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.
Thermal analysis of air-cooled PEM fuel cells
Abstract Air-cooled proton exchange membrane fuel cells (PEMFCs), having combined air cooling and oxidant supply channels, offer significantly reduced bill of materials and system complexity compared to conventional, water-cooled fuel cells. Thermal management of air-cooled fuel cells is however a major challenge. In the present study, a 3D numerical thermal model is presented to analyze the heat transfer and predict the temperature distribution in air-cooled PEMFCs. Conservation equations of mass, momentum, species, and energy are solved in the oxidant channel, while energy equation is solved in the entire domain, including the membrane electrode assembly (MEA) and bipolar plates. The model is validated with experiments and can reasonably predict the maximum temperature and main temperature gradients in the stack. Large temperature variations are found between the cool incoming air flow and the hot bipolar plates and MEA, and in contrast to water-cooled fuel cells, significant temperature gradients are detected in the flow direction. Furthermore, the air velocity and in-plane thermal conductivity of the plate are found to play an important role in the thermal performance of the stack.
A study of the effect of chemical structure on friction and wear : Part I-Synthetic ester base fluids
The proper formulation of lubricants starts with an understanding of the performance of the individual base stocks, Additives respond to various base stocks differently depending on the chemistry of the base stock and can result in either synergistic or antagonistic effects. This paper studies the effect of structure for various ester base stocks using a four-ball wear test machine to measure friction and wear. The authors evaluate several esters based on differing chemical structures of the alcohol and acid moletles used to synthesize the ester, The alcohols include neopentyl glycol (NPG). trimethylolpropane (TMP), and pentaerythritol (PE). Acids vary in length of the molecular chain and comparisons include both branched and linear molecules, The researchers blend various additives in the base stocks to study the interaction with the base fluids. Wear tests occur in the boundary tubrication regime with significant chemical structure differences observed.