Lubricants

17 pages, 7665 KiB

Open AccessArticle

Comparative Analysis of Rub-Impact Dynamics of Shrouded Blades Based on the Bilinear Hysteresis Model and the Coulomb Friction Model

by Dangdang Zheng, Geng Liu, Shangwen He and Bing Han

Lubricants 2022, 10(2), 31; https://doi.org/10.3390/lubricants10020031 - 20 Feb 2022

Cited by 3 | Viewed by 2214

Abstract

The bilinear hysteresis friction model and the Coulomb friction model are two typical macro slip models which are widely used by researchers in simulation analysis of rub-impact dynamics of shrouded blades. However, differences in the simulation results of shrouded blades based on these [...] Read more.

The bilinear hysteresis friction model and the Coulomb friction model are two typical macro slip models which are widely used by researchers in simulation analysis of rub-impact dynamics of shrouded blades. However, differences in the simulation results of shrouded blades based on these two friction models have not well been studied recently. In this paper, a two-dimensional lumped mass model of shrouded blades including axial displacements and tangential displacements is established, and the kinetic equations of the blades under different contact conditions are derived. The contact-separation and stick-slip transition points are determined by the bisection method. Using the fourth-order Runge–Kutta method, comparative analysis of the nonlinear characteristics and the vibration reduction characteristics of shrouded blades based on the bilinear hysteresis friction model and the Coulomb friction model are carried out. Numerical simulation results indicate that the nonlinear characteristics and the vibration reduction characteristics of shrouded blades based on these two friction models are not accordant. The discussion in this paper offers thinking for the selection of the friction model in a study on rub-impact dynamics of shrouded blades. Full article

(This article belongs to the Special Issue Friction and Wear in Machine Design)

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13 pages, 4593 KiB

Open AccessArticle

Influence Analysis of the Antifriction Layer Materials and Thickness on the Contact Interaction of Spherical Bearings Elements

by Anatoliy A. Adamov, Anna A. Kamenskikh and Anastasia P. Pankova

Lubricants 2022, 10(2), 30; https://doi.org/10.3390/lubricants10020030 - 18 Feb 2022

Cited by 8 | Viewed by 2720

Abstract

Bearings are the supporting elements of bridges. They perceive vertical and horizontal loads from the bridge span. Spherical bearings are one of the construction common types. The material and configuration of the anti-friction layers determine the bearing performance. The paper performed the contact [...] Read more.

Bearings are the supporting elements of bridges. They perceive vertical and horizontal loads from the bridge span. Spherical bearings are one of the construction common types. The material and configuration of the anti-friction layers determine the bearing performance. The paper performed the contact deformation analysis of spherical bearing elements at a nominal vertical load of 1000 kN. The six types of the spherical sliding layer material are considered: ultra-high molecular weight polyethylene (UHMWPE) from three different manufacturers, modified polytetrafluoroethylene (PTFE), and composite materials by PTFE with two different forms of reinforcing bronze inclusions. Young’s modulus, Poisson’s ratio, and strain curve are obtained experimentally for spherical sliding layer materials. Paper considered the influence of the sliding layer material on the contact parameters and deformation characteristics of the structure with a standard interlayer thickness by 4 mm. Research observed significant the composite interlayer deformation and the appearance of “no contact” zones on the mating surfaces. The option of increasing the sliding layer thickness up to 6–8 mm is considered. A decrease is observed in the maximum level of contact parameters by increase of the sliding layer thickness. The influence of the anti-friction layer materials becomes insignificant on the bearing deformation with an increase of the spherical sliding layer thickness. Full article

(This article belongs to the Special Issue Friction and Lubrication of Sliding Bearings, Volume II)

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18 pages, 4648 KiB

Open AccessArticle

Impact of Graphene Nano-Additives to Lithium Grease on the Dynamic and Tribological Behavior of Rolling Bearings

by Mohamed G. A. Nassef, Mina Soliman, Belal Galal Nassef, Mohamed A. Daha and Galal A. Nassef

Lubricants 2022, 10(2), 29; https://doi.org/10.3390/lubricants10020029 - 18 Feb 2022

Cited by 20 | Viewed by 4017

Abstract

In recent years, reduced graphene oxide (rGO) received considerable interest as a lubricant nano-additive for enhancing sliding and rolling contacts. This paper investigates the tribological and dynamic behavior of ball bearings lubricated by lithium grease at different weight percentages of rGO. Full bearing [...] Read more.

