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The valve train system synchronises the engine timing (inlet and exhaust) with the thermodynamics/combustion process. Thus, its optimal operation is vital for the health of the entire engine. The interplay between various forms of dynamics (e.g inertial, structural and impact/contact) and reactions due to loaded tribological conjunctions leads to a complex problem. The solution requires simplifications and assumptions based on careful analysis. The current chapter describes a modelling approach which integrates the fundamental aspects of valve train behaviour in a fast converging methodology.

This chapter considers some aspects of the developments in the past few decades arising from miniaturisation of many electromechanical systems. These mechanisms are progressively developed and used as microactuactors, switches and trigger devices, all of which have load-bearing conjunctions in the scale of minutiae. Consequently, there is a plethora of as-yet not fundamentally understood prevalent kinetics. The chapter describes the current knowledge about these interactions and uses this to predict the behaviour of some nanoscale conjunctions. It is found that overall, the predictions are in accord with observed phenomena in the case of microelectromechanical gears, but concern remains as to the fundamental and generic nature of the employed force laws.

This chapter deals with the fundamentals of contact mechanics and impact dynamics of ellipsoidal solids of revolution. It provides a brief review of Hertzian contact/impact dynamics with its underlying assumptions. It provides some examples of Hertzian contact/impact conditions for various contact geometries in rolling element bearings and cam-follower pairs. It also introduces the use of finite element analysis to study contact/impact problems in more detail. Other non-Hertzian type contact problems such as in non-conforming thin-layered solid pairs are studied by appropriate analytical approaches. A generic method decomposing pressure waves propagating into the bulk of solid contacting surfaces is also presented with generic results for both soft and hard-coated surfaces.

With miniaturisation of mechanisms and devices, load-bearing and transmitting conjunctions are progressively reducing in size. At the same time the gap size between contiguous solids is continually decreasing. These conjunctions are also subject to quite low loads. A whole new era in tribology has dawned which encompasses a wide area of interest from micro-electromechanical systems to data storage devices (ultra-smooth surfaces) to biological and bio-inspired systems, such as microfibres mimicking contacts of insects and geckos with very smooth surfaces. The field of study is broadly termed nano-tribology, but for biomimetics may be referred to as nano-biotribology. Relatively lightly loaded contacts also occur, for example in fairly rough elastomeric seals, prevalent in drug dispensing devices such as syringes and inhalers with low viscosity biocompatible compounds. Also, gels and cosmetic creams are applied with low load on fairly rough surfaces. Therefore, another new area of nano-tribology is emerging, which may be regarded as pharmaceutical tribology. In nearly all such conjunctions surface energy effects, adhesion, van der Waals interaction, electrostatic effect, meniscus action, hydration or solvation play more significant roles than the usual hydrodynamic viscous action as mechanisms of lubrication/tribology.

The paper provides some highlights in the developments of theories of lubrication and contact mechanics from early pioneering works of Reynolds and Hertz to the establishment of elastohydrodynamic phenomenon by Ertel and Grubin. Some historical discourse is made on the development of elastohydrodynamic theory in the past 6 decades, with particular attention paid to the contact of rolling element bearings. The steady miniaturisation of devices has led to progressively smaller contacts of individual features with lighter load share and diminishing gaps. The ultra-thin films are supported by interaction potentials that significantly deviate from bulk continuum behaviour of lubricating films, with insignificant contributions due to viscous–elastic nature of contacts. Using the same theme of rolling element contacts, the paper highlights the action of some of these dominant forces at close range.

For life cycle analysis of any component of a system realistic operating conditions under short or long transience are required. Therefore, the desired approach would be an integrated system approach, in which the behaviour tribological conjunctions should be incorporated. This approach necessarily includes many interacting physical phenomena, the integrated inclusion of which is referred to as a multi-physics framework. The framework comprises a hierarchical structure, in which the interacting phenomena take place across the physics of scale. These will usually include large rigid body motions such as crankshaft rotation, valve motion and piston primary translational motion in IC engines. It also encompasses structural vibration of elastic members, manifested by their compliance or modal behaviour, such as thermoelastic distortion of piston skirt (of the order of several tens of micrometer to tenths of millimeter), as well as contact deformation of contiguous solids and lubricant film formation in micro-scale. The paper shows that improved computational power and refined numerical techniques have paved the way for the simultaneous solutions of these interacting physics within one analysis. This approach can lead to very detailed, but time-consuming outcomes. Alternatively sufficient amount of detail may still be obtained with reduced modelling features with good degree of accuracy, and in accord with experimental observations. The paper primarily deals with the use of multi-physics approach in piston and valve train systems.

This paper presents a semi-analytical algorithm for the determination of the contact half width and surface pressure which results from both adhesive and non-adhesive contact problems involving functionally graded materials (FGM). The inhomogeneously elastic solid comprises a graded elastic coating whose shear modulus depends exponentially on the vertical coordinate and a homogeneously elastic substrate. The solid is assumed to be in a state of plane strain and thus a two-dimensional analysis is performed within this work. Using the work of Chidlow et al. (2011a) as a starting point, we derive a pair of integral equations which may be used to determine approximations to the contact pressure when either the surface deflection or the deflection gradient is known over the contact region. As these integral equations are non-singular, we use Galerkin's method to approximate the contact pressure and it is found that relatively small trial spaces allow accurate computation of the pressure. Information about the prescribed load is then used to formulate an iterative algorithm to determine the contact half width. A selection of numerical results are presented using this method and it is found that the solutions computed here compare favourably with those of other authors. A further investigation is then conducted into the solution of adhesive contact problems using the assumptions of Maugis (1992) and Johnson and Greenwood (2008) to inform the nature of the adhesive stresses outside of the contact. It is found that both JKR-like and DMT-like behaviour can be observed in contact problems involving FGMs.

This paper proposes a semi-analytical model for the two-dimensional contact problem involving a multi-layered elastic solid loaded normally and tangentially by a rigid punch. The solid is comprised of a homogeneous coating and substrate joined together by a graded elastic transition layer whose material properties exhibit an exponential dependence on the vertical coordinate. By applying the Fourier transform to the governing boundary value problem, we formulate analytic expressions for the stresses and displacements induced by the application of line forces acting both normally and tangentially at the origin. The superposition principle is then used to generalise these expressions to the case of distributed normal and tangential tractions acting on the solid surface. A pair of coupled integral equations are further derived for the parabolic stamp problem which are easily solved using collocation methods. The primary aim of this paper is to provide insight into the likely behaviour of graded materials under the combined effects of surface pressure and shear stress. In this study, the assumption of Coulomb friction is invoked and the effects of material gradation, coating/interlayer thickness and friction coefficient upon the contact footprint and sub-surface stress field are investigated in great detail. The results we obtain suggest that the thickness of the transition layer as well as the combined thickness of the coating and transition layer have a significant effect on the maximum sub-surface stress attained through contact. This indicates that small changes in the composition of the coating can lead to significant differences in material behaviour. We additionally find that an increase in the amount of friction present in the contact can cause dramatic changes in the pattern of the stress field and can give rise to a much larger maximum stress. This effect can be offset somewhat under certain conditions by changing the thickness of the transition layer. To the best of the authors belief, this work represents the first attempt made to characterise the effects of friction on the sub-surface stress field within a graded elastic material.