Lubricants

20 pages, 64732 KB

Open AccessArticle

Stability and Tribological Performance of Water-Emulsified Engine Oils for Hydrogen-Fuelled Internal Combustion Engines

by Nur Aisya Affrina Mohamed Ariffin, Jiahe Poy, King Jye Wong, Jo-Han Ng and William Woei Fong Chong

Lubricants 2025, 13(10), 464; https://doi.org/10.3390/lubricants13100464 - 21 Oct 2025

Abstract

Hydrogen-fuelled internal combustion engines (H₂ICEs) generate water vapour that can condense in the sump and form water-in-oil emulsions, altering lubricant performance. This study measures the viscosity–temperature behaviour, copper corrosivity, and boundary tribology of three commercial oils—synthetic (5W-40), semi-synthetic (10W-40), and mineral [...] Read more.

Hydrogen-fuelled internal combustion engines (H₂ICEs) generate water vapour that can condense in the sump and form water-in-oil emulsions, altering lubricant performance. This study measures the viscosity–temperature behaviour, copper corrosivity, and boundary tribology of three commercial oils—synthetic (5W-40), semi-synthetic (10W-40), and mineral (15W-40)—emulsified with 5–40 wt% water and tested in both freshly emulsified and aged (3 months; clarified oil layer) states. In fresh emulsions, viscosity rose with water fraction. At 25 ^∘C and 40 wt%, the increase was 44.4% (5W-40), 78.7% (10W-40), and 81.2% (15W-40) versus the neat oils. Ageing drove viscosities toward the baseline, with the strongest effect observed for 15W-40, indicating destabilisation. The Vogel–Fulcher–Tammann (VFT) model was fitted to all datasets (RMSE < 5%). A VFT-based screening map uses two ratios at the friction test temperature:

R_{η} = η / η_{neat}

(relative film-forming tendency) and

R_{s} = S / S_{neat}

with

S = B / {(T - T_{0})}^{2}

(thermal-thinning sensitivity). A Preferred regime,

R_{η} \geq 1.25

and

R_{s} \leq 0.95

, is correlated with lower friction, smaller wear scars, and copper rating 1a, with most aged conditions migrated out of this regime. Under boundary conditions, 5–10 wt% water generally reduced friction, whereas higher fractions and ageing increased friction and wear. Synthetic oil (5W-40) showed the most robust response. Full article

(This article belongs to the Special Issue Tribological Impacts of Sustainable Fuels in Mobility Systems)

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24 pages, 2714 KB

Open AccessArticle

Oil Transport Simulation and Oil Consumption Prediction with a Physics-Based and Data-Driven Digital Twin Model for Internal Combustion Engines

by Xinlin Zhong and Tian Tian

Lubricants 2025, 13(10), 463; https://doi.org/10.3390/lubricants13100463 - 21 Oct 2025

Abstract

Lubrication oil consumption (LOC) is one of the major sources of emissions from internal combustion (IC) engines; yet, analyzing and predicting it through modeling is challenging due to its multi-physics nature, which spans different time and length scales. In this work, a digital [...] Read more.

Lubrication oil consumption (LOC) is one of the major sources of emissions from internal combustion (IC) engines; yet, analyzing and predicting it through modeling is challenging due to its multi-physics nature, which spans different time and length scales. In this work, a digital twin model is developed to simulate oil transport in the piston ring pack of IC engines and predict the resulting oil consumption with all major physical mechanisms considered. Three main contributors to LOC, namely, top ring up-scraping, oil vaporization on the liner, and reverse gas flows through the top ring gap, are included in the model. It was found that their behaviors are heavily dependent on the arrangement of the piston ring gaps. Therefore, with the ring rotation behavior still not resolved, the current model can predict the LOC range of a given engine profile. Results show that the predicted range can well encapsulate the experimentally measured LOC value. Full article

(This article belongs to the Special Issue Future of Digital Tribology: Prediction of Tribological Performance Using Sensors, Signal Processing and Machine Learning)

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14 pages, 3658 KB

Open AccessArticle

Rheological Study and FTIR Analysis of Thermally Degraded Mineral and Biodegradable Hydraulic Fluids

by Andreea Mirela Teleașă, Nicolae-Alexandru Stoica, Alexandru Valentin Rădulescu, Sorin Cănănău, Ludmila Motelica and Radu Iulian Rădoi

Lubricants 2025, 13(10), 462; https://doi.org/10.3390/lubricants13100462 - 21 Oct 2025

Abstract

In this work, three hydraulic fluids—a paraffinic mineral hydraulic oil (H46) and two biodegradable oils (HETG46—hydraulic oil based on natural esters and HF-E46—hydraulic oil based on synthetic esters derived from fatty acids extracted from vegetable oils)—were studied in both fresh and thermally degraded [...] Read more.

In this work, three hydraulic fluids—a paraffinic mineral hydraulic oil (H46) and two biodegradable oils (HETG46—hydraulic oil based on natural esters and HF-E46—hydraulic oil based on synthetic esters derived from fatty acids extracted from vegetable oils)—were studied in both fresh and thermally degraded states. The study of these oils was performed both from a rheological and spectroscopic point of view using Fourier transform infrared spectroscopy (FTIR). The thermal degradation process consisted of repeated heating and cooling cycles at four different temperatures for 15 min performed eight times. The rheological characterization was initially performed for the fresh oils, and the results obtained were compared with those of the thermally degraded samples. For the rheological characterization, two rheological models (the Newtonian model and the power law model) were used, following which the rheological parameters were determined. At the same time, this work highlights how thermal degradation influences the rheological behavior and chemical structure of hydraulic fluids. The results obtained showed that the Newtonian model best describes the rheological behavior of the analyzed fluids. From a chemical point of view, FTIR analysis did not reveal significant changes between fresh fluids and those subjected to thermal degradation. Full article

(This article belongs to the Special Issue Condition Monitoring of Lubricating Oils)

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12 pages, 2595 KB

Open AccessArticle

Experimental Study of the Service Performance of Full Ceramic Silicon Nitride Ball Bearings

by Pengfei Wang and Xuegang Zhang

Lubricants 2025, 13(10), 461; https://doi.org/10.3390/lubricants13100461 - 20 Oct 2025

Abstract

As the operating conditions of rolling bearings become increasingly demanding, traditional steel bearings can no longer fully meet the performance requirements of critical equipment. Silicon nitride full ceramic ball bearings, with intrinsic properties such as a low thermal expansion coefficient, low density, corrosion [...] Read more.

