122 research outputs found

    An interactive software package for the investigation of hydrodynamic-slider bearing-lubrication

    Get PDF
    The temperature dependent character of viscosity complicates the numerical analysis of hydrodynamic slider bearings and the geometry of the flow cavity plays a significant role on the design and performance of the lubrication systems. In this paper, we represent a recent software tool, named as "HYDRO-LUB," capable of performing constant and variable viscosity runs in various pad styles with moving boundaries. Results of the demonstrating project are not only consistent with the available literature but also show the fast and reliable character of the package; which in return put forward the advantages of applying the program in the lubrication courses of mechanical engineering. © 2003 Wiley Periodicals, Inc

    Tribological optimisation of the internal combustion engine piston to bore conjunction through surface modification

    Get PDF
    Internal combustion (IC) engines used in road transport applications employ pistons to convert gas pressure into mechanical work. Frictional losses abound within IC engines, where only 38- 51% of available fuel energy results in useful mechanical work. Piston-bore and ring-bore conjunctions are fairly equally responsible for circa 30% of all engine friction - equivalent to 1.6% of the input fuel each. Therefore, reduction in piston assembly friction would have a direct impact on specific performance and / or fuel consumption. In motorsport, power outputs and duty cycles greatly exceed road applications. Consequently, these engines have a shorter useful life and a high premium is placed on measures which would increase the output power without further reducing engine life. Reduction of friction offers such an opportunity, which may be achieved by improved tribological design in terms of reduced contact area or enhanced lubrication or both. However, the developments in the motorsport sector are typically reactive due to a lack of relative performance or an ad-hoc reliance, based upon a limited number of actual engine tests in order to determine if any improvement can be achieved as the result of some predetermined action. A representative scientific model generally does not exist and as such, investigated parameters are often driven by the supply chain with the promise of improvement. In cylinder investigations are usually limited to bore surface finish, bore and piston geometrical form, piston skirt coatings and the lubricant employed. Of these investigated areas newly emerging surface coatings are arguably seen as predominate. This thesis highlights a scientific approach which has been developed to optimise piston-bore performance. Pre-existing methods of screening and benchmarking alterations have been retained such as engine testing. However, this has been placed in the context of validation of scientifically driven development. A multi-physics numerical model is developed, which combines piston inertial dynamics, as well as thermo-structural strains within a thermoelastohydrodynamic tribological framework. Experimental tests were performed to validate the findings of numerical models. These tests include film thickness measurement and incylinder friction measurement, as well as the numerically-indicated beneficial surface modifications. Experimental testing was performed on an in-house motored engine at Capricorn Automotive, a dynamometer mounted single-cylinder ‘fired’ engine at Loughborough University, as well as on other engines belonging to third party clients of Capricorn. The diversity of tests was to ascertain the generic nature of any findings. The multi-physics multi-scale combined numerical-experimental investigation is the main contribution of this thesis to knowledge. One major finding of the thesis is the significant role that bulk thermo-structural deformation makes on the contact conformity of piston skirt to cylinder liner contact, thus advising piston skirt design. Another key finding is the beneficial role of textured surfaces in the retention of reservoirs of lubricant, thus reducing friction

    Multi-physics for integrated analysis of flexible body dynamics with tribological conjunction in IC engines

    Get PDF
    Since the inception of internal combustion engine, there has been a continual strive to improve its efficiency and refinement. Until very recently, the developments in this regard have been largely based on an experiential basis, or backed by analytical investigations, confined to particular features of the engines. This has been due to lack of computational power, and analysis tools of an integrative nature. In recent years enhanced computing power has meant that complex models, chiefly based on multi-body dynamics could be developed, and further enhanced by the inclusion of component flexibility in the form of structural modes, obtained through finite element analysis. This approach has enabled study of dynamics/vibration response of engines in a more quantitative manner than hitherto possible. Structural integrity issues, as well as noise and vibration (refinement) can then be studied in an integrated manner. However, earlier models still lack sufficient detail to include, within the same analysis, issues related to efficiency, chiefly prediction of parasitic losses due to mechanical imbalance and friction. [Continues.

    Low Power Loss Gears: influence of design, materials and oil formulation

    Get PDF
    Estágio realizado na empresa CETRIB e orientado pelo Eng.º Luís MagalhãesTese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 201

    Modeling and simulation in tribology across scales: An overview

    Get PDF
    This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and micro-scales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions

    The Investigation of Hypervelocity Gouging

    Get PDF
    The slipper/rail interface of a hypervelocity rocket sled is subject to immense forces due to dynamic loads and impact of the slipper with the rail, and tremendous heating due to aerodynamic and frictional effects is produced at the interface. Under these severe loading conditions, the material in the rail will sometimes experience large non-linear deformations known as gouging. Hydrocodes are computational solvers designed to handle such non-linear, large deformation, high shock, hydrodynamic applications. The ability of the hydrocode CTH to handle gouge modeling is considered, as well as the manner in which temperature environments affect deformation and plastic strain. The solution techniques and material modeling are described. Using this numerical analysis tool, a study of how gouging occurs and tracing of its development at various impact velocities was undertaken, with emphasis on the effect of shock wave distribution. Modeling the intense aerodynamic and frictional heating near the contact region, the effects of temperature on gouge initiation were evaluated through the application of several thermal environment scenarios that have been developed. The effects of friction, slipper geometry, slipper velocity, and impact method have been considered. Finally, the differences between three-dimensional and two-dimensional analysis considering gouging have been evaluated

