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TADOKORO Chiharu
| Mechanical Science Division | Professor |
| Department of Mechanical Engineering and System Design |
Performance information
■ Paper- Numerical study on transient response of the bowed string
Miwa SUEDA; Yohei ONODA; Chiharu TADOKORO; Hiroki MORI; Ken NAKANO; Takuo NAGAMINE
Mechanical Engineering Journal, Mar. 2025, [Reviewed]
Japan Society of Mechanical Engineers, Scientific journal
DOI：https://doi.org/10.1299/mej.24-00441
DOI ID：10.1299/mej.24-00441, eISSN：2187-9745 - Controlling windscreen wiper vibration through yaw angle adjustments: A study of dynamic contact behavior using fluorescence observation
C. Tadokoro; H. Kobayashi; M. Sueda; T. Nagamine; S. C. Vlădescu; T. Reddyhoff; K. Nakano
Frontiers in Mechanical Engineering, Nov. 2024, [Reviewed], [Lead, Corresponding], ［Internationally co-authored］
English, Scientific journal
DOI：https://doi.org/10.3389/fmech.2024.1471045
DOI ID：10.3389/fmech.2024.1471045 - Noise reduction and power generation in blower duct using Helmholtz resonator with piezoelectric diaphragm
Chiharu Tadokoro; Takuma Ito; Takuo Nagamine
Engineering Research Express, Volume：5, Number：2, First page：025047, Last page：025047, May 2023, [Lead, Corresponding]
Abstract
Ventilation duct systems are indispensable for air purification and room temperature management in industrial and commercial buildings. The noise generated by blowers for ventilating spaces should be as low as possible. In addition, to power the wireless nodes for monitoring the ventilation conditions such as temperature and pressure at any positions in all the ducts, electric power is preferred to be generated in situ without batteries and wired power supply. In this study, to demonstrate simultaneous noise reduction and in situ power generation using a Helmholtz resonator with a piezoelectric diaphragm in a straight circular pipe duct, the frequency properties of the sound pressure level (SPL) with/without the piezoelectric diaphragm and its generated voltage were measured using an in-house apparatus simulating an industrial blower duct. The experimental results show that the Helmholtz resonator with the piezoelectric diaphragm has a noise reduction performance similar to that without the piezoelectric diaphragm. Power generation was improved not only by impedance matching between the inner and outer resistance but also by the frequency resonance between the frequency of pressure fluctuation in the Helmholtz resonator and the natural frequency of the piezoelectric diaphragm. The Helmholtz resonator with the piezoelectric diaphragm achieved a noise reduction of 10 dB from an SPL of 103 dB and power generation of 12 μW at an SPL of 93 dB.
IOP Publishing, Scientific journal
DOI：https://doi.org/10.1088/2631-8695/acd5ac
DOI ID：10.1088/2631-8695/acd5ac, eISSN：2631-8695 - Concentrated Polymer Brush in Reciprocating Seal Improves Sealing Performance with Low Friction Even for Rough Surfaces and Immiscible Fluids
Chiharu Tadokoro; Daichi Kitafuji; Takuo Nagamine; Ken Nakano; Shinya Sasaki; Takaya Sato; Keita Sakakibara; Yoshinobu Tsujii
Tribology Letters, Volume：70, Number：4, Sep. 2022, [Reviewed], [Lead, Corresponding]
To achieve both lowering the fluid leakage and lowering the friction loss in a reciprocating seal, the effect of coating a concentrated polymer brush (CPB) onto the rough surfaces of the reciprocating seal was examined using a homemade apparatus. The apparatus comprised a narrow gap of the reciprocating seal, which consisted of a ring and rod, and measured the leakage rate and friction coefficient. An ionic liquid, an alkane, and air were used; the ionic liquid was a good solvent for the CPB; the others were non-solvents for the CPB and immiscible fluids for the good solvent. The leakage rate measurements show that the swollen CPB by the good solvent prevents the fluid leakage even for the immiscible fluids and the rough surfaces of the reciprocating seal. In addition, the friction coefficient measurements show that the swollen CPB provides low friction under alkane lubrication even when the CPB is coated onto just one-side surface of the reciprocating seal. Graphical Abstract: [Figure not available: see fulltext.]
Springer Science and Business Media LLC, Scientific journal
DOI：https://doi.org/10.1007/s11249-022-01646-8
Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85137613139&origin=inward
Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85137613139&origin=inward
DOI ID：10.1007/s11249-022-01646-8, ISSN：1023-8883, eISSN：1573-2711, SCOPUS ID：85137613139 - Exploiting the Synergy between Concentrated Polymer Brushes and Laser Surface Texturing to Achieve Durable Superlubricity
Sorin-Cristian Vlădescu; Chiharu Tadokoro; Mayu Miyazaki; Tom Reddyhoff; Takuo Nagamine; Ken Nakano; Shinya Sasaki; Yoshinobu Tsujii
ACS Applied Materials & Interfaces, Volume：14, Number：13, First page：15818, Last page：15829, Mar. 2022, [Reviewed], [Corresponding]
American Chemical Society (ACS), Scientific journal
DOI：https://doi.org/10.1021/acsami.2c00725
DOI ID：10.1021/acsami.2c00725, ISSN：1944-8244, eISSN：1944-8252 - Processes of molecular adsorption and ordering enhanced by mechanical stimuli under high contact pressure
Seiya Watanabe; Chiharu Tadokoro; Koji Miyake; Shinya Sasaki; Ken Nakano
Scientific Reports, Volume：12, Number：1, Mar. 2022, [Reviewed], [Lead, Corresponding]
Abstract
Adsorbed molecular films, referred to as boundary films in tribology, are widely used in various industrial products as a keyway for surface functionalisation, such as lubricity, wettability, and adhesion. Because boundary films are thin nanometre-scale molecular layers and can easily be removed, their formation process cannot be elucidated in detail. In this study, to analyse the growth dynamics of boundary films, the film thickness and molecular orientation of the boundary film of a fatty acid used as an additive in rolling contact as mechanical stimuli were measured in situ. The measurements were performed on simple test lubricants, which were composed of n-hexadecane and stearic acid, at rolling tribological condition between steel and glass (or sapphire) surfaces by ultrathin film interferometry combined with sum-frequency generation spectroscopy according to a unique protocol. The results quantitatively demonstrate shear-induced boundary film formation. The insight gained from these results is anticipated to enable the formulation of high-performance lubricant additives to further reduce friction loss and high-performance glues that can be freely designed for removability.
Springer Science and Business Media LLC, Scientific journal
DOI：https://doi.org/10.1038/s41598-022-07854-5
DOI ID：10.1038/s41598-022-07854-5, eISSN：2045-2322 - Enhancing durability of concentrated polymer brushes using microgrooved substrates
Mayu Miyazaki; Ken Nakano; Chiharu Tadokoro; Sorin-Cristian Vlădescu; Thomas Reddyhoff; Shinya Sasaki; Yoshinobu Tsujii
Wear, Volume：482-483, First page：203984, Last page：203984, Oct. 2021, [Reviewed]
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.wear.2021.203984
DOI ID：10.1016/j.wear.2021.203984, ISSN：0043-1648 - Durability Improvement of Concentrated Polymer Brushes by Multiscale Texturing
Seiya Watanabe; Eri Kodama; Chiharu Tadokoro; Keita Sakakibara; Ken Nakano; Shinya Sasaki; Yoshinobu Tsujii
Tribology Letters, Volume：69, Number：3, Sep. 2021, [Reviewed]
Abstract: Concentrated polymer brushes (CPBs) are promising soft-material coatings for improving tribological properties under severe sliding conditions, even in the macroscopic scale. Therefore, they are expected to be applied to mechanical sliding components. However, the durability of CPBs has remained challenging for industrial applications. Previous studies revealed that applying a groove texture to the CPB substrate is effective in improving the durability of CPBs. In order to achieve further improvement of durability of CPBs, we attempted to apply nano-periodic structures, whereas the groove texture applied in previous studies has widths and depths in micrometres. In this study, the effect of the nano-periodic structure in addition to the groove texture applied to the CPB substrate on the durability of CPB is investigated. The results demonstrate a significant improvement in the durability of CPBs by up to 90% compared with non-textured CPB when an appropriate nano-periodic structure is applied (i.e. a nano-periodic structure oriented parallel to the groove texture). Graphic Abstract: [Figure not available: see fulltext.]