As the operating conditions of rolling bearings become increasingly demanding, traditional steel bearings can no longer fully meet the performance requirements of critical equipment. Silicon nitride full ceramic ball bearings, with intrinsic properties such as a low thermal expansion coefficient, low density, corrosion resistance, and wear resistance, offer significant advantages in extreme temperatures, high-speed operation, and harsh corrosive environments. As a result, they have become a key technical solution for the core transmission systems of high-end equipment. However, the dynamic evolution of their service performance under varying operating conditions—such as load and speed—remains insufficiently understood. This study systematically investigates the service performance evolution mechanism of silicon nitride full ceramic ball bearings under self-lubrication conditions. The key findings will provide a theoretical foundation for optimizing and regulating performance under extreme operating conditions. Full article

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19 pages, 4804 KB

Open AccessArticle

An Experimental Study on the Influence of Spring Support Structures and Hydrostatic Recess Areas on the Characteristics of Hybrid Tilting Pad Bearings Lubricated by High-Pressure CO₂

by Xiangyu Li, Lingfeng Huang, Shuxiang Yi, Xiaojing Wang, Xiaohan Zhang and Kunpeng Cheng

Lubricants 2025, 13(10), 460; https://doi.org/10.3390/lubricants13100460 - 20 Oct 2025

Abstract

The purpose of this study is to explore the influence of different spring support structures and hydrostatic recess areas on the characteristics of hybrid tilting pad bearings lubricated by high-pressure CO₂ to promote the development of high-pressure CO₂-lubricated bearings. A [...] Read more.

The purpose of this study is to explore the influence of different spring support structures and hydrostatic recess areas on the characteristics of hybrid tilting pad bearings lubricated by high-pressure CO₂ to promote the development of high-pressure CO₂-lubricated bearings. A high-pressure CO₂ hybrid tilting pad bearing experiment system was designed and built, and performance comparison experiments were carried out under various speed and load conditions. The performance differences of bearings with different spring support structures and hydrostatic recess areas under high-pressure CO₂ lubrication were obtained. The results show that compared with the bearing structure, the bearing stiffness has a more significant effect on the bearing performance. The design of the bearing should consider the matching of stiffness and rotor dynamics. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings, 2nd Edition)

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22 pages, 4780 KB

Open AccessArticle

A Fusion Estimation Method for Tire-Road Friction Coefficient Based on Weather and Road Images

by Jiye Huang, Xinshi Chen, Qingsong Jin and Ping Li

Lubricants 2025, 13(10), 459; https://doi.org/10.3390/lubricants13100459 - 20 Oct 2025

Abstract

The tire-road friction coefficient (TRFC) is a critical parameter that significantly influences vehicle safety, handling stability, and driving comfort. Existing estimation methods based on vehicle dynamics suffer from a substantial decline in accuracy under conditions with insufficient excitation, while vision-based approaches are often [...] Read more.

The tire-road friction coefficient (TRFC) is a critical parameter that significantly influences vehicle safety, handling stability, and driving comfort. Existing estimation methods based on vehicle dynamics suffer from a substantial decline in accuracy under conditions with insufficient excitation, while vision-based approaches are often limited by the generalization ability of their datasets, making them less effective in complex and variable real-driving environments. To address these challenges, this paper proposes a novel, low-cost fusion method for TRFC estimation that integrates weather conditions and road image data. The proposed approach begins by employing semantic segmentation to partition the input images into distinct regions—sky and road. The segmented images will be fed into the road recognition network and the weather recognition network for road type and weather classification. Furthermore, a fusion decision tree incorporating an uncertainty modeling mechanism is introduced to dynamically integrate these multi-source features, thereby enhancing the robustness of the estimation. Experimental results demonstrate that the proposed method maintains stable and reliable estimation performance even on unseen road surfaces, outperforming single-modality methods significantly. This indicates its high practical value and promising potential for broad application. Full article

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13 pages, 1251 KB

Open AccessArticle

A Multi-Parameter-Driven SC-ANFIS Framework for Predictive Modeling of Acid Number Variations in Lubricating Oils

by Yawen Wang, Haijun Wei and Daping Zhou

Lubricants 2025, 13(10), 458; https://doi.org/10.3390/lubricants13100458 - 20 Oct 2025

Viewed by 27

Abstract

The acid number is widely recognized as one of the most essential and frequently used indicators for evaluating the degradation state of lubricants. Changes in acid number serve as a direct reflection of the oil’s oxidative deterioration. Conventional prediction methods, however, often neglect [...] Read more.

The acid number is widely recognized as one of the most essential and frequently used indicators for evaluating the degradation state of lubricants. Changes in acid number serve as a direct reflection of the oil’s oxidative deterioration. Conventional prediction methods, however, often neglect the coupling effects among multiple physical factors and lack sufficient dynamic adaptability. Therefore, this study proposes a method for predicting the variation trend of lubricating oil acid number by integrating an Adaptive Neuro-Fuzzy Inference System (ANFIS) with Subtractive Clustering (SC), establishing an SC-ANFIS-based predictive model. The subtractive clustering technique automatically determines the number of fuzzy rules and initial parameters directly from the dataset, thereby eliminating redundant rules and simplifying the model architecture. The SC-ANFIS model further optimizes the parameters of the fuzzy inference system through the self-learning ability of neural networks. Lubricant aging tests were conducted using a laboratory oxidation stability tester. Regular sampling was carried out to acquire comprehensive lubricant performance degradation data. The input variables of the model include the current acid number, carbonyl peak intensity, metal element concentrations (Fe and Cu), viscosity, and water content of the lubricating oil, while the output variable corresponds to the rate of change in the acid number of the lubricating oil relative to the previous time step. The proposed model demonstrates effective prediction of the lubricating oil acid number variation trend. Posterior difference tests confirmed its high predictive accuracy, with all three evaluation metrics—RMSE, MAE, and MAPE—outperforming those of the BP model. Full article

(This article belongs to the Special Issue Condition Monitoring of Lubricating Oils)

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19 pages, 11176 KB

Open AccessArticle

Multiscale Investigation of the Anti-Friction Mechanism in Graphene Coatings on Copper Substrates: Substrate Reinforcement via Microstructural Evolution

by Di Ran, Zewei Yuan, Po Du, Ning Wang, Na Wang, Li Zhao, Song Feng, Weiwei Jia and Chaoqun Wu

Lubricants 2025, 13(10), 457; https://doi.org/10.3390/lubricants13100457 - 20 Oct 2025

Viewed by 45

Abstract

Graphene exhibits great potential as an anti-friction coating material in MEMS. However, its underlying microscopic friction-reduction mechanism remains unclear. In this paper, the microstructural evolution and nanomechanical behavior of graphene coatings on copper substrates were systematically investigated by AFM friction experiments and MD [...] Read more.

Graphene exhibits great potential as an anti-friction coating material in MEMS. However, its underlying microscopic friction-reduction mechanism remains unclear. In this paper, the microstructural evolution and nanomechanical behavior of graphene coatings on copper substrates were systematically investigated by AFM friction experiments and MD simulations. MD simulations reveal that the anti-friction properties of graphene coatings primarily stem from microstructural regulation and load-bearing reinforcement of the substrate. The graphene coatings increase indentation diameter by forming transition radii at the indentation edges, and suppress the plowing effect of the substrate by restricting atomic upward movement, both of which enhance the dislocation density and load-bearing capacity of the substrate. Additionally, graphene coatings also reduce the scratch edge angle, weakening the interlocking effect between the substrate and tip, further lowering the friction force. Experimental results indicate that the tribological behavior of graphene coatings exhibits staged characteristics: graphene coatings show excellent ultrafriction properties under intact structural conditions, while showing a higher friction force in wear and tear states. This research provides a theoretical basis and technical guidance for the development of anti-friction and wear-resistant coatings for micro-nano devices. Full article

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10 pages, 4746 KB

Open AccessArticle

Deep Eutectic Solvents as Green and Novel Lubricant Additives for Castor Oil with High Tribological Performance

by José M. Liñeira del Río, A. Aourdou, G. García-Marquínez, J. M. Amado and M. J. Tobar

Lubricants 2025, 13(10), 456; https://doi.org/10.3390/lubricants13100456 - 18 Oct 2025

Viewed by 184

Abstract

This research reveals the anti-friction and anti-wear performance of lubricants using a castor oil base and a deep eutectic solvent (DES1) as an additive. To this end, DES1 was synthesized in a successful manner using DL-menthol and dodecanoic acid as components. Mass concentrations [...] Read more.

