Lubricant reflow for 10 Å Z-Tetraol film is characterized for heat-assisted magnetic recording by numerical simulation using the experimentally determined thickness-dependent diffusion equation. The competition between laser-induced lubricant depletion (troughs) and subsequent healing by reflow is investigated as a function of lubricant depletion rate, trough width, trough depth, and duty cycle (reflow time between successive laser exposures). The simulations include 1, 5, 9 and 13 adjacent troughs. Trough width of 50 nm with an edge-to-edge separation distance of 50 nm and laser depletion rates of 1.0, 0.1 and 0.001 Å/cycle are simulated. Reflow kinetics on 13 troughs with a trough width of 20 nm and an edge-to-edge separation distance of 20 nm is also included to probe the effects in the limit of very small laser spots. Duty cycles of 10 and 100 millisec are used in the simulations. The results of the numerical simulations indicate that trough recovery by reflow increases with increasing duty cycle or decreasing number of adjacent troughs, trough separation distance and laser depletion rate. Conclusions based upon single trough studies are misleading for HAMR interfaces.

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The sliding contact of soft material surface due to a rigid indenter is different from metal and some other polymers. A stick-slip motion is more frequently obtained than a smooth motion. By modeling the soft material as low damping viscoelastic material, this study proposes an analytical model to identify the stick-slip behavior of sliding system. The sliding system is a fixed rigid indenter that slides against on a moving soft material surface. A stick-slip model is developed and the motion of the sliding system is assumed to be in a solely tangential direction. By implementing the simple coulomb friction law, an exact solution is presented in the case of no damping of the sliding system. Results show that the periodic displacement of the stick-slip model is strongly depending on the friction force, sliding velocity and material stiffness. Furthermore, the effect of a viscous damping and velocity-dependent friction on the behaviour of the sliding system are discussed.

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In this paper the effect of surface roughness on squeeze film lubrication between circular stepped plates is analysed. The modified non-linear averaged Reynolds type equation is derived on the basis of Christensen’s stochastic theory for rough surfaces for Rabinowitsch fluid model. Accordingly two types of one-dimensional surface roughness patterns, viz., azimuthal roughness pattern and radial roughness pattern are considered. Averaged non-linear Reynolds equation is solved by using the small perturbation method. Expressions are obtained for the load carrying capacity, squeeze film time. It is observed that the effect of azimuthal (radial) surface roughness pattern on squeeze film lubrication between circular stepped plates with Rabinowitsch fluid is to increase (decrease) the load carrying capacity and squeeze film time significantly as compared to the smooth case and the squeeze film performance improves (suffers) due to the use of dilatant (pseudo plastic) lubricants.

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The theoretical study and evaluation of stress-strain condition of the friction pair’s surfaces of total hip joint prosthesis with partially regular texture on a ball head surface, depending on the values of its characteristic parameters, using finite element modeling are performed. It has allowed formulating the recommendations for dimple’s spacing rationing and the extent of a surface rough site with partially regular texture, aiming to increase the prosthesis’ lifespan. The problem is solved from the condition of dry or boundary lubrication. For the indicated range of nominal contact pressure in hip joint, the quantitative evaluation of allowable roughness parameters to which it is necessary to process the ball head surface for metal-on-metal and metal-on-polymer friction pairs are obtained, considering the dimple’s spacing and size on the surface.

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Injection molding is the main process for the mass production of plastic products in the world. Some plastics are strongly corrosive against metals due to the generation of decomposition gases during the melting process. In this work the wear of Co-Cr-Mo alloy (hereafter CCM), Ni-based alloys, and steels in molten plastics was investigated using a newly developed wear tester. The specimens were rotated in molten glass fiber reinforced ethylene tetrafluoroethylene (ETFE) or polyphenylene sulfide (PPS) at 10 MPa and 100 rpm for 50 h. CCM exhibited excellent wear resistance characteristics compared with the Ni-alloys and steels. The worn CCM surface was investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The formation of Cr and Co oxides was determined to play an important role in the resistance of CCM against corrosion. The thickness of the Cr and Co oxide layer reached to a depth of 160 nm from the top surface of the CCM specimen. CCM is thus a potential candidate for application to machine parts in polymer molding that are exposed to severe wear in decomposed gases.

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The Japanese Society of Tribologists is pleased to announce that the 2015 Paper Award of Tribology Online was awarded to:

“Tribological Properties of Copper Molybdate Powder Solid Lubricants under High Temperature Conditions,” by Yoshinori Takeichi, Masato Inada, Kentaro Minami, Masahiro Kawamura, Marian Dzimko, Vol. 10, No. 2 (2015) 127-137.

and

“Friction Modification by Shifting of Phonon Energy Dissipation in Solid Atoms,” by Seiji Kajita, Mamoru Tohyama, Hitoshi Washizu, Toshihide Ohmori, Hideyuki Watanabe, Shinichi Shikata, Vol. 10, No. 2 (2015) 156-161.

The Award Medals were presented to the authors by Prof. Takahisa Kato, the President of the Japanese Society of Tribologists, at the JAST Annual Meeting on 24th May, 2016.

The Paper Award of Tribology Online is given annually to the author(s), either the JAST members or non-members, of the paper(s) judged as the best paper(s) published in Tribology Online (TROL) for the previous three years. All papers that appeared in TROL for the three years are reviewed by the JAST Awards Committee.

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