Springer Science and Business Media LLC, Scientific journal
DOI：https://doi.org/10.1007/s11249-021-01474-2
Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85109350464&origin=inward
Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85109350464&origin=inward
DOI ID：10.1007/s11249-021-01474-2, ISSN：1023-8883, eISSN：1573-2711, SCOPUS ID：85109350464 - Anti-vibration and traction control of rotary sliding systems by orthogonal rotation providing transverse sliding
Chiharu Tadokoro; Yuto Aso; Takuo Nagamine; Ken Nakano
Tribology International, Volume：159, First page：106992, Last page：106992, Jul. 2021, [Reviewed], [Lead, Corresponding]
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2021.106992
DOI ID：10.1016/j.triboint.2021.106992, ISSN：0301-679X - In Situ Raman-SLIM Monitoring for the Formation Processes of MoDTC and ZDDP Tribofilms at Steel/Steel Contacts under Boundary Lubrication
Hikaru Okubo; Chiharu Tadokoro; Shinya Sasaki
Tribology Online, Volume：15, Number：3, First page：105, Last page：116, May 2020, [Reviewed]
Japanese Society of Tribologists, Scientific journal
DOI：https://doi.org/10.2474/trol.15.105
DOI ID：10.2474/trol.15.105, eISSN：1881-2198 - Lubricating Properties of Cyano-Based Ionic Liquids against Tetrahedral Amorphous Carbon Film
Shouhei Kawada; Hikaru Okubo; Seiya Watanabe; Chiharu Tadokoro; Ryo Tsuboi; Shinya Sasaki; Masaaki Miyatake
Coatings, Volume：10, Number：2, First page：153, Last page：153, Feb. 2020, [Reviewed]
Ionic liquids have unique characteristics, which render them ideal candidates as new base oils or additives. In particular, there are great expectations from the combination of diamond-like carbon and cyano-based ionic liquids. Lubricating properties of cyano-based ionic liquids have been studied on specific tetrahedral amorphous carbon (ta-C) films. After lubrication, ta-C film/ta-C film contact interface exhibits exceedingly low friction. Therefore, it is necessary to understand this low friction phenomenon. The current study evaluated the lubricating mechanism of cyano-based ionic liquids against ta-C films. 1-Butyl-3-methylimidazolium dicyanamide ((BMIM)(DCN)) and 1-butyl-3-methylimidazolium tricyanomethane ((BMIM)(TCC)) were used as lubricants, with the latter exhibiting low friction coefficient of 0.03. Steel cylinders and disks with ta-C films were used as test specimens. Raman spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and thermogravimetric analysis (TGA) helped us understand the mechanism of low friction induced by (BMIM)(TCC). Graphitization of the ta-C film at high temperatures might have caused the reduction in friction between the films. Similarly, anion adsorption on the worn surface at high temperatures also led to reduced friction. However, the TGA result showed a different trend than that of the sliding test. Our results indicate that the cyano-based ionic liquids underwent tribo-decomposition at low temperatures. Further, a minimum temperature was required for the adsorption of anions onto the sliding surface.
MDPI AG, Scientific journal
DOI：https://doi.org/10.3390/coatings10020153
Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85080924179&origin=inward
Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85080924179&origin=inward
DOI ID：10.3390/coatings10020153, eISSN：2079-6412, SCOPUS ID：85080924179 - Concentrated Polymer Brush as Reciprocating Seal Material for Low Leakage and Low Friction
Chiharu Tadokoro; Kosuke Sato; Takuo Nagamine; Ken Nakano; Shinya Sasaki; Takaya Sato; Keita Sakakibara; Yoshinobu Tsujii
Tribology Transactions, Volume：63, Number：1, First page：20, Last page：27, Jan. 2020, [Reviewed], [Lead, Corresponding]
Recently, concentrated polymer brushes (CPBs) have attracted much attention as potential tribomaterials showing an ultralow friction coefficient (e.g., 10(-4) in a microtribological analysis). In this study, a homemade apparatus modeling reciprocating seals was developed, which consisted of an inner steel rod and an outer steel ring with a narrow clearance less than several tens of micrometers. A few-micrometer-thick CPB film of poly(methyl methacrylate) well-swollen with an ionic liquid was prepared on each steel surface, and the impact of applying the CPB film to the clearance of reciprocating seals was examined by measuring the leakage rate of a fluid and the friction coefficient in reciprocating motion. The results showed that the CPB film narrowed the clearance between the two steel surfaces, which improved its sealing performance. In addition, the CPB film yielded a quite low friction coefficient (e.g., 10(-3)), which assured its smooth motion with small energy loss.
Informa UK Limited, English, Scientific journal
DOI：https://doi.org/10.1080/10402004.2019.1650213
DOI ID：10.1080/10402004.2019.1650213, ISSN：1040-2004, eISSN：1547-397X, Web of Science ID：WOS:000493170200001 - Super-Low Friction of Thermal-Treatment-Concentrated Polymer Brushes (TT-CPBs) under Boundary Lubrication: A Practical Method to Shorten the Swelling Time of CPBs in Solvents
Hikaru Okubo; Chiharu Tadokoro; Keita Sakakibara; Ken Nakano; Shinya Sasaki; Yoshinobu Tsujii
Tribology Online, Volume：14, Number：4, First page：226, Last page：236, Nov. 2019, [Reviewed]
Concentrated polymer brushes (CPBs) are a class of thin polymer films that are composed of polymer chains densely grafted to substrate surfaces. Due to their excellent tribological performance derived from the highly stretched conformation of the polymer chains in suitable solvents, CPBs are expected to be applicable as tribological coatings in sliding components. However, a long swelling time is required to obtain fully swelled CPBs in solvents. To overcome this issue, we propose a simple method involving thermal treatment of CPBs in solvents. Our results showed that this method can dramatically reduce the swelling time of CPBs from more than 48 h to less than 3 min. Moreover, thermal-treatment-CPBs (TT-CPBs) can provide an extremely low friction coefficient (0.002) under the boundary lubrication regime at the TT-CPB/steel tribo-pair interface. All our results suggest that the thermal treatment method is a practical method that will allow the industrial application of CPBs.
Japanese Society of Tribologists, English, Scientific journal
DOI：https://doi.org/10.2474/trol.14.226
DOI ID：10.2474/trol.14.226, ISSN：1881-2198, eISSN：1881-2198, Web of Science ID：WOS:000507987500009 - MECHANICAL STRUCTURE DESIGN TO AVOID FRICTION-INDUCED INSTABILITIES: IN-PLANE ANISOTROPY AND IN-PLANE ASYMMETRY
Ken Nakano; Naohiro Kado; Chiharu Tadokoro; Takuo Nagamine
Facta Universitatis, Series: Mechanical Engineering, Volume：17, Number：2, First page：113, Last page：113, Jul. 2019, [Reviewed]
The stability of a two-degree-of-freedom (2DOF) sliding system with the velocity-weakening friction was examined by the eigenvalue analysis, where the in-plane anisotropy and the in-plane asymmetry were considered. The obtained eigenvalues were organized by using the minimum modal damping ratio as the stability maps. Selecting a stable point in the stability map corresponds automatically to embedding the Yaw-Angle-Misalignment (YAM) method in the mechanical structure design to avoid the instability. If we accept the mechanical structure design of sliding systems with the in-plane anisotropy and the in-plane asymmetry, we can find new stable conditions spread widely in the two-dimensional space, which are invisible from the conventional point of view.