This research reveals the anti-friction and anti-wear performance of lubricants using a castor oil base and a deep eutectic solvent (DES1) as an additive. To this end, DES1 was synthesized in a successful manner using DL-menthol and dodecanoic acid as components. Mass concentrations from 0.1 wt% up to 5 wt% of DES1 additives were chosen to formulate the lubricants. Friction experiments were conducted, yielding friction enhancements up to 4% compared to the castor oil base. Notably the greatest reduction was achieved for the lubricant with 0.1 wt% of DES1. In terms of the wear generated, the best anti-wear performance was achieved for the 0.5 wt% DES1 lubricant (with a wear reduction of 17%). Furthermore, by means of the profilometry of worn surfaces, it can be observed that the tribofilm formation of DES1 on steel surfaces is a potential lubrication mechanism. Full article

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14 pages, 9269 KB

Open AccessArticle

Study of the Micropore Structure and Tribological Properties of PTFE-Modified Porous Polyimide

by Xiaobo Sun, Xiaohui Shang, Yuanyuan Li, Xiaoya Zhang, Fei Chen, Keying Li and Ke Yan

Lubricants 2025, 13(10), 455; https://doi.org/10.3390/lubricants13100455 - 18 Oct 2025

Viewed by 152

Abstract

To address the challenges of regulating micropore properties and improving the tribological performance of porous polyimide (PPI), PPI/PTFE composites were fabricated via cold pressing–sintering. The effects of PTFE content on porosity, oil absorption/retention, and tribological behavior were systematically studied. Results show that PTFE [...] Read more.

To address the challenges of regulating micropore properties and improving the tribological performance of porous polyimide (PPI), PPI/PTFE composites were fabricated via cold pressing–sintering. The effects of PTFE content on porosity, oil absorption/retention, and tribological behavior were systematically studied. Results show that PTFE addition significantly reduced porosity—by 1.8% to 7.9% as PTFE increased from 5 wt% to 30 wt%—while markedly enhancing dry friction performance. The friction coefficient decreased from 0.22 to 0.06 with 30 wt% PTFE, with optimal performance at 20 wt% (friction coefficient: 0.068; wear rate: 1.5 × 10⁻⁶ mm³/N·m). Oil-impregnated samples exhibited further improved tribological properties (friction coefficient ≈ 0.047), attributed to lubricant release forming a protective oil film. Although PTFE promotes lubricant release, it increases wear at higher contents. A PTFE content of 0–10% balances porosity control and tribological performance. Full article

(This article belongs to the Special Issue Tribology of Polymeric Composites)

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18 pages, 2183 KB

Open AccessReview

A Review of Research on the Effect of Electromagnetic Field on Friction and Wear

by Qiangqiang Zhang, Xiaojian Yu, Xueyan Xu, Chuan Li, Zhiquan Yang, Xianguo Hu, Kunhong Hu and Tong Zhang

Lubricants 2025, 13(10), 454; https://doi.org/10.3390/lubricants13100454 - 17 Oct 2025

Viewed by 194

Abstract

With the trend towards intelligent and precision-oriented industrial equipment, the influence of electromagnetic fields on the properties of tribological pairs has attracted increasing attention. This paper systematically reviews recent research progress on tribological behavior under electromagnetic fields, summarizes experimental setups designed for investigating [...] Read more.

With the trend towards intelligent and precision-oriented industrial equipment, the influence of electromagnetic fields on the properties of tribological pairs has attracted increasing attention. This paper systematically reviews recent research progress on tribological behavior under electromagnetic fields, summarizes experimental setups designed for investigating such behavior, and examines the effects and underlying mechanisms of electromagnetic fields on friction and wear under various lubrication conditions, forms of contact, materials of tribo-pairs, and electromagnetic field application methods. Finally, based on current research, several perspectives are proposed to ensure the long-term reliability of critical components amid increasingly complex electromagnetic environmental interference in the future. Full article

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16 pages, 7284 KB

Open AccessArticle

Fretting Friction and Wear Characteristics of the Internal Spiral Contact Steel Wires in the Hoisting Wire Rope Under Different Service Conditions

by Kun Huang, Gongning Li, Xiangdong Chang, Zhou Zhou, Yuxing Peng and Ran Deng

Lubricants 2025, 13(10), 453; https://doi.org/10.3390/lubricants13100453 - 17 Oct 2025

Viewed by 124

Abstract

As a critical load-bearing component in mine hoisting systems, the service performance and lifespan of wire ropes are limited by the fretting wear behavior among their internal wires and strands. To investigate the effect of fretting parameters on the wear mechanisms in wire [...] Read more.

As a critical load-bearing component in mine hoisting systems, the service performance and lifespan of wire ropes are limited by the fretting wear behavior among their internal wires and strands. To investigate the effect of fretting parameters on the wear mechanisms in wire ropes, this paper systematically conducts fretting wear experiments on multi-wire contact pairs under varying fretting frequencies and tensile loads. The results show that as the fretting frequency increases from 0.5 Hz to 3.0 Hz, the coefficient of friction (COF) rises, with its steady-state value reaching approximately 0.65. Conversely, as the tension decreases from 150 N to 90 N, the COF increases, attaining a steady-state value of 0.71. The slip regime between the steel wires evolves from gross slip to partial slip with increasing frequency. With an increase in tensile load, the slip regime transitions from gross slip to partial slip and finally to adhesion. Higher fretting frequencies and greater tensile loads exacerbate both the wear rate and the severity of damage on the spiral contact wires inside the hoisting rope. The highest wear rate, 27.2 × 10⁻⁶ mm³/N·m, is observed at 3.0 Hz, while the maximum wear rate under tension is 39.6 × 10⁻⁶ mm³/N·m at 150 N. The dominant wear mechanisms at higher frequencies are abrasive wear, tribochemical reaction, and surface fatigue. Under greater tension, the primary wear mechanisms are abrasive wear, surface fatigue, and tribochemical reaction. Full article

(This article belongs to the Special Issue Tribological Behavior of Wire Rope)

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16 pages, 5622 KB

Open AccessArticle

The Enhancement of Friction Reduction and Anti-Wear Properties of Polyurea Greases Mediated by a Lithium Salt at Elevated Temperatures

by Shukang Nan, Xinhu Wu, Quan Zhou, Xiaozhen Wang, Bin Li, Junming Liu, Qin Zhao, Xiaobo Wang, Bingbing Wang and Kuiliang Gong

Lubricants 2025, 13(10), 452; https://doi.org/10.3390/lubricants13100452 - 17 Oct 2025

Viewed by 157

Abstract

Polyurea grease (PU) is widely used in the lubrication of heavy machinery, but it can still suffer from structural or performance degradation under extreme conditions such as high temperatures and heavy loads. This study successfully synthesized a hybrid polyurea grease (LiTFSI-PU) by incorporating [...] Read more.

