Arc extinction with nitrogen at 1-40 bar in a puffer-like contact configuration

To develop cost-efficient subsea switchgear for large sea depths, the extinction of arcs under high filling pressures must be understood. In this work, arc-extinction experiments have been performed with a puffer-like contact configuration using nitrogen at different filling pressures as the current interruption medium. The main finding is that, for the given contact configuration, the currentinterruption capability was lower at 20 and 40 barabs than at 1 and 10 barabs. While higher pressures result in higher cooling flow rates and longer flow times given the same puffer volume, compression spring and nozzle geometry; it does not necessarily improve the arc-extinction capability. This is probably because higher filling pressures increase the arc voltage and total energy dissipated in the arcing zone. Because the filling pressure greatly influences the flow characteristics, the puffer design should be optimized for each pressure level.

Differences in nano-topography and tribochemistry of ZDDP tribofilms from variations in contact configuration with steel and DLC surfaces

In this work, we evaluated the effect of the counter-body material (the same or dissimilar) and contact configuration (moving or stationary body), at similar contact tribological conditions, on the tribochemical and nanotopography characteristics of adsorbed surface films. Zinc dialkyldithiophosphate (ZDDP), the best performing anti-wear additive, was used in self-mated steel/steel and DLC/DLC contacts, which were compared with mixed steel/DLC and DLC/steel contacts in 1-h and 6-h sliding tests. The macroscale (tribometer) and nanoscale (atomic force microscopy) friction, thickness, topography, and chemical (attenuated total reflection-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy) properties of the tribofilms were studied. The results revealed unexpectedly large differences in all the studied tribofilm parameters; this is because all the tribofilms are completely different; this includes the chemical composition, which is known to have a crucial effect on the nano- and macro-scale tribological properties. These results clearly demonstrate that the surface material, additives, and common contact operating parameters, that is, pressure, velocity, and temperature, crucially affect the ZDDP tribofilm as well as the position of the moving or stationary surface within the contact, and the material of the moving/stationary bodies.

Influence of Chemical Heterogeneity and Third Body on Adhesive Strength: Experiment and Simulation

We investigate experimentally and numerically the influence of chemical heterogeneity and of third-body particles on adhesive contact. Chemical heterogeneity is generated by chemical treatment of the contacting bodies changing locally the surface energy. For studying the influence of the third body, two types of particles are used: sand particles with various geometrical shapes and sizes, and steel spheres of equal radius. Dependencies of the normal force on the indentation depth at both indenting and pull-off as well as the evolution of the contact configuration are investigated. Corresponding numerical simulations are carried out using the boundary element method (BEM).

Coefficient of friction of dry sliding Al 6061-T6 alloy under different loading conditions

Purpose This paper aims to focus on the effect of normal load, sliding speed and temperature on the coefficient of friction of Al 6061-T6 alloy under dry sliding conditions. Design/methodology/approach Dry sliding experiments were conducted using rotary type pin on disk tribometer. Pins with 3 mm radius of contact and circular disks of 165 mm diameter were fabricated to simulate Hertzian contact configuration. Experiments were conducted by applying three different normal loads (1, 1.5 and 2 kg) and three different sliding speeds (1.25, 2 and 3 m/s) at different temperatures [room temperature (31 ± 1 °C), 60 °C, 100 °C and 150 °C]. Findings Coefficient of friction at end of the first cycle of sliding, stabilized stage, unsteady state and steady state are reported elaborately in this study. Adhesive and abrasive wear mechanisms were observed in the dry sliding of Al 6061- T6 alloy contacts from the microscopic analysis of worn contact surfaces. The coefficient of friction was more influenced by the increase in normal load than the increase in sliding speed and temperature. Practical implications The results obtained from this study are significant for the design of aluminium-to-aluminium contacts in aerospace engineering and automobile engineering. Originality/value This study reveals the coefficient of friction of aluminium-to-aluminium (Al 6061-T6 alloy) contacts under cylinder on flat contact configuration.

First Principles Study of Bonding Mechanisms at the TiAl/TiO2 Interface

The adhesion properties of the TiAl/TiO2 interface are estimated in dependence on interfacial layer composition and contact configuration using the projector augmented wave method. It is shown that a higher value of the work of separation is obtained at the interface between the Ti-terminated TiAl(110) surface and the TiO2(110)O one than at that with the Al-terminated alloy. An analysis of structural and electronic factors dominating the chemical bonding at the interfaces is carried out. It is shown that low bond densities are responsible for low adhesion at both considered interfaces, which may affect the spallation of oxide scale from the TiAl matrix.

On the Role of Contact and System Stiffness in the Measurement of Principal Variables in Fretting Wear Testing

In this work, the role of the contact stiffness in the measurement of principal variables in fretting wear tests is assessed. Several fretting wear tribometers found in the literature, including one developed by the authors, are analysed and modelled using numerical methods. The results show the importance of the tribosystem stiffness and tangential contact stiffness in the displacement sensor calibration and in the correct numerical modelling of fretting wear tests, especially for flat-to-flat contact configuration. The study highlights that, in most cases, direct comparisons between fretting results with severe wear obtained with different tribometers cannot be performed if the contact stiffness is not properly considered during the development of the experiments.

Tribolumen: A Tribometer for A Correlation Between AE Signals and Observation of Tribological Process in Real-Time—Application to A Dry Steel/Glass Reciprocating Sliding Contact

This paper deals with the development of an original apparatus called TRIBOLUMEN designed specifically for friction experiments on transparent materials. The friction measurement is synchronized with an acoustic emission (AE) sensor and the device is also equipped with a high-speed camera offering a direct view at the interface to gain a deeper understanding of tribological mechanisms. The TRIBOLUMEN device is in ball-on-flat contact configuration with a range of strokes from 5 to 500 µm and an oscillation frequency from 5 to 600 Hz. The experiments showed that this device has an adequate rigidity and can detect subtle friction modifications of the oscillating contacts. The observation of a steel-on-glass contact in real-time highlighted the initiation of Hertzian cracks followed by the formation of debris in the contact. Using the synchronous measurement, these mechanisms were clearly associated with different stages in the friction measurement and in the AE signals, which permitted to identify the AE signature of Hertzian cracks.