Friction reduction is a major challenge in solving energy problems. Therefore, various methods for reducing friction are being researched. Many researches have also been done on the structure of the material itself with the aim of reducing friction. In particular, it is known that a material having a layered structure reduces friction by shearing between layers. This paper introduces materials with layered structure and describes their friction reduction technologies.

It is known that Graphite, MoS₂ and PTFE are common solid lubricants for bonded solid film lubricants (BSFL) and show synergistic effect on the tribological performance. This article gives an explanation focusing on the synergistic effect of BSFL and a feasibility study of graphene on BSFL.

Intercalation is a chemical reaction that inserts various atoms, molecules, or ions into the interlayer spacing of layered materials. Because this reaction can drastically change the chemical properties of layered materials, it has been widely applied in various fields such as environment science, agriculture, civil engineering, cosmetics industry, and medicine. We have vigorously investigated the potential of organically modified mica synthesized by an intercalation reaction as a solid lubricant. This article reviews the reaction mechanism of intercalation and tribological properties of mica intercalated with alkyl ammonium. Furthermore, the lubrication mechanism is discussed from the viewpoint of the interlayer adhesion strength.

New effective spring model to simulate the exfoliation process of an armchair-type graphene sheet from a graphite substrate surface is developed to use the structural symmetry of the graphene/graphite interface. First the transition of the graphene shape and the vertical force curve during the exfoliation process obtained by this model are in good agreement with those obtained by the previous potential model. The computation time by this potential model is reduced to 10^-4 compared to that by the previous model. Next, the typical vertical force curve is obtained by using the present model extended to include the effective stiffness of atomic force microscopy (AFM), which has opened a new research area of multiscale physics of the exfoliation process.

Carbon brushes are used as electrical sliding materials with a history of 100 years. The brush uses the lubricity of graphite to pass an electric current through the rotating body. This commentary describes the present situation of carbon brushes, research examples on brush wear reduction and future prospects.

Solid lubrication is an important because solid writing tools are used by sliding them against the writing surface. Pencil lead and lead for mechanical pencils utilizes the characteristic of graphite, which is a layered material for writing tools. Therefore, the layered structure of graphite relates to a smooth, comfortable writing experience. In recent years, technical development in the leads as a composite material with layered structure has continued in order to meet the demands in colored lead and nanomaterial composite lead. In this paper, the technical overview of solid writing tools using layered materials and the development of new products to which layered material applied in our research were explained.

Friction reduction by engine oil under low and high temperature conditions is required because of the increasing number of hybrid vehicles where oil temperature is low. Friction modifier (FM) technology to realize it are required. Friction performance of molybdenum dithiocarbamate (MoDTC) used with adsorption type FMs was investigated, which showed different results depending on types of adsorption type FMs: glycerol monooleate (GMO) inhibited friction reduction while polymer FM (PFM) did not. To understand the cause of the difference, the effect of reaction film formation by Zinc dithiophosphate (ZnDTP), which is crucial for the friction reduction by MoDTC, on adsorption type FMs was investigated. GMO inhibited the reaction film formation by ZnDTP, while PFM did not fully, observed with mini-traction machine spacer layer imaging (MTM-SLIM) and EPMA analysis. The cause was studied by their adsorption performance examined by quartz crystal microbalance (QCM). GMO showed higher adsorption density, while PFM showed lower compared to that of ZnDTP. The result indicated that GMO competitively adsorbed on the surface, inhibiting the reaction film formation by ZnDTP while polymer FM did not. Adsorption performance under co-existence of PFM and ZnDTP indicated that ZnDTP is capable to adsorb on the surface under the existence of PFM. The study indicated that the key to achieve low friction is to use PFM which does not fully inhibit ZnDTP reaction film formation.

Bump foil journal bearings are prospective applicants that can support a small-sized rotor of high-speed rotating machinery. The performance characteristics of the bearings are predicted by using a model bearing. When the air film thickness can be assumed to be uniform in the axial direction, a finite element (FE) model using curved beam element is appropriate to be applied in analyzing the displacement of bearing surface which is referred to as top foil. On the other hand, the top foil need be replaced with a thin shell in order to predict the performances of the bearing that has non-uniform air film thickness in the direction. In this study, an isoparametric shell element, which can couple the membrane and the bending effects of top foil, is introduced into the deformation analysis instead of a plate shell element adopted in the previous paper. The replacement of FE model is found to have a large influence on the bearing performance because of the change in the air film characteristics. It is concluded that the isoparametric shell element is appropriate in predicting the performance of the bearing that has non-uniform air film thickness in the axial direction.

An overshoot phenomenon of bearing temperature in hydrodynamic journal bearings may be observed during a sudden start-up experiment. This phenomenon implies that the maximum bearing temperature in acceleration operation may exceed the predicted one which can be predicted accurately by applying a state-of-the-art steady-state thermohydrodynamic lubrication (THL) model. This paper presents the maximum bearing temperature including the one during acceleration operation by using a simplified THL model that is newly proposed for a transient THL analysis. It is found that the overshooted temperature can be qualitatively predicted by using the transient THL model that incorporates properly the interaction between the motion of journal center and the viscous dissipation, even if it is a simple model. Next, the transient temperature during slow acceleration operation and also those toward higher dimensional steady-state journal rotational speed are calculated and they are found to be in qualitative agreement with the measurements. The oil film characteristics such as oil film pressure, temperature and thickness after reaching the steady-state equilibrium do not depend on the value of initial journal eccentricity ratio in the transient analysis. However, when the values are different, the characteristics immediately after starting rotation change largely. In the case of the value 1.00, it is found to give a prediction that agrees qualitatively with the characteristics measured in the experiment.