Polyurea grease (PU) is widely used in the lubrication of heavy machinery, but it can still suffer from structural or performance degradation under extreme conditions such as high temperatures and heavy loads. This study successfully synthesized a hybrid polyurea grease (LiTFSI-PU) by incorporating lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into polyurea matrix. LiTFSI coordinates with the carbonyl groups (C=O) in the thickener molecules to form weakly Lewis acidic complex, thereby reinforcing the soap fiber network structure. As a result, LiTFSI-PU exhibits increased apparent viscosity under shear. The tribological properties of LiTFSI-PU were evaluated under both ambient and elevated temperature conditions. At a load of 200 N and 150 °C, the average coefficient of friction for the 3 wt% LiTFSI-PU formulation was 0.094, which is 32.3% lower than that of the baseline polyurea grease (PU), while the wear volume was reduced by 77.5%. XPS and FIB-STEM/EDS analyses confirmed that LiTFSI-PU forms a multicomponent protective film in situ during friction, which simultaneously shields the substrate and provides lubrication. The additive strategy proposed in this work offers novel insights for the development of high-performance lubricants suitable for extreme thermomechanical conditions. Full article

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Graphical abstract

19 pages, 4385 KB

Open AccessArticle

On the Film Stiffness Characteristics of Water-Lubricated Rubber Bearings in Deep-Sea Environments

by Liwu Wang, Qilong Zhao, Wei Feng and Guo Xiang

Lubricants 2025, 13(10), 451; https://doi.org/10.3390/lubricants13100451 - 17 Oct 2025

Viewed by 236

Abstract

Rubber bearings play a critical role as core components within the transmission systems of marine equipment. Investigating the evolution of their water-film stiffness coefficient under deep-sea conditions can provide deeper insights into the dynamic characteristics of water-lubricated transmission systems. Employing a viscoelastic mixed-lubrication [...] Read more.

Rubber bearings play a critical role as core components within the transmission systems of marine equipment. Investigating the evolution of their water-film stiffness coefficient under deep-sea conditions can provide deeper insights into the dynamic characteristics of water-lubricated transmission systems. Employing a viscoelastic mixed-lubrication framework designed for water lubricated rubber bearings, this paper examines the necessity of accounting for rubber hyperelasticity and extreme subsea conditions (high pressure and low temperature) when analyzing the water-film stiffness coefficient of such bearings (at a depth of 1000 m, the relative error in the k_xz component between the linear viscoelastic model and the visco-hyperelastic model reaches as high as 18.41%.). On this basis, the influence of subsea environments together with rotational velocity on the water-film stiffness coefficient is further investigated, and the dependence of the dimensionless critical mass on the eccentricity ratio for water-lubricated rubber bearings operating under deep-ocean conditions is explored. The results provide a theoretical analysis tool for evaluating the water-film stiffness coefficient of subsea rubber bearings, and offer guidance for the forward design of water-lubricated rubber bearings applied in deep-sea service. Full article

(This article belongs to the Special Issue Friction–Vibration Interactions)

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38 pages, 7997 KB

Open AccessArticle

Investigation of Thermo-Mechanical Characteristics in Friction Stir Processing of AZ91 Surface Composite: Novel Study Through SPH Analysis

by Roshan Vijay Marode, Tamiru Alemu Lemma, Srinivasa Rao Pedapati, Sambhaji Kusekar, Vyankatesh Dhanraj Birajdar and Adeel Hassan

Lubricants 2025, 13(10), 450; https://doi.org/10.3390/lubricants13100450 - 16 Oct 2025

Viewed by 208

Abstract

The current study examines the influence of tool rotational speed (TRS) and reinforcement volume fraction (%vol.) of SiC on particle distribution in the stir zone (SZ) of AZ91 Mg alloy. Two parameter sets were analyzed: S1 (500 rpm TRS, 13% vol.) and S2 [...] Read more.

The current study examines the influence of tool rotational speed (TRS) and reinforcement volume fraction (%vol.) of SiC on particle distribution in the stir zone (SZ) of AZ91 Mg alloy. Two parameter sets were analyzed: S1 (500 rpm TRS, 13% vol.) and S2 (1500 rpm TRS, 10% vol.), with a constant tool traverse speed (TTS) of 60 mm/min. SPH simulations revealed that in S1, lower TRS resulted in limited SiC displacement, leading to significant agglomeration zones, particularly along the advancing side (AS) and beneath the tool pin. Cross-sectional observations at 15 mm and 20 mm from the plunging phase indicated the formation of reinforcement clusters along the tool path, with inadequate SiC transference to the retreating side (RS). The reduced stirring force in S1 caused poor reinforcement dispersion, with most SiC nodes settling at the SZ bottom due to insufficient upward movement. In contrast, S2 demonstrated enhanced particle mobility due to higher TRS, improving reinforcement homogeneity. Intense stirring facilitated lateral and upward SiC movement, forming an interconnected reinforcement network. SPH nodes exhibited improved dispersion, with particles across the SZ and more evenly deposited on the RS. A comparative assessment of experimental and simulated reinforcement distributions confirmed a strong correlation. Results highlight the pivotal role of TRS in reinforcement movement and agglomeration control. Higher TRS enhances stirring and promotes uniform SiC dispersion, whereas an excessive reinforcement fraction increases matrix viscosity and restricts particle mobility. Thus, optimizing TRS and reinforcement content through numerical analysis using SPH is essential for producing a homogeneous, well-reinforced composite layer with improved surface properties. The findings of this study have significant practical applications, particularly in industrial material selection, improving manufacturing processes, and developing more efficient surface composites, thereby enhancing the overall performance and reliability of Mg alloys in engineering applications. Full article

(This article belongs to the Special Issue Surface Machining and Tribology)

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18 pages, 8775 KB

Open AccessArticle

Effect of Low-Pressure Gas Oxynitriding on the Microstructural Evolution and Wear Resistance of Ti-6Al-4V Alloy

by Chih-Hao Yang, Chang-Yu Li, Ching-Cheng Chan, Po-Cheng Chi, Jing-Han Shih, Fang-Yu Liao and Shih-Hsien Chang

Lubricants 2025, 13(10), 449; https://doi.org/10.3390/lubricants13100449 - 16 Oct 2025

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Abstract

A Ti-6Al-4V titanium alloy exhibits low hardness and poor wear resistance under sliding contact. This study evaluates the effect of low-pressure gas oxynitriding (LPON) followed by low-temperature oxidation on its microstructure and tribological performance. Specimens were nitrided at 1000 °C for 100 min, [...] Read more.

