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Lubricants
Volume 13
Issue 11
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Lubricants, Volume 13, Issue 11 (November 2025) – 44 articles

Cover Story (view full-size image): Environmental contaminants such as particles and water ingress accelerate grease degradation and reduce tribological performance in machine components. This study evaluates the effects of SiO2 particle concentration and water contamination, alone and in combination, on the frictional, thermal, wear, and fatigue behavior of calcium-based grease in bearing steel contacts. By demonstrating a linkage between vibration-derived energy ratios and pitting evolution, the work provides mechanistic insight into degradation progression and supports advanced monitoring strategies for contaminated lubrication systems. View this paper
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23 pages, 3423 KB  
Article
The Influence of Initial Solution Estimate Method on Efficient Boundary Element Modeling of Rolling Contact
by Shuang Chen, Hongxiang Lai, Boyang An and Jiapeng Liu
Lubricants 2025, 13(11), 508; https://doi.org/10.3390/lubricants13110508 - 20 Nov 2025
Viewed by 359
Abstract
A novel methodology is proposed for accelerating the calculation efficiency of the boundary element modeling of rolling contact. This methodology involves the implementation of an initial solution estimate. The method is to provide the initial estimate value by means of simplifying the method, [...] Read more.
A novel methodology is proposed for accelerating the calculation efficiency of the boundary element modeling of rolling contact. This methodology involves the implementation of an initial solution estimate. The method is to provide the initial estimate value by means of simplifying the method, which is used for the iterative calculation of the boundary element method to solve the normal and tangential contact problems. In the normal contact problem, the normal pressure and contact patch are provided as the initial values for the iterative calculation of the boundary element method. In the tangential contact problem, the initial values for tangential stress and adhesion-slip distribution are provided. A first novel aspect is breaking the initial iteration setting of the traditional BEM, which can significantly reduce the iterations. A second novelty is that a method for determining the potential contact area is proposed to ensure the correctness of boundary element modeling without increasing the computational cost. In the following section, an analysis is conducted to ascertain the impact of the initial solution estimate method on the efficacy of boundary element modeling. The result is that efficiency increased by 69.1% of normal contact calculations, with the initial contact patch exerting the most significant influence. The efficiency of the process under investigation increased by 56.9%, and the most pronounced effect is the distribution of adhesion-slip. Full article
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18 pages, 6078 KB  
Article
Remaining Useful Life Prediction of Cutting Tools Based on a Depthwise Separable TCN-BiLSTM Model with Temporal Attention
by Shaoyan Wang, Haili Jia, Aimin Wang, Long Wu and Qianxiong Li
Lubricants 2025, 13(11), 507; https://doi.org/10.3390/lubricants13110507 - 20 Nov 2025
Viewed by 425
Abstract
The prediction of remaining tool life is critical in practical manufacturing, as it enables early identification of tool wear conditions, preventing downtime and quality issues caused by tool failure. This, in turn, helps reduce costs and improve production efficiency. To address the limitations [...] Read more.
The prediction of remaining tool life is critical in practical manufacturing, as it enables early identification of tool wear conditions, preventing downtime and quality issues caused by tool failure. This, in turn, helps reduce costs and improve production efficiency. To address the limitations of traditional models in modeling complex temporal dependencies and capturing critical moment information, a hybrid deep learning model based on a TCN-BiLSTM-Attention architecture was proposed. The model first enhanced low-level features from raw multivariate signals using an initial feature extraction module. Local temporal patterns were then extracted by an improved Temporal Convolutional Network (TCN), followed by a Bidirectional Long Short-Term Memory (BiLSTM) network to capture global sequential dependencies. An attention mechanism was further introduced to strengthen the model’s ability to focus on and select critical features over time, enabling deeper fusion and modeling of complex temporal dynamics. Finally, a multi-layer regression network was applied to predict the remaining tool life. Experimental validation on the PHM 2010 dataset demonstrates that the proposed model outperforms other comparative models. Among the three evaluation metrics (RMSE, MAE, and R2), the optimal results are 0.0184, 0.0127, and 0.9959 respectively, which fully proves that the model exhibits excellent prediction performance. Ablation studies further confirm the contribution of each module to the overall performance improvement. Full article
(This article belongs to the Special Issue Recent Advances in Tribological Properties of Machine Tools)
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37 pages, 59817 KB  
Article
Generation and Reproduction of Random Rough Surfaces
by Arthur Francisco and Noël Brunetière
Lubricants 2025, 13(11), 506; https://doi.org/10.3390/lubricants13110506 - 19 Nov 2025
Viewed by 451
Abstract
In both mixed lubrication and dry contact studies, statistically meaningful conclusions often require a large set of numerical rough surfaces. While such surfaces can be acquired through metrological tools such as interferometers, they rarely exhibit the exact height or spatial parameters of interest, [...] Read more.
In both mixed lubrication and dry contact studies, statistically meaningful conclusions often require a large set of numerical rough surfaces. While such surfaces can be acquired through metrological tools such as interferometers, they rarely exhibit the exact height or spatial parameters of interest, and the available datasets are typically limited. Although the numerical generation of rough surfaces is not a new subject, its relevance has grown, and important challenges remain. Building on our earlier work, in which a new generation method was introduced, the authors extend its scope to produce surfaces with prescribed height and spatial parameters, under non-periodicity constraints and arbitrary orientation anisotropy. In addition, we propose the reproduction of existing rough surfaces for future AI training applications and highlight topographic patterning as the next major challenge to address. Full article
(This article belongs to the Special Issue Intelligent Algorithms for Triboinformatics)
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30 pages, 3701 KB  
Article
Dynamic Prediction Model for Uneven Slipper Wear Under Complex Lubrication Conditions Considering Lubrication–Wear Coupling
by Hu Mo, Shigang Qin, Wei Zhou, Yunan Yang, Penghui Duan and Fu Peng
Lubricants 2025, 13(11), 505; https://doi.org/10.3390/lubricants13110505 - 19 Nov 2025
Viewed by 316
Abstract
It is difficult to experimentally determine the real-time wear coefficient of a slipper pair under complex lubrication conditions. To address this challenge, this study proposes a predictive method for slipper wear, eliminating the need for experimental measurement of the slipper pair’s friction coefficient [...] Read more.
It is difficult to experimentally determine the real-time wear coefficient of a slipper pair under complex lubrication conditions. To address this challenge, this study proposes a predictive method for slipper wear, eliminating the need for experimental measurement of the slipper pair’s friction coefficient under complex lubrication conditions. The force and motion characteristics of the slipper pair are analyzed to determine the non-uniform clearance distribution caused by elastic deformation and micro-motion. Based on the Greenwood–Williamson (G–W) model and Hertzian contact theory, the contact regions and stresses on the slipper bottom are accurately evaluated under mixed lubrication conditions. The Archard wear equation, combined with wear coefficients obtained from dry friction tests, is employed to calculate the instantaneous uneven wear of the slipper. This wear is then incorporated into iterative calculations of non-uniform clearance, forming a dynamic prediction model that captures the coupled relationship between lubrication and wear. The numerically simulated wear profile was compared with previously reported experimental measurements, and the discrepancies between them were analyzed. The results indicate that the proposed model can effectively predict the outer-side bottom wear of the slipper under steady-state operating conditions. Furthermore, the contact and wear behaviors under extreme conditions are investigated, the modeling results show revealing the variations in wear location and contact stress for ideal flat-bottom, low-speed, and high-speed operating states. The proposed model provides theoretical and methodological insights for optimizing the lubrication performance of slipper pairs during the stable wear stage. Full article
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21 pages, 4230 KB  
Article
Dynamic Analysis and Control Compensation of the Large Optical Mirror Processing Parallel Robot Considering Motion Pair Friction
by Hao Liu, Zujin Jin and Zixin Yin
Lubricants 2025, 13(11), 504; https://doi.org/10.3390/lubricants13110504 - 18 Nov 2025
Viewed by 358
Abstract
The dynamic performance of parallel robots directly determines the machining accuracy in large optical mirror processing (LOMP). However, limitations in traditional dynamic modeling methods hinder their application in real-time control, constraining further improvements in robotic precision. This paper aims to establish a high-precision [...] Read more.