In recent years, reduced graphene oxide (rGO) received considerable interest as a lubricant nano-additive for enhancing sliding and rolling contacts. This paper investigates the tribological and dynamic behavior of ball bearings lubricated by lithium grease at different weight percentages of rGO. Full bearing tests were conducted for experimental modal analysis, vibration analysis, ultrasonic analysis, and infrared thermography. Modal analysis indicated considerable improvements of the damping ratio values up to 50% for the bearings with rGO nano-additives. These findings were confirmed by the corresponding reductions in vibrations and ultrasound levels. The steady-state temperatures of bearings running with lithium grease reached 64 °C, whereas the temperature of bearings lubricated by grease with 2 wt.% rGO measured only 27 °C. A Timken Load test was conducted on grease samples with and without rGO additives. Grease samples having 2, 3.5, and 5 wt.% rGO showed the highest OK load with an increase of 25%, 50%, and 100% as compared to values of lithium grease. For comparison, all tests were conducted on samples of the same grease blended with graphite and MWCNTs’ nano-additives. The results proved the superiority of graphene in enhancing the load-carrying capacity and damping of grease in rolling bearings. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings)

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16 pages, 7298 KiB

Open AccessArticle

Tribological Properties of the Nanoscale Spherical Y₂O₃ Particles as Lubricant Additives in Automotive Application

by Álmos D. Tóth, Ádám I. Szabó, Máté Zs. Leskó, Jan Rohde-Brandenburger and Rajmund Kuti

Lubricants 2022, 10(2), 28; https://doi.org/10.3390/lubricants10020028 - 18 Feb 2022

Cited by 13 | Viewed by 2751

Abstract

The continuous tribological development of engine lubricants is becoming more and more vital due to its fuel efficiency improvement and lifetime increasing potential. The antiwear additives play a high role in the lubricants to protect the contacting surfaces even in the presence of [...] Read more.

The continuous tribological development of engine lubricants is becoming more and more vital due to its fuel efficiency improvement and lifetime increasing potential. The antiwear additives play a high role in the lubricants to protect the contacting surfaces even in the presence of thinner oil film. Nanoscale spherical particles in the lubricant may increase the necessary protecting effect. This paper presents the results of the experimental tribological investigation of nanoscale spherical Y₂O₃ (yttria) ceramic particles as an engine lubricant additive. The ball-on-disc tribological measurements have revealed an optimum concentration at 0.5 wt% with about 45% wear scar diameter and 90% wear volume decrease, compared to the reference, neat Group III base oil. The high-magnitude SEM analysis revealed the working mechanisms of yttria: the particles collected in the roughness valleys resulted in a smoother contacting surface, they were tribo-sintered and they have also caused slight plastic deformation of the outer layer of the metallic surface. Full article

(This article belongs to the Special Issue Tribology in Mobility)

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18 pages, 13605 KiB

Open AccessArticle

Comparative Studies on the Dry Sliding Behavior of a Low-Metallic Friction Material with the Addition of Graphite and Exfoliated g-C₃N₄

by Priyadarshini Jayashree, Vlastimil Matějka, Kryštof Foniok and Giovanni Straffelini

Lubricants 2022, 10(2), 27; https://doi.org/10.3390/lubricants10020027 - 15 Feb 2022

Cited by 12 | Viewed by 2313

Abstract

This study compares the effect of the addition of two types of lubricants on the dry sliding behavior of a simplified Cu-free phenolic resin-based composite material. The lubricants were commercial graphite and exfoliated graphitic carbon nitride (codenamed: TEX6). The graphite particles were rounded [...] Read more.