A Ti-6Al-4V titanium alloy exhibits low hardness and poor wear resistance under sliding contact. This study evaluates the effect of low-pressure gas oxynitriding (LPON) followed by low-temperature oxidation on its microstructure and tribological performance. Specimens were nitrided at 1000 °C for 100 min, then oxidized at 450–600 °C for 120 min. Microstructural and phase changes were characterized by SEM and XRD; surface roughness, hardness, and wear were assessed using 3D laser scanning microscopy, microhardness profiling, and pin-on-disk tests under 2 N and 4 N loads. XRD revealed TiN, Ti₂N, Ti₂AlN, and TiO₂ phases, with oxidation temperature governing TiN grain growth and nitride-to-oxide transformation. Oxidation at 500–550 °C formed a dense TiO₂-rich layer over a stable TiN/Ti₂N substrate, achieving hardness up to ~670 HV_0.025 and the lowest wear volume. At low load (2 N), nitriding alone provided the highest wear resistance, while at higher load (4 N), oxidation yielded only slight improvement due to oxide embrittlement. Excessive oxidation at 600 °C increased roughness, induced spallation, and reduced wear resistance. The optimal condition (550 °C) offered synergistic protection from nitrides and stable oxides, enhancing load-bearing capacity. Overall, duplex nitriding–oxidation is most effective for low-to-moderate load applications, with potential use in biomedical implants, aerospace fasteners, and precision components. Full article

(This article belongs to the Special Issue Tribology of Metals and Alloys)

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18 pages, 9922 KB

Open AccessArticle

Unraveling the Friction and Wear Mechanisms of a Medium-Carbon Steel with a Gradient-Structured Surface Layer

by Huaming Zhang, Baoyan Que, Li Dong, Zhenling Li, Yang Cheng and Xiaogui Wang

Lubricants 2025, 13(10), 448; https://doi.org/10.3390/lubricants13100448 - 14 Oct 2025

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Abstract

This study investigates the enhancement of tribological performance in coarse-grained (CG) 42CrMo steel through the development of gradient-structured (GS) samples using double-sided symmetrical surface mechanical rolling treatment (D-SMRT). Dry reciprocating sliding wear tests are performed against a GCr15 steel counter ball to evaluate [...] Read more.

This study investigates the enhancement of tribological performance in coarse-grained (CG) 42CrMo steel through the development of gradient-structured (GS) samples using double-sided symmetrical surface mechanical rolling treatment (D-SMRT). Dry reciprocating sliding wear tests are performed against a GCr15 steel counter ball to evaluate the influence of normal load on the wear resistance of CG and D-SMRT samples. Results demonstrate that D-SMRT significantly improves wear resistance under a 5 N load, attributed to the synergistic effects of surface strengthening and microstructure refinement. Characterization of worn surfaces via scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) confirms oxidative wear and abrasive wear as the dominant mechanisms at 5 N. With increasing load, wear transitions to abrasive and fatigue wear for the CG sample, while adhesive wear and plastic deformation dominate in the GS sample. This work concludes that D-SMRT technology effectively enhances the tribological properties of 42CrMo steel under normal loads below 10 N. Full article

(This article belongs to the Special Issue Tribological Performance of Steels)

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22 pages, 12725 KB

Open AccessArticle

Microstructure and Mechanical Properties of CuZr Thin-Film Metallic Glasses Deposited by Magnetron Sputtering

by Rui Zhang, Kai Yan, Zecui Gao, Huiyan Wu and Qimin Wang

Lubricants 2025, 13(10), 447; https://doi.org/10.3390/lubricants13100447 - 14 Oct 2025

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Abstract

As a novel class of thin films, thin-film metallic glasses (TFMGs) hold broad application prospects in biomedicine, electronic components, etc. In this study, CuZr TFMGs were deposited at room temperature using a medium-frequency magnetron sputtering (MFMS) technique. The effects of bias voltage on [...] Read more.

As a novel class of thin films, thin-film metallic glasses (TFMGs) hold broad application prospects in biomedicine, electronic components, etc. In this study, CuZr TFMGs were deposited at room temperature using a medium-frequency magnetron sputtering (MFMS) technique. The effects of bias voltage on the microstructure and properties of the films were systematically investigated. The results indicate that the CuZr system exhibits excellent glass-forming ability (GFA), with films possessing a smooth surface. As bias voltage increases, cross-sectional morphology transitions from a glassy morphology to a dimple-like structure. The high bias voltage induces reduced dimple size and significantly increased density. At a bias voltage of −50 V, the hardness of CuZr film reaches a maximum of 9.6 GPa. This hardness is approximately five times and twice that of pure Cu and Zr films, respectively. Compared with Zr film, CuZr TFMGs exhibit a significantly reduced friction coefficient while maintaining a low wear rate. All CuZr films demonstrate excellent electrical conductivity and hydrophobicity, providing the basis for future potential applications. Full article

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14 pages, 9085 KB

Open AccessArticle

From Conventional to Environmentally Acceptable Additives: Tribological Behaviour in Volatile Lubricants for Punching Stamping Operations

by Lucija Čoga, Marko Polajnar and Mitjan Kalin

Lubricants 2025, 13(10), 446; https://doi.org/10.3390/lubricants13100446 - 13 Oct 2025

Viewed by 385

Abstract

In this study, we investigated the tribological properties of various additives (lubricity, friction modifiers, anti-wear and extreme pressure) in a highly volatile paraffinic base oil formulated for stamping applications, using a newly developed methodology for tribological testing. The investigation focused on the short-term [...] Read more.

In this study, we investigated the tribological properties of various additives (lubricity, friction modifiers, anti-wear and extreme pressure) in a highly volatile paraffinic base oil formulated for stamping applications, using a newly developed methodology for tribological testing. The investigation focused on the short-term (10 cycles) and long-term (10,000 cycles) effects of the different additive mixtures on friction and wear behaviour. It was found that the performance of the additive mixtures evolves with sliding time, which is due to changes in contact conditions: the transfer of the Fe film from the steel sheet to the WC-Co surface increases the contact area, which in turn leads to a significant reduction in contact pressure and changes the activation of tribofilm formation. The presence of tribofilms influences the amount and size of the contact area and reduces the adhesion between the contact surfaces. Among the conventional additives, sulphurised additive mixtures show stable performance under both short and long-term conditions, while more aggressive chlorinated additive mixtures perform well in the short term, but their performance decreases with prolonged sliding. Importantly, the additives with a decreasing environmental impact outperformed the conventional additives under long-term conditions: the less harmful phosphorus-based mixture outperformed the sulphurised mixtures in terms of wear properties, while the performance of environmentally acceptable polyol ester was particularly encouraging, exhibiting the lowest friction coefficient (~0.11, compared with ~0.12 for S-oil and 0.14 for S-ester) and the second lowest wear coefficient (~1.1 × 10⁻¹ mm³/Nm compared with ~1.5 × 10⁻¹ mm³/Nm for S-ester). Overall, the polyol ester reduced the coefficient of friction by approximately 8 to 21% compared to sulphurised additive mixtures, and its wear coefficient was also about 27% lower. Full article

(This article belongs to the Special Issue Preparation, Tribological Behavior, and Applications of Lubricant Additives)

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34 pages, 9892 KB

Open AccessArticle

Fluid–Structure Interaction Mechanisms of Layered Thickness Effects on Lubrication Performance and Energy Dissipation in Water-Lubricated Bearings

by Lun Wang, Xincong Zhou, Hanhua Zhu, Qipeng Huang, Zhenjiang Zhou, Shaopeng Xing and Xueshen Liu

Lubricants 2025, 13(10), 445; https://doi.org/10.3390/lubricants13100445 - 12 Oct 2025

Cited by 1 | Viewed by 429

Abstract

Traditional single-layer water-lubricated rubber or plastic bearings suffer from water film rupture, excessive frictional losses, and insufficient load-carrying capacity, which limit performance and service life in marine propulsion and ocean engineering. To address these issues, this study introduces an innovative laminated bearing consisting [...] Read more.

