Koshi Adachi

Loads carrying capacity map for the surface texture design of SiC thrust bearing sliding in water

Water lubricated silicon carbide is expected to be widely used for sliding bearings and mechanical seals in hydraulic systems since it is environmentally friendly and saves energy. The purpose of this study is to find the optimum surface texture to improve the load carrying capacity of SiC bearings working in water. Micro-pits, evenly distributed in a square array, were selected as the texture pattern, and formed on one of the contact surfaces by reactive ion etching. Experiments, which simulate the working condition of thrust bearings, were carried out to evaluate the effects of the micro-pits on the critical load of the transition of the lubrication mode from hydrodynamic to mixed. The results are summarized in the form of a load carrying capacity map. It was found that an optimum geometric and distributive range of micro-pits exists, where the load carrying capacity can be increased at least twice over that of an untextured surface.  2002 Elsevier Science Ltd. All rights reserved.

The effect of laser texturing of SiC surface on the critical load for the transition of water lubrication mode from hydrodynamic to mixed

Abstract Experiments were carried out to verify if the low friction range of SiC in water lubrication can be expanded by micro-pores on the contact surface. Pores were formed by laser, with a diameter of 150 μm and a depth of about 8–10 μm and were distributed in a square array on the contact surface. Seven kinds of textured specimens with different intervals between the pores were tested and compared with the untextured specimen. The effect of the pore area ratio on friction coefficient and the critical load for the transition from hydrodynamic lubrication to mixed lubrication was reported and discussed.

Wear map of ceramics

Abstract The overall objective of this study is to introduce a wear map of ceramics which shows the regions of dominant wear modes observed in a wide range of materials and operating conditions. Furthermore, from the wear map, common necessary conditions for the application of various ceramics as wear-resistant tribo-materials in a wide range of operating conditions are discussed. For this purpose, friction and wear tests are carried out using three kinds of ceramics sliding against themselves under various contact pressures, sliding velocities and temperatures. Sliding wear phenomena of ceramics observed in all tests can be classified into two types: “mild wear” and “severe wear”, based on the ration of worn surface roughness Rx to the mean grain size Dg. The specific wear amount is always less than 10−16 mm3 (Nm) −1 when the worn surface roughness becomes relatively small ( R y D g ) in the mild wear region. On the other hand, the relatively rough worn surface ( R y D g > 0.5 ) in the severe wear region gives a wear rate larger than 10−6 mm3 (Nm)−1. The mild wear region is believed to be necessary for the application of ceramics as wear-resistant tribo-materials. The critical condition for mild and severe wear is analyzed with an intergranular fracture model from the view points of both mechanical and thermal aspects. A wear map of ceramics, which can define the regimes of mild and severe wear, is introduced using two dimensionless parameters, namely the mechanical severity of contact (Sc,m) and the thermal severity of contact ( S c ,γ ), which are used as vertical and horizontal axes, respectively. The availability of the wear map constructed by this method is proven by experimental results observed over a wide range of test materials and operating conditions.

Wear-mode mapping for the micro-scale abrasion test

Abstract The objective of this study was to develop a theoretical model and associated wear-mode map to identify the regimes in which two-body abrasion (grooving abrasion) and three-body abrasion (rolling abrasion) dominate in the micro-scale abrasive wear test (also known as the ball-cratering abrasion test). The critical condition for the transition between two-body and three-body abrasion was determined from a continuum mechanics model for the penetration of the abrasive particles into the surfaces of the ball and the specimen, coupled with considerations of equilibrium. Micro-scale abrasion tests were performed with different combinations of ball and specimen materials, under different test conditions such as abrasive concentration and load, and a wear-mode map has been produced which defines the regimes of abrasive particle motion. The map is plotted between two dimensionless groups as vertical and horizontal axes: the hardness ratio between the ball and the specimen, and a newly introduced parameter which represents the severity of contact. Experimental data generated in this work and also taken from previous studies show that the map represents behaviour in the micro-scale abrasion test well, for a wide range of ball and specimen counterface materials.

The comparisons of sliding speed and normal load effect on friction coefficients of self-mated Si3N4 and SiC under water lubrication

Abstract The effects of sliding speed and normal load on friction coefficients of self-mated Si 3 N 4 and SiC sliding in water after running-in in water were investigated with pin-on-disk apparatus at sliding speeds of 30 to 120 mm/s, normal loads of 1 to 14 N in ambient condition. The results showed that, after running-in in water, for two kinds of self-mated ceramics, friction coefficient increases with both decreasing sliding speed and increasing normal load when normal load is larger than a critical normal load. Friction coefficient was independent of normal load when normal load is smaller than the critical load. The lubrication film of Si 3 N 4 under water lubrication exhibited larger load carrying capacity than that of SiC did. Stribeck curves indicated that, for self-mated Si 3 N 4 ceramics, hydrodynamic lubrication will change into boundary lubrication abruptly when the sommerfeld number is less than a critical value; while for self-mated SiC ceramics, hydrodynamic lubrication will change into mixed lubrication and then into boundary lubrication gradually when the sommerfeld number is below critical value.