This study compares the effect of the addition of two types of lubricants on the dry sliding behavior of a simplified Cu-free phenolic resin-based composite material. The lubricants were commercial graphite and exfoliated graphitic carbon nitride (codenamed: TEX6). The graphite particles were rounded and of ‘flaky’ character. The TEX6 particles were not only flaky, but also irregular in shape, and ‘fluffy’. Both lubricants were added individually in the basic formulation and subjected to dry sliding tests on pin-on-disc testing equipment in mild conditions and against a grey cast-iron counterface. The tests with TEX6 observed a stable steady state in the friction coefficient (CoF) with lower scatter and lower average friction coefficient and pin wear magnitude when compared to samples containing graphite. Additionally, the worn surfaces of the TEX6-containing samples had extremely smooth, compact, and continuous secondary plateau coverage when compared to the graphite-containing samples. The counterface paired with the TEX6-containing samples observed much lower abrasive action compared to the graphite-containing samples. Through the wear testing and further evaluation of the secondary plateaus, the possible addition of TEX6 as a lubricant in friction material composition was explained, making it a promising component for automotive braking applications. Full article

(This article belongs to the Special Issue Automotive Tribology II)

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19 pages, 4721 KiB

Open AccessArticle

Friction Issues over the Railway Wheels-Axis Assembly Motion

by Bogdan Derbiszewski, Andrzej Obraniak, Marek Wozniak, Adam Rylski, Krzysztof Siczek and Przemyslaw Kubiak

Lubricants 2022, 10(2), 26; https://doi.org/10.3390/lubricants10020026 - 12 Feb 2022

Viewed by 2629

Abstract

The frictional issues during motion of the axis-wheels assembly occurring in contact wheel–rail and in bogie bearing were studied. The influence of greases upon friction therein was also considered. The lateral dynamic behavior of the four-axle freight wagon model with two-axle Y25 bogies [...] Read more.

The frictional issues during motion of the axis-wheels assembly occurring in contact wheel–rail and in bogie bearing were studied. The influence of greases upon friction therein was also considered. The lateral dynamic behavior of the four-axle freight wagon model with two-axle Y25 bogies equipped with swing bolster was analyzed. Simulation models of such a wagon with bogies with and without swing bolsters were elaborated for calculations considering the nonlinearities of wheel–rail contact geometry and nonlinear methods of bogie stability. In these two options, the cases of empty and fully loaded wagon bodies were considered. The lateral dynamic models with 22 and 24 degrees of freedom were considered to determine the nonlinear critical speeds of a freight wagon. It was found that the resistive torque in bearings of the assembly studied varied nonlinearly with wagon speed. During motion along the curve track, values of such a torque can be higher by 50% in case of the wheel under overloading and lower by 50% in case of the wheel under underloading, respectively, compared to those obtained during motion along straight track. Full article

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23 pages, 8942 KiB

Open AccessArticle

Using Machine Learning Methods for Predicting Cage Performance Criteria in an Angular Contact Ball Bearing

by Sebastian Schwarz, Hannes Grillenberger, Oliver Graf-Goller, Marcel Bartz, Stephan Tremmel and Sandro Wartzack

Lubricants 2022, 10(2), 25; https://doi.org/10.3390/lubricants10020025 - 11 Feb 2022

Cited by 7 | Viewed by 3552

Abstract

Rolling bearings have to meet the highest requirements in terms of guidance accuracy, energy efficiency, and dynamics. An important factor influencing these performance criteria is the cage, which has different effects on the bearing dynamics depending on the cage’s geometry and bearing load. [...] Read more.