University of Nis, Scientific journal
DOI：https://doi.org/10.22190/fume190415018n
DOI ID：10.22190/fume190415018n, ISSN：0354-2025, eISSN：2335-0164 - Wear acceleration mechanism of diamond-like carbon (DLC) films lubricated with MoDTC solution: Roles of tribofilm formation and structural transformation in wear acceleration of DLC films lubricated with MoDTC solution
Hikaru Okubo; Chiharu Tadokoro; Taro Sumi; Noriyoshi Tanaka; Shinya Sasaki
Tribology International, Volume：133, First page：271, Last page：287, May 2019, [Reviewed]
The wear acceleration mechanism of DLC films lubricated with MoDTC solution was investigated by using in-situ and ex-situ analytical techniques: Raman spectroscopy, XPS, ToF-SIMS and nano-indenter. Especially, to reveal the role of ZDDPs and ta-C films for inhibiting the wear acceleration, friction tests were carried out using a ball-on-disk setup at a-C:H/steel and ta-C/steel contacts lubricated with PAO, PAO + MoDTC and PAO + MoDTC + ZDDP. All our results suggest that the wear acceleration is caused by hard Mo-carbide containing tribofilms. Therefore, wear acceleration did not occur for the harder DLC, i.e., the ta-C films. Our results also suggest that ZDDPs play important roles in inhibiting the carburization of Mo-compounds involving DLC surfaces at the tribological contact.
Elsevier BV, English, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2018.12.029
DOI ID：10.1016/j.triboint.2018.12.029, ISSN：0301-679X, eISSN：1879-2464, Web of Science ID：WOS:000458943500026 - Diprotic ammonium palmitate ionic liquid crystal and nanodiamonds in aqueous lubrication. Film thickness and influence of sliding speed
F.J. Carrión; M.D. Avilés; K. Nakano; C. Tadokoro; T. Nagamine; M.D. Bermúdez
Wear, Volume：418-419, First page：241, Last page：252, Jan. 2019, [Reviewed]
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.wear.2018.12.011
DOI ID：10.1016/j.wear.2018.12.011, ISSN：0043-1648 - Macroscopic tribological properties of thick concentrated polymer brush on rough steel under lubrication with ionic liquid
Keisuke Sato; Hikaru Okubo; Yuki Hirata; Chiharu Tadokoro; Ken Nakano; Yoshinobu Tsujii; Shinya Sasaki
Jurnal Tribologi, Volume：20, First page：97, Last page：113, Sep. 2018, [Reviewed]
Scientific journal - Stabilizing effect arising from parallel misalignment in circular sliding contact
Chiharu Tadokoro; Takuo Nagamine; Ken Nakano
Tribology International, Volume：120, First page：16, Last page：22, Apr. 2018, [Reviewed], [Lead]
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2017.12.003
DOI ID：10.1016/j.triboint.2017.12.003, ISSN：0301-679X - Synergy of two fatty acids as additives on lubricity of a nematic liquid crystal 5CB
Chiharu Tadokoro; Shoki Araya; Masaya Watanabe; Hikaru Okubo; Ken Nakano; Shinya Sasaki
Lubrication Science, Volume：30, Number：3, First page：83, Last page：90, Apr. 2018, [Reviewed], [Lead, Corresponding]
In examining the lubricity of a nematic liquid crystal (4-pentyl-4-cyanobiphenyl [5CB]), synergy of 2 fatty acids (stearic acid [C18] and behenic acid [C22]) as additives was observed. In friction measurements using a ball-on-plate-type tribometer, the friction coefficient for the mixed-additive lubricant (5CB-C18-C22) was lower than those for the single-additive lubricants (5CB-C18 and 5CB-C22). This synergy mechanism was discussed with considering the results obtained in other tests: orientation observations in a stationary cell using polarising microscopy and surface topography measurements of adsorbed films using atomic force microscopy. As a result, it is believed that the microscopic patterned surface formed by the mixed additive strengthens the surface anchoring of 5CB, which leads to increase in the effective viscosity of 5CB and therefore to decrease in the macroscopic friction coefficient in the mixed lubrication regime.
Wiley, English, Scientific journal
DOI：https://doi.org/10.1002/ls.1406
DOI ID：10.1002/ls.1406, ISSN：0954-0075, eISSN：1557-6833, Web of Science ID：WOS:000426652800001 - Lubricating mechanism of cyano-based ionic liquids on nascent steel surface
S. Kawada; S. Watanabe; C. Tadokoro; R. Tsuboi; S. Sasaki
Tribology International, Volume：119, First page：474, Last page：480, Mar. 2018, [Reviewed]
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2017.11.019
DOI ID：10.1016/j.triboint.2017.11.019, ISSN：0301-679X - Effects of Alkyl Chain Length of Sulfate and Phosphate Anion-Based Ionic Liquids on Tribochemical Reactions
Shouhei Kawada; Seiya Watanabe; Chiharu Tadokoro; Shinya Sasaki
Tribology Letters, Volume：66, Number：1, Mar. 2018, [Reviewed]
Springer Science and Business Media LLC, Scientific journal
DOI：https://doi.org/10.1007/s11249-017-0962-1
DOI ID：10.1007/s11249-017-0962-1, ISSN：1023-8883, eISSN：1573-2711 - Rotational Motions Excited by Vertical Harmonic Motions
Chiharu Tadokoro; Kei Kadowaki; Hiroki Mori; Takuo Nagamine
Transactions of Nanjing University of Aeronautics & Astronautics, Volume：35, Number：1, First page：51, Last page：57, Feb. 2018, [Reviewed], [Lead, Corresponding]
Scientific journal - Proposal of Biomimetic Tribological System to Control Friction Behavior under Boundary Lubrication by Applying 3D Metal Printing Process
Misa Yonehara; Hikaru Okubo; Chiharu Tadokoro; Shinya Sasaki; Braham Prakash
Tribology Online, Volume：13, Number：1, First page：8, Last page：14, 2018, [Reviewed]
A new concept was proposed as biomimetic tribological (BMT) system by using three-dimensional (3D) printing process. The BMT had a lubricant supply path (LSP) beneath the sliding surface. The tribological properties could be actively controlled by directly supplying lubricant additives (anti-wear additive and friction modifier) alone to the sliding surface through the LSP during a friction process. To confirm the effectiveness of the LSP surface, for improving the tribological performance, under boundary lubrication, friction tests were conducted on a plate specimen with a lubricant supply path that was manufactured by a 3D metal printer. Experimental results suggest that the LSP surface system was more effective for friction reduction than a conventional system, and it offered an effective way to actively control the tribological performance under boundary lubrication.
