Achieving low-friction and robust tribosystems is an open and challenging question to tribologists. In this study, we are considering the diamond films as candidates. Quantification of friction is obtained here using an original technique, so called the oscillating relaxation tribometry. It is based on the study of the oscillating motion of a free-damped 1-DOF mechanical oscillator, the sliding contact acting as a main source of mechanical dissipation (“relaxation”). Therefore, it is possible to determine friction value and its sliding speed dependency, i.e. a kind of “Stribeck curve“ under non-stationary conditions. The interest of such “relaxation tribometer“ is to characterize low friction with an unequalled sensitivity, and to directly obtain the “friction law“ thanks to a robust and rapid experimental test. Polycrystalline diamond films are deposited by the Hot Filament CVD method on SiC substrate, which were partly polished and finished to gradient surface roughness with random-textured asperities. Stainless steel balls of 6.0 mm diameter are used as the rubbing counterface. The normal force is varied between 50 and 300 mN, leading respectively to a maximum Hertzian contact pressure of 0.30 and 0.71 GPa, respectively. Taking into account the experimental setup, the sliding speed is decaying as a damped pseudo-sine motion, the maximum sliding value being set to 0.16 m/s, progressively decaying to 0 when mechanical equilibrium is reached, within a typical duration of 5 s. First results are reported here, using this innovative friction characterization technique. The different contributions to friction of the surface roughness are analyzed and discussed. These results show the major interest of the use of this method to characterize the low-friction behavior of textured diamond films. These results are discussed and the high potential of such textured films in actual tribosystems is presented here.

Conventionally, several reports on quantification of wear of current collecting materials have been published. The objectives of these reports were to predict the wear of current collecting materials in field. However, the measure to reduce the wear of current collecting materials has not been proposed yet. In this paper, the authors focus on wear mode transition phenomena to propose the wear reduction measure, and carry out an electric potential distribution analysis and a temperature distribution analysis. From the analysis results, it is found that the relationship between electric potential and temperature is formed parabolic curve, and the curve depends on only a contact voltage. Further, the authors propose a “wear mode map” which shows transition conditions between the wear modes under electric flowing condition by formulating the parabolic curve. According to the wear mode map, the authors identify the three dominant parameters of wear mode transition as a contact voltage, contact resistances include film resistance and melting points of current collecting materials.

Modified Reynolds-Darcy equation for ferrofluid lubricated squeeze-film bearing, made by flat circular porous upper and flat circular impermeable lower discs, is derived. The ferrofluid is controlled by oblique variable magnetic field (VMF) and VMF is important because of its advantage of generating maximum field at the required active contact zone. The porous matrix is considered because of its advantageous property of self-lubrication. Moreover, the validity of the Darcy’s law is assumed in the porous matrix. Expression for dimensionless film pressure p in terms of Bessel function by considering the effect of existence of pressure difference at the film-porous interface is obtained. The expression for dimensionless load-carrying capacity W is also obtained. The effects of dimensionless radial parameter, inverse of the dimensionless film thickness parameter (h₀ / h) , magnetization parameter and squeeze velocity are studied on p, whereas the effects of the inverse of the dimensionless film thickness parameter and magnetization parameter and squeeze velocity are studied on W. Moreover, the effect of dimensionless pressure difference P at the film-porous interface is studied on W_n (which is the term because of existence of the pressure difference at the film-porous interface). The results show that p increases for smaller values of radial parameter, larger values of magnetization parameter and when (h₀ / h) ≤ 12, whereas W increases for larger values of magnetization parameter and when (h₀ / h) ≤ 12. The squeeze velocity have no effects on the variation of p and W. Moreover, the results for W_n show that it increases with the increase of P.

Micropitting is a type of rolling contact fatigue (RCF) associated with rough surfaces and severe lubrication conditions. In the present study, we developed an estimation method for micropitting life. An S-N curve, which is a relationship between micropitting life and stresses acting in the region affected by surface asperities (near-surface stress), is established by using data from RCF tests and estimated histories of near-surface stresses (stress history). Changes in the surface topography and residual stresses including the initial condition are measured in order to estimate the stress history. This enables us to consider the influences of surface topography and residual stresses on micropitting. Micropitting life under an arbitrary operating condition is estimated from the established S-N curve and the estimated stress history up to a finite cycle. It is revealed that micropitting life can be accurately estimated from the established S-N curve within the range of our experiment. The median, minimum, and maximum of the relative life ratio (ratio of actual micropitting life to the estimated life) were 0.89, 0.49, and 1.82, respectively. Further analysis confirms that the accuracy is improved by considering residual stresses.

Performance of bearings used in modern machinery is significantly affected by the elasticity of the bearing liner and viscosity of the lubricant. This paper considers couple stress fluid (CSF) model of the lubricant along with elasticity of bearing liner. The three dimensional (3-D) model of elasticity is used to consider the effect of elasticity. Finite element method (FEM) has been utilized to comprehend the governing equation of fluid flow in the clearance space between the journal and the bearing. Various performance characteristics such as load capacity, dynamic coefficients and stability parameters have been evaluated for a range of CSF parameter and elasticity parameter. Results show that elasticity and CSF have significant effect on the performance of the journal bearing. Stability of the journal bearing increases as the value of elastic coefficient increases. Further the stability of the elastic journal bearing system is found to be increased by increase in couple stress parameter.

The ionic liquid (IL) having a short perfluorether group and a hydroxy group was synthesized newly. The monolayer thickness of the IL and Z-Tetraol (Molecular Weight: approximately 2300) was 1.2 nm and 1.8 nm respectively which is measured by their spreading profiles experimentally. The adhesion and friction force of the lubricant thin film were measured by pin-on-disk microtribotester. While the adhesion force of Z-Tetraol increase with decreasing film thickness, the IL exhibits very small adhesion forces despite high polar energy measured by the contact angle. These adhesion measurement results implied that the interaction between pin and the IL lubricated disk is determined by considering the balance of Van der Walls attraction and electrostatic repulsion.