Rolling bearings have to meet the highest requirements in terms of guidance accuracy, energy efficiency, and dynamics. An important factor influencing these performance criteria is the cage, which has different effects on the bearing dynamics depending on the cage’s geometry and bearing load. Dynamics simulations can be used to calculate cage dynamics, which exhibit high agreement with the real cage motion, but are time-consuming and complex. In this paper, machine learning algorithms were used for the first time to predict physical cage related performance criteria in an angular contact ball bearing. The time-efficient prediction of the machine learning algorithms enables an estimation of the dynamic behavior of a cage for a given load condition of the bearing within a short time. To create a database for machine learning, a simulation study consisting of 2000 calculations was performed to calculate the dynamics of different cages in a ball bearing for several load conditions. Performance criteria for assessing the cage dynamics and frictional behavior of the bearing were derived from the calculation results. These performance criteria were predicted by machine learning algorithms considering bearing load and cage geometry. The predictions for a total of 10 target variables reached a coefficient of determination of

R^{2} \approx 0.94

for the randomly selected test data sets, demonstrating high accuracy of the models. Full article

(This article belongs to the Special Issue Machine Learning in Tribology)

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12 pages, 40798 KiB

Open AccessArticle

A Study on Early Stages of White Etching Crack Formation under Full Lubrication Conditions

by Walter Holweger, Alexander Schwedt, Viktorija Rumpf, Joachim Mayer, Christof Bohnert, Jürgen Wranik, Joshua Spille and Ling Wang

Lubricants 2022, 10(2), 24; https://doi.org/10.3390/lubricants10020024 - 09 Feb 2022

Cited by 9 | Viewed by 2627

Abstract

The appearance of White Etching Cracks (WEC), not covered by the ISO 281 modified failure rate calculation, leads to difficulties in predicting bearing reliability. This uncertainty in bearing applications leads to a worldwide activity in order to understand and prevent this situation since [...] Read more.

The appearance of White Etching Cracks (WEC), not covered by the ISO 281 modified failure rate calculation, leads to difficulties in predicting bearing reliability. This uncertainty in bearing applications leads to a worldwide activity in order to understand and prevent this situation since the WEC failure mode deviates from the traditional Rolling Contact Fatigue (RCF) mode. Plenty of factors have been found to influence this phenomenon over the years, however the precise initiation of the WEC is still under debate. In order to understand the initiation and analyze the temporal evolution, interrupted tests on the same material were performed under conditions that were known to lead to WEC formation and RCF. To avoid the added complexity of boundary lubrication, a Deep Groove Ball Bearing (DGBB) test rig under full lubrication (Elastohydrodynamic Lubrication, EHL) was chosen. Within a standard operating mode, named Mode 1 (RCF), the bearings are solely subjected to a radial load. By suspending the tests at different time steps, a continuous progress of changes in the subsurface material structure seen as equiaxed grains with low dislocation densities, identified as ferrite, is observed. The bearings did not fail up to load cycles of 10⁹. In contrast, a Mode 2 Electrical Charged Contact Fatigue (ECCF) test provoked the early formation of cracks and crack networks, first without WEA, then later with WEA. It became obvious when comparing Mode 1 (RCF) with Mode 2 (ECCF) that Mode 2 (ECCF) achieves far fewer load cycles until failure occurs. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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17 pages, 5935 KiB

Open AccessArticle

Weight Loss, Thermodynamics, SEM, and Electrochemical Studies on N-2-Methylbenzylidene-4-antipyrineamine as an Inhibitor for Mild Steel Corrosion in Hydrochloric Acid

by Israa Abd Alkadir Aziz, Makarim H. Abdulkareem, Iman Adnan Annon, Mahdi M. Hanoon, Mohammed H. H. Al-Kaabi, Lina M. Shaker, Ahmed A. Alamiery, Wan Nor Roslam Wan Isahak and Mohd S. Takriff

Lubricants 2022, 10(2), 23; https://doi.org/10.3390/lubricants10020023 - 09 Feb 2022

Cited by 20 | Viewed by 3220

Abstract

The use of N-2-methylbenzylidene-4-antipyrineamine as an acid corrosion inhibitor for mild steel surfaces in hydrochloric acid is discussed in this article by means of weight loss, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) methods. The experimental findings exhibited that N-2-methylbenzylidene-4-antipyrineamine is [...] Read more.

