Tribology in Industry

391-399

Authors: M. Pantić, S. Mitrović, M. Babić, D. Jevremović, T. Kanjevac, D. Džunić, D. Adamović

The aim of this study is presenting AFM analysis of surface roughness of Lithium disilicate glass ceramic (IPS e.max CAD) under different finishing procedure (techniques): polishing, glazing and grinding. Lithium disilicate glass ceramics is all-ceramic dental system which is characterized by high aesthetic quality and it can be freely said that properties of material provide all prosthetic requirements: function, biocompatibility and aesthetic. Experimental tests of surface roughness were investigated on 4 samples with dimensions: 18 mm length, 14 mm width and 12 mm height. Contact surfaces of three samples were treated with different finishing procedure (polishing, glazing and grinding), and the contact surface of the raw material is investigated as a fourth sample. Experimental measurements were done using the Atomic Force Microscopy (AFM) of NT-MDT manufacturers, in the contact mode. All obtained results of different prepared samples are presented in the form of specific roughness parameters (Rа, Rz, Rmax, Rq) and 3D surface topography.

413-420

Authors: D. Džunić, S. Mitrović, M. Babić, I. Bobić, M. Pantić, D. Adamović, B. Nedeljković

Nanoindentation has been widely used for material mechanical characterization. In this study, nanocompozite of ZA-27 alloy matrix reinforced with different volume fractions of nanometric Al2O3 ceramic particles ranging from 0 to 5 %, were produces using compocasting technique. Nanoindentation tests were performed using Berkovich three sided diamond pyramid, with maximum load of 100 mN and maximum load holding time of 15 s. Indentation imprints were investigated using optical and atomic force microscopy (AFM). Average particle size was 20-30 nm. Nanoindentation tests showed that nanocomposites have higher values of hardness and lower values of elastic modulus in comparison to the ZA-27 matrix alloy. Obtained results have different values in comparison to the theoretical investigations.

427-433

Authors: O. Maršálek, J. Dlugoš, P. Raffai, P. Novotný, J. Knotek

The main goal of this article is to experimentally evaluate the contact area and to compare the measured results with the different contact model theories. The experiment takes advantage of the electrical contact resistivity principle in a dry piston/cylinder liner test rig assembly. Analytical contact models are implemented into the computational simulation. The calculated contact area depends on the dynamics and precomputed database of contact pressure and contact area in the relation to the separation distance of surfaces. Multibody System (MBS) is augmented by a user-written FORTRAN subroutine and used for the solution.

440-448

Authors: A.P. Markopoulos, N.M. Vaxevanidis, D.E. Manolakos

In the present paper the influence of the friction and material modelling on the results of the Finite Element simulations of machining is investigated. An orthogonal cutting model is proposed, which incorporates Coulomb’s friction law. The validity of this model is tested against similar experimental and numerical results from the relevant literature and the influence of the friction coefficient is investigated. Then, a second model, with a friction model based on Zorev’s stick-slip theory, is prepared and compared to the first one. Furthermore, simulations with Johnson-Cook material model for both kinds of friction modelling are presented and compared to the other models. The results of the different kinds of models although exhibit small discrepancies between models’ results such us cutting forces, affect temperatures and chip morphology.

455-463

Authors: E.A. Zadorozhnaya, S.V. Cherneyko, M.I. Kurochkin, N.A. Lukovich

An ensuring of the axial and radial rotor stability is one of the main objectives in the design and operation of the small-sized turbo-machinery. Hydrodynamic thrust bearings must securely restrain unbalanced axial forces, arising during any possible operating modes. Using of the different types of intermediate elements provides a stable position of the rotor in the radial bearings. Recently flexible rotors have been widely used in small-sized turbo-machines. The complexity of the implementation of methods for calculating the dynamics of these rotors is to solve a system of motion equations. The system of motion equations, which is presented in this work, contains the motion equation for the each bearing element, including the floating rings and elements of the rotor (wheels of the turbine and compressor, the central mass). The load acting on the bearings includes the masses of elements, the reaction of lubricating layers and the rotor imbalance, potential impact loads and forces torques, acting on the rotor from the other elements of the rotor. To calculate the reactions of lubricating layers for two-layer bearings the hydrodynamic pressure field and the friction losses were considered for a real bearing design, on the surface of which the sources of the lubrication is always located. The thrust bearings with segments of various designs have been considered, including laser texturing surface. The trajectories of the rotor elements of the turbo-machinery for various rotation velocities, as well as the elastic line of the rotor at different time points are represented as the results of the calculation.

473-481

Authors: E. Surojo, Jamasri, V. Malau, M.N. Ilman

Some vehicles use brake shoe made from semi-metallic materials. Semi-metallic brake shoes are made from a combination of metallic and non-metallic materials. Metallic particles are added in the formulation of brake shoe material to improve composites characteristics. In this paper, friction behaviors of brake shoe material using metallic filler were investigated. Machining chips of cast iron and copper wire of electric motor used were incorporated in composite as metallic fillers with amount 0, 2, and 4 vol. %. Friction testing was performed to measure coefficient of friction by pressing surface specimen against the surface of rotating disc. The results show that cast iron chip and Cu short wire have effect on increasing coefficient of friction of brake shoe material. They form contact plateau at contact surface. At contact surface, the Cu short wires which have parallel orientation to the sliding contact were susceptible to detach from the matrix.

491-499

Authors: T.R. Prabhu

Metal matrix hybrid composites are usually preferred for high energy aircraft (1-10 MJ) brake pads (HEABP) applications. The report focuses mainly on the evaluation of the wear and braking performance of the composite for the military aircraft applications. In this paper, the design and processing of a typical HEABP composite have been discussed in detail. The airworthiness qualification tests for the HEABP and the brake units are outlined with details. Also, brake testing parameters calculations derived from the typical aircraft data are presented for both the laboratory and full scale dynamometer tests. A case study of Fe-Si3N4- graphite composite pads is presented to exemplify the steps involved in the design, development, and airworthiness certification of HEABPs for the 8 MJ energy military aircraft. From the microstructure and wear surface morphology analysis and the results of brake performance parameters, functional tests and aircraft trials, it is concluded that the Fe-Si3N4- graphite composite has a minimum life of 200 normal energy landings with excellent braking performances.

525-538

Authors: P.S. Dellis

The issue of laser induced fluorescence calibration for engine and simulating rigs was studied using both a static calibration rig and a dynamic method involving a modified piston-ring specimen. The technique used to measure oil film thickness was laser induced fluorescence through optical fibres. Previous experimental studies have been conducted in test rigs and engines to obtain in-situ results showing the uncertainties lying within every applied method. In this study a comparison of two proposed methods is performed – bench calibration (micrometer based) and dynamic for a single piston-ring test rig application. Engine in-situ calibration was not an option so that uncertainties that follow the direct measurements in the piston cylinder engine assembly and the difficulty in determining the exact properties of the lubricant at the ring-pack, which simultaneously affect fluorescence (e.g. local temperature at point of measurement, lubricant degradation) could be avoided. A temperature parametric study of the dynamic calibration coefficient is also presented and a comparison between results from capacitance transducer minimum oil film thickness measurements and the LIF measurements. The discussion that follows the results, tries to enlighten the reasons behind inconsistencies found between the proposed methods.