Japanese Society of Tribologists, English, Scientific journal
DOI：https://doi.org/10.2474/trol.13.8
DOI ID：10.2474/trol.13.8, ISSN：1881-2198, eISSN：1881-2198, Web of Science ID：WOS:000458273600003 - MoDTC-induced wear acceleration mechanism of a hydrogenated amorphous carbon diamond-like carbon film
Hikaru OKUBO; Hiroaki MAEDA; Shouhei KAWADA; Chiharu TADOKORO; Shinya SASAKI
Transactions of the JSME (in Japanese), Volume：84, Number：861, First page：17, Last page：00564, 2018, [Reviewed]
Japan Society of Mechanical Engineers, Scientific journal
DOI：https://doi.org/10.1299/transjsme.17-00564
DOI ID：10.1299/transjsme.17-00564, ISSN：2187-9761, eISSN：2187-9761, J-Global ID：201802273712836223 - Piezoelectric power generation using friction-induced vibration
Chiharu Tadokoro; Aya Matsumoto; Takuo Nagamine; Shinya Sasaki
Smart Materials and Structures, Volume：26, Number：6, First page：065012, Last page：065012, Jun. 2017, [Reviewed], [Lead, Corresponding]
In order to examine the feasibility of power generation by using friction-induced vibration with a piezoelectric element, we performed experiments and numerical analysis. In the experiments, the generated power in the piezoelectric element and the displacement of an oscillator were measured by a newly developed apparatus that embodied a single-degree-of-freedom (1-DOF) system with friction. In the numerical analysis, an analytical model of a 1-DOF system with friction and piezoelectric element was proposed to simulate the experiments. The experimental results demonstrated that the power of a few microwatts was generated by sliding between a steel ball and a steel plate lubricated with glycerol. In this study, a maximum power of approximately 10 mu W was generated at a driving velocity of 40 mm s(-1) and a normal load of 15 N. The numerical results demonstrated good qualitative agreement with the experimental results. This implies that this analytical model can be applied to optimize the oscillator design in piezoelectric power generation using friction-induced vibration.
IOP Publishing, English, Scientific journal
DOI：https://doi.org/10.1088/1361-665x/aa7042
DOI ID：10.1088/1361-665x/aa7042, ISSN：0964-1726, eISSN：1361-665X, Web of Science ID：WOS:000401631700001 - The Effects of Surface Texturing on Friction Performance under Reciprocating Sliding Condition
Tianchi Qin; Chiharu Tadokoro; Shinya Sasaki
Key Engineering Materials, Volume：739, First page：36, Last page：41, Jun. 2017, [Reviewed]
In this research, we focus on the improvement of frictional performance of piston ring achieved by Laser Surface Texturing. Five kinds of samples (non-texture, dimple 100μm, dimple120μm, groove 45 degrees to sliding direction and groove 90 degrees to sliding direction) were tested under reciprocating sliding condition. The results showed that the sample of groove 90 degrees to sliding condition has the maximum decrease on either average friction coefficient (26%) or friction coefficient at end points of stock (33%). And we think that under boundary lubrication regime, the uniformity of distribution of the texture and flow of oil in contact surface are the key factors which affect the friction coefficient.
Trans Tech Publications, Ltd., Scientific journal
DOI：https://doi.org/10.4028/www.scientific.net/kem.739.36
DOI ID：10.4028/www.scientific.net/kem.739.36, eISSN：1662-9795 - Measurements of lubricant film thickness by optical interference
K. Nakano; C. Tadokoro; S. Maegawa
Journal of the Surface Science Society of Japan, Volume：38, Number：3, First page：111, Last page：116, Mar. 2017, [Reviewed], [Invited]
公益社団法人 日本表面科学会, Japanese, Scientific journal
DOI：https://doi.org/10.1380/jsssj.38.111
DOI ID：10.1380/jsssj.38.111 - Effects of Si particles of Al-Si alloys on frictional properties of hydrogenated amorphous carbon (a-C:H) films/Al-Si alloys tribopairs under lubrication with fully formulated oil
Hikaru OKUBO; Yuki NODA; Chiharu TADOKORO; Yuki HIRATA; Shinya SASAKI
Transactions of the JSME (in Japanese), Volume：83, Number：850, First page：16, Last page：00543, 2017, [Reviewed]
Japan Society of Mechanical Engineers, Scientific journal
DOI：https://doi.org/10.1299/transjsme.16-00543
DOI ID：10.1299/transjsme.16-00543, ISSN：2187-9761, eISSN：2187-9761, J-Global ID：201702219853058216 - Effects of Molecular Structure of Zinc Dialkyldithiophosphates on Tribological Properties of a Hydrogenated Amorphous Carbon Film under Boundary Lubrication
Hikaru Okubo; Seiya Watanabe; Chiharu Tadokoro; Yuki Hirata; Shinya Sasaki
Tribology Online, Volume：12, Number：5, First page：221, Last page：228, 2017, [Reviewed]
The effects of the molecular structure of zinc dialkyldithiophosphates (ZDDPs) on the tribological properties of a hydrogenated amorphous carbon (a-C:H) film under boundary lubrication were investigated. Friction tests were performed at a-C:H/a-C:H and steel/steel contacts under lubrication with poly-alpha olefin (PAO) and PAO containing five types of ZDDPs with different alkyl groups (primary-C4 ZDDP, secondary-C4 ZDDP, primary-C6 ZDDP, primary-C8 ZDDP and primary-C12 ZDDP). All our results suggest that the structure of the alkyl chain of ZDDPs strongly influence the tribological properties of the a-C:H/a-C:H and steel/steel tribopairs lubricated with ZDDP solutions.
Japanese Society of Tribologists, English, Scientific journal
DOI：https://doi.org/10.2474/trol.12.221
DOI ID：10.2474/trol.12.221, ISSN：1881-2198, eISSN：1881-2198, Web of Science ID：WOS:000415194300002 - In Situ Raman Observation of the Graphitization Process of Tetrahedral Amorphous Carbon Diamond-Like Carbon under Boundary Lubrication in Poly-Alpha-Olefin with an Organic Friction Modifier
Hikaru Okubo; Chiharu Tadokoro; Yuki Hirata; Shinya Sasaki
Tribology Online, Volume：12, Number：5, First page：229, Last page：237, 2017, [Reviewed]
Copyright © 2017 Japanese Society of Tribologists The graphitization process of a tetrahedral amorphous carbon (ta-C) film under lubrication was investigated using a laboratory-built in situ Raman tribometer. The coating was lubricated with poly-alpha-olefin (PAO), PAO with an added friction modifier (FM), glycerol mono-oleate (GMO). Friction tests were carried out using a ball-on-disk setup, in which a 19-mm diameter ta-C-coated ball was loaded and rubbed against a steel disk that was immersed in a lubricant solution. In situ optical microscopy and Raman spectroscopy were used to monitor the graphitization process and wear tracks of the ta-C-coated ball. Raman analysis was conducted on the rubbed surface of the rotating ta-C-coated ball when it was located under an objective lens every three minutes during sliding. In this study, the degree of graphitization of the ta-C surface was estimated by calculating the intensity ratio of the D-peak and G-peak (ID/IG) in the Raman spectra of the ta-C film during friction tests with different lubricants. All our results suggest that the friction modifier inhibits the progression of graphitization of DLC films by reducing friction, in other words, reducing the contact temperature, and the wear progression of DLC films under boundary lubrication can be induced by graphitization of DLC surfaces at the sliding contact.
Japanese Society of Tribologists, Scientific journal
DOI：https://doi.org/10.2474/trol.12.229
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Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85035363835&origin=inward
DOI ID：10.2474/trol.12.229, ISSN：1881-218X, eISSN：1881-2198, SCOPUS ID：85035363835 - Influence of Ink Composition on Tribological Properties of Ballpoint Pen
Mariko Isokane; Chiharu Tadokoro; Shinya Sasaki; Braham Prakash
Tribology Online, Volume：12, Number：5, First page：257, Last page：261, 2017, [Reviewed]In this work, the influence of ink composition on the tribological properties of ballpoint pens has been examined with a view to improve writing smoothness and pen lifetime. Friction experiments were performed using a ball on plate tribometer in order to simulate the sliding contact of a ballpoint pen. Ballpoint pen ink is composed of various solvents, resins, friction modifiers, colorants. To determine the basic tribological properties of ballpoint pen ink, this study focuses on the investigating the influence of different ink compositions: solvents, resins, and phosphate on the tribological behavior. The worn surfaces of specimens from tribological tests using different ink compositions were analyzed by using Fourier-transform infrared spectroscopy. Tribological tests were performed on eight different lubricant compositions including: i) the solvents without additives ii) the solvents with the resins and iii) the solvents with the friction modifiers. The results showed that for Oil A the tribological properties were affected by the molecular weight of the resin and the addition of phosphate reduced the coefficients of friction. Similar results were not observed for Oil B. In addition, it was found that the ratio of the components of the base oil affects the tribological properties of ballpoint pen ink.