The use of N-2-methylbenzylidene-4-antipyrineamine as an acid corrosion inhibitor for mild steel surfaces in hydrochloric acid is discussed in this article by means of weight loss, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) methods. The experimental findings exhibited that N-2-methylbenzylidene-4-antipyrineamine is a significant corrosion inhibitor for the mild steel in 1.0 M HCl solution and that its protection efficiency touches the peak at 5 × 10^–4 M, exhibiting 91.8% for N-2-methylbenzylidene-4-antipyrineamine. The inhibitory efficiency increases as the inhibitor concentration rises and reduces as the temperature rises. Temperature has a significant impact on corrosion and blocking activities, which is extensively examined and explained. According to the gravimetric results, the examined inhibitor inhibits mild steel surface corrosion by providing a barrier at the metal–hydrochloric acid medium interface. Thermodynamic characteristics were combined with a quantum chemistry investigation using density functional theory to provide more insight into the inhibitory effect mechanism. The tested inhibitor adsorbs on the mild steel surface based on Langmuir’s adsorption isotherm method. Full article

(This article belongs to the Special Issue Corrosion and Tribocorrosion Behavior of Metals and Alloys)

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15 pages, 1358 KiB

Open AccessArticle

Design of Amorphous Carbon Coatings Using Gaussian Processes and Advanced Data Visualization

by Christopher Sauer, Benedict Rothammer, Nicolai Pottin, Marcel Bartz, Benjamin Schleich and Sandro Wartzack

Lubricants 2022, 10(2), 22; https://doi.org/10.3390/lubricants10020022 - 07 Feb 2022

Cited by 4 | Viewed by 3910

Abstract

In recent years, an increasing number of machine learning applications in tribology and coating design have been reported. Motivated by this, this contribution highlights the use of Gaussian processes for the prediction of the resulting coating characteristics to enhance the design of amorphous [...] Read more.

In recent years, an increasing number of machine learning applications in tribology and coating design have been reported. Motivated by this, this contribution highlights the use of Gaussian processes for the prediction of the resulting coating characteristics to enhance the design of amorphous carbon coatings. In this regard, by using Gaussian process regression (GPR) models, a visualization of the process map of available coating design is created. The training of the GPR models is based on the experimental results of a centrally composed full factorial 2³ experimental design for the deposition of a-C:H coatings on medical UHMWPE. In addition, different supervised machine learning (ML) models, such as Polynomial Regression (PR), Support Vector Machines (SVM) and Neural Networks (NN) are trained. All models are then used to predict the resulting indentation hardness of a complete statistical experimental design using the Box–Behnken design. The results are finally compared, with the GPR being of superior performance. The performance of the overall approach, in terms of quality and quantity of predictions as well as in terms of usage in visualization, is demonstrated using an initial dataset of 10 characterized amorphous carbon coatings on UHMWPE. Full article

(This article belongs to the Special Issue Machine Learning in Tribology)

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18 pages, 2869 KiB

Open AccessArticle

SACGNet: A Remaining Useful Life Prediction of Bearing with Self-Attention Augmented Convolution GRU Network

by Juan Xu, Shiyu Duan, Weiwei Chen, Dongfeng Wang and Yuqi Fan

Lubricants 2022, 10(2), 21; https://doi.org/10.3390/lubricants10020021 - 03 Feb 2022

Cited by 8 | Viewed by 2998

Abstract

In recent years, the development of deep learning-based remaining useful life (RUL) prediction methods of bearings has flourished because of their high accuracy, easy implementation, and lack of reliance on a priori knowledge. However, there are two challenging issues concerning the prediction accuracy [...] Read more.