The dynamic performance of parallel robots directly determines the machining accuracy in large optical mirror processing (LOMP). However, limitations in traditional dynamic modeling methods hinder their application in real-time control, constraining further improvements in robotic precision. This paper aims to establish a high-precision and practical dynamic model that considers joint friction for parallel robots used in LOMP, and to design an efficient real-time friction compensation control strategy to effectively enhance trajectory tracking and repetitive positioning accuracy. The novelty of this work lies in proposing a dynamic modeling approach that integrates the static mechanics-based “Disassembly Method” with a “Coulomb + Viscous” friction model. First, static analysis of the mechanism is conducted using the “Disassembly Method” to accurately compute the joint constraint reactions in any pose, providing critical input for friction calculation. Subsequently, a complete dynamic model incorporating friction in joints such as Hooke joints, composite spherical hinges, and ball screws is developed based on the Newton–Euler formulation. This method overcomes the shortcomings of traditional approaches in solving joint reactions and managing model complexity. Numerical simulations demonstrate that, compared to conventional friction-neglected models, the proposed model reveals a maximum increase of approximately 350 N in driving chain joint reaction forces and significant peaks in driving forces at motion reversal instants (e.g., 0.28 s, 0.45 s), quantitatively proving that neglecting friction severely underestimates the actual system loads. Experimental validation shows that the feedforward PD friction compensator designed based on this model reduces the rotational tracking errors of the moving platform around the X- and Y-axis from 0.295° and 0.286° to 0.134° and 0.128°, respectively, achieving an error reduction of about 55% and effectively improving motion control accuracy. This study provides a reliable dynamic modeling foundation and an effective real-time control compensation solution to address force output errors and trajectory deviations caused by joint friction in high-precision LOMP. Full article
(This article belongs to the Special Issue Machine Design and Tribology)
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14 pages, 4117 KB  
Article
Tool Wear Condition Monitoring Based on Improved Symmetrized Dot Pattern Enhanced Resnet18 Under Small Samples
by Xiaoqin Chen, Gonghai Wang, Yuandie Fu, Huan Zhang and Chen Gao
Lubricants 2025, 13(11), 503; https://doi.org/10.3390/lubricants13110503 - 17 Nov 2025
Viewed by 358
Abstract
Timely and effective identification of the tool wear condition is crucial for ensuring the machining quality of CNC machine tools. In most industrial scenarios, the cost of sample collection is high, so only a small number of samples are available for model training, [...] Read more.
Timely and effective identification of the tool wear condition is crucial for ensuring the machining quality of CNC machine tools. In most industrial scenarios, the cost of sample collection is high, so only a small number of samples are available for model training, making it difficult for the existing tool wear condition monitoring (TCM) methods based on deep learning to achieve high performance. To address this problem, this paper proposes a TCM method based on the improved symmetric dot pattern (SDP) enhanced ResNet18. Firstly, the time series sample data is converted into grayscale matrices through SDP, the correlation coefficient between the grayscale matrices is calculated, and the optimal parameter combination of SDP is determined according to the objective of minimizing the correlation coefficient. Then, the cutting force signal is converted into a lobe diagram of the optimized SDP to enrich the sample feature information. Next, the SDP lobe diagram is input into ResNet18 for few-shot learning. The results of a series of TCM experiments demonstrate that the proposed method is significantly superior to the STFT and GAF based methods. Full article
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17 pages, 8739 KB  
Article
Study on the Effect of Laser Shock Angle on Surface Integrity and Wear Performance of H13 Steel
by Ke Tang, Jiang Zhu, Zejie Li, Shiqi Chen, Yuqiang Zhang, Yunfeng Yan, Qing Hao, Bicheng Guo, Fasheng Zhong, Weiwen Chen, Shizhang Liu and Jiashun Gao
Lubricants 2025, 13(11), 502; https://doi.org/10.3390/lubricants13110502 - 17 Nov 2025
Viewed by 372
Abstract
The internal surfaces of hot-working dies are prone to wear and fatigue fracture during service, often necessitating surface modification and strengthening. Among available techniques, laser shock peening (LSP) is an effective surface strengthening method. However, when treating internal surfaces, achieving perpendicular laser incidence [...] Read more.
The internal surfaces of hot-working dies are prone to wear and fatigue fracture during service, often necessitating surface modification and strengthening. Among available techniques, laser shock peening (LSP) is an effective surface strengthening method. However, when treating internal surfaces, achieving perpendicular laser incidence is difficult, and irradiation must often be applied at an angle. To clarify the relationship between the laser incidence angle and the strengthening effect, this study applied laser shock peening to H13 steel at various incidence angles(0°, 15°, 30°, 45°) with a spot diameter of 3 mm, using laser energies of 8 J, 8.2 J, 9.2 J, and 11.3 J, respectively, and maintaining a fixed power density of 1.41 GW/cm2. By maintaining a consistent power density through laser energy compensation, the influence of the incidence angle on surface integrity and wear resistance of the hole structure was systematically investigated. The results show that as the impact angle increases from 0° to 45°, the depth of the affected material layer gradually decreases. Surface microhardness and residual compressive stress peak at a 30° impact angle, reaching values of 633.5 HV1 and 517.4 Mpa, respectively. Wear tests indicated that the friction coefficient was lowest at 30° (0.542), with the dominant wear mechanism shifting from abrasive to adhesive wear. Under controlled power density conditions, oblique laser impact improves surface properties at the expense of a reduced thickness of the affected layer. Full article
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28 pages, 7297 KB  
Article
Tailored Cage Shapes on Lubricant Migration and Friction Behaviours in Both Ball-Cage and EHL Contacts
by Kecheng Zhou, Xuyang Jin, Xinming Li, Qinghua Bai, Xiongrong Huang, Hao Jiang, Guohui Zhang, Feng Guo, Chenglong Liu and Jinjie Li
Lubricants 2025, 13(11), 501; https://doi.org/10.3390/lubricants13110501 - 17 Nov 2025
Viewed by 405
Abstract
The cage shape plays a critical role in controlling lubricant distribution and replenishment and enhancing lubrication performance within rolling bearings. This study investigates the effect of four tailored cage shapes on lubricant migration and frictional characteristics at both Ball-Cage (B-C) and Ball-Disc (B-D) [...] Read more.
