This article reviews laboratory friction and wear test methods for evaluating fundamental tribological properties under controlled operating conditions. Key considerations for obtaining reliable data, the importance of standardization and de facto standards, and recent trends in customized testing approaches are also discussed.

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The design of friction testing machines requires a delicate balance between academic rigor and practical flexibility. This guideline summarizes key considerations based on extensive hands-on experience as a manufacturer of friction testers. It covers essential components such as force detection systems, drive mechanisms, load application methods, specimen holding structures, and control technologies. Special attention is given to load cell selection and calibration, strain amplifier characteristics, resonance mitigation in drive systems, and advanced control strategies for precise and repeatable testing. Beyond standardized protocols, this document emphasizes practical insights and craftsmanship that influence real-world performance, aiming to bridge the gap between theoretical research and industrial practice for reliable friction and wear evaluation.

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A micro-reciprocating tribometer was developed to investigate friction and wear behavior during the initial and running-in stages of sliding contact, where conventional tribological tests often exhibit poor reproducibility due to rapid changes in surface conditions. The system employs a three-point contact configuration using spherical-ended pins, which minimizes misalignment and suppresses specimen tilting caused by alternating friction forces during reciprocating motion. This design helps maintain stable contact conditions and improves measurement repeatability. A high-precision servo motor enables accurately controlled reciprocating motion with sliding amplitudes as small as 60 μm, which is smaller than the Hertzian contact diameter. Consequently, nearly the same contact regions can repeatedly interact, making the apparatus particularly suitable for studying transient friction phenomena and running-in processes. Experimental studies using mirror-polished SUS304 stainless steel specimens under different atmospheric conditions revealed reproducible friction transitions during the first few sliding cycles. Additional experiments with hydrogenated diamond-like carbon (DLC) coatings demonstrated the influence of sliding patterns on running-in behavior and friction reduction. These results show that the developed tribometer is a useful research tool for fundamental investigations of friction mechanisms during the critical early stages of sliding contact.

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In recent years, friction and wear testing has increasingly focused not only on elucidating the fundamental mechanisms of friction and wear but also on reproducing the operating conditions of actual machinery. Furthermore, the application of AI (artificial intelligence) to friction and wear testing has attracted considerable attention. This paper describes the development of a new tribometer capable of reproducing the sliding conditions encountered in actual machinery. It also presents an AI-powered approach for monitoring the condition of sliding surfaces and identifying sensor data useful for this purpose. Wear tests were conducted using Al-Sn-Si alloy bearing materials. The results demonstrated that the newly developed tribometer can be used to investigate wear processes under a wide range of sliding conditions relevant to actual machinery. In addition, SHAP (SHapley Additive exPlanations), an XAI (explainable artificial intelligence) method, was applied to interpret machine-learning-based monitoring results of sliding surface conditions. The results showed that SHAP is effective in providing interpretability to anomaly detection results, which is difficult to achieve using conventional unsupervised learning alone. By quantifying the contribution of each sensor signal, the proposed approach enables a more detailed understanding of sliding surface conditions and wear processes.

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We observed friction phenomena occurring on the skin surface and analyzed the physical origins of tactile sensations using a force plate equipped with sensors such as piezoelectric elements and strain gauges to measure the reaction forces generated by movement. By integrating a high-speed camera, it enables in-situ observation of human motion and the mechanical stimuli applied to the skin. We present findings from analyzing the tactile sensation of water, the application feel of nail enamel, the grasping and cutting sensation with scissors, and the hair combing process using this sensing system.

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Understanding tribological properties is critical in the development of sliding components. These properties are typically evaluated through friction and wear tests and applied to design. However, correlation with actual systems is often poor. Therefore, improved testing methods and simulation of real operating conditions are employed. This paper presents case studies evaluating sliding conditions in products using conventional friction tests and a newly developed simulation test apparatus.

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Friction losses in timing chain systems for internal combustion engines are important factors affecting engine efficiency under recent operating and lubrication conditions. A timing chain system consists of several components such as chains, sprockets, guides, and tensioners, and its total friction loss is generated by the combination of multiple contact mechanisms. This article describes the mechanisms of friction generation in timing chain systems, including sliding between the chain and guides, internal articulation of chain links, and meshing between the chain and sprockets. In addition, various evaluation methods are introduced, ranging from system-level measurements based on torque differences to component-level and element-level tribological tests. The characteristics of different test methods, such as chain drive test rigs and joint tribometers, are also explained. These evaluation approaches are useful for understanding friction behavior and for improving the efficiency of timing chain systems.

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With the recent trend toward higher operating pressures in mechanical systems, ZnDTP rapidly converts into insoluble compounds after fulfilling its antioxidant function. These degradation products can cause problems such as filter clogging, thereby increasing the importance of lubricant condition monitoring. In recent years, online condition-monitoring sensors capable of detecting early-stage abnormalities have attracted considerable attention. In particular, monitoring changes in the relative dielectric constant of lubricating oils provides valuable information on their physical and chemical properties, the degree of degradation, and their remaining useful life. In this study, we investigated the effects of contaminants associated with ZnDTP degradation by measuring the relative dielectric constant of sample oils before and after filtration using a multi-functional fluid sensor (MFS), and comparing the results with those obtained from a commercially available sensor. The results showed that the relative dielectric constant increased with increasing oil temperature only in the sample whose change in pressure was 10 PSI using an RPVOT, and decreased markedly after filtration. Scanning electron microscopy (SEM) analysis of residues collected during filtration revealed that morphological changes in the particles influenced the temperature dependence of the relative dielectric constant. These findings indicate that the MFS is capable of real-time monitoring of ZnDTP degradation.

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Many studies have been conducted on the friction of ice and snow, and several theories have been proposed, including pressure melting, frictional melting, adhesion, and pseudo-liquid film lubrication. However, each theory has its own issues, and no satisfactory theory that can rationally explain the slipperiness of ice has yet been established. In this study, many previous reports on the friction of ice and snow were investigated, and the following new friction model was proposed. That is, in the friction between the ice particle and the slider, the adhesion area of the ice particle undergo plastic deformation and become high temperature, generating high-pressure water vapor and water. The generation of water vapor and water eliminates the contact area between the ice particle and the slider, significantly reducing the shear stress on the friction surface. This phenomenon occurs continuously on the friction surface, resulting in a low coefficient of friction. By adopting this water vapor generation model, it became possible to rationally explain the friction characteristics of ice and snow, and also to resolve issues with previous theories. Furthermore, this model provides a reasonable explanation for why soft materials like rubber exhibit a high coefficient of friction against ice and snow.

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[in Japanese]

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