In recent years, the development of deep learning-based remaining useful life (RUL) prediction methods of bearings has flourished because of their high accuracy, easy implementation, and lack of reliance on a priori knowledge. However, there are two challenging issues concerning the prediction accuracy of existing methods. The run-to-failure sequential data and its RUL labels are almost inaccessible in real-world scenarios. Meanwhile, the existing models usually capture the general degradation trend of bearings while ignoring the local information, which restricts the model performance. To tackle the aforementioned problems, we propose a novel health indicator derived from the original vibration signals by combining principal components analysis with Euclidean distance metric, which was motivated by the desire to resolve the dependency on RUL labels. Then, we design a novel self-attention augmented convolution GRU network (SACGNet) to predict the RUL. Combining a self-attention mechanism with a convolution framework can both adaptively assign greater weights to more important information and focus on local information. Furthermore, Gated Recurrent Units are used to parse the long-term dependencies in weighted features such that SACGNet can utilize the important weighted features and focus on local features to improve the prognostic accuracy. The experimental results on the PHM 2012 Challenge dataset and the XJTU-SY bearing dataset have demonstrated that our proposed method is superior to the state of the art. Full article

(This article belongs to the Special Issue Advances in Bearing Lubrication and Thermal Sciences)

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18 pages, 18711 KiB

Open AccessArticle

Tilting-Pad Journal Bearings—Frequency-Dependent Dynamic Coefficients and Pivot Flexibility Effects

by Laurence F. Wagner and Paul E. Allaire

Lubricants 2022, 10(2), 20; https://doi.org/10.3390/lubricants10020020 - 03 Feb 2022

Cited by 5 | Viewed by 3320

Abstract

Tribologists have generally accepted that the dynamic modeling of tilting-pad journal bearings (TPJB) must consider the frequency dependency of the dynamic properties. Industrial compressors, turbines, and other rotating machines are subjected to instability drivers, such as blades, impellers, and seals, leading to dominant [...] Read more.

Tribologists have generally accepted that the dynamic modeling of tilting-pad journal bearings (TPJB) must consider the frequency dependency of the dynamic properties. Industrial compressors, turbines, and other rotating machines are subjected to instability drivers, such as blades, impellers, and seals, leading to dominant vibratory frequencies that are generally quite different from rotational frequency. Though the literature has provided related methods and numerical results, full understanding of the physics of TPJB frequency dependency is not generally available to the design community, and theorists and experimentalists are often not in agreement. This investigation hinges on a single-pad, two degree-of-freedom model that creates a basis for understanding the various geometries and operating conditions related to frequency dependency for a full bearing. The analytical results indicate that both stiffness and damping coefficients show frequency dependency, and that the dependency is primarily associated with the pad rotational damping and the flexibility of the pivot contact region that provides support for the pad. Understanding the role of pivot flexibility in combination with the fluid film provides a key to improving agreement between theory and experiment. This article is a revised and expanded version of the paper presented at the ASME 2019 Turbo Expo in Phoenix, Arizona from 17 to 21 June. The paper number was GT2019-90195 and it was titled “On the Frequency Dependency of Tilting-Pad Journal Bearings”. Full article

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3 pages, 184 KiB

Open AccessEditorial

Acknowledgment to Reviewers of Lubricants in 2021

by Lubricants Editorial Office

Lubricants 2022, 10(2), 19; https://doi.org/10.3390/lubricants10020019 - 27 Jan 2022

Viewed by 1471

Abstract

Rigorous peer-reviews are the basis of high-quality academic publishing [...] Full article

25 pages, 6926 KiB

Open AccessArticle

A Semantic Annotation Pipeline towards the Generation of Knowledge Graphs in Tribology

by Patricia Kügler, Max Marian, Rene Dorsch, Benjamin Schleich and Sandro Wartzack

Lubricants 2022, 10(2), 18; https://doi.org/10.3390/lubricants10020018 - 25 Jan 2022

Cited by 3 | Viewed by 3950

Abstract

Within the domain of tribology, enterprises and research institutions are constantly working on new concepts, materials, lubricants, or surface technologies for a wide range of applications. This is also reflected in the continuously growing number of publications, which in turn serve as guidance [...] Read more.