The cage shape plays a critical role in controlling lubricant distribution and replenishment and enhancing lubrication performance within rolling bearings. This study investigates the effect of four tailored cage shapes on lubricant migration and frictional characteristics at both Ball-Cage (B-C) and Ball-Disc (B-D) contacts. Utilizing a bearing cage friction and lubrication test rig (BCFL), adapted from an optical elastohydrodynamic lubrication (EHL) apparatus, the variation in grease films and friction forces was examined under varying entrainment speeds, grease properties, and grease quantities. Cage-induced lubricant redistribution on the ball surface, replenishment at the B-D contact, and the formation mechanism of thicker film thickness were recognized. The influence of cage design for four distinct shapes on mechanisms enhancing grease lubrication efficiency and friction reduction was examined. The findings provide critical insights for designing next-generation self-aligning cage structures with improved lubrication performance and reduced friction force. Full article
(This article belongs to the Special Issue Advances in Lubricated Bearings, 2nd Edition)
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26 pages, 3487 KB  
Article
Intelligent Tool Wear Prediction Using CNN-BiLSTM-AM Based on Chaotic Particle Swarm Optimization (CPSO) Hyperparameter Optimization
by Fei Ma, Zhengze Yang, Hepeng Zhang and Weiwei Sun
Lubricants 2025, 13(11), 500; https://doi.org/10.3390/lubricants13110500 - 16 Nov 2025
Viewed by 366
Abstract
Against the backdrop of the rapid development of the manufacturing industry, online monitoring of tool wear status is of great significance for enhancing the reliability and intelligence of CNC machine tools. This paper presents an intelligent tool wear condition monitoring model (CPSO-CNN-BiLSTM-AM) that [...] Read more.
Against the backdrop of the rapid development of the manufacturing industry, online monitoring of tool wear status is of great significance for enhancing the reliability and intelligence of CNC machine tools. This paper presents an intelligent tool wear condition monitoring model (CPSO-CNN-BiLSTM-AM) that integrates the improved Chaotic Particle Swarm Optimization (CPSO) algorithm with the CNN-BiLSTM network incorporating an attention mechanism. The aim is to extract the global features of long-sequence monitoring data and the local features of multi-spatial data. Chaos theory and the mutation mechanism are introduced into the CPSO algorithm, which enhances the algorithm’s global search ability and its capacity to escape local optimal solutions, enabling more efficient optimization of the hyperparameters of the CNN-BiLSTM network. The CNN-BiLSTM network with the introduced attention mechanism can more accurately extract the spatial features of wear signals and the dependencies of time-series signals, and focus on the key features in wear signals. The study utilized the IEEE PHM2010 Challenge dataset, extracted wear features through time-domain, frequency-domain, and time-frequency domain methods, and divided the training set and validation set using cross-validation. The results show that in the public PHM2010 dataset, the average MAE of the model for tools C1, C4, and C6 is 0.83 μm, 1.01 μm, and 1.34 μm, respectively; the RMSE is 0.99 μm, 1.79 μm, and 0.88 μm, respectively; and the MAPE is 0.95%, 1.41%, and 1.01%, respectively. In the self-built dataset, the average MAE for tools A1, A2, and A3 is 1.35 μm, 1.19 μm, and 1.83 μm, respectively; the RMSE is 1.41 μm, 1.98 μm, and 1.90 μm, respectively; and the MAPE is 1.67%, 1.55%, and 1.81%, respectively. All indicators are superior to those of comparative models such as LSTM and PSO-CNN. The proposed model can effectively capture changes in different stages of tool wear, providing a more accurate solution for tool wear condition monitoring. Full article
(This article belongs to the Special Issue Advances in Tool Wear Monitoring 2025)
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19 pages, 4277 KB  
Article
Investigation of Performance Degradation in Calcium-Based Grease Under Combined SiO2 Particle and Water Contamination
by Thi-Na Ta, Shin-Yuh Chern, Jeng-Haur Horng, Chun-Wei Kuo and Sheng-Jie Liao
Lubricants 2025, 13(11), 499; https://doi.org/10.3390/lubricants13110499 - 15 Nov 2025
Viewed by 410
Abstract
Environmental contamination critically affects the durability and performance of lubricants in machine components. Over long operating periods, particles and water ingress through degraded seals accelerate grease degradation and deteriorate tribological behavior. This study evaluates the effects of SiO2 particle concentration and water [...] Read more.
Environmental contamination critically affects the durability and performance of lubricants in machine components. Over long operating periods, particles and water ingress through degraded seals accelerate grease degradation and deteriorate tribological behavior. This study evaluates the effects of SiO2 particle concentration and water contamination, alone and in combination, on the performance of calcium-based grease in bearing steel contacts. Friction coefficients, grease temperatures, wear, pitting, and vibration signals were analyzed. The results show that an increase in particle concentration raised both friction and temperature, leading to more severe wear and pitting. The addition of 0.6 wt% water reduced fluctuations in friction and temperature, but when combined with high particle concentrations, it significantly worsened wear and pitting. The vibration-based energy ratio correlated strongly with pitting evolution, highlighting its potential as a sensitive parameter for monitoring surface fatigue. These findings provide insights into lubricant degradation under contaminated conditions and offer guidance for improving the reliability of lubricated systems. Full article
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21 pages, 3711 KB  
Article
Hybrid ML-Based Cutting Temperature Prediction in Hard Milling Under Sustainable Lubrication
by Balasuadhakar Arumugam, Thirumalai Kumaran Sundaresan and Saood Ali
Lubricants 2025, 13(11), 498; https://doi.org/10.3390/lubricants13110498 - 14 Nov 2025
Viewed by 469
Abstract
The field of hard milling has recently witnessed growing interest in environmentally sustainable machining practices. Among these, Minimum Quantity Lubrication (MQL) has emerged as an effective strategy, offering not only reduced environmental impact but also economic benefits and enhanced cooling performance compared to [...] Read more.
The field of hard milling has recently witnessed growing interest in environmentally sustainable machining practices. Among these, Minimum Quantity Lubrication (MQL) has emerged as an effective strategy, offering not only reduced environmental impact but also economic benefits and enhanced cooling performance compared to conventional flood cooling methods. In hard milling operations, cutting temperature is a critical factor that significantly influences the quality of the finished component. Proper control of this parameter is essential for producing high-precision workpieces, yet measuring cutting temperature is often complex, time-consuming, and costly. These challenges can be effectively addressed by predicting cutting temperature using advanced Machine Learning (ML) models, which offer a faster and more efficient alternative to direct measurement. In this context, the present study investigates and compares the performance of Conventional Minimum Quantity Lubrication (CMQL) and Graphene-Enhanced MQL (GEMQL), with sesame oil serving as the base fluid, in terms of their effect on cutting temperature. The experiments are structured using a Taguchi L36 orthogonal array, with key variables including cutting speed, feed rate, MQL jet pressure, and the type of cooling applied. Additionally, the study explores the predictive capabilities of various advanced ML models, including Decision Tree, XGBoost Regressor, K-Nearest Neighbor, Random Forest Regressor, and CatBoost Regressor, along with a Hybrid Stacking Machine Learning Model (HSMLM) for estimating cutting temperature. The results demonstrate that the GEMQL setup reduced cutting temperature by 36.8% compared to the CMQL environment. Among all the ML models tested, HSMLM exhibited superior predictive performance, achieving the best evaluation metrics with a mean absolute error of 3.15, root mean squared error (RMSE) of 5.3, mean absolute percentage error of 3.9, coefficient of determination (R2) of 0.91, and an overall accuracy of 96%. Full article
(This article belongs to the Special Issue Sustainable and Advanced Lubrication Strategies for Industrial and Environmental Applications)
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15 pages, 3015 KB  
Article
Assessing Impact of Wheel–Rail Force on Insufficient Displacement of Switch Rail in High-Speed Railway
by Pu Wang, Lei Han, Xiaohua Wei, Dongsheng Yang, Daolin Si, Moyan Zhang, Shuguo Wang and Guoqing Jing
Lubricants 2025, 13(11), 497; https://doi.org/10.3390/lubricants13110497 - 14 Nov 2025
Viewed by 359
Abstract
High-speed railway turnouts play important roles in the efficient operation of trains. However, the complex mechanical structure of turnouts and insufficient displacement of switch rails under dynamic conditions create a point of vulnerability for high-speed railways. The insufficient displacement of switch rails in [...] Read more.
