Open Access Editorial Issue
Guest editorial: Special Issue on Artificial Intelligence and Emerging Computational Approaches for Tribology
Friction 2024, 12 (6): 1057-1059
Published: 02 April 2024
Open Access Review Article Issue
AI for tribology: Present and future
Friction 2024, 12 (6): 1060-1097
Published: 12 March 2024

With remarkable learning capabilities and swift operational speeds, artificial intelligence (AI) can assist researchers in swiftly extracting valuable patterns, trends, and associations from subjective information. Tribological behaviors are characterized by dependence on systems, evolution with time, and multidisciplinary coupling. The friction process involves a variety of phenomena, including mechanics, thermology, electricity, optics, magnetics, and so on. Hence, tribological information possesses the distinct characteristics of being multidisciplinary, multilevel, and multiscale, so that the application of AI in tribology is highly extensive. To delineate the scope, classification, and recent trends of AI implementation in tribology, this review embarks on exploration of the tribology research domain. It comprehensively outlines the utilization of AI in basic theory of tribology, intelligent tribology, component tribology, extreme tribology, bio-tribology, green tribology, and other fields. Finally, considering the emergence of "tribo-informatics" as a novel interdisciplinary field, which combines tribology with informatics, this review elucidates the future directions and research framework of "AI for tribology". In this paper, tribo-system information is divided into 5 categories: input information (I), system intrinsic information (S), output information (O), tribological state information (Ts), and derived state information (Ds). Then, a fusion method among 5 types of tribo-system information and different AI technologies (regression, classification, clustering, and dimension reduction) has been proposed, which enables tribo-informatics methods to solve common problems such as tribological behavior state monitoring, behavior prediction, and system optimization. The purpose of this review is to offer a systematic comprehension of tribo-informatics and to inspire new research ideas of tribo-informatics. Ultimately, it aspires to enhance the efficiency of problem-solving in tribology.

Open Access Research Article Issue
Prediction of contact resistance of electrical contact wear using different machine learning algorithms
Friction 2024, 12 (6): 1250-1271
Published: 10 January 2024

H62 brass material is one of the important materials in the process of electrical energy transmission and signal transmission, and has excellent performance in all aspects. Since the wear behavior of electrical contact pairs is particularly complex when they are in service, we evaluated the effects of load, sliding velocity, displacement amplitude, current intensity, and surface roughness on the changes in contact resistance. Machine learning (ML) algorithms were used to predict the electrical contact performance of different factors after wear to determine the correlation between different factors and contact resistance. Random forest (RF), support vector regression (SVR) and BP neural network (BPNN) algorithms were used to establish RF, SVR and BPNN models, respectively, and the experimental data were trained and tested. It was proved that BP neural network model could better predict the stable mean resistance of H62 brass alloy after wear. Characteristic analysis shows that the load and current have great influence on the predicted electrical contact properties. The wear behavior of electrical contacts is influenced by factors such as load, sliding speed, displacement amplitude, current intensity, and surface roughness during operation. Machine learning algorithms can predict the electrical contact performance after wear caused by these factors. Experimental results indicate that an increase in load, current, and surface roughness leads to a decrease in stable mean resistance, while an increase in displacement amplitude and frequency results in an increase in stable mean resistance, leading to a decline in electrical contact performance. To reduce testing time and costs and quickly obtain the electrical contact performance of H62 brass alloy after wear caused by different factors, three algorithms (random forest (RF), support vector regression (SVR), and BP neural network (BPNN)) were used to train and test experimental results, resulting in a machine learning model suitable for predicting the stable mean resistance of H62 brass alloy after wear. The prediction results showed that the BPNN model performed better in predicting the electrical contact performance compared to the RF and SVR models.