Within the domain of tribology, enterprises and research institutions are constantly working on new concepts, materials, lubricants, or surface technologies for a wide range of applications. This is also reflected in the continuously growing number of publications, which in turn serve as guidance and benchmark for researchers and developers. Due to the lack of suited data and knowledge bases, knowledge acquisition and aggregation is still a manual process involving the time-consuming review of literature. Therefore, semantic annotation and natural language processing (NLP) techniques can decrease this manual effort by providing a semi-automatic support in knowledge acquisition. The generation of knowledge graphs as a structured information format from textual sources promises improved reuse and retrieval of information acquired from scientific literature. Motivated by this, the contribution introduces a novel semantic annotation pipeline for generating knowledge in the domain of tribology. The pipeline is built on Bidirectional Encoder Representations from Transformers (BERT)—a state-of-the-art language model—and involves classic NLP tasks like information extraction, named entity recognition and question answering. Within this contribution, the three modules of the pipeline for document extraction, annotation, and analysis are introduced. Based on a comparison with a manual annotation of publications on tribological model testing, satisfactory performance is verified. Full article

(This article belongs to the Special Issue Machine Learning in Tribology)

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16 pages, 5757 KiB

Open AccessArticle

Numerical Analysis for Wetting Behaviors of an Oil Jet Lubricated Spur Gear

by Yu Dai, Chongyu Liang, Xi Chen and Xiang Zhu

Lubricants 2022, 10(2), 17; https://doi.org/10.3390/lubricants10020017 - 20 Jan 2022

Cited by 4 | Viewed by 2734

Abstract

As it is widely employed in the aeronautical transmission system, a better understanding of the oil jet lubrication behavior is vital to determine the total system energy consumption. Firstly, this study presents related theoretical models such as the sum of oil jet resistance [...] Read more.

As it is widely employed in the aeronautical transmission system, a better understanding of the oil jet lubrication behavior is vital to determine the total system energy consumption. Firstly, this study presents related theoretical models such as the sum of oil jet resistance torque, impingement depth, and wetted area of the oil film for calibrating the physical characteristics of the impact of the oil jet on the gear flank. Then, in terms of the flow phenomenology of the liquid column for the oil jet impact on an isolated spur gear, a detailed transient and spatial flow field analysis becomes available, benefiting from an overset mesh method integrating with a volume-of-fluid (VOF) method. Furthermore, not only the oil jet resistance torque, but also the impingement depth as well as the spatial and temporal evolution of wetted surface by the oil film on the gear tooth given by numerical investigations were compared well with the theoretical calculations. Full article

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18 pages, 2537 KiB

Open AccessArticle

Analysis of the Physicochemical Properties of Some Selected Non-Edible Vegetable Oil-Based Cutting Fluids Using the Design of Experiment (DOE) Approach

by Rasaq A. Kazeem, David A. Fadare, Omolayo M. Ikumapayi, Stephen A. Akinlabi, Sunday A. Afolalu and Esther T. Akinlabi

Lubricants 2022, 10(2), 16; https://doi.org/10.3390/lubricants10020016 - 19 Jan 2022

Cited by 6 | Viewed by 2204

Abstract

The pursuit of environmentally friendly cutting fluids is ongoing as the problems of traditional cutting fluids become more apparent. The bulk of vegetable oils used in studies are consumable and, if marketed, may conflict with human utilization, making cutting fluids more costly. However, [...] Read more.