High-speed railway turnouts play important roles in the efficient operation of trains. However, the complex mechanical structure of turnouts and insufficient displacement of switch rails under dynamic conditions create a point of vulnerability for high-speed railways. The insufficient displacement of switch rails in high-speed railway No. 18 turnouts critically impacts operational safety. This study establishes a coupled finite element model of the switch rail and sliding track bed plate to analyse the effects of the friction coefficient and wheel–rail force. The results show that without considering the force of the iron block, the maximum insufficient displacement of a switch rail occurs at sleeper No. 27, and the maximum insufficient displacement increases linearly with the friction coefficient, with a regression coefficient of 1.02. When considering the wheel–rail force of the train, the maximum insufficient displacement of the switch rail occurs at sleeper No. 25, with the regression coefficient reduced to 0.67. Through dynamic and static tests and a case analysis, the influence of wheel–rail force on the insufficient displacement of a switch rail is verified. The results show that the application of a lateral wheel–rail force in the model significantly reduces the insufficient displacement of the switch rail, with an improvement of more than 90%. This study can significantly improve the optimisation of turnout design and the operational efficiency of a railway network. Full article
(This article belongs to the Special Issue Tribological Challenges in Wheel-Rail Contact)
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14 pages, 1985 KB  
Review
Toughening Mechanisms of Diamond-like Carbon Films via Non-Carbide Metal Doping
by Jiahao Liu, Zhifang Yang, Guangying Cui, Jiayin Lv and Xiang Yu
Lubricants 2025, 13(11), 496; https://doi.org/10.3390/lubricants13110496 - 14 Nov 2025
Viewed by 432
Abstract
The inherent brittleness and poor fracture toughness of diamond-like carbon (DLC) films significantly limit their long-term reliability in mechanical and tribological applications. Among various strategies to enhance toughness, doping with non-carbide-forming metals (e.g., Ag, Cu) has emerged as a highly effective approach due [...] Read more.
The inherent brittleness and poor fracture toughness of diamond-like carbon (DLC) films significantly limit their long-term reliability in mechanical and tribological applications. Among various strategies to enhance toughness, doping with non-carbide-forming metals (e.g., Ag, Cu) has emerged as a highly effective approach due to their ductile properties and compatibility with carbon matrices. This review comprehensively examines the underlying toughening mechanisms induced by non-carbide metal doping in DLC films. We systematically analyze how metal incorporation influences film microstructure, stress state, and crack behavior throughout the entire lifecycle—from deposition to mechanical testing. Five primary toughening mechanisms are identified and discussed: (I) bombardment-induced compressive stress relaxation during film growth; (II) refinement of carbon atomic clusters and enhancement of grain boundary sliding; (III) inhibition of dislocation accumulation through moderated carbon atom repulsion; (IV) plastic deformation, crack bridging, and strain field relaxation at crack tips; (V) shear-induced stress relief via soft metal particles. Among these, Mechanism IV (ductile phase toughening) is identified as the dominant contributor, and their synergistic action can lead to orders of magnitude improvement in wear resistance and a significant increase in crack propagation resistance. Furthermore, the critical role of doping content is emphasized, revealing an optimal concentration range (e.g., ~10–15 at.% for Ag and Cu) beyond which toughness may deteriorate due to excessive boundary formation or hardness loss. This work provides a mechanistic framework for designing toughened DLC films and guides future efforts in developing high-performance, durable carbon-based coatings. Full article
(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)
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17 pages, 4038 KB  
Article
Dynamic Characteristics of Cylindrical Roller Bearing with Cage Pocket Deformation
by Baogang Wen, Song Li, Xiaoye Qi, Zhan-Ge Zhang, Meiling Wang and Jingyu Zhai
Lubricants 2025, 13(11), 495; https://doi.org/10.3390/lubricants13110495 - 13 Nov 2025
Viewed by 348
Abstract
Cage pocket beam deformation occurs due to susceptibility to impact loads under high-speed operating conditions and ultimately alters the bearing’s dynamic characteristics. Regarding the dynamics of localized cage deformation, rollers’ interactions, raceways, and a cage were incorporated, and a rigid–flexible coupled cylindrical roller [...] Read more.
Cage pocket beam deformation occurs due to susceptibility to impact loads under high-speed operating conditions and ultimately alters the bearing’s dynamic characteristics. Regarding the dynamics of localized cage deformation, rollers’ interactions, raceways, and a cage were incorporated, and a rigid–flexible coupled cylindrical roller bearing was modeled dynamically, considering localized cage deformation. The dynamic equations were solved using an adaptive variable-step BDF predictor–corrector algorithm to characterize the behavior of the bearing system. Localized deformations of the cage affected the dynamic characteristics of the bearing. The results show that the cage beams deformed, which increased the local clearance between rollers to a certain extent and was beneficial for the stability of roller motion. However, further increases in clearance can induce roller slippage, suggesting that changes in local clearance are the primary cause of roller slippage. Full article
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13 pages, 2370 KB  
Article
Investigation of the Rheological Behaviour of Three Industrial Lubricants at High Shear Rates and Pressures
by Xin Zhao, Chuang Wu and Chao Wei
Lubricants 2025, 13(11), 494; https://doi.org/10.3390/lubricants13110494 - 12 Nov 2025
Viewed by 416
Abstract
This paper aims to investigate the rheological behaviour of industrial lubricants at high shear and high pressure. A twin-disk rheometer based on a standard UMT apparatus is used to measure the rheological features and film thickness of three lubricants, namely, 150N, UB-3, and [...] Read more.
This paper aims to investigate the rheological behaviour of industrial lubricants at high shear and high pressure. A twin-disk rheometer based on a standard UMT apparatus is used to measure the rheological features and film thickness of three lubricants, namely, 150N, UB-3, and 15W/40, with the shear rate ranging from 0 s−1 to 107 s−1 and the pressure at GPa. A semiempirical rheological model that considers the influence of heat, shear, and fluidic plasticity was proposed to adequately fit the experimental data of three organic lubricants. The rheology of the lubricants has a linear to nonlinear relationship with increasing shear rate, indicating shear thinning, which is then followed by a sharp decrease at approximately 106 s−1 because of thermal effects. At a higher shear rate, the shear stress saturates to a critical value. Moreover, the critical traction coefficients in the saturation region show similar changes in pressure and temperature for the three lubricants. The coefficients are greater at 1 GPa but decrease and saturate above 1.45 GPa, probably because the molecular-free volume is compressed by the constraint. The coefficients change little with varying inlet temperature at 1.45 GPa. This research sheds light on the complex rheological behaviour of three lubricants at high shear rates and high pressures and attempts to explain them theoretically. Full article
(This article belongs to the Special Issue Experimental Modelling of Tribosystems)
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31 pages, 2622 KB  
Review
Review and Prospect of Research Status on Sliding Bearing Coatings
by Fengming Du, Zhen Guo, Renhao Mo, Wenqing Lin and Shuai Zhang
Lubricants 2025, 13(11), 493; https://doi.org/10.3390/lubricants13110493 - 12 Nov 2025
Viewed by 672
Abstract
With the advancement of industrial technology toward high speed, heavy load, precision, and automation, traditional sliding bearing materials have been unable to meet modern industrial demands. Surface coating technology, as an efficient surface modification method, has become a key means to enhance the [...] Read more.
