Fractal evaluation aspects in characterizing the roughness of a driving wheel from a locomotive (original) (raw)
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Fractal rigidity of the wheel-rail contact
IOP Conference Series: Materials Science and Engineering, 2020
One of the essential parameters of the roughness with effects on the vibration of the wheel and the rail is the contact stiffness. This rigidity considers the geometry and material of the wheel and rail, which are considered elastic. Also, the micro-geometry of the roughness and the load on the wheel, with elastic, elastoplastic and plastic deformations, depending on the deterministic or random character of the roughness were considered. The dependence of the stiffness on the deformation state of the roughness may explain the different amplitude of the vertical vibrations at the same force on the wheel and the same height of the roughness, but one roughness with different fractal parameters. For the analysis of the dynamic forces in contact, the continuous and underived analytical function that modelled the roughness measured experimentally on the rail was applied.
Wear characterization by fractal mathematics for quality improvement of machine
Purpose -The objective of the present work is to find an alternative approach for gearbox condition monitoring using wear particle characterization incorporated with image vision systems. Design/methodology/approach -It is a quite well-known phenomenon that wear generates whenever two metallic bodies have contact with each other; hence the present work tries to investigate the effect of improper lubrication in the gearbox due to wear particle generation between gear wheels. Since the identification of wear for machine condition monitoring needs much expertise knowledge and is time-consuming using the conventional process, fractal mathematics with image morphological analysis has been utilized to overcome this situation in the present work. Findings -The type of wear has been found for the present method by utilizing the lubricant used in the system ferrographically and a great deal of image processing has been done to characterize the type of particle so that the proper maintenance strategy can be undertaken. Originality/value -Wear particle characterization is a quite common method in maintenance engineering, especially when fault diagnosis of any equipment is concerned. In the present work, the CCD acquisition of the images has been done for different particles, but one analysis amongst them has been shown in this paper. Among all other methodologies, the new technique of fractal mathematics has been used in the present work to minimize the imaging hazards and to make the system more user-friendly.
Fractal Characterisation of Worn Surfaces
Tribological behaviour – friction, wear and lubrication – of machine elements highly depend on the operating state and also the original topography of working pair. In our study wear experiments and surface roughness measurements before and after wear were performed. Investigations extended to wear in the course of the non-lubricated ceramic-steel, ferrodo-steel and bronze-steel material pairs. Fractal dimension of topographies before and after wear were calculated using power spectral density, height-difference correlation and scale-analysis methods. The aim of this study was to compare the capability of three different surface characterisation techniques through the analysis of worn surfaces and also to examine the changes of fractal character of topographies in wear.
Fractal Relation with Conventional Roughness Parameters for Surface Topography Generated in Grinding
2005
Surface roughness plays an important role in product quality and manufacturing process planning. Surface topography is generally characterized by statistical parameters such as centerline average (Ra), root mean square average (Rq), mean line peak spacing (Rsm) etc. Since surface topography is non-stationary and multi-scaled, these parameters are not sufficient to describe the characteristics of the surface. Fractal dimension, on the other hand, describes surface roughness invariant with length scale and fractals can be extremely useful when applied to tribology. Obtaining fractal descriptions of engineering surfaces requires surface topography information to be measured, digitized and processed. The present work describes the evaluation of the fractal dimensions of the surface profiles generated by grinding with different machining conditions such as work-piece speed, longitudinal feed and radial in-feed. The measured roughness parameters and fractal dimension are analyzed using AN...
On the use of fractal geometry methods for the wear process characterization
Wear, 2005
Irregular fluctuations of friction coefficient around the mean value were analysed by means of fractal geometry methods. Particular data were recorded during the steady-state stage of dry sliding tests carried out in Si 3 N 4 ball -on -Si 3 N 4 /SiC nanocomposite disc configuration. It was proven that the set of points {sliding distance (time), friction coefficient}, considered as a geometric object in a two-dimensional space, has the property of a fractal curve. The fractal dimension of this curve increased with increasing wear rate gained in a particular wear test. This could indicate a possible correlation between the wear rate and the fractal dimension of friction coefficient as a function of sliding distance (time).
Tribology International, 2013
This paper proposes a new method of roughness peaks curvature radii calculation and its application to tribological contact analysis as characteristic signature of tribological contact. This method is introduced via the classical approach of the calculation of radius of asperity. In fact, the proposed approach provides a generalization to fractal profiles of the Nowicki's method [Nowicki B. Wear Vol.102, p.161-176, 1985] by introducing a fractal concept of curvature radii of surfaces, depending on the observation scale and also numerically depending on horizontal lines intercepted by the studied profile. It is then established the increasing of the dispersion of the measures of that lines with that of the corresponding radii and the dependence of calculated radii on the fractal dimension of the studied curve.
A Review on Treating Tribological Problems with Fractals
Bulletin of the Polytechnic Institute of Iași. Machine constructions Section
Fractals and chaos theory provide means of modeling dynamic changes in micro and nano topography on friction surfaces caused by various tribological mechanisms and processes. Friction and wear phenomena in tribological systems can be interpreted on a macroscopic scale. With the development of miniaturized scale and nanoscale systems, it has been launched the hypothesis that macro-level systems cannot reflect the microscale and nanoscale phenomena. A conclusive case is given by the calculation of frictional torque in microscale orientation, in this situation being found that models created by bearing producers cannot validate experimental results. By applying the “box-counting” method, it is possible to estimate the fractal dimension both directly and indirectly by comparing the area-perimeter-scale relations. Based on scaling equations, a system was created for this operation. The conclusion is that all existing theories in tribology should be adapted to take into account fractal si...
Fractal analysis of shear joint roughness
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1997
The morphology of mortar replicas of two natural joints (a granite and a schist) made from the silicone rubber casts was characterized using a laser sensor profilograph to create three-dimensional topographic maps before and after each shear test. Three successive direct constant normal load shear tests under three normal stress levels have been carried out on the joint replicas: σ n = 0.4, 0.8, 1.2MPa and σ n = 0.4, 0.8, 1.4MPa for the schist and the granite joint replicas, respectively. Based on geostatistical methods, the variation in surface roughness in the course of shear tests is described using the fractal dimension D ƒ computation. A roughness parameter SR s and a degradation parameter D w were also defined and computed. SR s and D w quantify respectively the degree of joint surfaces roughness and the degree of degradation of sheared joint surfaces. The variation of D ƒ as a function of σ n have been compared to the variation of SR s as a function of σ n in the course of shear tests. Results indicate a good correlation between D ƒ and SR s .
Fractal and spectral analysis of aggregate surface profile in polishing process
Wear, 2011
Studies are conducted to the characterization of the aggregate-surface texture in polishing process by fractal and spectral approaches based on rubber friction theory. The Wehner/Schulze (W/S) polishing machine is adopted to simulate the vehicle tyre polishing action. The commonly used aggregates in wearing courses named basalt, gabbros and greywacke are investigated. The surface profile texture and dynamic friction coefficient were monitored in polishing process. The dynamic friction coefficient was observed to reach a stable equilibrium phase after a sharp decrease at the initial polishing stage and the friction evolution in W/S polishing process can be described with power law. Fractal analysis reveals that the changes of amplitude and curve length of the profiles are the main contribution to the loss of friction. Spectral analysis reveals that the polishing action plays an important role in the changes of micro-texture. It can be concluded that the evolution of friction of the a...