The Japanese Society of Tribologists is pleased to announce that the 2009 Paper Award of Tribology Online was awarded to:
“Development of Three-Dimensional Non-Contact Surface Profilometer and Application of Impact Erosion of Metal Matrix Composites,” by Yoshiro Iwai, Masato Kitasho, Eisuke Sentoku, Tomomi Honda, Toru Matsubara and Kazuhisa Yanagi, Vol. 3, No. 1 (2008) 19-24.
The Award Medals were presented to the authors by Dr. Hisashi Machida, the former President of the Japanese Society of Tribologists, at the Annual Meeting on 18th May, 2010.
An unsteady numerical simulation was carried out to evaluate the sliding surface temperature of polyoxymethylene (POM) for wear test. The numerical model consists of two-dimensional hollow circular cylindrical POM, metallic shaft, and ambient air. The effect of conductive and convective heat transfer on the sliding surface temperature was investigated. Simulation results are in a good agreement with experiments. The influence of sliding conditions on the sliding surface temperature and limiting PV value was also discussed. Moreover, ON-OFF operation was performed in order to consider actual sliding conditions.
Diamond-like carbon (DLC) coatings are currently being used in a wide variety of industrial fields because of their outstanding properties such as high hardness and low friction, among others. However, they have a problem regarding adhesion with the base material, which is a major factor hindering their expanded application in other fields. The adhesion of DLC coatings is generally evaluated in the Rockwell test and scratch test. These test methods induce damage in the specimen with applying load by one way or one pass without the cyclic sliding. Accordingly, there is a weak point of low correlation between such test results and evaluations of the adhesion of coatings on components that undergo repeated sliding cycles. With the aim of resolving that problem, this study evaluated the damage condition of DLC coatings using cyclic sliding test methods of applying a continuously increasing load. The evaluation results obtained with these methods differed from the results of Rockwell tests and scratch tests. This paper describes the test procedures and the evaluation results obtained.
A method was developed for applying a diamond-like carbon (DLC) coating on aluminum alloys to obtain sufficient adhesion strength and wear resistance. The key points of this technology consist of two main processes. First, the surface of the aluminum substrate is modified by forming a top layer of dispersed fine tungsten particles on a mechanically hardened layer obtained in a fine tungsten particle shot-peening process. Second, the sharp top edges formed by the shot-peening process are polished lightly to remove them. A DLC film is then coated on the aluminum substrate by plasma chemical vapor deposition (PE-CVD). The adhesion strength and wear resistance of the DLC film were evaluated in sliding tests under a continuously increasing load. The critical load, which was defined as the load where the friction coefficient increased markedly, was compared for three types of DLC-coated samples. One sample had the DLC film coated directly on the smooth surface of aluminum substrate after polishing; another had the DLC film coated on the rough surface following tungsten shot-peening; the third had the DLC film coated on the substrate surface with plateau roughness obtained by polishing the top edges lightly after the shot-peening process. The critical load of the DLC coating on the substrate with light polishing after the tungsten shot-peening process was 40-70% higher than that of the coating on the polished substrate, while that of the coating on the substrate subjected only to tungsten shot-peening was markedly lower.
Conventional friction force microscopes (FFMs), where micro cantilever probes are used, have a disadvantage that the accurate quantification of friction force has not been established yet. This comes from the difficulty of measurement of the probe torsion angle. On the other hand, a recently developed dual-axis micro-mechanical probe does not require the torsion angle but the lateral displacement for the quantification of friction force. This probe measures the friction force with a double cantilever beam and the normal force with a torsion beam. Since the measurement of the lateral displacement is easier than that of the torsion angle, the dual-axis micro-mechanical probe is expected to provide more accurate and reproducible quantification. In this paper, we investigated two calibration methods for dual-axis micro-mechanical probes; probe adhesion and step structure methods. The probe adhesion method showed rather poor reproducibility for the lateral displacement detection. In contrast, the step structure method showed good reproducibility and good accuracy with the minimum detection limit of the order of 0.1 nm, which corresponds to the friction force of sub-nN for the probes with a spring constant of the order of 1 N/m. The dual-axis micro-mechanical probe can be used to quantify the nanotribological properties accurately.
