1,721,012 research outputs found
Friction Models for a Sustainable Design: Friction Coefficient in Lubricated Conformal Pairs
No full textTribological aspects must be taken into account for a sustainable design of new components and materials developed to obtain weight reduction and greater efficiency. Reducing friction and wear produces energy and material savings, both connected with several Sustainable Development Goals. To limit the time consuming expensive experimental tests on new materials and components, simulations can be performed for which reliable values of the friction coefficient are necessary. In this work, some basic aspects of the lubrication regimes are firstly reviewed with the related friction coefficient trends represented with the Stribeck and Lambda curves, also evidencing the reasons of the similarity between the two curves. Formulas and diagrams are then reported for the friction coefficient of full lubricated conformal pairs. For thrust bearings the friction coefficient f can be expressed as a function of the parameter m and is related to the Kingsbury number K. For tilting pads f is proportional to K the power of 0.5. For plain journal bearings f is a function of the dimensionless eccentricity ε and is related to the the Sommerfeld number S to powers ranging roughly from 0.5 to 0.8 depending on the ratio between the axial length and the diameter for S smaller than 0.1, and tending to 1 for higher values of S. The reported formulas and diagrams can be used for design purpose
Elastohydrodynamic lubrication. Present Development. Part II
No full textStudies were carried out to establish the connection between theoretical, numerical and experimental results in elastohydrodynamic lubricated contacts. More accuracte measurements can be made using thin metal films as transducers and contacts with rough surfaces have been examined. The behaviour of various types of oil and additives was tested. The application of elastohydrodynamic lubrication to roller bearings and gears was particularly examined. The minimum thickness was used as a factor in the assessment of component life. (H.C.B.
A Statistical Method to Compute the Dynamic Coefficients of a Tilting Pad Journal Bearing
No full textIn this work, a statistical method to determine the dynamic coefficients of Tilting Pad Journal Bearings (TPJBs) is described. The method is based on a priori modelling of the dependency of the dynamic coefficients on the excitation frequency, on the estimation of the forces
acting on bearing as a function of the estimated displacements (using a linear model) and, finally, on a search of the optimum functions by minimization of the squares of the normalized residuals of displacements and forces on bearings. Normalization is done by dividing the residuals by estimating the standard deviation of the forces and displacements.
The results for a flooded Rocker Back TPJB are presented
Comparison of two sealing coupling geometries for a direct fuel injector
No full textThe present paper describes some Finite Elements simulations carried out in order to investigate the contact problem in the sealing region of a direct fuel injector. In particular two different design solutions have been analyzed, both patent pending, one characterized by a conformal contact of two conic surfaces and the other one by a non-conformal contact between a cone and a sphere. Pressure distribution, contact width and von Mises equivalent stress have been calculated and employed as comparison parameters. Two different loading conditions have been considered: nominal loads and nominal loads plus undesired effects. Also deviations from the nominal geometry, obtained from profile detection of 40 samples, have been introduced for considering a real-like case. Numerical results stress the robustness of the non-conformal solution with respect to geometrical tolerances and real loading conditions
Random error propagation and uncertainty analysis in the dynamic characterization of Tilting Pad Journal Bearings
Full text linkIn this work a new statistical method for the determination of the dynamic coefficients of Tilting Pad Journal Bearings is described. The method is applied to the results obtained testing a 5 pads tilting pad journal bearing with 280 mm diameter. Tests were performed on an advanced experimental apparatus specifically realized for investigations on large size high performance bearings for turbomachinery. The linear coefficient identification procedure is based on the dynamic measurement of forces, accelerations and relative displacements of rotor and bearing, as function of excitation frequency for different operating conditions. The post-processing of the dynamic data is performed in the frequency domain using the Fast Fourier Transform. Along with a description of the experimental test and identification procedure, this paper presents a least-square minimization technique for determining the dynamic coefficients and a bootstrap statistical technique for estimating their confidence intervals
Tribology and Sustainable Development Goals
No full textTribology, which deals with all problems related to friction, wear and lubrication, is intrinsically connected to sustainability. In this work, after a very brief historical overview of Tribology and Sustainable Development Goals, the main tribological research fields are described. A possible organization in six tribological branches is proposed: Fundamental Tribology, Tribology of materials and lubricants, Micro and Nanotribology, Industrial Tribology, Biotribology and Ecotribology. Several aspects of all branches are related to sustainability and can be included in another specific recent discipline termed Green Tribology. Different tribological aspects that contribute to reduce energy losses, and therefore CO2 emissions, and material waste by reducing friction and wear, are reported in the paper. Tribology affects many targets of the Goals. Goal 12, Responsible Consumption and Production, is probably the most affected by tribological findings, but also Goals 3, 6, 7, 8, 9, 11, 13, 14 and 15 are directly influenced. The remaining Goals are indirectly affected in different ways
Experimental aspects of a cam-follower contact
No full textAn experimental apparatus for investigations on cam-follower contacts is briefly described and some results related to a tested cam are presented. The apparatus is able to measure the film thickness and shape using optical interferometry and all components of the contact force through a system of nine annular load cells. The equations for the evaluation of the fundamental kinematic quantities of cam-follower pairs are reported. They are applied to the tested cam for detecting the angular positions of the most interesting conditions, as the points of maximum lift, velocity and acceleration, and the trend of the entraining velocity. The methodologies used for recording by a high speed camera connected to a microscope the interference images for the analysis of the lubricated contact are described. Some sample interference images recorded both at low and high magnification are presented showing the different conditions of the contact during a complete rotation of the cam and the capabilities of the experimental apparatus
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