Japanese Society of Tribologists, English, Scientific journal
DOI：https://doi.org/10.2474/trol.12.257
DOI ID：10.2474/trol.12.257, eISSN：1881-2198, CiNii Articles ID：130006250699 - Polarization Observations of Adsorption Behavior of Fatty Acids Using Optical Anisotropy of Liquid Crystal
Chiharu Tadokoro; Shoki Araya; Hikaru Okubo; Ken Nakano; Shinya Sasaki
Tribology Letters, Volume：64, Number：2, Nov. 2016, [Reviewed], [Lead, Corresponding]
Chemical interactions and formation of adsorbed films of additives strongly affect the tribological behavior in boundary lubrication. In order to examine the relationship between the adsorption behavior and friction properties of fatty acids, polarization observations using a liquid crystal and friction measurements were performed. A nematic liquid crystal [4-pentyl-4'-cyanobiphenyl (5CB)] and normal fatty acids with 16-22 C chains were base fluid and additive, respectively. The adsorption behavior of the fatty acids was observed using polarization microscopy and analyzing the optical anisotropy of 5CB. The adsorbed film of fatty acids induced a change in the orientation of 5CB from planar to homeotropic. The expansion speed of the homeotropic domain increased as the chain length of the fatty acid decreased. The friction coefficient of the test lubricants was measured in a steel-steel sliding contact using a low-speed reciprocating tribometer. At the first cycle of reciprocating sliding motion, the lower friction coefficient was measured using fatty acids with the shorter alkyl chain length. The friction coefficient at the first cycle showed a strong correlation with the expansion speed of the homeotropic domain. These results show that the shorter-chain fatty acids form an adsorbed film highly oriented perpendicular to the solid surface, and the adsorbed film provides a lower friction coefficient at the first cycle.
Springer Science and Business Media LLC, English, Scientific journal
DOI：https://doi.org/10.1007/s11249-016-0765-9
DOI ID：10.1007/s11249-016-0765-9, ISSN：1023-8883, eISSN：1573-2711, Web of Science ID：WOS:000386776100012 - Effects of structure of zinc dialkyldithiophosphates on tribological properties of tetrahedral amorphous carbon f ilm under boundary lubrication
Hikaru Okubo; Seiya Watanabe; Chiharu Tadokoro; Shinya Sasaki
Tribology International, Volume：98, First page：26, Last page：40, Jun. 2016, [Reviewed]
© 2016 Elsevier Ltd. All rights reserved. Effects of the structure of zinc dialkyldithiophosphates (ZDDPs) on the tribological properties of a tetrahedral amorphous carbon (ta-C) film were investigated. Friction tests were performed at diamond-like carbon (DLC)/DLC and steel/steel contacts under lubrication with poly-alpha olefin (PAO) and PAO containing six types of ZDDPs with different alkyl groups. The tribological properties of the ta-C film depended on the chemical composition of ZDDP-derived tribofilms on the outermost surface, which depended on the abundance ratio of neutral-ZDDP and basic-ZDDP in the ZDDP solution. Thus, the ZDDP forms play important roles in the tribological properties of the ta-C film. All these results suggest that the ZDDP forms can determine the tribological properties of the ta-C film lubricated with the ZDDP solution.
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2016.02.025
Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84960092837&origin=inward
Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84960092837&origin=inward
DOI ID：10.1016/j.triboint.2016.02.025, ISSN：0301-679X, SCOPUS ID：84960092837 - Effects of concentration of zinc dialkyldithiophosphate on the tribological properties of tetrahedral amorphous carbon films in presence of organic friction modifiers
Hikaru Okubo; Seiya Watanabe; Chiharu Tadokoro; Shinya Sasaki
Tribology International, Volume：94, First page：446, Last page：457, Feb. 2016, [Reviewed]
© 2015 Elsevier Ltd. All rights reserved. The effects of the concentration of zinc dialkyldithiophosphate (ZDDP) on the tribological properties of a tetrahedral amorphous carbon (ta-C) film in the presence of organic friction modifiers (FMs) were investigated. Friction tests were conducted under lubrication with poly-alpha-olefin (PAO) and PAO containing glycerol-mono-oleate (GMO), tallow-diethanol-amine (TDEA), ZDDP, GMO+ZDDP, and TDEA+ZDDP. For PAO+GMO+ZDDP, the friction coefficients increased as the concentration of ZDDP increased. For PAO+TDEA+ZDDP, the ultralow friction was observed at the ta-C/ta-C contact regardless of the concentration of ZDDP. Surface analyses demonstrated the combination of TDEA and ZDDP promoting the formation of sulfur-rich tribofilms, which play important roles in the low friction of the ta-C film.
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2015.10.008
Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84946135760&origin=inward
Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84946135760&origin=inward
DOI ID：10.1016/j.triboint.2015.10.008, ISSN：0301-679X, SCOPUS ID：84946135760 - Effect of microstructure of low-carbon steels on frictional and wear behaviour
Akihiro Naka; Takashi Kobayashi; Shinji Katou; Ryo Tsuboi; Chiharu Tadokoro; Shinya Sasaki
Tribology International, Volume：93, First page：696, Last page：701, Jan. 2016, [Reviewed]
The friction and wear properties of low-carbon steel and conventional carbon steel were investigated through sliding tests, hardness measurements, and microstructure observations. An understanding of these properties is essential to facilitate the application of low-carbon weld steel doped with minor and trace elements to tribological products.The results of the sliding tests showed that the initial wear of the minor and trace element-doped low-carbon steel was higher than that of conventional carbon steel. The results of the hardness measurements showed that conventional steel hardened faster than the minor and trace element-doped steel. The microstructure observations showed that the grain size of conventional steel decreased after the sliding test was performed. Hence, it was suggested that the change in the grain size of conventional steel promoted hardening. (C) 2015 Elsevier Ltd. All rights reserved.
Elsevier BV, English, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2015.05.014
DOI ID：10.1016/j.triboint.2015.05.014, ISSN：0301-679X, eISSN：1879-2464, Web of Science ID：WOS:000366788000024 - Ultralow Friction of a Tetrahedral Amorphous Carbon Film Lubricated with an Environmentally Friendly Ester-Based Oil
Hikaru Okubo; Seiya Watanabe; Chiharu Tadokoro; Shinya Sasaki
Tribology Online, Volume：11, Number：2, First page：102, Last page：113, 2016, [Reviewed]
© Copyright 2016 Japanese Society of Tribologists. The tribological properties of diamond-like carbon (DLC) films that were lubricated with an environmentally friendly ester-based oil were investigated. Sliding tests were performed on two types of DLC films, hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (ta-C) films, using a steel cylinder that was in contact with a steel disk coated with either a-C:H or ta-C under boundary lubrication. To compare the tribological properties of ester-based oils and other based oils, Trimethylolpropane (TMP) ester, polypropylene glycol (PPG), and poly-alpha olefin (PAO) were used as the test lubricants. The ta-C film that was lubricated with TMP ester exhibited the ultralow friction coefficient of 0.015; however, the a-C:H film that was lubricated with TMP ester did not exhibit the ultralow friction. On the other hand, results obtained by a quartz-crystal microbalance with dissipation indicated that the adsorption properties of based oils depended on the type of sensor material (carbon or iron) and the type of based oil used in the measurements. Moreover, the frequency change of based oils increased with decreases in the average frictional coefficients of the steel-steel tribopair and the DLC-steel tribopair. Results of surface analysis indicated that TMP ester formed tribofilms on the ta-C surfaces, which exhibited high viscosity and low friction. All these results suggest that the combination of the ta-C film and TMP ester is the new ultra-low-friction and environmentally friendly sliding system.
