A. S. Miranda

An Experimental Investigation of the Effect of Groove Location and Supply Pressure on the THD Performance of a Steadily Loaded Journal Bearing

This paper aims to present the results of parametric experiments carried out in order to study the influence of groove location and supply pressure on the performance of a steadily loaded journal bearing with a single-axial groove, Hydrodynamic pressure and temperature distributions on the bush surface, shaft temperature, flow rate and bush torque were measured at variable supply pressure, using bushes with a single groove located at three different positions. A series of tests were carried out for variable applied load and rotational speed. The experimental evidence shows that some bearing characteristics are significantly sensitive to changes in groove location and supply pressure. One groove located at 30 degrees in relation to the load line, in the direction of shaft rotation, can conduct to reductions in maximum temperature, maximum hydrodynamic pressure and bush torque, with a moderate increase in oil flow rate.

An analysis of the influence of oil supply conditions on the thermohydrodynamic performance of a single groove journal bearing

Abstract In this work a thermohydrodynamic analysis has been developed in order to investigate the influence of oil supply conditions on the performance of a journal bearing. The supply conditions considered were oil supply temperature, supply pressure, groove length and groove location. To carry out this study, the hydrodynamic pressure distribution inside the bearing has been determined using a mass-conserving cavitation model with realistic supply conditions. The energy equation and the heat conduction equation have been used for the determination of oil film and bush temperature distributions. The agreement observed between theoretical predictions and experimental published data is acceptable. Quantitative information shows that the oil supply conditions affect bearing performance parameters in different ways. Oil flowrate was markedly affected by all supply parameters studied. Power loss, maximum bush temperature and minimum film thickness were mainly dependent on oil supply temperature. The effect of supply pressure on minimum film thickness was dependent on groove location. An axial groove located at 90° to the load line gave rise to more favourable bearing performance characteristics.

Experimental Investigation of the Influence of Supply Temperature and Supply Pressure on the Performance of a Two-Axial Groove Hydrodynamic Journal Bearing

An experimental study of the influence of oil supply temperature and supply pressure on the performance of a 100mm plain journal bearing with two axial grooves located at ±90o to the load line was carried out. The hydrodynamic pressure at the mid-plane of the bearing, temperature profiles at the oil-bush and oil-shaft interfaces, bush torque, oil flow rate, and the position of the shaft were measured for variable operating conditions. Shaft rotational speed ranged from 1000 to 4000rpm and two different values of applied load were tested (2kN and 10kN). The supply temperature ranged from 35 to 50oC, whereas the oil supply pressure range was 70kPa to 210kPa. Bearing performance is strongly dependent on the supply conditions. It was found that the existence of the downstream groove significantly affects the temperature profile at the oilbush interface except for the low load, low feeding pressure cases, where the cooling effect of the upstream groove is significant. Feeding temperature has a strong effect on the minimum film thickness. The increase in maximum temperature is significantly lower than the corresponding increase in supply temperature. Increases in supply pressure lead to a significant rise in oil flow rate but have little effect on the maximum temperature and power-loss, except in the case of the lightly-loaded bearing. Shaft temperature was found to be close to the bearing maximum temperature for low applied loads, being significantly smaller than this value for high loads. The mean shaft temperature is only significantly higher than the outlet temperature at high shaft speeds.

Tribological properties of AlNCeO2Si3N4 cutting materials in unlubricated sliding against tool steel and cast iron

Abstract Ceramic pins of the AlN-CeO 2 -Si 3 N 4 system were tested in a pindashondashdisc tribometer against discs of tool steel and grey cast iron, at room temperature, without lubrication, in different conditions of humidity and sliding speed. Ceramic samples were selected on the basis of their mechanical properties (hardness and fracture toughness), and microstructural characteristics, namely porosity, volume of intergranular phase and nitrogen content of the glass phase. Water vapour increased the weight loss of the nitride by promoting the tribo-oxidation wear mode and by weakening the adhesion of debris to the ceramic surfaces. In dry air, the adhering wear debris provided protection to the sliding surfaces and the wear coefficients of the ceramic converged to similar values for tests with both iron alloys. For the ceramic/tool steel tribopairs, the ceramic surfaces become more protected as the amount of the intergranular glassy layer of the nitride is increased, as the glassy phase gives enhanced debris adhesion. Microcracking of the ceramic surface was the dominant wear mode and the volumic wear rate was found to be dependent on the inverse of hardness and fracture toughness. In humid environments, the effect of roughness of the grey cast iron worn surface surmounted the dependence of the wear rate on microstructural and mechanical properties of the nitride, which was found in the ceramic/steel tribopairs. The sliding speed has a strong effect on the wear behaviour. At low speeds, no protective plates of debris were detected on the worn surfaces. When the speed was increased above 0.5 ms −1 , the wear coefficient values fell down almost one order of magnitude. The wear coefficients of porous nitride materials of relative open porosity close to 20%, tested against cast iron, were unexpectedly lower than the values obtained for dense materials of same composition (K ≈ × 10 −15 Pa −1 for porous samples and K ≈ 1.5 × 10 −14 Pa −1 , for fully dense samples). SEM observations showed an extensive coating by the metallic rich debris, that performed a solid lubricant action.

