Surface texturing is a design technique to generate irregularities on the surface of industrial products for changing touch feeling or friction properties. In this paper, we introduce a parametric shape optimization method for designing a macro-size texture. In this method, the surface texture is parameterized in advance, and the parameters are determined with the response surface method. The surface textures are modelled based on the orthogonal array of Design of Experiments, and the friction or the tactile characteristics between the surface texture model and the finger model are evaluated using the nonlinear finite element contact-sliding analysis. A 3D multi-layered finger model with fingerprints and the mechanoreceptors inside is constructed. The objective function and the constraint conditions are defined combining the desired characteristics such as average friction coefficient, average friction amplitude, or stress of the mechanoreceptors. The parameters of the texture are determined by the mathematical programming and the response surfaces (or surrogate functions). Numerical examples show that the proposed method is effective for the design of macro-size surface textures.

In this report, some notable research on the use of textured surfaces in hydrodynamic lubrication are reviewed. The use of textured surfaces started attracting research interest about 20 years ago. Textured surfaces are expected to improve lubrication characteristics in a wide range of lubrication regimes―from boundary to mixed to hydrodynamic lubrication. Compared to other lubrication regimes, more quantitative models for hydrodynamic lubrication have been suggested owing to more sophisticated theories being established for hydrodynamic lubrication. The micro wedge action, which is a hydrodynamic wedge action caused by geometrical textured patterns, produces various mechanisms to improve the lubrication performance in a wide range of situations. Several related studies are introduced in this report.

When applying the concept of biomimetics to tribo-materials as a new tribo-surface architecture, the creation of a three-dimensional fine structure is the key point, and the use of a 3D printer can be considered as a processing technology that makes this possible. This paper introduces the features of metal 3D printers and their application examples from the viewpoint of surface texturing.

Improving surface functionalities by introducing surface textures is of great interest not only in the tribological fields, but also in other various fields. The author's research group has developed a surface texturing technique using the micro-vibration-assisted cutting. In the technique, a cube-corner diamond indenter is vibrated in the cutting depth direction with an amplitude of tens of microns or less during the cutting process to fabricate the surface texture composed by periodically arrayed micro-dimples. The burrs or pileups generated around all the micro-dimples after the texturing can be removed by conducting additional normal micro-cutting on the machine. The author’s group has also studied on the improvement in tribological properties of textured metal surfaces by the developed technique. Verification through the dry sliding experiments revealed that the coefficient of friction and wear decreased as the area density of the texture increased.

A 3-dimensional surface processing through elimination by mechanical removing (3-dSupremer) has been developed for creating the textured surface onto artificial materials. The 3-dSupremer is categorized into a top-down mechanical removal method, so that there are few restrictions on the type of materials for creation the textured surface. The 3-dSupremer equipped a five-axis computer-controlled system, which can create the textured geometrical surfaces onto a wide range of three-dimensional surface. The 3d-Supremer composes of both pre- and post-processing. In the pre-processing, a masking processing is performed to increase machining accuracy, where a dispensing system or a ink-jet system places an abrasion-resistant material onto a three-dimensional surface. In the post-processing, a microscopic mechanical removal processing is performed, where a slurry-jet is applied in accordance with the pre-processed surface. Although the surface-processing accuracy of the system will be lower than that of a nanoimprint technology, the system can be used to create a texture design on a variety of materials and will be applicable for a large-scale 3D surface. The system will contribute towards the application of a surface design onto a variety of industrial products.

A lot of tribology elements are used for a rocket engine, and most of those are taking charge of important feature for rocket engines. Especially, the technology of high-speed cryogenic bearing and shaft seal system for rocket engine turbopump are proud to the world. But those are rarely noticeable. This report introduces “turbopump bearing and shaft seal for next generation rocket”, “tribological technology for valves”and “the trend of rocket developments in recent year”.

Zinc dialkyldithiophosphate (ZDDP) improves wear resistance by forming a tribo-film on the sliding surface. However, the tribo-film is known to cause an increase in the friction coefficient. In order to reduce the friction coefficient as well as the wear, it is expected to combine an organic friction modifier (OFM) with ZDDP. In this study, a macro-friction test was conducted using a reciprocating sliding tester under the lubrication with the combined oils of ZDDP and OFMs. In order to understand the lubrication mechanism of the combined oils, the formation process of tribo-film was evaluated by using AFM in-situ observation. NMR analysis of the combined oil and XPS analysis of the sliding surface were performed. Glycerol monooleate (GMO) was found to suppress the formation of ZDDP-derived tribo-film. On the other hand, it was found that tallow diethanolamine (TDEA) changes the composition and mechanical properties of the ZDDP-derived tribo-film and exerts a friction-reducing effect. It was considered that the combined effect of OFM is due to the competitive adsorption phenomenon and the change of ZDDP molecular structure in the mixed oil.

In order to suppress electric wear of current collecting materials such as a contact wire and a contact strip in an electric railway, it is necessary to estimate the relationship between current and melting volume at a contact loss point. In this paper, we focused on a molten bridge which is considered as the main factor of electric wear at the contact loss point. And we proposed the estimation method of melting volume of contact wire and contact strip; in which film resistance is considered by using the relationship between the electric potential and the temperature at the contact spot. From estimation results, it is found that the melting volume increases as current increases, and that it increases as a contact boundary factor decreases. In addition, the authors carried out wear tests and measured a melting depth, a melting radius, and a melting volume under two conditions of current. From wear test results, experimental values of melting volume of the contact wire were in the range where contact boundary factor α was estimated from 0.90 to 0.94.

Prediction methodology which represents friction properties of rubber block on ice has been studied towards understanding of tribology mechanisms and improvement of grip performances of winter tire on icy road surface. 2-D simple block model and mechanical analysis methodology have been applied in order to elucidate and recognize the heat balance and the complex friction phenomenon on ice intuitively. Ice temperature distribution, boundary of adhesion/lubrication area and friction coefficient distribution in the contact patch are predicted as the consequences of frictional heat and thermal conduction. Characteristics of the predicted friction coefficient with regard to sliding speed and contact pressure have been partly validated with experimental results. The adhesion/lubrication ratio of the contact patch has been introduced as the new conceptual evaluation index which relevant to the aspects of friction surface and the contribution of adhesion and fluid lubrication on the friction characteristics.