Japanese Society of Tribologists, Scientific journal
DOI：https://doi.org/10.2474/trol.11.102
Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84969497804&origin=inward
Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84969497804&origin=inward
DOI ID：10.2474/trol.11.102, ISSN：1881-218X, eISSN：1881-2198, SCOPUS ID：84969497804 - Evaluation of Frictional Behavior of Textured Surface by Using a Newly Proposed GPS Parameter
Hiroshi Nagasaki; Chiharu Tadokoro; Ryo Tsuboi; Yuki Tokuta; Shinya Sasaki
Tribology Online, Volume：11, Number：2, First page：354, Last page：359, 2016, [Reviewed]
Surfaces with different topographies are formed by the various types of manufacturing processes. To express the characteristics of these surfaces, the International Organization for Standardization (ISO) defines two-dimensional (2-D) surface roughness parameters, which are used for geometrical product specification (GPS). 2-D surface roughness parameters are widely used in engineering fields. In contrast, 3-D surface roughness parameters have been standardized with the development of measurement technologies. In the field of tribology, the relationship between the surface roughness parameters and tribological characteristics has been extensively studied. However, surface roughness parameters for the expression of tribological characteristics have not yet been reported. In this research, the fast Fourier transform (FFT) method was applied to evaluate the periodicity of sliding surfaces. Using the 2-D FFT method, the 2-D power spectral density (PSD) was obtained for actual surfaces. The relationships between the 2-D PSDs and the friction characteristics of anisotropic surfaces were examined. From these results, it was determined that all the data from the 2-D PSD are required to determine the optimal direction of sliding. A new 3-D surface roughness parameter to express these relationships was proposed. It was shown that this parameter is able to determine the sliding angle where the lowest or highest friction coefficients are attained for common industrial surfaces. This parameter could be used in the design of sliding surfaces as a GPS parameter to express friction characteristics.
Japanese Society of Tribologists, English, Scientific journal
DOI：https://doi.org/10.2474/trol.11.354
DOI ID：10.2474/trol.11.354, ISSN：1881-2198, eISSN：1881-2198, CiNii Articles ID：130005149917 - Effect of Surface Texturing on Friction Transition of C/C Composite Material
Satoshi Hoshino; Chiharu Tadokoro; Shinya Sasaki
Tribology Online, Volume：11, Number：2, First page：426, Last page：431, 2016, [Reviewed]
Carbon-carbon (C/C) composites are widely used as sliding materials owing to their excellent mechanical properties. However, it is well known that the C/C composites exhibit an unstable frictional behavior called the friction transition, the main mechanism of which remains unclear. In this study we focused on the mechanism of the friction transition by examining the morphology of wear debris obtained using a thrust-cylinder-type tribotester. Moreover, to improve the tribological properties of C/C composites, we discussed the effect of surface texturing. The sliding results suggested that agglomeration of wear debris caused the friction transition. Furthermore, the friction transition was prevented by the effects of surface texturing.
Japanese Society of Tribologists, English, Scientific journal
DOI：https://doi.org/10.2474/trol.11.426
DOI ID：10.2474/trol.11.426, ISSN：1881-2198, eISSN：1881-2198, CiNii Articles ID：130005149920 - Tribological properties of a diamond-like carbon film under lubrication with commercial fully formulated oils
Hikaru OKUBO; Hirochika FUKUDA; Ryo TSUBOI; Chiharu TADOKORO; Shinya SASAKI
Transactions of the JSME (in Japanese), Volume：82, Number：838, First page：15, Last page：00679, 2016, [Reviewed]
Japan Society of Mechanical Engineers, Scientific journal
DOI：https://doi.org/10.1299/transjsme.15-00679
DOI ID：10.1299/transjsme.15-00679, ISSN：2187-9761, eISSN：2187-9761, J-Global ID：201602242176687045 - Correlation between Nano-Mechanical and Macro-Tribological Properties of Tribofilms Derived from Organic Phosphoric Additives
Chisaki Hashimoto; Hikaru Okubo; Chiharu Tadokoro; Shinya Sasaki
Tribology Online, Volume：11, Number：5, First page：632, Last page：638, 2016, [Reviewed]
Copyright © 2016 Japanese Society of Tribologists. Correlation between nano-mechanical and macro-tribological properties of the tribofilm derived from phosphoric additives was investigated. Macro friction test was performed at steel/steel contact under lubrication with poly-alpha olefin (PAO) containing these types of phosphoric additives; tricresyl phosphate (TCP), diphenyl phosphate (DPP), triphenyl phosphate (TPP). The nano-mechanical properties (viscoelasticity, adhesion, hardness, friction coefficient, and effective elastic modulus) of the tribofilms were evaluated by using atomic force microscopy (AFM) and nanoindentation tester. From the results of friction tests and surface analysis, the macro-tribological properties depended on the nano-mechanical properties of tribofilms derived from phosphoric additives under the boundary lubrication. In particular, the thick viscous tribofilm derived from the phosphoric additive exhibited the low friction phenomena. It was suggested that the nano-mechanical properties of tribofilms were the important factors governing the macro-tribological properties under the boundary lubrication.
Japanese Society of Tribologists, Scientific journal
DOI：https://doi.org/10.2474/trol.11.632
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DOI ID：10.2474/trol.11.632, ISSN：1881-218X, eISSN：1881-2198, SCOPUS ID：84988733973 - Quick measurement of electrorheological effect for small amounts of nematic liquid crystal
Chiharu Tadokoro; Yuki Hosomi; Ken Nakano
Measurement Science and Technology, Volume：26, Number：8, First page：085303, Last page：085303, Aug. 2015, [Reviewed], [Lead, Corresponding]
IOP Publishing, Scientific journal
DOI：https://doi.org/10.1088/0957-0233/26/8/085303
DOI ID：10.1088/0957-0233/26/8/085303, ISSN：0957-0233, eISSN：1361-6501 - Evaluation of ultraviolet-nanoimprint-lithography release agent properties by using TriboIndenter
Kota Funakoshi; Chiharu Tadokoro; Ian Thomas Clark; Toshiro Okawa; Jun Taniguchi; Shinya Sasaki
Microelectronic Engineering, Volume：141, First page：150, Last page：154, Jun. 2015, [Reviewed]
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.mee.2015.02.007
DOI ID：10.1016/j.mee.2015.02.007, ISSN：0167-9317 - Tribological properties of a tetrahedral amorphous carbon (ta-C) film under boundary lubrication in the presence of organic friction modifiers and zinc dialkyldithiophosphate (ZDDP)
Hikaru Okubo; Chiharu Tadokoro; Shinya Sasaki
Wear, Volume：332-333, First page：1293, Last page：1302, May 2015, [Reviewed]
Diamond-like carbon (DLC) films provide low friction and high wear resistance under lubricated conditions. In particular, tetrahedral amorphous carbon (ta-C) film has shown ultralow friction behavior under boundary lubrication with an organic friction modifier (FM), such as glycerol mono-oleate (GMO). On the other hand, there are many studies on the tribological properties of DLC films that are lubricated with oils with added zinc dialkyldithiophosphate (ZDDP). ZDDP, however, shows quite different tribological performance, which depends on the type of DLC film. The lubrication mechanism of ZDDP against DLC films has not yet been fully clarified. This research studied the effects of ZDDP additives on the tribological properties of a ta-C film under boundary lubrication with oils that contained organic friction modifiers. The tribological properties were evaluated using the reciprocating type cylinder-on-disk tribo-tester. ZDDP and three types of organic additives (GMO, glycerol mono-oleoyl ether (GME), and tallow diethanol amine (TDEA)) were added to poly-alpha olefin (PAO). Friction tests were carried out for the DLC/DLC tribo-pair under lubrication with PAO and PAO-based oils containing GMO, GME, TDEA, ZDDP, GMO+ZDDP, GME+ZDDP, and TDEA+ZDDP additives. Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) were used for analyses of the ta-C surface after the friction tests. The ta-C film lubricated with PAO+FMs reached an ultralow friction coefficient of 0.02-0.03. On the other hand, the films with PAO+GMO+ZDDP and PAO+GME+ZDDP had increased friction coefficients and wear volumes compared to the PAO+FMs oils. The ta-C film lubricated with PAO+TDEA+ZDDP reached an ultralow friction coefficient of 0.028. The surface analyses demonstrated that the formation rate and chemical composition of the ZDDP-derived tribofilm depended on the combination of ZDDP and each FM. It was concluded that the formation rate and chemical composition of the ZDDP-derived tribofilm played an important role in the low friction behavior of the ta-C films that were lubricated with any of the oils with added ZDDP. (C) 2015 Elsevier B.V. All rights reserved.
