Interfacial Mechanics Analysis of a Brittle Coating–Ductile Substrate System Involved in Thermoelastic Contact
In this paper, interfacial stress analysis for a brittle coating/ductile substrate system, which is involved in a sliding contact with a rigid ball, is presented. By combining interface mechanics theory and the image point method, stress and displacement responses within a coated material for normal load, tangential load, and thermal load are obtained; further, the Green’s functions are established. The effects of coating thickness, friction coefficient, and a coating’s thermoelastic properties on the interfacial shear stress, τxz, and transverse stress, σxx, distributions are discussed in detail. A phenomenon, where interfacial shear stress tends to be relieved by frictional heating, is found in the case of a coating material’s thermal expansion coefficient being less than a substrate material’s thermal expansion coefficient. Additionally, numerical results show that distribution of interfacial stress can be altered and, therefore, interfacial damage can be modified by adjusting a coating’s structural parameters and thermoelastic properties.
A two-dimensional contact model between a multilayered solid and a rigid cylinder
Abstract Multilayer coatings are often reported in the papers on surface engineering and have been proved to be able to enhance the toughness, anti-wear and bonding strength, while an understanding of their mechanical behavior is essential to their optimal design and tribological application. In this paper, a two-dimensional contact model of a multilayered solid in line contact with a rigid cylinder is developed based on a semi-analytical method. The frequency response functions, which are essential to producing the influence coefficients of the displacements and stresses components in the contact model with a conversion method based on the fast Fourier transform, are obtained by solving a system of linear equations concerning the unknown constants in the elastic field general solution of layered materials with a numerical method. The present model is validated by comparisons of the contact pressure and von Mises stress between the solutions of the present model and those of the Hertz theory and the finite element contact model. The effect of the elasticity modulus changing mode as well as the layer number of the multilayered solid is further studied by utilizing the present model.
Numerical investigation of the impact of gas and cooling flow configurations on current and water distributions in a polymer membrane fuel cell through a pseudo-two-dimensional diphasic model
For optimal performances, proton exchange membrane fuel cells require fine water and thermal management. Accurate modelling of the physical phenomena occurring in the fuel cell is a key issue to improve fuel cell technology. Here, an analytic steady state diphasic 2D model of heat and mass transfer is presented. Through this model, the aim of this work is to study the influence of local events on the global performances of a fuel cell. A part of the complete model is a microscopic representation of the coupling between water transport and charge transfers in the electrodes. The thickness of the liquid layer around the reactive agglomerates is deduced from the saturation. The evolution of the quantity of water within the catalyst layer is monitored and its influence on the global performances of the cell is investigated. In gas diffusion layers (GDLs), liquid and vapour water transport through are computed regarding the temperature. The flow direction of cooling water modifies the current density distribution along the cell. The impact of the direction of air and hydrogen feeding channels are investigated. It can modify greatly the fuel cell mean current density and the net water transport coefficient. The counter-flow mode was preferable. Likewise, thanks to a better membrane hydration, it results in independent performances regarding the hydrogen inlet relative humidity or stoichiometry.