With the advancement of industrial technology toward high speed, heavy load, precision, and automation, traditional sliding bearing materials have been unable to meet modern industrial demands. Surface coating technology, as an efficient surface modification method, has become a key means to enhance the tribological properties, wear resistance, corrosion resistance, and fatigue resistance of sliding bearings, thus extending their service life. This paper systematically reviews the research progress of coating technology for sliding bearings in the past, aiming to fill the gap in comprehensive summaries of multi-material systems and multi-process technologies in existing reviews. In terms of materials, it focuses on the performance characteristics and application scenarios of three major coating types—metal-based, ceramic-based, and polymer-based—clarifying their advantages and limitations. In terms of processes, it analyzes the technical characteristics of mainstream methods including electroplating, magnetron sputtering, and laser cladding, as well as their innovative applications in replacing traditional processes. Furthermore, this review summarizes the latest research results in coating performance evaluation, such as tribological testing via pin-on-disk testers and corrosion resistance analysis via salt spray tests. Finally, it discusses future development trends in new materials, new process applications, and environmental sustainability. This work is expected to provide a valuable reference for related research and engineering applications in the field of sliding bearing coatings. Full article
(This article belongs to the Special Issue Advanced Surface Treatments and Coatings for Friction and Wear Reduction)
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19 pages, 4593 KB  
Article
Effects of Grooved Surfaces and Lubrication Media on the Performance of Hybrid Gas Journal Bearings
by Adesh Kumar Tomar, Krishnkant Sahu, Satish C. Sharma and Max Marian
Lubricants 2025, 13(11), 492; https://doi.org/10.3390/lubricants13110492 - 10 Nov 2025
Viewed by 449
Abstract
Gas bearings are attractive for sustainable, high-speed, and cryogenic applications, where gases replace liquid lubricants. This study numerically analyzed hybrid gas journal bearings lubricated with hydrogen, nitrogen, air, and helium, and quantifies the impact of circumferential micro-grooves. The compressible Reynolds equation was solved [...] Read more.
Gas bearings are attractive for sustainable, high-speed, and cryogenic applications, where gases replace liquid lubricants. This study numerically analyzed hybrid gas journal bearings lubricated with hydrogen, nitrogen, air, and helium, and quantifies the impact of circumferential micro-grooves. The compressible Reynolds equation was solved by the finite element method with constant-flow valve restrictors, while Gauss–Seidel iterations were used for convergence. The model was verified against published theoretical and experimental data with maximum deviations below 6%, and mesh independence is confirmed. The parametric results show that the gas type and texturing jointly controlled static and dynamic performance. Helium (highest viscosity) yielded the largest minimum film thickness, whereas hydrogen (lowest viscosity) attained higher peak pressures at a lower film thickness for a given load. Grooves redistributed pressure and reduced both the maximum pressure and the minimum film thickness, but they also lowered the frictional torque. Quantitatively, the hydrogen-lubricated grooved bearing reduced the frictional torque by up to 50% compared with the non-grooved air-lubricated bearing at the same load. Relative to air, hydrogen increased stiffness and damping by up to 10% and 50%, respectively, and raised the stability threshold speed by 110%. Conversely, grooves decreased the stiffness, damping, and stability threshold speed compared with non-grooved surfaces, revealing a trade-off between friction reduction and dynamic stability. These findings provide design guidance for selecting gas media and surface texturing to tailor hybrid gas journal bearings to application-specific requirements. Full article
(This article belongs to the Special Issue Advances in Lubricated Bearings, 2nd Edition)
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20 pages, 563 KB  
Review
Sustainable and Advanced Lubricating Materials for Automotive Industrial Applications
by Vijay Bhooshan Kumar
Lubricants 2025, 13(11), 491; https://doi.org/10.3390/lubricants13110491 - 10 Nov 2025
Viewed by 746
Abstract
The automotive industry is undergoing a transformative shift toward sustainability, driven by stringent environmental regulations, rising energy demands, and the pursuit of enhanced performance and efficiency. Lubricating materials play a pivotal role in reducing friction, wear, and energy losses in automotive systems, yet [...] Read more.
The automotive industry is undergoing a transformative shift toward sustainability, driven by stringent environmental regulations, rising energy demands, and the pursuit of enhanced performance and efficiency. Lubricating materials play a pivotal role in reducing friction, wear, and energy losses in automotive systems, yet conventional lubricants, primarily petroleum-based, pose significant ecological and operational challenges. This review examines the development and performance of sustainable and advanced lubricant including bio-based oils, synthetic esters, nanolubricants, and ionic/solid lubricants for automotive applications. Drawing on tribological principles and recent advances in materials science, the article categorizes these lubricants based on source, chemical structure, and tribological behavior. A comparative framework is introduced to evaluate key performance indicators such as viscosity index, thermal stability, oxidation resistance, biodegradability, and compatibility with modern engine designs. The review also highlights emerging trends, including nanotechnology-based additives, green synthesis techniques, and novel antioxidant systems that enhance lubricant functionality and lifespan. Furthermore, a strategic research roadmap is proposed, outlining short-, medium-, and long-term priorities that integrate technical, environmental, and economic dimensions. By bridging foundational science with practical innovation, this article aims to guide researchers, manufacturers, and policymakers toward the adoption of high-performance, eco-compatible lubricants that support the transition to cleaner and more efficient mobility systems. Future directions and challenges in scaling, cost-effectiveness, and lifecycle assessment are discussed to guide innovation in this critical domain. Full article
(This article belongs to the Special Issue Sustainable and Advanced Lubrication Strategies for Industrial and Environmental Applications)
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18 pages, 11079 KB  
Article
Friction-Reduction Mechanism and Performance Optimization of Biomimetic Non-Smooth Surfaces Inspired by Dung Beetle Microstructures
by Honglei Zhang, Liquan Tian, Zhong Tang, Meng Fang and Biao Zhang
Lubricants 2025, 13(11), 490; https://doi.org/10.3390/lubricants13110490 - 9 Nov 2025
Viewed by 478
Abstract
Agricultural machinery components suffer from severe soft abrasive wear when interacting with flexible materials like rice stalks. To address this, we investigate the friction-reduction mechanism, parameter optimization, and experimental validation of a biomimetic non-smooth surface inspired by the dung beetle’s microstructure. The bionic [...] Read more.