The pursuit of environmentally friendly cutting fluids is ongoing as the problems of traditional cutting fluids become more apparent. The bulk of vegetable oils used in studies are consumable and, if marketed, may conflict with human utilization, making cutting fluids more costly. However, few investigations on the use of lesser-known vegetable oils as cutting fluids have been conducted. As a result, the goal of this research is to examine how effective some lesser-known vegetable oils will be if used as a cutting fluid. Based on some physicochemical properties such as acid value and viscosity, the developed vegetable oil-based cutting fluids (watermelon and jatropha) were statistically analyzed using 24 full factorial techniques. This paper aimed at determining the interaction of the physicochemical properties on the developed cutting fluids. Emulsifiers, antifoam agents, biocide, and anti-corrosive agents were considered as natural variables. The effect of the natural variables on the acidity index and viscosity of cutting fluids were fully analyzed with ANOVA, contour, and surface plots. From the responses obtained from the experiment as explained by the independent variables (emulsifying agent, anti-corrosion agent, biocide, and antifoam agent), the watermelon seed oil-based cutting fluid was 89% accurate, while the jatropha oil-based cutting fluid was 75% accurate. Full article

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10 pages, 943 KiB

Open AccessArticle

History-Dependent Stress Relaxation of Liquids under High-Confinement: A Molecular Dynamics Study

by Hongyu Gao

Lubricants 2022, 10(2), 15; https://doi.org/10.3390/lubricants10020015 - 19 Jan 2022

Cited by 1 | Viewed by 2006

Abstract

When liquids are confined into a nanometer-scale slit, the induced layering-like film structure allows the liquid to sustain non-isotropic stresses and thus be load-bearing. Such anisotropic characteristics of liquid under confinement arise naturally from the liquids’ wavenumber dependent compressibility, which does not need [...] Read more.

When liquids are confined into a nanometer-scale slit, the induced layering-like film structure allows the liquid to sustain non-isotropic stresses and thus be load-bearing. Such anisotropic characteristics of liquid under confinement arise naturally from the liquids’ wavenumber dependent compressibility, which does not need solidification to take place as a prerequisite. In other words, liquids under confinement can still retain fluidity with molecules being (sub-)diffusive. However, the extensively prolonged structural relaxation times can cause hysteresis of stress relaxation of confined molecules in response to the motions of confining walls and thereby rendering the quasi-static stress tensors history-dependent. In this work, by means of molecular dynamics, stress tensors of a highly confined key base-oil component, i.e., 1-decene trimer, are calculated after its relaxation from being compressed and decompressed. A maximum of 77.1 MPa normal stress discrepancy has been detected within a triple-layer boundary film. Analyses with respect to molecular morphology indicate that among the effects (e.g., confinement, molecular structure, and film density) that can potentially affect confined stresses, the ordering status of the confined molecules plays a predominant role. Full article

(This article belongs to the Special Issue Advances in Friction Modifiers and Liquid Confinement)

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19 pages, 2560 KiB

Open AccessReview

Friction Challenge in Hydraulic Fracturing

by Yanbao Guo, Min Zhang, Hui Yang, Deguo Wang, Melvin A. Ramos, Travis Shihao Hu and Quan Xu

Lubricants 2022, 10(2), 14; https://doi.org/10.3390/lubricants10020014 - 18 Jan 2022

Cited by 9 | Viewed by 5077

Abstract

Hydraulic fracturing has become one of the most popular techniques for exploring sustainable energy sources. However, friction is associated with the entire fracturing process, presenting significant challenges for development. Facing the huge friction challenges, this review is elaborated in the following three aspects: [...] Read more.

Hydraulic fracturing has become one of the most popular techniques for exploring sustainable energy sources. However, friction is associated with the entire fracturing process, presenting significant challenges for development. Facing the huge friction challenges, this review is elaborated in the following three aspects: (1) the fundamentals of hydraulic fracturing, including three aspects of rock fracture mechanism, fracturing fluid, and proppant; (2) the friction challenges in hydraulic fracturing, which mainly exist in friction along the path and friction near wellbore; (3) hydraulic fracturing drag reduction technologies, which are considered proppant segment plug, fracturing fluid viscosity enhancement, and proppant surface modification technologies. Therefore, we should not only understand the challenges in hydraulic fracturing but also know how to mitigate them. Additionally, we call for a strong focus on environmentally friendly, green friction-reducing technologies for oil and gas fields in the future development of the fracturing industry. Full article

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Lubricants, Volume 10, Issue 2 (February 2022) – 18 articles

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