of experiments was conducted to delineate the effect of MAF processing conditions on the yield stress of the MAF brush. The experimental data were fitted into commonly used rheology models. The Herschel–Bulkley (HB) model was found to be the most suitable fit (lowest sum of square errors (SSE)) for the shear stress–shear rate data obtained from the rheology tests and used to calculate the yield stress of the MAF brush. Processing parameters, such as magnetic flux density, weight ratio of iron and abrasives, and abrasive (black ceramic in this study) size, with p-values of 0.031, 0.001 and 0.037, respectively, (each of them lower than the significance level of 0.05), were all found to be statistically significant parameters that affected the yield stress of the MAF brush. Yield stress increased with magnetic flux density and the weight ratio of iron to abrasives in MAF brush and decreased with abrasive size. A new process model, a rheology-integrated model (RM), was formulated using the yield stress data from HB model to determine the indentation depth of individual abrasives in the workpiece during the MAF process. The calculated indentation depth enabled us to predict the material removal rate (MRR) and the instantaneous surface roughness. The predicted MRR and surface roughness from the RM model were found to be a better fit with the experimental data than the pre-existing contact mechanics model (CMM) and wear model (WM) with a R2 of 0.91 for RM as compared to 0.76 and 0.78 for CMM and WM. Finally, the RM, under parametric variations, showed that MRR increases and roughness decreases as magnetic flux density, rotational speed, weight ratio of iron to abrasive particles in MAF brush, and initial roughness increase, and abrasive size decreases. Full article
(This article belongs to the Special Issue State-of-the-Art of Tribology in North America)
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