Elsevier BV, English, Scientific journal
DOI：https://doi.org/10.1016/j.wear.2015.01.023
DOI ID：10.1016/j.wear.2015.01.023, ISSN：0043-1648, eISSN：1873-2577, Web of Science ID：WOS:000357438100080 - Observation of the Tribo-Film Formation Derived from ZnDTP by Using FT-IR
Hirotomo Watanabe; Chiharu Tadokoro; Shinya Sasaki
Key Engineering Materials, Volume：642, First page：259, Last page：263, Apr. 2015, [Reviewed]
To understand the effects of tribo-film formation derived from ZnDTP (zinc dialkyl ditio phosphate) on friction behavior, friction tests were carried out with varying sliding time. The sliding surfaces were analyzed using Fourier transform infrared spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). On the basis of the surface analytical results of the tribo-film, the absorption bands in the region of 1300-1000 cm-1 assigned as polyphosphate appeared in all IR spectra after the sliding. The friction behavior of ZnDTP was related to the intensity change of the IR spectra peak at 1200 cm-1.
Trans Tech Publications, Ltd., Scientific journal
DOI：https://doi.org/10.4028/www.scientific.net/kem.642.259
DOI ID：10.4028/www.scientific.net/kem.642.259, eISSN：1662-9795 - Complex Impedance Measurement Applied to Short-Time Contact Between Colliding Steel Surfaces
Takahiro Nihira; Kazuyoshi Manabe; Chiharu Tadokoro; Shingo Ozaki; Ken Nakano
Tribology Letters, Volume：57, Number：3, Mar. 2015, [Reviewed]
Springer Science and Business Media LLC, Scientific journal
DOI：https://doi.org/10.1007/s11249-015-0478-5
DOI ID：10.1007/s11249-015-0478-5, ISSN：1023-8883, eISSN：1573-2711 - Vibrational Spectroscopic Study on Lubrication and Corrosive Wear Mechanisms of Imidazolium Based Ionic Liquids
Watanabe, S.; Nakano, M.; Miyake, K.; Tadokoro, C.; Sasaki, S.
Ionic Liquids - Current State of the Art, First page：545, Last page：556, 2015, [Reviewed]
English, Scientific journal
DOI：https://doi.org/10.5772/59132
DOI ID：10.5772/59132, ORCID：45208080, Web of Science ID：WOS:000404740400021 - Effects of ZnDTP on lubricity of ashless friction modifiers for H-free DLC film
Hikaru OKUBO; Ryo TSUBOI; Chiharu TADOKORO; Shinya SASAKI
Transactions of the JSME (in Japanese), Volume：81, Number：824, First page：14, Last page：00656, 2015, [Reviewed]
Japan Society of Mechanical Engineers, Scientific journal
DOI：https://doi.org/10.1299/transjsme.14-00656
DOI ID：10.1299/transjsme.14-00656, ISSN：2187-9761, eISSN：2187-9761, J-Global ID：201502280449859474 - Effects of Hydrogen on Frictional Properties of DLC Films
Hikaru Okubo; Kenta Oshima; Ryo Tuboi; Chiharu Tadokoro; Shinya Sasaki
Tribology Online, Volume：10, Number：6, First page：397, Last page：403, 2015, [Reviewed]
Copyright © 2015 Japanese Society of Tribologists. The tribological behavior of diamond-like carbon films (DLC) is strongly dependent on the hydrogen content, sp2/sp3 ratio, and sliding environment. Some hydrogenated amorphous carbon films (a-C:H) exhibit superlow friction in hydrogen conditions. However, previous works have not clarified the dominant factors of the superlow friction phenomena of DLC films. In this research, we focused on the effects of hydrogen derived from the surrounding atmosphere and the hydrogen within the DLC films on superlow friction phenomena. To investigate these effects, friction tests were conducted on three DLC films having different hydrogen contents (0, and 18, 30 at%) in the air and in low-pressure-hydrogen conditions at various hydrogen pressures. After the friction tests, the wear tracks were examined by confocal laser scanning microscopy, Raman spectroscopy, elastic recoil detection (ERDA) analysis, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The hydrogen derived from the surrounding atmosphere and the formation of the hydrogen-rich tribofilm were key factors for the superlow friction phenomena.
Japanese Society of Tribologists, Scientific journal
DOI：https://doi.org/10.2474/trol.10.397
Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84954551743&origin=inward
Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84954551743&origin=inward
DOI ID：10.2474/trol.10.397, ISSN：1881-218X, eISSN：1881-2198, SCOPUS ID：84954551743 - Minimization of Friction at Various Speeds Using Autonomous Viscosity Control of Nematic Liquid Crystal
Chiharu Tadokoro; Takahiro Nihira; Ken Nakano
Tribology Letters, Volume：56, Number：2, First page：239, Last page：247, Nov. 2014, [Lead]
Springer Science and Business Media LLC, Scientific journal
DOI：https://doi.org/10.1007/s11249-014-0404-2
DOI ID：10.1007/s11249-014-0404-2, ISSN：1023-8883, eISSN：1573-2711 - Effect of yaw angle misalignment on brake noise and brake time in a pad-on-disc-type apparatus with unidirectional compliance for pad support
Naohiro Kado; Naoya Sato; Chiharu Tadokoro; Antonin Skarolek; Ken Nakano
Tribology International, Volume：78, First page：41, Last page：46, Oct. 2014, [Reviewed]
Elsevier BV, Scientific journal
DOI：https://doi.org/10.1016/j.triboint.2014.04.033
DOI ID：10.1016/j.triboint.2014.04.033, ISSN：0301-679X - Kinetic Friction Coefficient Measured in Tribotesting: Influence of Frictional Vibration
Naohiro Kado; Chiharu Tadokoro; Ken Nakano
Tribology Online, Volume：9, Number：2, First page：63, Last page：70, 2014, [Reviewed]
Japanese Society of Tribologists, Scientific journal
DOI：https://doi.org/10.2474/trol.9.63
DOI ID：10.2474/trol.9.63, eISSN：1881-2198 - Yawing Angular Misalignment Provides Positive Damping to Suppress Frictional Vibration: Basic Applicability to Disc Brake Systems
Ken Nakano; Chiharu Tadokoro; Naohiro Kado
SAE International Journal of Passenger Cars - Mechanical Systems, Volume：6, Number：3, First page：1493, Last page：1498, Sep. 2013, [Reviewed]
SAE International, Scientific journal
DOI：https://doi.org/10.4271/2013-01-2069
DOI ID：10.4271/2013-01-2069, ISSN：1946-4002 - ALE Finite Element Analysis of Plastic Indentation Process of Lubricated Plate by the Ball Collision
Masanori TSUKUI; Shingo OZAKI; Kazuyoshi MANABE; Chiharu TADOKORO; Ken NAKANO
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A, Volume：79, Number：800, First page：477, Last page：488, 2013, [Reviewed]
In the present study, we apply an Arbitrary Lagrangian-Eulerian (ALE) finite element method, which can rationally solve the interaction behavior between the fluid flow and the nonlinear solid deformation, to the simulation of indentation process of lubricated elastoplastic plates by the ball collision. As have been reported by numerous experimental works, it is also shown by the present numerical approach that the characteristic of lubricant affects indentation profiles. For instance, the indentation profile represents the conical shape due to viscous property of lubricant, while the profile represents the bowl-type shape under the dry condition. Based on the systematic numerical investigation, it is confirmed in the case of lubricated condition that the indentation is formed through the pressure of a fluid. Then, a squeeze effect of viscous flow and a shut-up of lubricant, which is caused by velocity of lateral flow, are observed. Furthermore, it is understood that the conical shape of indentation profile is formed at an initial contact stage, and then its size similarly grow up during loading. Thus, it is confirmed that the ALE finite element method is one of effective methods for the examination of impact problems on lubricated surfaces.
