An averaged approach to asperity contact interactions for non-gaussian lubricated surfaces

An averaged approach to asperity contact interactions for non-gaussian lubricated surface

The influence of large scale surface roughness on flow factors

The influence of large scale surface roughness on flow factor

Asperity contact modelling for measured surfaces

The analysis of surface roughness in contacts forms a major part of tribology in almost all application. In any contact in which asperity interactions occur their load carrying capacity must be considered however the separation at which asperity interaction first occurs and the load carrying capacity at that separation are due to the stochastic nature of the surface roughness of the two surfaces. A model that can accurately and quickly provide an estimation of the load carrying capacity as a function of surface separation is required for the specific surfaces used in such conjunctions from implementing surface data. The paper presented provides details of a procedure for modeling asperity interactions of rough surfaces from measured data. The model is validated against a deterministic approach before being applied to measured surfaces

Effect of surface topography upon micro-impact dynamics

Often the effect of interactions at nano-scale determines the tribological performance of load bearing contacts. This is particularly the case for lightly loaded conjunctions where a plethora of short range kinetic interactions occur. It is also true of larger load bearing conjunctions where boundary interactions become dominant. At the diminutive scale of fairly smooth surface topography the cumulative discrete interactions give rise to the dominance of boundary effects rather than the bulk micro-scale phenomena, based on continuum mechanics. The integration of the manifold localised discrete interactions into a continuum is the pre-requisite to the understanding of characteristic boundary effects, which transcend the physical length scales and affect the key observed system attributes. These are energy efficiency and vibration refinement. This paper strives to present such an approach. It is shown that boundary and near boundary interactions can be adequately described by surface topographical measures, as well the thermodynamic conditions

Friction reduction in piston ring cylinder liner contact using textured surfaces

The automotive industry is increasingly required to meet tough emission standards such as Euro 6 which will be implemented in September 2014. Improved fuel efficiency is envisaged to be a direct contributory factor in reducing harmful emissions among other factors. Therefore, reduction of frictional losses in contact conjunctions is progressively an important issue. The compression ring-bore conjunction is responsible for consuming almost 5% of fuel energy. One intensely researched area is enhancement of tribological performance through surface texturing of contacting solid surfaces in order to retain micro-reservoirs of lubricant in regions which are prone to poor lubrication, for example in piston-cylinder system [1,2]. The current work comprises of a validated numerical model which has been created for analysis of surface texturing in the piston ring cylinder liner contact. The model employs a two dimensional solution of Reynolds equation as well as the inclusion of Greenwood and Tripp boundary friction model [3]. The model is used to investigate the underlying mechanism of lubrication with textured surfaces. The understanding of surface texturing developed during this study enables design and positioning of textured patterns in piston ring - cylinder liner contact

A numerical and experimental approach in understanding the performance of textured surfaces in sliding contacts

A numerical and experimental approach in understanding the performance of textured surfaces in sliding contact

Combined numerical and experimental investigation of the micro-hydrodynamics of chevron-based textured patterns influencing conjunctional friction of sliding contacts

Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions. Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved microwedge flow. The results show good agreement between numerical predictions and experimental measurements using a precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for given conditions, dependent on the intended application under laboratory conditions. The translation of the same into practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain. This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue than that obtained under ideal laboratory conditions

A time efficient thermal and hydrodynamic model for multi disc wet clutches

Wet Clutches are used in automotive powertrains to enable compact designs and efficient gear shifting. During the slip phase of engagement, significant flash temperatures arise at the friction disc to separator interface because of dissipative frictional losses. An important aspect of the design process is to ensure the interface temperature does not exceed the material temperature threshold at which accelerated wear behavior and/or thermal degradation occurs. During the early stages of a design process, it is advantageous to evaluate numerous system and component design iterations exposed to plethora of possible drive cycles. A simulation tool is needed which can determine the critical operational conditions the system must survive for performance and durability to be assured. This paper describes a time-efficient multiphysics model developed to predict clutch disc temperatures with a runtime in the order of minutes. It consists of a simplified 1D numerical model of heat conduction and storage within the clutch pack. A novel analytical interfacial model considers the effects of hydrodynamics and frictional heat generation at the sliding interface, including radial groove and squeeze flows, to calculate the heat transfer between the clutch surfaces and the fluid. The model has been validated against experiments. The assumptions made are demonstrated to be prudent as the presented model is shown to closely predict the disc and interface temperatures. Finally, the model is exercised to examine the effect of varying clutch plate number on temperature during an urban drive cycle

Automotive e-motor bearing electrical discharge phenomena: An experimental and numerical investigation

Electrically instigated bearing wear phenomena such as electrical discharge machining are a common cause of failure in electrical machines such as electrical vehicles. To reduce the prevalence of this failure mode an enhanced understanding of physical interactions that take place at the rotor bearings is required. This paper demonstrates a novel combined experimental and numerical methodology to enhance understanding of electrical discharge wear. The combined approach highlights the capability to produce controlled electrical failures and understand their electro-mechanical origins. The modelling approach provides a valuable tool to enable mitigative design of both bearings and lubricants.</p

Transient nanoscale tribofilm growth: analytical prediction and measurement

A new method for simultaneous in situ measurement and characterisation of molybdenum-based tribofilms is presented, based on lateral force microscopy. The simultaneity of measurements is crucial for a fundamental understanding of the tribochemical phenomena. A new analytical method is also presented, which combines a BET multi-layer adsorption/desorption model for boundary-active lubricant species-surface combination with the modified shear-promoted thermal activation Arrhenius equation. Therefore, the expounded method integrates the mechanical, physical and chemical aspects of the adsorption-bonding process as a detailed multi-step phenomenon. The method provides detailed explanations of the measured tribofilm growth, in a fundamental manner, not hitherto reported in the literature. Therefore, the combined experimental methodology and modelling approach provides a significant advance in the understanding of tribofilm formation. Furthermore, the developed model has the potential to explain the behaviour of many complex lubricant formulations and the resulting multi-species tribofilms, generated through synergistic and/or antagonistic constituent adsorption and shear-promoted activation