The Lubrication Effect of Micro-Pits on Parallel Sliding Faces of SiC in Water

Silicon carbide is regarded as a promising material for sliding bearings and mechanical seals working in water. In order to improve its load carrying capacity (or anti-seizure ability) in water, micro-pits were formed on one of the contact surfaces by ion reaction etching. The effect of micro-pits on the critical load for the transition from EHL to mixed lubrication was studied experimentally in the cases of bearing type contact (with relatively rich water supply) and seal type contact (with relatively poor water supply). In order to understand the mechanisms of the lubrication effect of micro-pits, the experimental results obtained from bearing type contact and seal type contact were compared, and a theoretical analysis was carried out. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

The Difference in Running-In Period and Friction Coefficient Between Self-Mated Si3N4 and SiC Under Water Lubrication

Running-in periods and friction coefficients of SiC and Si3N4 sliding against themselves under water lubrication were investigated with a pin-on-disk apparatus at sliding speed of 120 mm/s and a normal load of 5 N under ambient conditions. It was found that the running-in period of self-mated Si3N4 is much shorter than that of self-mated SiC, and also that the steady-state friction coefficient of self-mated Si3N4 was lower (≤0.0035) than that of self-mated SiC (0.01). The difference in mechanism was analyzed from the point of view of electronic structure and surface chemistry.

Formation of smooth wear surfaces on alumina ceramics by embedding and tribo-sintering of fine wear particles

The role of the wear particles for the formation of various wear surfaces, especially mirror-like wear surface, was investigated based on detailed observations of wear surfaces and by introduction of two types of model experiments. Smooth wear surfaces (R max <1 μm) are formed by two processes of micro-wear of asperity peaks of alumina grains and filling in surface hollows with fine wear particles. In order to form the mirror-like wear surface (R max < 0.1 μm) of alumina, tribo-sintering of wear particles is necessary in addition to necessary condition for smooth surface formation introduced in previous works [K. Adachi, K. Kato, N. Chen, Wear 203-204 (1997) 291-301; K. Adachi, K. Kato, E. Inoue, R. Takizawa, Proc. Int. Trib. Conf. Yokohama (1995) 415-420]. Finally, friction conditions which can give mirror-like wear surfaces as a result of wear are proposed by analyses from both the view points of fracture mechanics [K. Adachi, K. Kato, N. Chen, Wear 203-204 (1997) 291-301; K. Adachi, K. Kato, E. Inoue, R. Takizawa, Proc. Int. Trib. Conf. Yokohama (1995) 415-420] and embedding or sintering of wear particles.

The micro-mechanism of friction drive with ultrasonic wave

Abstract The micro-mechanism of friction drive with ultrasonic wave was analyzed experimentally and theoretically by using a newly developed apparatus. With this apparatus, it was possible to measure the friction force at the contact interface between a rotational disk and an oscillatory pin induced by ultrasonic wave. This friction couple simulated the contact behavior of the ultrasonic wave motor. The type of pin motion (whether reciprocating or circular), its amplitude and rotational speed of disk could be controlled in this apparatus. The friction force increased with the increase of the rotational speed of disk and the decrease of the amplitude of pin motion. In the case of circular pin motion, the friction force was applied in a negative direction when the rotational speed of disk was below a critical value. The micro-mechanisms of this friction drive were analyzed theoretically by introducing a relationship between tangential coefficient and micro-displacement at the contact region, and the observed friction force as a function of the rotational speed of disk and the amplitude of pin motion was well explained by the introduced theory.

Map of low-frequency stick–slip of a creep groan

Abstract A map that shows the necessary condition for avoiding the generation of low-frequency stick–slip of a creep groan is introduced. The map is obtained as a result of comprehensive investigation employing a novel caliper–slider experimental model. According to the map, creep groan generation is controlled by two dimensionless parameters, designated as stiffness ratio, Sr, and low-frequency stick–slip index, Ls. Stiffness ratio, Sr, is the ratio of structure stiffness to the stiffness at contact interface and Ls is an index formed by various parameters such as normal force, sliding velocity, and difference between static and kinetic coefficients of friction. On the experimental model, creep groan generation can be avoided if one or both of the following conditions is fulfilled: (a) stiffness ratio, Sr, larger than 40 (Sr>40) and/or (b) low-frequency stick–slip, Ls, index larger than 400 (Ls index>400). It is expected that the map can be used as a useful guideline for avoiding the generation of similar phenomenon on a real brake system.