Agricultural machinery components suffer from severe soft abrasive wear when interacting with flexible materials like rice stalks. To address this, we investigate the friction-reduction mechanism, parameter optimization, and experimental validation of a biomimetic non-smooth surface inspired by the dung beetle’s microstructure. The bionic design was first established by characterizing the beetle’s unique micro-bump array. To ensure simulation accuracy, the critical bonding parameters of a flexible rice stalk DEM model were precisely calibrated via three-point bending tests combined with Response Surface Methodology (RSM). Subsequent DEM simulations revealed that the bionic surface disrupts continuous sliding by reducing the contact area and inducing high-frequency micro-vibrations in the stalk. Using RSM, the bump geometry was systematically optimized, yielding an optimal combination of a 2.975 mm diameter and a 1.0 mm spacing, which theoretically reduces the average normal contact force by 69.3%. Finally, reciprocating wear tests confirmed that the optimized bio-inspired surface exhibited significantly lower mass loss and effectively suppressed the formation of plowing grooves compared to a smooth surface, showing high agreement with simulation predictions. This study provides both a fundamental understanding of the friction-reduction mechanism and precise quantitative guidance for engineering wear-resistant agricultural components. Full article
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21 pages, 2977 KB  
Article
Tribological and Micro-Mechanical Properties of Modified Composite Polypropylene
by Martin Ovsik, Adam Cesnek and Michal Stanek
Lubricants 2025, 13(11), 489; https://doi.org/10.3390/lubricants13110489 - 7 Nov 2025
Viewed by 414
Abstract
This study describes the effect of electron radiation on the macro- and micro-mechanical and tribological properties of composite polypropylene filled with 25% glass fiber. Micro-mechanical and tribological properties were investigated both on the sample surface and at various depths below the surface. Polypropylene [...] Read more.
This study describes the effect of electron radiation on the macro- and micro-mechanical and tribological properties of composite polypropylene filled with 25% glass fiber. Micro-mechanical and tribological properties were investigated both on the sample surface and at various depths below the surface. Polypropylene was irradiated with radiation doses of 15, 33, 45, 66 and 99 kGy. As the results show, electron radiation has an influence on the change in PP’s structure, in which due to the electron radiation, a crosslinked phase and an increase in crystallinity are formed. These changes in morphology are reflected in an enhancement of micro-mechanical and tribological properties both at the surface and in deeper layers below the surface. More crosslinking and recrystallization occur across the sample’s cross-section up to a depth of 2 mm, where greater micro-mechanical and tribological properties are also measured. The difference between the surface and the center of the material can be up to 32%. The optimum radiation dose appears to be 45 kGy, where the maximum crosslinking, highest crystallinity and best micro-mechanical and tribological properties are found. The difference between non-irradiated and irradiated filled PP is 52% in indentation hardness. In terms of macro-mechanical properties, the tensile modulus increased by 44% (45 kGy). This translates into higher surface wear resistance and the overall stiffness of the part. Higher doses of radiation cause the beginning of degradation processes, which are manifested by a decrease in the degree of embedding, crystallinity and thus micro-mechanical and tribological properties. Full article
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12 pages, 2977 KB  
Article
Improving the Surface Finish of Spur Gears Using Palm Oil-Based Lapping: Comparison with Other Industrial Lapping Solutions
by İbrahim Pazarkaya
Lubricants 2025, 13(11), 488; https://doi.org/10.3390/lubricants13110488 - 6 Nov 2025
Viewed by 392
Abstract
Palm oil is among the most produced plant oils in the world and is solid at room temperature. This study aims to produce a palm oil-based lapping solution that contributes to sustainable manufacturing. A palm oil-based lapping solution was compared with grease and [...] Read more.
Palm oil is among the most produced plant oils in the world and is solid at room temperature. This study aims to produce a palm oil-based lapping solution that contributes to sustainable manufacturing. A palm oil-based lapping solution was compared with grease and industrial lapping solutions. Lapping processes were conducted on cylindrical spur gear wheels following the Taguchi L27 experimental design, utilizing three distinct RPMs and varying times. The average surface roughness value after the lapping procedure diminished by 39.45% with the palm oil lapping solution, demonstrating greater effectiveness than the other treatments. The most significant percentage change among all lapping solutions was −59.06%, achieved with palm oil at 32 rpm for 10 min. On the other hand, the Taguchi L27 signal-to-noise analysis shows that the palm oil lapping solution yielded the optimal outcome at 50 rpm and 16 min. A palm oil-based lapping solution was seen as capable of replacing mineral oil-based lapping solutions. Full article
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14 pages, 5587 KB  
Article
Tribological Properties of Aluminum–Silicon Alloy Cylinder Liners Paired with DLC and CKS Piston Rings
by Yong Guan, Cheng-Di Li, Xiao Chen, Shuang-Xia Zhu, Lian-Jie Dong, Peng Ye, Xian-Feng Deng, Ling-Bo Zhou and Lin-Ya Wu
Lubricants 2025, 13(11), 487; https://doi.org/10.3390/lubricants13110487 - 6 Nov 2025
Viewed by 424
Abstract
With the increasing demand for energy conservation and emission reduction in the automotive industry, optimizing the performance of cylinder liner and piston ring pairs in engines has become crucial. Aluminum–silicon alloy cylinder liners, known for their lightweight and excellent thermal conductivity, have emerged [...] Read more.
With the increasing demand for energy conservation and emission reduction in the automotive industry, optimizing the performance of cylinder liner and piston ring pairs in engines has become crucial. Aluminum–silicon alloy cylinder liners, known for their lightweight and excellent thermal conductivity, have emerged as a new trend in cylinder liner materials. Given the relatively moderate hardness of Al-Si alloys, judicious selection of piston rings is imperative to ensure optimal performance. This study investigates the tribological properties of aluminum–silicon alloy cylinder liners paired with CKS and DLC piston rings. The surface morphology and hardness of the test materials were characterized, and reciprocating friction and wear tests were conducted, using a tribometer to simulate operating conditions. The friction coefficient and wear volume were used as indicators to evaluate the tribological properties of the piston rings. The results show that, when the aluminum–silicon alloy cylinder liner was paired with a DLC piston ring, the friction coefficient was 27.82% lower, and the wear volume of the cylinder liner was 83.52% lower, compared to pairing with a CKS piston ring. When paired with a CKS piston ring, wear was exacerbated because silicon particles were easily dislodged to form abrasive particles. This particle detachment is mainly caused by the collision between the fine ceramic particles embedded in the CKS coating and the silicon particles (≤5 μm) uniformly distributed in the Al-Si alloy cylinder liner during the sliding process. The DLC piston ring, containing both sp2 and sp3 hybridized carbon–carbon bonds, combined excellent lubrication properties with high hardness, resulting in minimal wear on both the cylinder liner and piston ring. Specifically, the DLC coating has a hardness of 2300 HV0.3, which is 2.42 times that of the CKS piston ring (950 HV0.3); the sp3-hybridized carbon in the DLC coating enhances its wear resistance to resist scratching from silicon particles in the cylinder liner, while the sp2-hybridized carbon forms a graphite-like transfer layer at the friction interface to reduce frictional resistance. In conclusion, the aluminum–silicon alloy cylinder liner paired with a DLC piston ring exhibits superior tribological properties. Selecting an appropriate piston ring can significantly enhance the tribological properties of the cylinder liner–piston ring pair, thereby extending the engine’s service life. Full article
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23 pages, 3467 KB  
Article
Non-Equilibrium Molecular Dynamics Simulations of Different Base Oils (Mineral and Vegetable) and an Oil Blend
by Jack Nasr and Diana-Luciana Cursaru
Lubricants 2025, 13(11), 486; https://doi.org/10.3390/lubricants13110486 - 6 Nov 2025
Viewed by 404
Abstract
In a previous experimental study, a high-frequency reciprocating rig tribotester was used to test several base oils, including a mineral oil and a vegetable oil, as well as a blend of the two, with and without the addition of carbon-based nanoparticles. The results [...] Read more.