Open Access Review Article Issue
Tribo-informatics approaches in tribology research: A review
Friction 2023, 11 (1): 1-22
Published: 02 May 2022

Tribology research mainly focuses on the friction, wear, and lubrication between interacting surfaces. With the continuous increase in the industrialization of human society, tribology research objects have become increasingly extensive. Tribology research methods have also gone through the stages of empirical science based on phenomena, theoretical science based on models, and computational science based on simulations. Tribology research has a strong engineering background. Owing to the intense coupling characteristics of tribology, tribological information includes subject information related to mathematics, physics, chemistry, materials, machinery, etc. Constantly emerging data and models are the basis for the development of tribology. The development of information technology has provided new and more efficient methods for generating, collecting, processing, and analyzing tribological data. As a result, the concept of "tribo-informatics (triboinformatics)" has been introduced. In this paper, guided by the framework of tribo-informatics, the application of tribo-informatics methods in tribology is reviewed. This article aims to provide helpful guidance for efficient and scientific tribology research using tribo-informatics approaches.

Open Access Review Article Issue
Metal matrix nanocomposites in tribology: Manufacturing, performance, and mechanisms
Friction 2022, 10 (10): 1596-1634
Published: 04 January 2022

Metal matrix nanocomposites (MMNCs) become irreplaceable in tribology industries, due to their supreme mechanical properties and satisfactory tribological behavior. However, due to the dual complexity of MMNC systems and tribological process, the anti-friction and anti-wear mechanisms are unclear, and the subsequent tribological performance prediction and design of MMNCs are not easily possible: A critical up-to-date review is needed for MMNCs in tribology. This review systematically summarized the fabrication, manufacturing, and processing techniques for high-quality MMNC bulk and surface coating materials in tribology. Then, important factors determining the tribological performance (mainly anti-friction evaluation by the coefficient of friction (CoF) and anti-wear assessment with wear rate) in MMNCs have been investigated thoroughly, and the correlations have been analyzed to reveal their potential coupling/synergetic roles of tuning tribological behavior of MMNCs. Most importantly, this review combined the classical metal/alloy friction and wear theories and adapted them to give a (semi-)quantitative description of the detailed mechanisms of improved anti-friction and anti-wear performance in MMNCs. To guarantee the universal applications of these mechanisms, their links with the analyzed influencing factors (e.g., loading forces) and characteristic features like tribo-film have been clarified. This approach forms a solid basis for understanding, predicting, and engineering MMNCs’ tribological behavior, instead of pure phenomenology and experimental observation. Later, the pathway to achieve a broader application for MMNCs in tribo-related fields like smart materials, biomedical devices, energy storage, and electronics has been concisely discussed, with the focus on the potential development of modeling, experimental, and theoretical techniques in MMNCs’ tribological processes. In general, this review tries to elucidate the complex tribo-performances of MMNCs in a fundamentally universal yet straightforward way, and the discussion and summary in this review for the tribological performance in MMNCs could become a useful supplementary to and an insightful guidance for the current MMNC tribology study, research, and engineering innovations.

Open Access Research Article Issue
Tribo-informatics: Concept, architecture, and case study
Friction 2021, 9 (3): 642-655
Published: 05 November 2020

Friction plays a vital role in energy dissipation, device failure, and even energy supply in modern society. After years of research, data and information on tribology research are becoming increasingly available. Because of the strong systematic and multi-disciplinary coupling characteristics of tribology, tribology information is scattered in various disciplines with different patterns, e.g., technical documents, databases, and papers, thereby increasing the information entropy of the system, which is inconducive to the preservation and circulation of research information. With the development of computer and information science and technology, many subjects have begun to be combined with information technology, and multi-disciplinary informatics has been born. This paper describes the combination of information technology with tribology research, presenting the connotation and architecture of tribo-informatics, and providing a case study on implementing the proposed concept and architecture. The proposal and development of tribo-informatics described herein will improve the research efficiency and optimize the research process of tribology, which is of considerable significance to the development of this field.

