In this paper, friction and wear properties of a copper/carbon/rice bran ceramics (Cu/C/RBC) composite under water-lubricated conditions were investigated experimentally. The mass fractions of copper, carbon and the RB ceramics particulates were 60, 35 and 5 mass%, respectively. The mean diameter of the RB ceramics particulate was 4.9 μm. Friction tests were conducted with a pin-on-disk friction apparatus under water-lubricated conditions. The Cu/C/RBC composite and a copper/carbon (Cu/C) composite were used as disk specimens. The Cu/C composite is a conventional pantograph slider material in Japan. A copper alloy was used as a pin specimen, which was used to simulate a contact wire. The friction coefficients for the Cu/C/RBC composite were lower and more stable than those for the Cu/C composite. The Cu/C/RBC composite showed superior friction and wear properties such as 70.0% reduction in friction coefficient, 86.1% reduction in the specific wear rate of the composite disk and 99.1% reduction in that of the copper-alloy pin compared with the Cu/C composite.

View full abstract

This paper pertains to the observations of the sliding friction force from different moving bodies. The paper derives the equations required to predict the forces on the free-body diagrams of two sliding bodies when observed from a third moving body. The force equations were determined with the application of virtual work to determine system equilibrium. The results show that any sliding force equation including the classical Newtonian tractive equation must be multiplied by an intrinsic theoretical equation to obtain equilibrium on the isolated body when observed from a third moving body. This intrinsic equation is defined as the instantaneous percent sliding of the contact.

View full abstract

A process for bonding a carbon nanotube (CNT) film to a Au film at low temperature was developed with a view to using the CNT films as electrical contact materials in radio-frequency microelectromechanical systems (RF MEMS) switches. First, a CNT film was synthesized on a silicon substrate at 750 °C and subsequently coated with Au at room temperature. Finally, the Au-coated CNT film was bonded at 100 °C to a Au film, which was then deposited on a silicon substrate to act as a transmission line. An apparatus was developed to measure contact resistances and forces under contact conditions mimicking those that will be encountered in actual RF MEMS switches, such as micronewton loads and square-micrometer contact areas. Contact resistance and force of the bonded CNT film sample were simultaneously measured as a function of displacement between the sample and an electrode Au tip and compared with those for a Au film and Au-coated CNT film. The bonded CNT film sample had no adhesion force, but higher contact resistance than the other samples.

View full abstract

In order to examine the frictional behavior between the ball and the material during the ball rolling process, the rolling friction test apparatus in which the peripheral speed of the ball and the processing load can be measured was developed. In dry and lubricated conditions, soon after the process starts, the difference in the behavior of the horizontal force and the peripheral speed of the ball are observed. It is considered that the contacting conditions vary depending on the amplitude of the plastic flow in the material at the early stage of the process. Since the lubricant oil is captured at the valley part of the roughened surface caused by the forward plastic flow, the surface defects remained at the processed surface in lubricated condition.

View full abstract

In this report, a new ball burnishing process in which the ball is forced to be rotated is proposed. A ball rolling friction test apparatus in which the rotational speed of the ball can be controlled was developed. Controlling the rotational speed of the ball can generate any slip speed at the ball and workpiece substrates. It is found that the friction force produced by the slip speed improves the surface roughness of the workpiece. The lubricant oil, which remains at contacting interface, can act a factor to rough the workpiece surface. However, with the proposed process, even in lubricated condition, the processed surface is obtained the similar surface that was observed in dry condition. If the slip speed is not zero, the lowest surface roughness becomes 0.017 μmRa. This result is better than the case of free rotation (the slip speed is zero). Minus rotation (the slip speed is minus) effectively vanish valley parts of the surface. From the spectrum analysis, in minus rotation, the peaks at wide range of wavelength are disappeared.

View full abstract

The tribological properties under abrasive wear conditions, the tensile properties, the thermal properties and the structure have been investigated on the polyamide 6 (PA6) fibers dispersed with vapor-grown carbon fibers (VGCF’s) in order to analyze the effects of dispersing VGCF’s on the wear resistance of PA6 fibers. The wear resistance of the fibers have been determined using a method previously proposed by the present authors. The coefficient of friction decreased by dispersing a small amount of VGCF’s but increased with increasing VGCF fraction at large VGCF fractions. The wear resistance increased with increasing VGCF fraction. Under the experimental conditions adopted in this study, the dispersion of VGCF’s more effectively increased the wear resistance of PA6 fibers than the heat treatment. These experimental results have been analyzed based on a model with which the coefficient of friction (μ) and the wear rate (W_s) have been related to the microhardness (H), the resistance against sliding (σ_s), the fracture probability (f) the shape factor (g) and a constant (k) as μ = gσ_s/(kH) and W_s = gf/(kH).

View full abstract

This paper describes the influence of fiber length of lithium-soap thickener of greases on friction under boundary lubrication conditions. Ball-on-disk sliding tests were conducted with lithium soap greases with polyol ester as the base oil. The tests revealed that the greases had a lower friction coefficient than that for the base oil. The grease with a long soap fiber structure had a lower friction coefficient than that for the grease with a short soap fiber structure. The tests with only soap fibers showed that the soap fibers had better lubricity than the base oil under the boundary conditions tested, but there was little difference in the lubricity of the longer fibers and the shorter fibers. The partial coat tests revealed that the grease with longer soap fibers was easily entrained into the contact. It was concluded that this entrainment capability of the grease led to favorable lubrication to maintain low friction coefficient.

View full abstract