Analysis of Hydrodynamic Journal Bearings Considering Lubricant Supply Conditions

A method of analysis of steadily loaded hydrodynamic journal bearings with a single axial groove (either on the load line or at 90° to the load line) or two diametrically opposed axial grooves is described. The method is based on Elrods cavitation algorithm (which ensures conservation of mass flow in both the full film and the cavitated regions) and is able to accommodate specified lubricant supply conditions, namely groove size and location and supply pressure. Special attention has been given to the determination of flowrate. The equation governing the distribution of pressure around the bearing has been solved numerically using a finite differences approximation and multi-grid techniques to accelerate the convergence of the solution. Performance predictions of the analysis are compared with published experimental data and with experimental measurements obtained in laboratory tests carried out by the authors. The data used cover all grooving arrangements studied.

Thermohydrodynamic modelling of journal bearings under varying load angle and negative groove flow rate

The performance of hydrodynamic journal bearings is affected by the conditions under which the lubricant is fed to the bearing gap. Axial grooves are often used and, depending on their location relatively to the load line, they might substantially interfere with the hydrodynamic pressure generation and the thermal behaviour of the bearing. However, many of the existing tools for predicting bearing performance are not able to suitably predict bearing behaviour under varying load angle given the oversimplified way under which they treat lubricant feeding conditions. The present work proposes a detailed thermohydrodynamic approach which realistically incorporates these conditions into the bearing analysis. Special care is put on the mass and energy-conserving models of the ruptured film region and on a detailed treatment of lubricant mixing within the vicinity of grooves. This includes the first full modelling of the effect of negative flow rate in a groove, a phenomenon originally described experimentally in detail by the authors in previous publications, and which happens for a broad range of load/groove angles. An extensive investigation on the influence of loading direction on the performance of twin groove journal bearings has been performed. This parameter is found to affect deeply all major performance parameters due to the interference of groove regions in the hydrodynamic pressure generation and in the flow rates at each groove.

Wear Mechanisms in Functionally Graded Aluminium Matrix Composites: Effect of the Presence of an Aqueous Solution

Functionally graded aluminium matrix composites reinforced with SiC particles are attractive materials for a broad range of engineering applications whenever a superior combination of surface and bulk mechanical properties is required. In general, these materials are developed for the production of high wear resistant components. Also, often this kind of mechanical part operates in the presence of aggressive environments, such as marine atmospheres. In this work, aluminium composites with functionally graded properties, obtained by centrifugal cast, are characterised by reciprocating pin-on-plate sliding wear tests against nodular cast iron. Three different volume fractions of SiC reinforcing particles in each functionally graded material were considered. Sliding experiments were performed with and without the presence of a lubricant (3% NaCl aqueous solution). In the case of the lubricated tests, electrochemical parameters (corrosion potential) were monitored during sliding. Friction values were in the order of 0.42 for unlubricated conditions, but varied between 0.22 and 0.37 when the aqueous solution was present. For all test conditions, relatively high wear rates (over 1×10-6 gm-1) were obtained, particularly for the cast iron pin. The volume fraction of SiC particles exerted a net effect on the tribological response of the composites, although conditioned by the presence or absence of the aqueous solution. The worn surface morphology of the composites indicated that the presence of the aqueous solution modifies the protective action promoted by the combined effect of the presence of reinforcing particles as load bearing elements and the formation of adherent iron-rich tribolayers. The evolution of the corrosion potential during the sliding action is in accordance to the degradation mechanisms proposed for these systems.

Effect of Functionally Graded Properties on the Tribological Behaviour of Aluminium-Matrix Composites

In this work, aluminium based matrix composites with functionally graded properties are tested against cast iron in a pin-on-disc tribometer. SiC particulate reinforced F3S-20S aluminium matrix composite (Duralcan) was melted and centrifugally cast in order to obtain a gradient regarding the ceramic particle area fraction and mean particle diameter. Three different cross sections of the functionally graded material were considered for tribological characterisation. Friction and wear tests were performed at room temperature, constant sliding speed (0.5 ms -1 ) and at 5 N of normal load. The morphological features of the sliding surfaces were analysed by SEM/EDS in order to understand the prevailing wear mechanisms. The wear coefficient was relatively low for both matting surfaces (in the order of 10 -6 mm 3 N -1 m -1 ), with the composites presenting the lowest wear values due to the combined effect of reinforcing particles as load bearing elements and the formation of protective adherent iron-rich tribolayers. A comparative analysis is established between the functionally graded properties of the aluminium based composites and the tribological response at different cross sections. Results suggests that there is a critical area fraction of SiC particles above which severe wear, attributed to lack in fatigue strength, is observed.

The role of nitrogen in the intergranular glass phase of Si3N4 on high temperature applications and wear

Abstract The hot hardness of Si 3 N 4 tool materials of the CeO 2 and CeO 2 AIN doping systems, oxidation in air from 900 to 1450 °C, and turning of tool steel with ceramic inserts of the same compositions were investigated to determine the effect of the N content of intergranular phase. Si/N grain boundary diffusion was found to be the main controlling mechanism at high temperature for densification, mechanical behavior and chemical degradation of these materials in air, the passivation oxidation rate of the CeO 2 AINSi 3 N 4 system being dependent on the atomic fraction of N of the intergranular phase, with lower values for the N-rich compositions.

Influence of Wear Properties on Fretting Fatigue Life of a CK45 Alloy and the Al7175 Alloy

The main objective of this work was to study the influence of the wear properties of two commercial alloys (CK45 and Al7175) on their fretting fatigue behavior. It is verified the effect of material local degradation by wear on a fatigue strength reduction factor, namely the stress concentration factor, and on the overall fretting fatigue life of these materials. The fretting fatigue phenomenon is a synergetic effect between wear and fatigue. It is dependent on both the fatigue and the wear properties of the materials. Material properties promoting an increase in wear resistance should enhance fretting fatigue life.