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.

Fretting wear resistance of uncoated and surface modified biomedical titanium alloys (Ti-6Al-7Nb) in air and Ringer fluid has been investigated in the present work. Laser nitrided specimen has shown superior performance with minimum surface damage and wear rate (<0.1 × 10-6 mm3/Nm) despite high friction coefficient in air (0.6) compared to uncoated and plasma nitrided (>12 × 10-6 mm3/Nm) specimens. This is due to presence of TiN dendrites (60-80%) in the laser nitrided layer. Plasma nitrided surface is relatively softer and hence wear rates and surface damage are comparable with uncoated alloys. Friction coefficient is high for uncoated (0.8) and plasma nitrided alloys (0.6) in air as well as Ringer fluid. Fretting induced electrochemical dissolution is responsible for higher wear rates in uncoated and plasma nitrided specimens. The fretting damage resistance is primarily governed by relative hardness and modified layer thickness of the mating components. © 2006 Elsevier B.V. All rights reserved.

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.

Powder metallurgy gears are becoming popular in the drives in many fields for power transmission. In order to expand the scope of PM gears to commercial applications, their worthiness has to be proved by thorough testing. To test the P/M gears in the laboratory, an absorption type test rig has been designed and fabricated. Various facilities available in the test rig to evaluate the P/M gears and the monitoring techniques incorporated in testing are discussed in the paper.

In any proton-exchange membrane fuel cell, the bipolar plates grab attention because of the high production cost and heavyweight. Hence, the open-cell nickel foams are considered as an alternative to these grooved plates. The reliability of the metallic foams used as flow distributors and gas diffusion layers plays a vital role in the fuel cell's overall performance. Fretting wear damage of the metal foam at strut/strut interface and strut/supporting frame interface due to the vehicular vibrations and pressurized fuel flow is expected to affect the performance and is investigated. This paper discusses the fretting wear behaviour of nickel foam strut that constitutes open-cell nickel foam based on laboratory tests. The experiments are performed by using two different contact configurations: steel ball on wrought nickel flat and nickel strut on wrought nickel flat. The test results reveal the fretting friction coefficient's dependence on the normal load, surface roughness and contact geometry. Although the nickel strut versus nickel flat fretting wear tests showed a low coefficient of friction, severe damages were observed on the nickel struts’ worn surfaces compared to the wrought nickel flat. Scanning electron microscope images of worn scars on nickel foam struts indicate the presence of shallow grooves, craters, micro-cracks and delamination craters at higher loads.

Polyamide 66/hectorite nanocomposites exhibit superior mechanical properties compared with pure polymers and are promising for structural applications. X-ray diffraction results revealed reduced degree of exfoliation with increase in organoclay content. Flexural fatigue characteristics of polyamide 66/hectorite nanocomposites containing different quantities of clay content were investigated, under deflection control mode, using a custom built flexural fatigue test rig. Addition of organoclay improved the moduli of the material. An enhanced resistance to cyclic softening was noticed at high temperatures with the incorporation of organoclay. Nanocomposite samples exhibited a significant improvement in fatigue life compared with pure polymers; however, the degree of enhancement is governed by the nanostructure of organoclay in polymer matrix. The fatigue life of nanocomposite samples is strongly affected by specimen temperature and induced stress. Macroscopic fracture surfaces changed from flat featureless structure to a highly perturbed structure with increase in organoclay content. © 2010 Society of Plastics Engineers.

Introduction of compressive residual stress on the surface of dynamically loaded structural members improves the fatigue life. Oil jet peening is a new surface modification technique that can be potentially applied to introduce compressive residual stresses. Effect of oil jet peening on the surface modification and fatigue behavior of medium carbon steel, AISI 1040, is reported. The compressive residual stress on the surface of oil jet peened specimen was in the order of 332 MPa and the depth of compressive stress induced was about 50 μm. The surface hardness increased due to the oil jet peening. Oil jet peening improved the fatigue strength under cantilever-bending conditions to about 19% compared to unpeened specimens. © 2006 Elsevier B.V. All rights reserved.

Rolling element bearings experience fretting wear type of failures due to small relative oscillatory motion existing between races and rolling elements of the bearing. Small oscillatory motion between contacting surfaces that occur due to overall machine or system vibration and unexpected loads in service causes accumulation of wear debris in the contact zone and accelerate the wear process. A fretting wear test rig is designed and developed in the laboratory for understanding the fretting wear behavior of bearing materials. The test rig is designed for testing at slip amplitudes ranging from 20 to 200 μm and test frequencies ranging from 1 to 30 Hz. Preliminary studies for understanding the fretting wear characteristics were conducted on hardened and tempered bearing steel, En31 and widely employed hardened and tempered structural steel, En24 at various normal loads. Coefficient of friction during fretting tests was high during the initial stages of fretting tests and reached a steady state. The coefficient of friction depends on the normal load. Wear scar morphology reveals the nature of contact exhibited by the fretting contacts. © 2004 Elsevier Ltd. All rights reserved.

Due to continual improvements of the powder material processing, it is possible for powder metal alloys to compete even in some of the most demanding applications. The main lure of powder metallurgy (PM) components amongst the several challenging mass production methods plays an imperative role, as saving material, energy and also provides good fatigue properties, which are equally good and substitute for the conventional methods. The investigation on the lubricated rolling-sliding contact fatigue damage mechanisms in sintered and hardened steel (FLC 4608-110HT) containing combination of closed and interconnected pores has been carried out. Rolling-sliding contact conditions are simulated in twin disc type experimental set up for various contact pressure and slide/roll ratio. The damaged surface of sintered and hardened steel is examined under image analyzer for different sliding conditions. It is observed that the peel of material and surface crack opening is seen for the higher slide/roll ratio. Wear debris analysis is also carried out by dual-ferrograph analyzer for sintered and wrought steels for comparison study. The characteristics of wear morphology and the size, shape and concentration of worn particles are also analysed for different sliding contact conditions. © 2006 Elsevier B.V. All rights reserved.

This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples. © 2012 Copyright Taylor and Francis Group, LLC.