Traditional single-layer water-lubricated rubber or plastic bearings suffer from water film rupture, excessive frictional losses, and insufficient load-carrying capacity, which limit performance and service life in marine propulsion and ocean engineering. To address these issues, this study introduces an innovative laminated bearing consisting of a rubber composite layer and an ultra-high-molecular-weight polyethylene (UHMWPE) layer. A three-dimensional dynamic model based on fluid–structure interaction theory is developed to evaluate the effects of eccentricity, rotational speed, and liner thickness on lubrication pressure, load capacity, deformation, stress–strain behavior, and frictional power consumption. The model also reveals how thickness matching governs load transfer and energy dissipation. Results indicate that eccentricity, speed, and thickness are key determinants of lubrication and structural response. Hydrodynamic pressure and load capacity rise with eccentricity above 0.8 or higher speeds, but frictional losses also intensify. The rubber layer performs optimally at a thickness of 5 mm, while excessive or insufficient thickness leads to stress concentration or reduced buffering. The UHMWPE layer exhibits optimal performance at 5–7 mm, with greater deviations resulting in increased stress and deformation. Proper thickness matching improves pressure distribution, reduces local stresses, and enhances energy dissipation, thereby strengthening bearing stability and durability. Full article

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22 pages, 3981 KB

Open AccessArticle

Experimental Investigation and Modelling of High-Speed Turn-Milling of H13 Tool Steel: Surface Roughness and Tool Wear

by Hamid Ghorbani, Bin Shi and Helmi Attia

Lubricants 2025, 13(10), 444; https://doi.org/10.3390/lubricants13100444 - 10 Oct 2025

Viewed by 325

Abstract

Turn-milling is a relatively new process which combines turning and milling operations, offering a number of advantages such as chip breaking and interrupted cutting, which improves tool life. In addition to providing the capability of producing eccentric forms or shapes, it increases productivity [...] Read more.

Turn-milling is a relatively new process which combines turning and milling operations, offering a number of advantages such as chip breaking and interrupted cutting, which improves tool life. In addition to providing the capability of producing eccentric forms or shapes, it increases productivity for difficult-to-machine material at lower cost. This study investigates the influence of cutting speed and feed on surface roughness and tool wear in conventional turning and turn-milling of H13 tool steel. The tests were conducted for longitudinal and face machining strategies. It was found that the range of surface roughness in turning is lower than in turn-milling. In longitudinal turning, face-turning, and face turn-milling operations, surface roughness is elevated in the higher feeds. However, the surface roughness in longitudinal turn-milling operations can be reduced by increasing the feed. Although the simultaneous rotation of the tool and workpiece in turn-milling could negatively affect the surface quality, this operation provides the advantage of an interrupted cutting mechanism that produces discontinuous chips. Also, the wear of the endmill in longitudinal and face turn-milling operations is lower than the wear of the inserts used in conventional longitudinal and face turning. Using Response Surface Methodology (RSM), mathematical models were developed for surface roughness and tool wear in each operation. The RSM models developed in this study achieved coefficients of determination (R²) above 90%, with prediction errors below 7% for surface roughness and below 3% for tool wear. The analysis of variance (ANOVA) revealed that the feed and cutting speed are the most influential parameters on the surface roughness and tool wear, respectively, with p-value < 0.05. The experimental results demonstrated that tool wear in turn-milling was reduced by up to 50% compared to conventional turning. Full article

(This article belongs to the Special Issue Recent Advances in Materials Forming, Machining and Tribology)

28 pages, 16935 KB

Open AccessArticle

Hybrid h-BN/ZnO Nanolubricant Additives in 5W-30 Engine Oil for Enhanced Tribological Performance of Magnesium Alloys

by Turan Gürgenç

Lubricants 2025, 13(10), 443; https://doi.org/10.3390/lubricants13100443 - 9 Oct 2025

Viewed by 476

Abstract

Magnesium alloys are widely used in automotive and aerospace applications due to their light weight but suffer from poor tribological performance. This study investigates the effects of base oil (SAE 5W-30) with 100% hBN, 100% ZnO, and various ratios of hBN/ZnO hybrid nanoparticles [...] Read more.

Magnesium alloys are widely used in automotive and aerospace applications due to their light weight but suffer from poor tribological performance. This study investigates the effects of base oil (SAE 5W-30) with 100% hBN, 100% ZnO, and various ratios of hBN/ZnO hybrid nanoparticles on the tribological performance of AZ91D magnesium alloy. Pin-on-disk tribometer tests were conducted on AZ91D magnesium alloy under loads of 10–60 N and a sliding distance of 1000 m. Dry sliding produced the highest coefficient of friction (COF, ~0.30) and the greatest wear. Base oil lubrication reduced COF to ~0.14 and improved wear resistance by more than 50%. The 100% hBN nanolubricant provided the lowest wear and a COF of ~0.114, while the 75hBN/25ZnO hybrid achieved the lowest COF (~0.110) with wear values close to hBN. Surface analyses confirmed that hBN formed a lamellar tribofilm that minimized metal-to-metal contact, and ZnO contributed to the formation of load-bearing oxide layers that enhanced surface stability. Overall, the results demonstrate that hBN and ZnO, in single or hybrid form, can significantly reduce friction and wear, showing strong potential for applications in automotive, aerospace, defense, and industrial systems. Full article

(This article belongs to the Special Issue Tribology of Metals and Alloys)

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18 pages, 2078 KB

Open AccessReview

The Role of Tribocatalysis in Friction and Wear: A Review

by Diana Berman and Ali Erdemir

Lubricants 2025, 13(10), 442; https://doi.org/10.3390/lubricants13100442 - 8 Oct 2025

Viewed by 601

Abstract

When exposed to high contact pressure and shear conditions, the sliding and/or rolling contact interfaces of moving mechanical systems can experience significant friction and wear losses, thereby impairing their efficiency, reliability, and environmental sustainability. Traditionally, these losses have been minimized using high-performance solid [...] Read more.