    Investigation of metallurgical coatings for automotive applications

    Get PDF
    Metallurgical coatings have been widely used in the automotive industry from component machining, engine daily running to body decoration due to their high hardness, wear resistance, corrosion resistance and low friction coefficient. With high demands in energy saving, weight reduction and limiting environmental impact, the use of new materials such as light Aluminum/magnesium alloys with high strength-weight ratio for engine block and advanced high-strength steel (AHSS) with better performance in crash energy management for die stamping, are increasing. However, challenges are emerging when these new materials are applied such as the wear of the relative soft light alloys and machining tools for hard AHSS. The protective metallurgical coatings are the best option to profit from these new materials\u27 advantages without altering largely in mass production equipments, machinery, tools and human labor. In this dissertation, a plasma electrolytic oxidation (PEO) coating processing on aluminum alloys was introduced in engine cylinder bores to resist wear and corrosion. The tribological behavior of the PEO coatings under boundary and starve lubrication conditions was studied experimentally and numerically for the first time. Experimental results of the PEO coating demonstrated prominent wear resistance and low friction, taking into account the extreme working conditions. The numerical elastohydrodynamic lubrication (EHL) and asperity contact based tribological study also showed a promising approach on designing low friction and high wear resistant PEO coatings. Other than the fabrication of the new coatings, a novel coating evaluation methodology, namely, inclined impact sliding tester was presented in the second part of this dissertation. This methodology has been developed and applied in testing and analyzing physical vapor deposition (PVD)/ chemical vapor deposition (CVD)/PEO coatings. Failure mechanisms of these common metallurgical hard coatings were systematically studied and summarized via the new testing methodology. Field tests based on the new coating characterization technique proved that this methodology is reliable, effective and economical

    Investigation and modelling of rubber friction

    Get PDF
    PhDThe friction between a rubber surface in contact with a rigid surface is still not fully understood. Unlike other materials, friction behaviour in rubber is significantly dependent upon a variety of parameters due to its viscoelastic nature. The aim of this work is to understand frictional phenomena occurring on different length scales of intrest. In the first part of this work the influence of an entirely geometric factor on friction is confirmed by FEA and is validated by experiments for the first time. Under certain conditions, it can increase the frictional force significantly above that expected from a consideration of the interfacial coefficient of friction alone. This term is thought likely to make a considerable contribution to frictional sliding applications such as a tyre on a road surface. In the second part of this work an instability, observed at the rubber surface during sliding, is investigated. Despite experimental research in the past, virtually no information has been published on the modelling of the so-called Schallamach waves using FEA techniques. This work models successive Schallamach waves, giving the opportunity to investigate the transition of individual waves throughout the area of contact, for the first time. The use of FEA allows for a detailed stress and strain analysis at the interface and thus gives new insights into the onset of buckling instabilities. So far, Schallamach waves have only been observed experimentally for optically smooth rubber surfaces, however, during this work, surface waves have been also noticed for rough rubber surfaces. Furthermore, the examination of the frequency dependence of Schallamach waves allows for the consideration of a relationship to stick-slip behaviour. The third part of this work investigates the influence of the rubber surface topography as well as the rigid slider geometry on rubber friction under a wide range of experimental conditions. It was noted that subtle changes of surface finish significantly change the resulting frictional force. The knowledge gained from this can help in the design and understanding of more complex frictional interfaces

    Numerical, analytical, experimental study of fluid dynamic forces in seals

    Get PDF
    NASA/Lewis Research Center is sponsoring a program for providing computer codes for analyzing and designing turbomachinery seals for future aerospace and engine systems. The program is made up of three principal components: (1) the development of advanced three dimensional (3-D) computational fluid dynamics codes, (2) the production of simpler two dimensional (2-D) industrial codes, and (3) the development of a knowledge based system (KBS) that contains an expert system to assist in seal selection and design. The first task has been to concentrate on cylindrical geometries with straight, tapered, and stepped bores. Improvements have been made by adoption of a colocated grid formulation, incorporation of higher order, time accurate schemes for transient analysis and high order discretization schemes for spatial derivatives. This report describes the mathematical formulations and presents a variety of 2-D results, including labyrinth and brush seal flows. Extensions of 3-D are presently in progress

    Machine Learning in Tribology

    Get PDF
    Tribology has been and continues to be one of the most relevant fields, being present in almost all aspects of our lives. The understanding of tribology provides us with solutions for future technical challenges. At the root of all advances made so far are multitudes of precise experiments and an increasing number of advanced computer simulations across different scales and multiple physical disciplines. Based upon this sound and data-rich foundation, advanced data handling, analysis and learning methods can be developed and employed to expand existing knowledge. Therefore, modern machine learning (ML) or artificial intelligence (AI) methods provide opportunities to explore the complex processes in tribological systems and to classify or quantify their behavior in an efficient or even real-time way. Thus, their potential also goes beyond purely academic aspects into actual industrial applications. To help pave the way, this article collection aimed to present the latest research on ML or AI approaches for solving tribology-related issues generating true added value beyond just buzzwords. In this sense, this Special Issue can support researchers in identifying initial selections and best practice solutions for ML in tribology
    corecore