Open Access Research Article Issue
Multiscale analysis of friction behavior at fretting interfaces
Friction 2021, 9 (1): 119-131
Published: 19 March 2020

Friction behavior at fretting interfaces is of fundamental interest in tribology and is important in material applications. However, friction has contact intervals, which can accurately determine the friction characteristics of a material; however, this has not been thoroughly investigated. Moreover, the fretting process with regard to different interfacial configurations have also not been systematically evaluated. To bridge these research gaps, molecular dynamics (MD) simulations on Al-Al, diamond-diamond, and diamond-silicon fretting interfaces were performed while considering bidirectional forces. This paper also proposes new energy theories, bonding principles, nanoscale friction laws, and wear rate analyses. With these models, semi-quantitative analyses of coefficient of friction (CoF) were made and simulation outcomes were examined. The results show that the differences in the hardness, stiffness modulus, and the material configuration have a considerable influence on the fretting process. This can potentially lead to the force generated during friction contact intervals along with changes in the CoF. The effect of surface separation can be of great significance in predicting the fretting process, selecting the material, and for optimization.

Open Access Research Article Issue
Abrasive wear behavior of PTFE for seal applications under abrasive-atmosphere sliding condition
Friction 2020, 8 (4): 755-767
Published: 02 October 2019

Abrasive wear is a common failure phenomenon that often limits the service life of sealing elements. Evaluation and comparison of the abrasion resistance of polytetrafluoroethylene (PTFE) were conducted using Al2O3 particles with sizes in the range 5 to 200 μm on a pin-on-flat tribo-tester under dry reciprocating sliding conditions at room temperature. Based on the examined worn surface characteristics of both PTFE and 316L stainless steel (as a counterpart) and the analyzed coefficient of friction (COF) evolutions, the wear mechanism and particle size effect have been explored in detail. The results demonstrate that the abrasive size is the main contributing factor, which can drastically impact the wear mechanism and tribological properties of tribo-pairs. The COF exhibits different evolution characteristics (trends) for different abrasive sizes. For moderate particle sizes, the COF trends become more complicated and the most evident wear of the metallic counterpart is evident. The activity behaviors of abrasives are dominated by the particle size. Particles can becomes embedded in one of the tribo-pair materials to plough-cut the counterpart, thus causing two-body abrasive wear. The abrasives can also behave as free rolling bodies, which play the role of third body to realize three-body "PTFE- abrasive-316L" abrasion. When abrasives are involved in the wear process, both the wear rate and COF of the metallic counterpart increase, but the material removal rate of the PTFE is reduced. The results obtained can offer guidelines regarding the design and protection of seals.

Open Access Review Article Issue
Fundamental theories and basic principles of triboelectric effect: A review
Friction 2019, 7 (1): 2-17
Published: 10 August 2018

Long-term observation of the triboelectric effect has not only proved the feasibility of many novel and useful tribo-devices (e.g., triboelectric nanogenerators), but also constantly motivated the exploration of its mysterious nature. In the pursuit of a comprehensive understanding of how the triboelectric process works, a more accurate description of the triboelectric effect and its related parameters and factors is urgently required. This review critically goes through the fundamental theories and basic principles governing the triboelectric process. By investigating the difference between each charging media, the electron, ion, and material transfer is discussed and the theoretical deduction in the past decades is provided. With the information from the triboelectric series, interesting phenomena including cyclic triboelectric sequence and asymmetric triboelectrification are precisely analyzed. Then, the interaction between the tribo-system and its operational environment is analyzed, and a fundamental description of its effects on the triboelectric process and results is summarized. In brief, this review is expected to provide a strong understanding of the triboelectric effect in a more rigorous mathematical and physical sense.

Open Access Research Article Issue
Design approach for optimization of a piston ring profile considering mixed lubrication
Friction 2016, 4 (4): 335-346
Published: 23 December 2016

To reduce the friction of a piston ring while maintaining a large oil film load-carrying capacity, an approach comprising of the inverse method and the sequential quadratic programming algorithm was proposed. The approach considers the variation of mixed lubrication and variable lubricant viscosity with temperature along the engine stroke, is developed to optimize the profile of a piston ring. A piston ring profile is represented by a polynomial function. A case study of the second piston ring shows that the proposed method can be applied for the optimization of a piston ring profile. In addition, this paper illustrates the effects of the degree of a polynomial function. The results show that the minimization of friction and maximization of oil film load-carrying capacity can be balanced simultaneously when the degree of the polynomial is 2 and 5.

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