In a previous experimental study, a high-frequency reciprocating rig tribotester was used to test several base oils, including a mineral oil and a vegetable oil, as well as a blend of the two, with and without the addition of carbon-based nanoparticles. The results showed synergy between certain nanoparticles and the oil blend. As such, in this study, molecular dynamics simulations are conducted on three systems to find the model that most accurately represents the experimental setup. These systems consist of lubricant molecules sandwiched between two iron oxide surfaces. The lubricant molecules represent the three types of lubricant used in the experimental study: hexadecane for the mineral base oil, a mixture of fatty acids for the rapeseed oil, and a mixture of both hexadecane and fatty acids for the oil blend. Three system sizes were considered: the first with 100 molecules, the second with 200 molecules, and the third with 300 molecules. The density, velocity, and temperature profiles, as well as the shear rate and coefficient of friction, are analyzed. The results show that the 300-molecule systems show a similar trend to that observed in the experimental study, with the vegetable oil model having the lowest coefficient of friction, followed by the blend model and finally the hexadecane model. The different analyzed profiles provide valuable insights into the interactions within the lubricant film. Full article
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33 pages, 5867 KB  
Article
Quantitative Study on the Friction of Different Types of Base Oils Based on Stribeck Curve and Traction Curve Characterization
by Xinao Guo, Yan Zhao, Wenjing Lou, Binbin Zhang, Xiaobo Wang, Feng Guo and Haichao Liu
Lubricants 2025, 13(11), 485; https://doi.org/10.3390/lubricants13110485 - 3 Nov 2025
Viewed by 556
Abstract
Oils with low-friction performance are essential to meet the evolving requirements of the modern industry. Except for the viscosity, there is still a lack of a high-pressure rheological parameter that can quantitatively compare the friction performance of base oils. This study investigated the [...] Read more.
Oils with low-friction performance are essential to meet the evolving requirements of the modern industry. Except for the viscosity, there is still a lack of a high-pressure rheological parameter that can quantitatively compare the friction performance of base oils. This study investigated the frictional behavior of six types of base oils with identical viscosity at 40 °C—paraffinic mineral oil 500N, naphthenic mineral oil, polyalphaolefin (PAO), oil-soluble polyether, ester oil, and alkyl naphthalene. Stribeck and traction curves were measured. The limiting shear stress (LSS) has been proposed and modeled for the quantitative comparison of the friction behavior of the base oils at high pressures (1.2–1.7 GPa). Results indicate that the PAO exhibits the lowest friction coefficient. Additionally, the LSS of all tested oils has a linear relation with the average contact pressure (R2 > 99%), suggesting that the LSS at different mean contact pressures can be predicted using a linear LSS-pressure fitting model. This work contributes to providing fluid rheological models for the quantitative EHL friction prediction and provides guidance for choosing low-friction base oils for EHL-lubricated rolling/sliding contacts. Full article
(This article belongs to the Special Issue Rheology of Lubricants in Lubrication Engineering)
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32 pages, 7332 KB  
Article
Scuffing Calculation of Cylindrical Gears Facing Loss of Lubrication
by Bernd Morhard, Thomas Lohner and Karsten Stahl
Lubricants 2025, 13(11), 484; https://doi.org/10.3390/lubricants13110484 - 2 Nov 2025
Viewed by 571
Abstract
Loss of lubrication in aeronautic drivetrains can lead to catastrophic gearbox failure, and drivetrains must be tested to prove their resistance to loss of lubrication. Research led to a better understanding of the modes of action, interdependencies, and effective measures to optimize drivetrains [...] Read more.
Loss of lubrication in aeronautic drivetrains can lead to catastrophic gearbox failure, and drivetrains must be tested to prove their resistance to loss of lubrication. Research led to a better understanding of the modes of action, interdependencies, and effective measures to optimize drivetrains for a loss of lubrication event. However, there are currently no calculation methods available, so gear design against loss of lubrication is mainly based on experience. This study proposes a novel calculation method that builds upon the scuffing load calculation from ISO/TS 6336-21 to allow for scuffing safety calculation for cylindrical gears facing loss of lubrication. The proposed method synthesizes existing knowledge in the context of loss of lubrication and incorporates further research results concerning the friction, temperature, and scuffing of gears. The calculation method considers relevant gear design aspects and enables estimation of the time-to-failure. A calculation study is used to compare different measures for cylindrical gears facing loss of lubrication. The results demonstrate the remarkable potential for enhancing loss of lubrication performance through increased oil share in the fluid flow, the application of coatings, the adoption of low-loss gear designs, the use of low-friction lubricants, and the incorporation of additives that increase the scuffing temperature. Full article
(This article belongs to the Topic Engineered Surfaces and Tribological Performance)
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32 pages, 6786 KB  
Review
Advances in DFT-Based Computational Tribology: A Review
by Haochen Feng, Ziwen Cheng, Zhibin Lu and Qichang He
Lubricants 2025, 13(11), 483; https://doi.org/10.3390/lubricants13110483 - 31 Oct 2025
Cited by 1 | Viewed by 746
Abstract
The rapid advancement of micro/nano-electromechanical systems (MEMS/NEMS) and precision manufacturing has fundamentally challenged traditional friction theories at the nanoscale. Classical continuum models fail to capture energy dissipation mechanisms at the atomic level, which are influenced by interfacial phenomena such as electron transfer, charge [...] Read more.
The rapid advancement of micro/nano-electromechanical systems (MEMS/NEMS) and precision manufacturing has fundamentally challenged traditional friction theories at the nanoscale. Classical continuum models fail to capture energy dissipation mechanisms at the atomic level, which are influenced by interfacial phenomena such as electron transfer, charge redistribution, and energy level realignment. Density functional theory (DFT), renowned for its accurate description of ground-state properties in many-electron systems, has emerged as a key tool for uncovering quantized friction mechanisms. By quantifying potential energy surface (PES) fluctuations, the evolution of interfacial charge density, and dynamic electronic band structures, DFT establishes a universal correlation between frictional dissipation and electronic behavior, transcending the limitations of conventional models in explaining stick–slip motion, superlubricity, and non-Amonton effects. Research breakthroughs in the application of DFT include characterizing frictional chemical potentials, designing heterojunction-based superlubricity, elucidating strain/load modulation mechanisms, and resolving electronic energy dissipation pathways. However, these advances remain scattered across interdisciplinary studies. This article systematically summarizes methodological innovations and cutting-edge applications of DFT in computational tribology, with the aim of constructing a unified framework for carrying out the “electronic structure–energy dissipation–frictional response” predictions. It provides a state of the art of using DFT to help design high-performance lubricants and actively control interfacial friction. Full article
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20 pages, 8413 KB  
Article
An Analytical and Numerical Study of Wear Distribution on the Combine Harvester Header Platform: Model Development, Comparison, and Experimental Validation
by Honglei Zhang, Zhong Tang, Liquan Tian, Tiantian Jing and Biao Zhang
Lubricants 2025, 13(11), 482; https://doi.org/10.3390/lubricants13110482 - 30 Oct 2025
Viewed by 549
Abstract
The header platform of a combine harvester is subjected to severe abrasive and corrosive wear from rice stalks and environmental factors, which significantly limits its service life and operational efficiency. Accurately predicting the complex distribution of this wear over time and across the [...] Read more.