When exposed to high contact pressure and shear conditions, the sliding and/or rolling contact interfaces of moving mechanical systems can experience significant friction and wear losses, thereby impairing their efficiency, reliability, and environmental sustainability. Traditionally, these losses have been minimized using high-performance solid and liquid lubricants or surface engineering techniques like physical and chemical vapor deposition. However, increasingly harsh operating conditions of more advanced mechanical systems (including wind turbines, space mechanisms, electric vehicle drivetrains, etc.) render such traditional methods less effective or impractical over the long term. Looking ahead, an emerging and complementary solution could be tribocatalysis, a process that spontaneously triggers the formation of nanocarbon-based tribofilms in situ and on demand at lubricated interfaces, significantly reducing friction and wear even without the use of high-performance additives. These films often comprise a wide range of amorphous or disordered carbons, crystalline graphite, graphene, nano-onions, nanotubes, and other carbon nanostructures known for their outstanding friction and wear properties under the most demanding tribological conditions. This review highlights recent advances in understanding the underlying mechanisms involved in forming these carbon-based tribofilms, along with their potential applications in real-world mechanical systems. These examples underscore the scientific significance and industrial potential of tribocatalysis in further enhancing the efficiency, reliability, and environmental sustainability of future mechanical systems. Full article

(This article belongs to the Special Issue Tribo-Catalysis)

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22 pages, 3103 KB

Open AccessArticle

Measurement Strategies for the Monitoring of the Electric Behavior of Journal Bearings

by Florian Koetz and Eckhard Kirchner

Lubricants 2025, 13(10), 441; https://doi.org/10.3390/lubricants13100441 - 8 Oct 2025

Viewed by 281

Abstract

The condition monitoring of machine elements and, more precisely, journal bearings, is beneficial to prevent unnecessary wear and identify critical operating conditions. One method for that is the monitoring of the electric behavior of the bearing by monitoring its capacitance. While the general [...] Read more.

The condition monitoring of machine elements and, more precisely, journal bearings, is beneficial to prevent unnecessary wear and identify critical operating conditions. One method for that is the monitoring of the electric behavior of the bearing by monitoring its capacitance. While the general electric behavior of journal bearings is known, assessments of suitable measurement setups and data analysis methods are usually neglected. This contribution identifies potential measurement setups and analysis methods used in the literature for monitoring rolling-element bearings or journal bearings. These setups and analysis methods are then discussed theoretically and based on measurements of the electric behavior of journal bearings. The findings show that voltage divider setups with AC signals are the most promising solution to monitor the journal bearing electrically. Linear regression algorithms can be used to obtain the amplitude and phase of the measured voltage signal. These values are then used to calculate the impedance and capacitance of the bearing. Lastly, this contribution investigates how existing PCT (percent contact time) analyses need to be altered to improve the precision and robustness of the analysis and allow for the physical interpretation of the measurement results. These findings may be used in the future to predict wear and identify critical operating conditions in journal bearings, such as mixed lubrication. Full article

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31 pages, 2687 KB

Open AccessReview

Advances and Challenges in Bio-Based Lubricants for Sustainable Tribological Applications: A Comprehensive Review of Trends, Additives, and Performance Evaluation

by Jay R. Patel, Kamlesh V. Chauhan, Sushant Rawal, Nicky P. Patel and Dattatraya Subhedar

Lubricants 2025, 13(10), 440; https://doi.org/10.3390/lubricants13100440 - 6 Oct 2025

Viewed by 493

Abstract

Bio-based lubricants are rapidly gaining prominence as sustainable alternatives to petroleum-derived counterparts, driven by their inherent biodegradability, low ecotoxicity, and strong alignment with global environmental and regulatory imperatives. Despite their promising tribological properties, their widespread adoption continues to confront significant challenges, particularly related [...] Read more.

Bio-based lubricants are rapidly gaining prominence as sustainable alternatives to petroleum-derived counterparts, driven by their inherent biodegradability, low ecotoxicity, and strong alignment with global environmental and regulatory imperatives. Despite their promising tribological properties, their widespread adoption continues to confront significant challenges, particularly related to oxidative and thermal instability, cold-flow behavior, and cost competitiveness in demanding high-performance applications. This comprehensive review critically synthesizes the latest advancements in bio-based lubricant technology, spanning feedstock innovations, sophisticated chemical modification strategies, and the development of advanced additive systems. Notably, recent formulations demonstrate remarkable performance enhancements, achieving friction reductions of up to 40% and contributing to substantial CO₂ emission reductions, ranging from 30 to 60%, as evidenced by comparative life-cycle assessments and energy efficiency studies. Distinguishing this review from existing literature, this study offers a unique, holistic perspective by integrally analyzing global market trends, industrial adoption dynamics, and evolving regulatory frameworks, such as the European Union Eco-Label and the U.S. EPA Vessel General Permit, alongside technological advancements. This study critically assesses emerging methodologies for tribological evaluation and benchmark performance across diverse, critical sectors including automotive, industrial, and marine applications. By connecting in-depth technical innovations with crucial socio-economic and environmental considerations, this paper not only identifies key research gaps but also outlines a pragmatic roadmap for accelerating the mainstream adoption of bio-based lubricants, positioning them as an indispensable cornerstone of sustainable tribology. Full article

(This article belongs to the Special Issue Tribological Properties of Biolubricants)

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14 pages, 3429 KB

Open AccessArticle

Thermo-Responsive Wax Millicapsules as Lubricating Agents Carriers

by Tomasz Kubiak and Karol Ciesielski

Lubricants 2025, 13(10), 439; https://doi.org/10.3390/lubricants13100439 - 5 Oct 2025

Viewed by 478

Abstract

Encapsulation of lubricating agents has many advantages, as it helps to protect them from external factors, oxidation and degradation, can support their controlled and prolonged release, and also preserves the environment from accidental contamination with these substances. In our experiments various types of [...] Read more.

Encapsulation of lubricating agents has many advantages, as it helps to protect them from external factors, oxidation and degradation, can support their controlled and prolonged release, and also preserves the environment from accidental contamination with these substances. In our experiments various types of thermo-responsive, paraffin wax capsules capable of safely transporting liquid and semi-solid lubricants were designed, fabricated and tested. Lubricating oils were primarily encapsulated inside hemispherical wax shells closed with special caps, but also in wax spherocylinders and two-compartment structures. Greases were protected with wax coatings with the thickness ranging from 0.187 to 0.774 mm. The payload release from our core–shell capsules occurred not only due to the exerted mechanical force but also in a controlled manner upon prolonged contact with a heated surface. The wax shells of the capsules lying on the plate, whose temperature was increased at a rate of 0.025°C/s, began to melt gradually, starting from ≈55.5 °C. This temperature-triggered lubricant liberation can be useful when, for example, a machine element becomes excessively hot due to friction. The wax itself also has lubricating properties, so the crushed or melted coating cannot be treated as waste, but only as an additional factor supporting lubrication. The practical applications of our wax capsules were demonstrated with five examples. Full article

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20 pages, 4524 KB

Open AccessArticle

An Analysis on Negative Effects of Shaft Deflection on Angular Misalignment of Rollers Inside Tapered Roller Bearing

by Zhenghai Wu, Junmin Kang and Sier Deng

Lubricants 2025, 13(10), 438; https://doi.org/10.3390/lubricants13100438 - 2 Oct 2025

Viewed by 336

Abstract

Shaft deflection degrades roller alignment and intensifies stress concentration/edge effects at roller-ends and raceway edges, ultimately compromising service performance of tapered roller bearings (TRBs). Therefore, a dynamic model was developed for a TRB subjected to a deflected shaft in which Johnson’s load–deformation relationship [...] Read more.

