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.

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.

The relative slippage between the open-cell metal foam flow fields and other parts in a fuel cell due to vehicular and flow-induced vibrations causes fretting. The material degradation due to fretting in nickel struts contaminate the stack and is investigated using simulated experiments. The as-formed strut surfaces are rough and increases the material loss during fretting. The total wear volume associated with a single contact in 22,000 cycles is 4.66 E−04 mm3. The contamination in the stack is estimated assuming a dodecahedron unit cell geometry and neglecting the fretting corrosion. About 47 g of debris is expected to be generated when an 8 ppi nickel foam flow fields used in a 50-cell stack for 8700 hours of operation. In addition, the generated flake shaped debris (<10 μm) can obstruct the flow of gases by clogging the gas diffusion layer. The proposed contamination estimation methodology will aid in performance prediction during service.

Additive Manufacturing (AM) represents a sustainable means of production, reducing the need for energy and resources and thus creating eco-friendly products. Homogeneous composites based on metal, polymer, and ceramic are currently used to meet the requirements of the end product. The current investigation attempts to identify functional needs and selective reinforcing with appropriate materials. The effectiveness of heat dissipation, one of the prime requirements in many applications, in metal-integrated polymer systems is assessed using simple representative samples. Representative parts are constructed using material extrusion processing with biodegradable Polylactic Acid (PLA) parts. Given its superior thermal conductivity for selective reinforcement, aluminium (Al) is chosen as the secondary material. The dimensional accuracy of the printed parts is fine-tuned using the different layer parameters to ensure the required interface clearances. A constant heat supply is provided thus to understand the influence of metal reinforcement in interaction with the polymer at the interface. The temperature is measured through the volume to record the heat conduction and dissipation. The metal-polymer sample with the interference fit is found to have the best heat dissipation compared to other alternative geometries. Either an insulating void or the absence of metal-polymer contact reduces the heat dissipation efficiency.

Sustainability and environmental concerns lead to the development of natural fiber-based eco-friendly materials. Coconut fiber, known as coir fiber, is the natural fiber extracted from coconut husk which mostly goes as agricultural waste. Coir fiber can replace synthetic fibers in many applications provided their merits and limitations are well understood. Low density, good sound absorptivity, high strength, and less health-hazardous properties make coir fiber suitable for a variety of applications. The porous coir fibers are treated with low concentrations of alkali (NaOH) solutions to alter their physical and mechanical properties based on the functional requirement. Alkali treatment results in a reduction in diameter and an increase in surface roughness. Fiber friction is a crucial parameter for developing fiber-based products which are not reported. This research aims to study the frictional behavior of single coir fiber. A novel experimental device based on the capstan friction testing apparatus is developed following the ASTM D3412 standard to investigate the friction coefficient of single fibers. The friction coefficient of alkali-treated and untreated coir fibers is measured by rubbing the surfaces of fibers against a counter-surface rotating cylinder made of polyamide. The effect of treatment on the friction and damage of fiber due to sliding against the polymeric surfaces is discussed.

The world is looking for alternate green, sustainable, eco-friendly and recyclable materials for synthetic materials in various applications. Green and economic composites can be manufactured using various types of lignocellulosic fibres. Coir fibres are one of the promising candidates due to their good mechanical and physical properties. The interfacial bonding between the fibre and polymer matrix restricts its applications and attempts are made to improve bonding using different surface treatments. The effect of alkaline treatment of coir fibre on the interfacial bonding between fibres and polylactic acid (PLA) matrix is analysed by a single fibre pull-out test in the current investigations. The fibres were alkaline treated with 5% NaOH aqueous solution for 48 h at room temperature. The alkaline treatment removes the surface impurities such as dirt particles, wax and a fraction of the lignin content from the micro pits present on the surface of the fibre, which makes the fibre surface rough and allows the mechanical interlocking to the polymer matrix. For the single fibre pull-out test, coir fibre was kept in between two additive-manufactured (AM) thin PLA sheets and compressed at 80 °C. The pull-out test was performed on the alkaline treated and untreated coir fibre using a universal testing machine. The alkaline treated fibre shows higher interfacial shear strength (IFSS) as compared to untreated fibres, which signifies the increase in the interfacial bonding and mechanical interlocking of fibre and matrix.

In the present study, the effect of thermal oxidation (TO) treatment duration on the fretting wear behavior of Ti6Al4V alloy in Ringer's solution was investigated. The treatment was carried out on Ti6Al4V coupons at 650 °C for different treatment durations of 16 h, 24 h, and 48 h in air. Fretting wear tests were carried out in Ringer's solution on TO-treated and untreated coupons using a ball-on-flat contact configuration with the following test parameters: displacement amplitude of 50 ± 5 μm, a normal load of 0.98 N, frequency of 5 Hz, counter body of alumina ball of 10 mm diameter. TiO2 layer formed due to TO treatment has been found to influence friction coefficient and the fretting wear resistance. TO treatment for 48 h resulted in about 80% reduction in wear rate compared to that of the untreated coupons.

Industries are endeavoring to use the low-density materials for load bearing applications to increase the efficiency of the machines. Ease of manufacturing and distinctive properties of short fiber polymer composites make it suitable for sprocket application. In service, sprockets are subjected to wear due to elongation in chain length. According to standards the permissible elongation of chain in service is 2 to 3% of the initial length. To investigate the effect of elongation in chain, the interaction between standard sprocket, and, standard chain (0%) and elongated chain (2%) is simulated under 2D planar conditions. ABAQUS is used to estimate the contact behavior of the sprocket interacting with the rollers of the chain under dynamic conditions. To estimate the contact behavior, angle between the first engaged and last engaged roller on the sprocket is divided in to 12 segments in the interval of 20°. The significant increase in the peak contact pressure of 23% and nearly 1.7 times increase in sliding distance is observed as the sprocket engages the roller of elongated chain. Further, an abrupt change in contact pressure is observed among the engaged rollers of 2% elongated chain.

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.