Japan Society of Mechanical Engineers, Japanese, Scientific journal
DOI：https://doi.org/10.1299/kikaia.79.477
DOI ID：10.1299/kikaia.79.477, ISSN：0387-5008, eISSN：1884-8338, CiNii Articles ID：130003374621 - Design Criteria on Effective Static Friction Coefficient of Elastomers
Satoru MAEGAWA; Fumihiro ITOIGAWA; Takatoshi SHINYOSHI; Atsushi SUZUKI; Chiharu TADOKORO; Ken NAKANO
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series C, Volume：79, Number：803, First page：2622, Last page：2634, 2013, [Reviewed]
In sliding friction of elastomers, the effective static friction coefficient μseff observed is not necessarily equal to the inherent real one μs possessed by the material; usually μseff < μs because of the elastic deformations of sliding objects and the propagation of shear fracture in the contact area. This indicates that focusing on elastic deformation of sliding objects can derive a new criterion of μseff for machine design. In this study, mainly through numerical simulations for a physical model assured by experiments in which measuring frictional force and observing contact area were carried out for a longitudinal line contact of polymethyl methacrylate, it is found that the stiffness ratio κ = Kbtot / Kctot (where Kbtot and Kctot are the total bulk stiffness and total tangential contact stiffness of the elastic sliding object, respectively) dominates the value of μseff.
Japan Society of Mechanical Engineers, Japanese, Scientific journal
DOI：https://doi.org/10.1299/kikaic.79.2622
DOI ID：10.1299/kikaic.79.2622, ISSN：0387-5024, eISSN：1884-8354, CiNii Articles ID：130003375132 - Measurement Error of Kinetic Friction Coefficient Generated by Frictional Vibration
Naohiro KADO; Chiharu TADOKORO; Ken NAKANO
TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series C, Volume：79, Number：803, First page：2635, Last page：2643, 2013, [Reviewed]
To measure true values of kinetic friction coefficient in a force balance between the frictional force and spring force, an anti-vibration tribometer (AVT) has been developed. The AVT utilizes a novel principle that an angular misalignment between the two velocities (i.e., the driving velocity of one of contact surfaces and the moving velocity of the other surface) produces a positive damping effect to stabilize the equilibrium point and suppress frictional vibration autonomously. For example, when a sliding contact between a steel ball and a steel plate is lubricated by glycerin, the AVT provides a force balance situation at a misalignment angle φ = 30° (i.e., an anti-vibration setting), although strong frictional vibration occurs at φ = 0° (i.e., a conventional setting). By comparing the kinetic friction coefficients obtained at φ = 0° and 30°, it has been found that frictional vibration can lead to a serious error of measuring kinetic friction coefficient (e.g., a 35% underestimation at a low driving speed).
Japan Society of Mechanical Engineers, Japanese, Scientific journal
DOI：https://doi.org/10.1299/kikaic.79.2635
DOI ID：10.1299/kikaic.79.2635, ISSN：0387-5024, eISSN：1884-8354, CiNii Articles ID：130003375133 - Friction and Wear Properties of PTFE Sliding Seals -Influence of Surface Conditions of Seal Gland on Friction Properties-
Chiharu Tadokoro; Yasuo Yoshii; Hitoshi Hattori; Daisuke Nishino
Tribology Online, Volume：5, Number：6, First page：266, Last page：270, 2010, [Reviewed], [Lead, Corresponding]
Sealing devices are needed to prevent dust and water invading the positioning mechanisms of outdoor equipment. The frictional resistance generated by the seal frequently obstructs the smooth motion of the mechanism. The friction properties for high-speed and precision control mechanisms are required to be low and stable without lowering the sealing performance. In this study, the influence of the surface conditions of seal gland for PTFE sliding seal on friction properties was investigated experimentally. As a result, it has been found that the suitable surface condition of the seal gland for a high-speed and precision control mechanism is the electroless-nickel-plated surface of 0.1 μm Ra
Japanese Society of Tribologists, English, Scientific journal
DOI：https://doi.org/10.2474/trol.5.266
DOI ID：10.2474/trol.5.266, ISSN：1881-2198, eISSN：1881-2198, CiNii Articles ID：130000453551 - 微小動荷重制御による摩擦振動抑制法
田所 千治; 中野 健
Volume：50, Number：11, First page：799, Last page：807, Feb. 2005, [Reviewed], [Lead]
Scientific journal - 摩擦変動スペクトルに基づく接触面情報の抽出
中野健; 田所千治; 早川純平; 山本浩司
Volume：50, Number：5, First page：409, Last page：415, Sep. 2004, [Reviewed]
Scientific journal
- 複合添加剤によるナノテクスチャ構造の自律形成手法の開発
01 Apr. 2021 - 31 Mar. 2024
Grant amount(Total)：4680000, Direct funding：3600000, Indirect funding：1080000
Grant number：21K14065 - Development of lubrication system for friction reduction using self-assembled nanotexture
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Early-Career Scientists, 01 Apr. 2018 - 31 Mar. 2021
Tadokoro Chiharu, Saitama University
Grant amount(Total)：4160000, Direct funding：3200000, Indirect funding：960000
This research work aims to develop a lubrication system for friction reduction using self-assembled nanotexture formed by additives of lubricant. To investigate the formation process of self-assembled nanotexture, we have developed a measurement system that can measure the film thickness distribution with high accuracy under rolling contact. The measurement system can measure a spatial distribution of lubricant film thickness with a resolution of 0.1 nm, which sufficient to detect the existence of lubricant molecules. Using the measurement system, the effect of additive types and combinations on the formation of self-assembled nanotextures were examined. As a result of the examination for straight-chain fatty acids, which are oiliness improvers, it was found that even when a single-component additive is used an island-shaped lubricant film is formed, and using two-component additives, the island-shaped unevenness is finer.
Grant number：18K13676 - Biomimetic Surface Architecture for tribology
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), 01 Apr. 2016 - 31 Mar. 2019
SASAKI Shinya; Sakai Kenichi; Kawada Syouhei, Tokyo University of Science
Grant amount(Total)：41470000, Direct funding：31900000, Indirect funding：9570000
We carried out research aiming to further deepen the concept of multi-scale texturing and establish an innovative sliding surface system that is self-adaptive to surface damage and changes in the sliding environment. A sliding surface architecture imitating the skin structure of a living body is constructed, and its optimization was attempted by numerical simulations, and a three-dimensional microstructure was realized by applying a surface creation process technology by a 3D metal printer. We demonstrated the advantages and usefulness of the environment adaptive performance of the sliding surface and mechanical elements.
Grant number：16H02310