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It is shown that the force which opposes the sliding of a hard relatively smooth surface over a softer surface can be explained as the force needed to push waves of plastically deformed material along the soft surface ahead of asperities on the hard surface. For rougher surfaces and/or poorer lubrication it is shown how the wave can be torn off or material removed by a chip formation process and wear...
On the basis of deviation theory of a random function a model has been developed for determining the parameters of acoustic emission (AE) accompanying contact friction of solids. The relationships are formulated for calculations of amplitude distribution, its parameters, and count rate of acoustic emission pulses. General characteristics of materials composing the friction pair were determined as...
Super-hard and low-friction diamond-like carbon (DLC) coatings deposited at low temperatures are currently of great interest for wear protection and friction reduction. However, their high hardness (50-80 GPa), intrinsic stresses, and poor adhesion limit their use to applications where contact pressures are below 1 GPa and the coating thickness is below 0.5 μm to prevent cracking and delamination...
Many previous works concerning non-lubricated friction have aimed at understanding friction force variations under different conditions (sliding or not) of the interface. It has been found that the static friction coefficient is usually represented as a function of stationary contact time and the kinetic friction coefficient appears to vary with the sliding velocity. This work shows the results of...
This paper describes a microscopic investigation of the deformation in the surface crystal grains and the initial step of wear mechanism in sliding friction using a metallographic microscope integrated in a pin-on-flat apparatus (frictional surface microscope). The in situ observation of the change in the surface crystal grains is performed during the sliding frictional process to reveal the generation...
Sliding contact causes dramatic changes near the interface in metals. These include the development of large plastic strains and associated changes in defect concentration, microstructure, crystallographic texture and phase content. In addition, interactions with the counterface material and the environment and mechanical mixing processes can modify the material on both sliding surfaces. Structural...
The sliding behavior of several coatings based on non-hydrogenated diamond-like carbon (DLC) is described. Coatings were produced by using a magnetron sputter-assisted pulsed laser deposition process developed at the Air Force Research Laboratory. Results are compared for two types of coatings: DLC with WC nanoparticles and DLC with both WC particles and WS 2 (''WCS''). Sliding tests were...
Frictional properties of nonwoven substrates have been investigated using a sliding friction apparatus. Nonwoven substrates were developed using a modern needle-punching nonwoven technology. The experiment was conducted over a range of applied normal loads. The study was aimed at understanding the effect of testing speeds on the frictional properties of needle-punched nonwoven substrates. Frictional...
Lubrication is critical for minimizing wear in mechanical systems that operate for extended time periods. Developing lubricants that can be used in engineering systems without replenishment – particularly those that are environmentally friendly – is very important for increasing the functional lifetime of mechanical components. In the present investigation, extended duration pin-on-disk experiments...
Titanium alloys and their composites have the potential to reduce truck disc brake component weight and improve their resistance to road-salt corrosion. A titanium alloy rotor can weigh approximately 37% less than a conventional cast iron rotor with the same dimensions, while offering good high-temperature strength and much better resistance to corrosion from road-deicing salts. Friction coefficients...
The aim of this paper is to confirm the role of the electric charges on the friction behaviour of non-conductive materials. This correlation is proven using tribo-tests and SEMME (Scanning Electron Microscope Mirror Effect) measurements carried out on the neat epoxy matrix and on two GFRE composites, which only differ by the sizing of the fibres.For the matrix, the influence of friction is only obvious...
Effect of low sliding speeds (0.01–1.0ms −1 ) on wear behaviour of an AZ91D magnesium alloy was studied under dry sliding condition using a pin-on-disc configuration. The wear rates were measured under a constant load of 10N but two different sliding distances (1 and 10km). Analyses of the wear tracks, worn surfaces and wear debris were carried out using scanning electron microscope and X-ray...
Following research in 2000 in which the benefits of using lateral creep to establish friction levels in the wheel/rail contact region were established, the author and his team pushed the operating regime to include the smaller, slower realm of hand-operated tribometry. Implementing and managing of both flange lubrication, and top of rail friction modification programs have become more widely adopted...
Polystyrene–acrylonitrile mixed with different carbon nanotube (CNT) fractions has been successfully prepared by means of in situ polymerization method. The tribological behaviors of the nanocomposites are investigated by friction and wear tester under dry conditions. Compared with the polystyrene–acrylonitrile, polystyrene–acrylonitrile–CNTs shows not only the lower friction coefficient but also...
High-power piezo-electric motors with power densities of 1.4kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40kHz with amplitudes between 2.5μm and 5μm. The tribometers are equipped with means to measure amplitude, frequency, power required to...
Scratch tests is one of the most efficient tests to investigate the mechanical resistance of coated and uncoated surfaces. Nevertheless, the complexity of material and interface makes difficult the comprehension of this test. For that purpose, efficient computational modeling is required. In this paper, we present a remeshing procedure specially developed for the computational modeling of scratch...
The relationship between magnetization of a friction surface and wear phenomena is discussed for the case of rubbing of nickel on nickel. Experiments were performed by sliding-friction tests of the pin-on-block type. Magnetization of the friction surface was estimated by measuring changes in the magnetic flux density with a Tesla meter, and the effects of lubrication and various normal loads on changes...
Self-mated wear and friction of Alloy 600 superalloy was studied in a water-submersed ring-on-rod configuration, loading the side of a 6.35mm diameter rod across the flat surface of a rotating annular ring of 100mm outer diameter and 70mm inner diameter producing two sliding contacts along the ring. Tests were conducted at sliding speeds of 0.178 and 0.330m/s for sliding distances of 100m. Normal...
In this work, Lateral Force Microscopy (LFM) has been used to measure the frictional characteristics of the contact of 20μm glass beads and UO 3 particles attached to silicon tapping mode cantilevers. The substrates used were glass, mica and UO 2 single crystals cleaved to form flat surfaces. Flatness of the substrate is necessary to remove the influence of the topography of the substrate...
When nanoindentation is used for thin film characterization, the penetration of the indenter is usually limited to shallow indents to avoid the spurious effect of the substrate. However, the surface effects stemming from the sample surface topography and friction are the most pronounced in shallow indentation depths, potentially resulting in variations of the evaluated material parameters. A numerical...
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