Shaft deflection degrades roller alignment and intensifies stress concentration/edge effects at roller-ends and raceway edges, ultimately compromising service performance of tapered roller bearings (TRBs). Therefore, a dynamic model was developed for a TRB subjected to a deflected shaft in which Johnson’s load–deformation relationship was applied to reflect non-uniform cross-sectional structures of the tapered rollers and raceways, viscous damping was integrated into the roller/cage interaction, and friction actions at the raceways and flange areas were treated separately. Then, moment load and angular misalignment of the tapered roller were analyzed under various shaft deflection and operating conditions. Results indicate that tilt angle remains orders of magnitude smaller than skew angle. Shaft deflection amplifies both skew and tilt, and the influence level is proportional to the bearing size. Centrifugal effect primarily affects skew motion, whereas gyroscopic effect mainly influences tilt motion. Axial forces exert greater influence on roller skew than tilt. The flange typically constrains roller skew, whereas both raceways may induce bidirectional tilt/skew motion. Full article

(This article belongs to the Special Issue Nonlinear Dynamics of Frictional Systems)

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20 pages, 2127 KB

Open AccessArticle

Real-World Fuel Consumption of a Passenger Car with Oil Filters of Different Characteristics at High Altitude

by Edgar Vicente Rojas-Reinoso, Cristian Malla-Toapanta, Paúl Plaza-Roldán, Carmen Mata, Javier Barba and Luis Tipanluisa

Lubricants 2025, 13(10), 437; https://doi.org/10.3390/lubricants13100437 - 1 Oct 2025

Viewed by 595

Abstract

This study evaluates media-level filtration behaviour and short-term fuel consumption outcomes for five spin-on lubricating oil filters operated under real driving conditions at high altitude. To improve interpretability, filters are reported using parameter-based identifiers (media descriptors and equivalent circular diameter, ECD) rather than [...] Read more.

This study evaluates media-level filtration behaviour and short-term fuel consumption outcomes for five spin-on lubricating oil filters operated under real driving conditions at high altitude. To improve interpretability, filters are reported using parameter-based identifiers (media descriptors and equivalent circular diameter, ECD) rather than internal codes. Pore-scale morphology was quantified by microscopy and expressed as ECD, and bulk fluid cleanliness was summarised using ISO 4406 codes. Trials were conducted over representative urban and extra-urban routes at altitude; fuel consumption was analysed using ANCOVA. The results indicated clear media-level differences (tighter pore envelopes and cleaner ISO codes, particularly for two OEM units). However, fuel-consumption differences were not statistically significant (ANCOVA, p = 0.29). Accordingly, findings are reported as short-term cleanliness and media characterisation under high-altitude duty rather than durability or efficiency claims. The parameter-based framing clarifies trade-offs across metrics and avoids over-generalisation from brand or part numbers. The work highlights the value of ECD as a comparative pore metric and underscores limitations of microscopy/cleanliness data for inferring engine wear or long-term consumption. Future work will incorporate formal multi-pass testing (ISO 4548-12), direct differential-pressure instrumentation, used-oil viscosity tracking, and wear-metal spectrometry to enable cross-vendor benchmarking and causal interpretation. Findings are presented as short-term cleanliness and media characterisation; no durability claims are made in the absence of direct wear measurements. Full article

(This article belongs to the Special Issue Sustainable and Advanced Lubrication Strategies for Industrial and Environmental Applications)

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38 pages, 21368 KB

Open AccessArticle

Machine Learning-Based Dynamic Modeling of Ball Joint Friction for Real-Time Applications

by Kai Pfitzer, Lucas Rath, Sebastian Kolmeder, Burkhard Corves and Günther Prokop

Lubricants 2025, 13(10), 436; https://doi.org/10.3390/lubricants13100436 - 1 Oct 2025

Viewed by 464

Abstract

Ball joints are components of the vehicle axle, and their friction characteristics must be considered when evaluating vibration behavior and ride comfort in driving simulator-based simulations. To model the three-dimensional friction behavior of ball joints, real-time capability and intuitive parameterization using data from [...] Read more.

Ball joints are components of the vehicle axle, and their friction characteristics must be considered when evaluating vibration behavior and ride comfort in driving simulator-based simulations. To model the three-dimensional friction behavior of ball joints, real-time capability and intuitive parameterization using data from standardized component test benches are essential. These requirements favor phenomenological modeling approaches. This paper applies a spherical, three-dimensional friction model based on the LuGre model, compares it with alternative approaches, and introduces a universal parameter estimation framework using machine learning. Furthermore, the kinematic operating ranges of ball joints are derived from vehicle measurements, and component-level measurements are conducted accordingly. The collected measurement data are used to estimate model parameters through gradient-based optimization for all considered models. The results of the model fitting are presented, and the model characteristics are discussed in the context of their suitability for online simulation in a driving simulator environment. We demonstrate that the proposed parameter estimation framework is capable of learning all the applied models. Moreover, the three-dimensional LuGre-based approach proves to be well suited for capturing the dynamic friction behavior of ball joints in real-time applications. Full article

(This article belongs to the Special Issue New Horizons in Machine Learning Applications for Tribology)

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16 pages, 4474 KB

Open AccessArticle

Fabrication and Characterization of SnSb11Cu6 Babbitt-Infiltrated Open-Cell AlSn6Cu-SiC Matrix Composites

by Mihail Kolev, Rumiana Lazarova, Veselin Petkov, Rositza Dimitrova, Tatiana Simeonova, Rumen Krastev, Georgi Stoilov, Krasimir Kolev and Ilian Atanasov

Lubricants 2025, 13(10), 435; https://doi.org/10.3390/lubricants13100435 - 1 Oct 2025

Viewed by 408

Abstract

This study investigates the fabrication and performance of a novel composite material by infiltrating SnSb11Cu6 babbitt alloy into an open-cell AlSn6Cu-SiC matrix. The composites, produced via a multi-stage liquid-state processing route, were comprehensively characterized for their microstructural, mechanical, and tribological properties. The inclusion [...] Read more.

This study investigates the fabrication and performance of a novel composite material by infiltrating SnSb11Cu6 babbitt alloy into an open-cell AlSn6Cu-SiC matrix. The composites, produced via a multi-stage liquid-state processing route, were comprehensively characterized for their microstructural, mechanical, and tribological properties. The inclusion of 5 wt.% silicon carbide reinforcement resulted in a significant improvement in tribological performance under dry-sliding conditions. Specifically, the reinforced composite exhibited a 24.8% reduction in wear and a 10.8% reduction in the coefficient of friction compared to its unreinforced counterpart. Crucially, this enhancement in wear resistance was achieved while the bulk compressive mechanical properties and ductile deformation behavior remained virtually identical to the unreinforced material. Microstructural analysis confirmed that the high-hardness SiC particles act as primary load-bearing agents, shielding the softer metallic matrix from severe wear. These findings demonstrate the successful development of a high-performance composite with enhanced tribological durability without a mechanical trade-off, making it a promising candidate for advanced bearing applications. Full article

(This article belongs to the Special Issue Microstructure and Tribological Properties of Alloys)

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