In tribological applications, surface textures are used to increase load capacity and reduce friction losses in hydrodynamic lubricated contacts. However, there is no systematic, efficient and general approach allowing for the optimization of surface texture shapes to give an optimal performance. The work conducted is, in most cases, by “trial and error”, i.e. changes are introduced and their effects studied. This is time consuming and inefficient. In this paper, a unified computational approach to the optimization of texture shapes in bearings is proposed. The approach aims at finding the optimal texture shape that supports the maximum load and/or minimizes friction losses in one dimensional hydrodynamic bearings. The texture shape optimization problem is transformed into a nonlinearly constrained mathematical programming problem with general constraints that can be solved using optimal control software. Load-carrying capacity or friction force of a bearing becomes an objective functional that is maximized or minimized, subject to: (i) any Reynolds equations given by first order ordinary differential equations, (ii) pressure boundary conditions and (iii) functions/parameters that define the surface texture shape. This newly developed approach is demonstrated on examples of parallel textured hydrodynamic bearings. The effects of non-Newtonian fluids, cavitation and viscosity varying with temperature are considered.
In this study, the flat thrust bearing was developed by actively exploiting the slip flow generated on a water-repellent surface. In order to produce a load, bearing has a structure that generates pressure flow by using the discontinuity of the shear flow rate at the interface between a water-repellent surface that generates a slip flow and an untreated surface free from slip flow. This structure results in a completely flat bearing that has no geometrical variations in its surface level. Startup test and friction test on a water-repellent thrust bearing that consists of three water-repellent sections and three untreated sections on the surface of a glass disk were performed. The results verified that this water-repellent thrust bearing functioned well with a low friction, approximately 1/100 of the friction of non treatment glass.
Blending an optimum amount of friction modifiers into lubricant is one of the important measures to reduce fuel consumption induced by the frictional loss for automobiles. However, the agents containing metal or phosphorus compounds can cause catalyst poisoning and clogging in the filters of the exhaust gas refining system. Thus, development of metal-free and phosphorus-free agents with a long-term stability under real working condition is highly desirable. In the present work, the friction coefficients on the metal surface in lubricants containing different friction modifiers were investigated by the reciprocating friction test in detail. A statistical method based on the quantitative structure-property relationship (QSPR) analysis has been employed to correlate the chemical nature of additives with their effect on the friction reduction behaviors. An empirical equation relating the molecular structure and its friction reduction efficiency has been proposed as a standard for a good friction modifier. Furthermore, a surface-sensitive vibration spectroscopy, sum frequency generation (SFG) spectroscopy, has been used to analyze the molecular structures of the lubricants adsorbed on the metal surface. The SFG observation suggested that a certain relationship between the adsorption structure and friction reduction effect of these agents.
We theoretically investigated influences of film deposition condition on a friction of diamond-like carbon (DLC) film using our developed molecular dynamics method. The method can deal with chemical reactions on the basis of our original stochastic equation. DLC slab model was firstly constructed, and carbon atoms were deposited onto its surface with various kinetic energies (1, 10 and 30 eV) to mimic physical vapor deposition process. Lower sp3 carbon concentration and density were obtained for the 1 eV case and “subplantation” phenomenon was found for each model. The dynamical friction of the deposited DLC film/iron oxide combination was also simulated. The friction coefficient for the deposited film with kinetic energy of 1 eV was much lower than that of 10 and 30 eV cases due to the friction-induced structural change. The simulations provided us an important insight on DLC film preparation to achieve low friction regime.
Dispersion-type lubricants formulated with calcium carbonate were experimentally studied to achieve improved hot-rolling characteristics of stainless steel. Two types of lubricants; over-based calcium sulfonate dispersed in oil (fluid type; FT) and calcium carbonate dispersed in grease (semi fluid type; ST) were prepared. ST containing larger particles of calcium carbonate exhibited a better lubricity in rolling of steel than FT. Although the particle size of calcium carbonate powder is about 1 μm, the dispersed state was stable in ST. Following the rolling tests, the surfaces of tribo-films were analyzed using XPS and TOF-SIMS. A lubrication model with calcium carbonate particles was proposed based on the surface analysis.