The header platform of a combine harvester is subjected to severe abrasive and corrosive wear from rice stalks and environmental factors, which significantly limits its service life and operational efficiency. Accurately predicting the complex distribution of this wear over time and across the platform’s surface, however, remains a significant challenge. This paper, for the first time, systematically establishes a quantitative mapping relationship from “material motion trajectory” to “component wear profile” and introduces a novel method for time-sequence wear validation based on corrosion color gradients, providing a complete research paradigm to address this challenge. To this end, an analytical model based on rigid-body dynamics was first developed to predict the motion trajectory of a single rice stalk. Subsequently, a full-scale Discrete Element (DEM) model of the header platform–flexible rice stalk system was constructed. This model simulated the complex flow process of the rice population with high fidelity and was used to analyze the influence of key operating parameters (spiral auger rotational speed, cutting width) on wear distribution. Finally, real-world wear data were obtained through in situ mapping of a header platform after long-term service (1300 h) and multi-period (0–1600 h) image analysis. Through a three-way quantitative comparison among the theoretical trajectory, simulated trajectory, and the actual wear profile, the results indicate that the simulated and theoretical trajectories are in good agreement in terms of their macroscopic trends (Mean Squared Error, MSE, ranging from 0.4 to 6.2); the simulated and actual wear profiles exhibit an extremely high degree of geometric similarity, with the simulated wear area showing a 95.1% match to the actual measured area (Edit Distance: 0.14; Hamming Distance: 1). This research not only confirms that the flow trajectory of rice is the determining factor for the wear distribution on the header platform but, more importantly, the developed analytical and numerical methods offer a robust theoretical basis and effective predictive tools for optimizing the wear resistance and predicting the service life of the header platform, thereby demonstrating significant engineering value. Full article
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25 pages, 16666 KB  
Article
Effect of Die Design and Lubricant on ZnAl15% Wire Drawing: An Experimental Approach with Pressure/Hydrodynamic and Conventional Drawing Dies
by Juan Carlos del Rey, Guillermo Guerrero-Vacas, Miguel Ochoa-Rodríguez and Oscar Rodríguez-Alabanda
Lubricants 2025, 13(11), 481; https://doi.org/10.3390/lubricants13110481 - 30 Oct 2025
Viewed by 1113
Abstract
The wire drawing process, used for both ferrous and non-ferrous metals, employs different machines depending on the material and wire diameter: breakdown, single- or multi-wire machines for non-ferrous, and bull block machines for ferrous and non-ferrous alloy wires. In all cases, wire is [...] Read more.
The wire drawing process, used for both ferrous and non-ferrous metals, employs different machines depending on the material and wire diameter: breakdown, single- or multi-wire machines for non-ferrous, and bull block machines for ferrous and non-ferrous alloy wires. In all cases, wire is drawn through dies by tensile forces, with die design, material, and lubrication crucial for reducing friction, dissipating heat, and ensuring quality. Die type and geometry, lubricant, drawing speed, and machine configuration are the main process variables. The present work evaluates the effects of die type, lubricant, and drawing speed on Zn–Al alloy wire drawing (Ø2.18 to Ø2.00 mm) using a Taguchi L9 (33) design of experiments. Three lubricants (Multidraw oil/water, Multipress oil and water/oil emulsion), three dies (conventional, carbide 19.38-grade pressure die, carbide H3F-grade pressure die), and three drawing speeds (0.16 to 0.28 m/s) were tested. Results have shown that lubricant and die geometry dominate process performance. Pressure dies reduced drawing force by up to 8% versus the conventional die, and emulsion increased force by 14% compared to oils. Output wire temperatures increased with speed, peaking at 46.5 °C with water emulsion oil and pressure die with H3F carbide, while Multidraw oil kept values ~20% lower. However, emulsions lowered the die output temperatures by 15–25% compared to oils. The coefficient of friction averaged μ = 0.104, with pressure dies yielding the lowest values (0.091–0.096, ~20% below conventional). Surface quality was governed mainly by lubricant effectiveness, with pressure-drawing dies ensuring dimensional accuracy and surface cleanliness. The study identifies lubricant selection as the most influential factor, followed by die type, providing a basis for optimizing efficiency and product quality in the wire drawing of ZnAl15% alloy. Full article
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17 pages, 5179 KB  
Article
Influence of Piston Elastic Deformation and Structure Design on the Lubrication Characteristics of Piston Pair: Simulation Analysis
by Guang-Ming Sun, Guo-Xiang Li, Shu-Zhan Bai, Liang Zheng, Dong-Wei Wu and Guang-Qiang Shi
Lubricants 2025, 13(11), 480; https://doi.org/10.3390/lubricants13110480 - 29 Oct 2025
Viewed by 366
Abstract
Piston pair is a key friction pair of the axial piston pump, but the influence of elastic deformation and the structure design method is not clear. To reveal the real performance of piston pair, a new fluid–solid coupling calculation method is proposed. With [...] Read more.
Piston pair is a key friction pair of the axial piston pump, but the influence of elastic deformation and the structure design method is not clear. To reveal the real performance of piston pair, a new fluid–solid coupling calculation method is proposed. With the method, the oil film pressure and thickness field, elastic deformation, axial viscous friction and leakage of the piston pair are studied. The influences of the elastic deformation of the piston pair on oil film pressure, axial viscous friction, and leakage were revealed. To reduce the impact brought by deformation, a new piston with hollow piston structure (piston B) is designed. Compared with the traditional structure (piston A), piston B is featured with small elastic deformation, small leakage, large peak pressure, and large viscous friction force. The new fluid–solid coupling calculation method and hollow piston structure of this paper lay the foundation for the piston pair design of the axial piston pump. Full article
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23 pages, 4640 KB  
Article
Sensitivity of Texture Evolution and Performance to Eccentricity, Misalignment, and Oil Supply in Journal Bearings with the Circumferential Oil Groove: An Adjoint-Based Optimization Study
by Di Zhang, Haijun Wei and Chunxing Gu
Lubricants 2025, 13(11), 479; https://doi.org/10.3390/lubricants13110479 - 29 Oct 2025
Viewed by 380
Abstract
Previous studies on improving journal bearing performance have predominantly overlooked the combined effects of the surface textures, circumferential oil grooves, eccentricity ratio, and misalignment. To address this gap, this study employed an adjoint -based optimization framework to optimize the LCC (load-carrying capacity) of [...] Read more.
Previous studies on improving journal bearing performance have predominantly overlooked the combined effects of the surface textures, circumferential oil grooves, eccentricity ratio, and misalignment. To address this gap, this study employed an adjoint -based optimization framework to optimize the LCC (load-carrying capacity) of journal bearings based on the mixed lubrication model. By incorporating the influence of the circumferential oil groove, the influences of the oil supply pressure, eccentricity ratio, and misalignment angle on the bearing performance and optimal texture evolution were studied. The results show that increased inlet oil pressure shortens textures and reduces the LCC enhancement, while misalignment boosts the absolute LCC but diminishes the relative benefit of textures. Bidirectionally optimized textures maintain robust performance under reverse rotation, with LCC improvements of 12.00 N at an eccentricity ratio (ER) of 0.8. In contrast, unidirectional textures may impair performance, with a reduction of up to –19.53 N. It is recommended to employ symmetric textures for bidirectional operation and to limit misalignment in order to retain the benefits of surface texturing. This research provides a practical foundation for designing high-performance journal bearings. Full article
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