Effect of fluid inertia force on thermal elastohydrodynamic lubrication of elliptic contact

A non-Newtonian thermal elastohydrodynamic lubrication (TEHL) model for the elliptic contact is established, into which the inertia forces of the lubricant is incorporated. In doing so, the film pressure and film temperature are solved using the associated equations. Meanwhile, the elastic deformation is calculated with the discrete convolution and fast Fourier transform (DC-FFT) method. A film thickness experiment is conducted to validate the TEHL model considering the inertia forces. Further, effects of the inertia forces on the TEHL performances are studied at different operation conditions. The results show that when the inertia forces are considered, the central and minimum film thicknesses increase and film temperature near the inlet increases obviously. Moreover, the inertial solution of the central film thickness is closer to the experimental result compared with its inertialess value.

Numerical algorithm for predicting wheel flange wear in trams – Validation in a curved track

In tram operations, flange wear is predominant due to the low-radius curves and inappropriate technical conditions of the infrastructure; hence, investigations should be focused on the interaction between the wheel flange and the rail gauge corner. Moreover, the calculation methods based on the Hertzian model (elliptic contact patch) provide less accurate results due to the contact occurrence in the wheel flange region. This paper presents a methodology of a finite element method to predict the tram wheel wear in complex motions. The new procedure is based on the Abaqus software and several other sub-procedures written in Python and Fortran. Multibody simulations were used to determine the wheel–rail alignment. In this method, accuracy was chosen at the expense of the computational effort. The main steps are: preparation of models and ride scenarios, multibody simulation for calculating the wheel–rail alignment for different track scenarios and multiple runs of finite element method analysis to determine the wear magnitude. The proposed methodology presents a good agreement with the measurements and can be considered as guidelines for a proper configuration of the flange-designing experimental setup where the influence of the technical conditions of the infrastructure should be introduced adequately.

Elastic Contact Between a Geometrically Anisotropic Bisinusoidal Surface and a Rigid Base

In the current study, a semi-analytical model for contact between a homogeneous, isotropic, linear elastic half-space with a geometrically anisotropic (wavelengths are different in the two principal directions) bisinusoidal surface on the boundary and a rigid base is developed. Two asymptotic loads to area relations for early and almost complete contact are derived. The Hertz elliptic contact theory is applied to approximate the load to area relation in the early contact. The noncontact regions occur in the almost complete contact are treated as mode-I cracks. Since those cracks are in compression, an approximate relation between the load and noncontact area can be obtained by setting the corresponding stress intensity factor (SIF) to zero. These two asymptotic solutions are validated by two different numerical models, namely, the fast Fourier transform (FFT) model and the finite element (FE) model. A piecewise equation is fit to the numerical solutions to bridge these two asymptotic solutions.

Influence of Two-Sided Surface Waviness on the EHL Behavior of Rolling/Sliding Point Contacts Under Thermal and Non-Newtonian Conditions

The influence of the transversely and/or longitudinally oriented surface waviness on the lubricating behavior in the rolling/sliding elliptic contact composed of two steel bodies and lubricated with a non-Newtonian lubricant was investigated theoretically with full numerical solution of the thermal elastohydrodynamic lubrication. The entrainment velocity was assumed to be along the minor axis of the Hertzian contact ellipse. The waviness of each surface was given by a sinusoidal function. The non-Newtonian flow of the lubricant was described by the Eyring model with a constant Eyring shear stress at the ambient pressure and temperature. The velocity of the faster surface was assumed to be four times as that of the slower surface in order not only to highlight the thermal and non-Newtonian effects, but also to ensure a cyclic solution when both surfaces were with transversely oriented waviness. Starting from a quasisteady solution, the cyclic time-dependent solution was achieved numerically time step by time step. The results show that the thermal and non-Newtonian effects can be enlarged significantly by the surface waviness, and the worst configuration of the surface topography is that both surfaces are with longitudinal waviness.

An Elliptical Microcontact Model Considering Elastic, Elastoplastic, and Plastic Deformation

This study developed an elastic-plastic microcontact model that considers the elliptical contact of surface asperities. In the elastoplastic regime, the relations of the mean contact pressure and contact area of asperity to its contact interference are modeled considering the continuity and smoothness of variables across different modes of deformation. Results obtained from this model are compared with other existing models such as that calculated by the GW, CEB, Zhao and Horng models. The elliptic contact model and circular contact model can deviate considerably in regard to the separation and real area of contact.