Papers by Keyword: Asperity

Abstract: Abrasion wear is a mechanical process when the surfaces of a friction coupling decay and which occurs with material removal from the softer surfaces that get into contact with the asperities of the harder surface located in the space between the coupling elements. The paper aims to determine the wear trace remained on a softer surface following the slidding of a harder one, for a brass/iron coupling. The lubrication of coupling and the processing way of the coupling surfaces are factors that directly influence the tribological behaviour of the friction coupling.

Abstract: The paper presents the results of experimental research on the possibilities of micro-geometry modification of conductible and semiconductor surfaces, that gives them new functional properties. It emphasizes that surface micro-geometry modification occurs in practically all cases of the action by concentrated sources of energy, but a prescribed geometry can be reached only under strict conditions. The process of this geometry formation is a function of the physical and mechanical properties and the chemical composition of the processed material, the gradient of applied energy, the intensity of electric field applied in the interstice between the workpiece and the tool-electrode, the connection mode of the workpiece (as anode or as cathode) in the discharge circuit of the current impulse generator, etc. It highlights the fact that on the processed surface can be formed spherical shaped craters, round asperities or Taylor cone shaped asperities. Depending on the shape and the size of asperities, the active surface area, and, respectfully, the emission and absorption properties of elementary particles and light radiation are modified.

Abstract: The elastic-plastic finite element and atomistic models for the frictionless contact of a deformable sphere pressed by a rigid flat is presented. The evolution of the elastic-plastic contact with increasing interference is analyzed using two different analysis tools. The simulation results show that deformation mechanisms revealed in the two different analysis tools are quite different from each other. The physical phenomena “jump-to-contact” and “force drops during dislocation emission” are observed in our atomistic simulations which can not be seen in the continuum analysis.

Abstract: Wear is defined as the process of destruction of the shallow layer of a coupling in a small volume of material, that leads to the wear particle occurence. The mechanism of wear particle formation depends to a great extent on the strain state in the contact area (elastic, plastic, elasto-plastic), on the nature of the material (breaking tenssion, flowing tenssion etc) and on the working conditions (pressure, velocity, temperature etc). The harder material, function on the maximum strain on the friction surface, function on the angle and the geometry of roughness (or abrasive particles) may be elastically or plastically distorted, thus changing the state of the conjugate surface.The paper proposes an answer mode analysis of the materials of a friction coupling with sliding motion, for materials with different hardness.

Abstract: Compared with the conventional piston engines, the new rotary engine has many significant advantages, such as smaller volume and higher power density. Current studies at home and abroad are mainly focusing on aspects of its structural design, kinematics, dynamics analysis, except mechanical efficiency. In conventional piston engines, frictional loss of the piston group accounted for 65% of the total friction power loss ^[1]. In order to provide the scientific basis for designing low friction piston of the rotary engine, this paper combine the average two-dimensional Reynolds equation, the asperity contacts equation, viscosity-temperature equation and loads balance equation, proposing a method for calculating the friction power loss, and the applying the method to calculate the friction power loss of piston group of a new rotary engine.

Abstract: In order to improve quality of wheelset assembly, a method for calculating interference between two sliding asperities that corresponding to the wheelset assembly interference is presented. A finite element model of sliding spherical asperity has been built with the finite element software ABAQUS to analyze the interaction among mating surface roughness, stress-strain state and press-fit curve. This study shows that final fitting force greatly increases with roughness when roughness is lower then 1.8μm and it is unpredicted when roughness is higher. Contact stress and friction coefficient between mating surfaces increase with roughness.

Abstract: In order to understand the contact property of the end face for mechanical seal, simulation models of the elastic contact area ratio, the elastic-plastic contact area ration and the plastic contact area ratio of the end face are established using fractal parameters to characterize the surface topography. The effects of surface topography fractal parameters of B104a-70 mechanical seal on contact properties of the end faces are analyzed by theoretical simulation. The results show that the elastic contact area ratio increases rapidly at first and then decreases gradually, the elastic-plastic contact area ration decreases rapidly at first and then changes slightly, and the plastic contact area ratio changes slightly at first and then increases gradually with the increases of fractal dimension; the elastic contact area ratio decreases, and both the elastic-plastic contact area ratio and the plastic contact area ratio increase with the increases of the characteristic length scale; the proportion of the elastic contact area is larger, and the proportions of the elastic-plastic contact area and the plastic contact area are smaller when the end face is smooth; there exist an optimal value of fractal dimension between the faces of mechanical seal to make the elastic contact area ratio biggest, and the wear smallest. For B104a-70 mechanical seal, the optimal fractal dimension of the end face of the soft ring is about 1.63.

Abstract: Rolling contact fatigue (RCF) will eventually become an issue for machine elementsthat are repeatedly over-rolled with high contact loads and small relative sliding motion. Thedamage consists of cracks and craters in the contact surfaces. Asperities on the contact surfacesact as local stress raisers and provide tensile surface stresses which can explain both initiationand propagation of surface initiated RCF damage. A parametric study was performed to inves-tigate the contribution of surface roughness, friction and a residual surface stress to the RCFdamage process. The effects on initiation, crack path and fatigue life at both early and devel-oped damage were examined for a gear application. Both a one-parameter-at-a-time approachand a 2-level full factorial design were carried out. Surface roughness and local friction prop-erties were found to control crack initiation, whereas the simulated crack path was primarilyaffected by the residual surface stress, especially for developed damage. Reduced surface rough-ness, improved lubrication and a compressive residual surface stress all contributed to increasethe simulated fatigue life. The asperity point load model could predict effects on RCF that areobserved with experiments. The results further support the asperity point load mechanism asthe source behind surface initiated RCF.

Abstract: Through analysis and research on the surface topography of reinforced copper matrix composite materials, taking advantage of fractal statistical method to discuss distribution law about characteristics parameter which symbolizes the asperity, combining Monte-Carlo method with fractal theory to set up mathematics model of characteristics parameter which symbolizes size of asperity , talking about the construction of iterated function system in fractal interpolated theory, a easy realizable friction materials surface topography simulation algorithm was put forward.

Abstract: In this paper, the lubrication of three-dimensional EHL point contact with surface defect was solved, the lubrication film shape and film pressure distribution were presented and the characteristics of EHL point contact with defect were analyzed, the effect of surface defect on EHL point contact was studied. The results were presented that convex defect could lead to film pressure peak increasing, there was obvious micro-EHL effect, concave defect could lead to film pressure hollow and peak, film pressure peak was also increasing. The results also shown that convex and concave defects would have negative impact on EHL lubrication, there was great influence of surface defect on EHL lubrication pressure, the significant fluctuation of local film pressure was caused by surface defect, and generating greater pressure peak, maximum film pressure was rapid growth with the defect size increasing, so any kind defect should be to avoid in EHL lubrication.