R Gnanamoorthy

Bearings in the electric vehicle drive motors experience stray currents and voltages, leading to local damage and an increase in noise and vibration. A method suggested to mitigate the electric current induced failures is to use an insulated coating, typically made of alumina on either the inner race or outer race. An ideal insulated coating can protect the bearings from damage due to extreme currents. The current research work is aimed to estimate the coating parameters, such as thickness, needed to minimize the flow of current inside the bearing parts. Numerical simulations are carried out to evaluate the insulation coating’s effectiveness in the bearing using commercial finite element software, and the results were validated with the analytical estimates. Porosity in the ceramic coatings plays an essential role in the flow of current through the bearings. The results will help determine an optimized coating thickness which will prevent premature failure of drive motor bearings due to electrical loads.

The proton exchange membrane fuel cells (PEMFCs) are clean and affordable alternative energy sources for next-generation mobility. Each cell comprises bipolar plates, gas diffusion layers, endplates, gaskets and a membrane. A fuel cell stack fixed to the mainframe experiences extreme vehicular vibrations due to road unevenness, acceleration, and braking. The vehicular vibrations will result in small relative displacements within the stack. The more recent designs employ metal foams as a flow distributor in the fuel cell, and the low amplitude displacements in the assembly may lead to fretting damage. This study is directed towards understanding the possible relative displacements between components due to vehicular vibrations through numerical simulation. A 3-D finite element model of PEMFC unit cell having the metal foam as flow distributors assembled using eight through-bolts was created and analyzed using the commercial software. The vehicular vibrations mimicked by giving a displacement boundary condition perpendicular to bolt pretension load at one end of the fuel cell while the nut surfaces fixed on the other end. The obtained equivalent stress and total deformations of each component are compared with conventional graphite bipolar plates fuel cell design. The maximum equivalent stress of 110 MPa is noticed in the conventional fuel cell, whereas 94 MPa is observed in the cell with metal foam as flow fields. The relative slippage of 10.4 µm is noticed at the gas diffusion layer (GDL)/metal foam’s interface close to the fixed end. A relative slippage of 3.48 µm is noticed at the aluminium plate/metal foam interface close to the displacement end.

The influence of temperature on the tribological performance of alloy 718 is studied in the present work. The alloy 718 samples were used in double aged condition for reciprocating wear test with a ball on flat configurations. The wear tests were conducted at two conditions viz: room temperature and 300 °C temperature. The testing temperature had a significant influence on the coefficient of friction (COF) and wear resistance of alloy 718. The alloy 718 sample, subjected to high-temperature testing environment had a lower COF and higher wear rate compared to samples tested at ambient temperature. The lower COF values of the alloy 718 samples subjected to high wear testing temperature conditions were attributed to the extent and presence of glaze layer formation, which is insignificant in the case of samples subjected to ambient temperature. The higher wear rate values of the alloy 718 samples subjected to high wear testing temperature conditions were attributed to the due to occurrence of tribo-chemical reactions at the contact zone of tribo-pair.

Oil jet peening is a surface modification process developed for the introduction of compressive residual stresses. In this process, a high-pressure oil jet impinges on the surface to be peened. Specimens made of AISI 1040 steel were peened at oil pressure of 50 MPa. Residual stresses induced on the oil jet peened specimen was in the order of -200 MPa. Standoff distance influenced the residual stress induced and also the erosion and surface roughness. Fully reversed cantilever bending tests conducted on the peened and unpeened conditions revealed the improved performance of the oil jet peened specimens.

Ti-6Al-4V alloy was subjected to surface mechanical attrition treatment (SMAT) by using SAE 52100 steel balls of 5 mm diameter for two treatment durations (30 and 60 min). SMAT resulted in the formation of nanostructured material on the surface and near surface regions, increased hardness, increased surface roughness and compressive residual stress on the surface. Treated samples exhibited lower tangential force coefficient (TFC) compared to untreated samples. Samples treated for 60 min exhibited higher grain refinement, higher hardness, lower surface roughness and higher TFC compared to the samples treated for 30 min. Fretting wear resistance of the samples treated for 30 min was higher than that of untreated samples and the samples treated for 60 min. Due to very high hardness and presumably reduced ductility, the fretting wear resistance of the samples treated for 60 min was lower than that of the untreated samples and samples treated for 30 min. © (2012) Trans Tech Publications.