Fretting contact study of Ti-6Al-4 V/graphite couples in a dry shaft/bearing contact with thrust: Influence of plasma nitriding of the titanium alloy

Fretting wear or wear by small displacements is defined when two contacting surfaces (first-bodies) are subjected to small amplitude reciprocating motion of micron order. This phenomenon is observed in many mechanical assemblies and it can significantly reduce the contact mechanisms life.This paper reports on the influence of nitriding treatment of the titanium alloy on the fretting tribological behaviour of graphite/Ti-6Al-4 V couple in a dry shaft/bearing contact with thrust. Two contact geometries are investigated: cylinder-in-cylinder and flat/flat. These fretting contacts are subjected to low-amplitude oscillatory movements, with temperature reaching 270 °C.The nitriding treatment for the Ti-6Al-4 V was carried out with a gas mixture N₂/H₂ at moderate temperature (700 °C) for 12 h. In these conditions, the maximum surface hardness was improved by a factor three.In this study, the mechanism of transfer and wear of graphite against Ti-6Al-4 V nitrided or not, have been studied with a scanning electron microscope, an optical microscope and an interferential microscope.The morphological and profile analysis performed on rubbing surfaces showed various aspects of wear: prints, craters, transfer ... and allowed to explain the location, development and origin of the degradation.The friction couples have showed differences between the tests realised with the shafts with or without nitriding and especially at an elevated temperature.We discuss the experimental results and we suggest several possibilities in order to understand some specific tribological behaviour: impact of the third body, of the abrasion, etc.     

A study on high ratio cup drawing by Maslennikov’s process

Deep drawing of sheet metals using Maslennikov’s technique has been analyzed by analytical and finite element simulation approaches. A new friction model based on local contact conditions has been used in the finite element (FE) simulations of the process. Compared to traditional Coulomb friction model, the results of FE simulations with the new friction model show good correlation with analytical calculations. The effects of key process parameters such as rubber ring thickness, ring inner diameter, die hole diameter, and die profile radius on the results have been investigated. The results showed that very deep cups without thinning in the side wall portion can be achieved with this process. Based on the results of FE analysis, it was found that the maximum drawing ratio can be achieved by adopting a combination of process parameters which correspond to points nearest to the fracture limit.     

Analysis of deep drawing of sheet metal using the Marform process

This paper deals with the deep drawing of metal cups using the Marform process. Using this technique, higher limiting drawing ratios can be obtained compared with the conventional deep drawing process. The analytical model of the process is presented initially, followed by the finite element simulations using ABAQUS software. A new friction model based on local contact conditions is presented and used in the finite element (FE) simulations of the process. Compared with traditional Coulomb friction model, the results of the FE simulations with the new friction model showed good correlation with experimental results. The results showed that the maximum thinning occurs at the punch profile portion, and by increasing the forming pressure, thinning of the sheet metal propagates from the punch profile portion to the side wall. At low forming pressures, wrinkles appear in the flange, whilst at higher pressures, fracture is the main defect of the Marform process.     

Synthesis and morphological control of europium doped cadmium sulphide nanocrystals

Europium doped cadmium sulphide (Cd(0.98)Eu(0.2)S) nanostructures were synthesised by chemical co-precipitation method using ethylene glycol (EG) and deionized water (Eu:CdS-1), and isopropyl alcohol (IPA) and deionized water (Eu:CdS-2) as mixed solvents. It has been found that the nanostructure of the europium doped CdS can be controlled by simply varying the mixed solvent system. Powder XRD pattern reveals the formation of hexagonal (wurtzite) and cubic (zinc blende) structure for Eu:CdS-1, and Eu:CdS-2, respectively. The crystallite size of the sample prepared using IPA and deionized water was measured to be 2.64 nm which is much smaller than that of the sample prepared using EG and deionized water as mixed solvent (3.65 nm). Morphology of the materials can also be changed from flower shaped crystals to paddy like structures by varying the mixed solvents. Band gap values of Eu3+ doped CdS nanocrystals synthesized from two different solvents were estimated using UV-reflectance spectra. The size and crystallinity of the samples were confirmed by HRTEM and SAED analysis. A significant change in the PL emission of the CdS nanocrystals was observed for the europium doped CdS which is mainly due to the presence of EU3+ ions which also play a significant role in the energy transfer process. It was also observed that the shift in the emission and efficiency depends on size and shape of the synthesised nanoparticles.     

Effect of helium xenon as working fluid on centrifugal compressor of power conversion unit of closed Brayton cycle power plant

Closed Brayton cycle (CBC) having single-shaft, centrifugal type compressor is considered as an efficient energy-conversion option associated for gas-cooled reactor (GCR) heat source. In terrestrial power plants and space power systems noble gases are considered as an efficient working fluid for most of the GCR's and CBC engines. The effectiveness of various noble gases as working fluid in closed cycle power plants for the power conversion units is of imperative concern. Although pure helium is relatively difficult to compress nonetheless it is measured as the best coolants for closed Brayton cycle power plants due to its better transport properties. Due to compression properties, its use resulted in the requirement of more mass, bigger size, higher cost and relatively more dynamic problems of rotatory machines in energy conversion system. The mixture of xenon with helium up to a molecular weight of <40 g/mol resulted in an increase of the coefficient of heat transfer as well as the significant increase in the loading of the compressor. Therefore, performance analysis is conducted for a novel design of helium xenon centrifugal compressor. The performance analysis is conducted with different molecular weight mixtures of helium xenon using similarity criteria. It is concluded that the use of helium xenon 40 g/mol is the optimum choice for space applications and 15 g/mol for closed Brayton cycle terrestrial power plants.     

The enhanced S cone syndrome: an analysis of receptoral and post-receptoral changes

The purpose of the study was to test the hypothesis that the retinae of patients with enhanced S cone syndrome (ESCS) have more S cones than the normal retina and these cones have replaced some of the L and M cones. Standard and spectral full-field electroretinograms, measurements of L, M, and S cone system sensitivities and S cone acuity were obtained from three patients with ESCS. The results were qualitatively consistent with the presence of more S cones and more S cone ganglion cells. To test this hypothesis further, a model of the receptoral and post-receptoral components of the S cone system was used in conjunction with psychophysical measurements of S cone system sensitivity under flashed and steady-state adaptation conditions. Within the context of the model, the data were consistent with an increase in the number of S cones and S - (L + M) ganglion cells and with a decrease in the total L + M cone input to each S - (L + M) ganglion cell.     

Resveratrol Interferes with an Early Step in the Fibrillization Pathway of Human Lysozyme and Modulates it towards Less‐Toxic,Off‐Pathway Aggregates

The effect of resveratrol, a polyphenol in red wine, on the amyloid fibril formation of human lysozyme (HuL) was investigated, towards elucidating the mechanism of resveratrol action and probing its role as a possible modulator of lysozyme aggregation and toxicity. By using a number of biophysical tools, resveratrol was observed to alter the fibrillization kinetics of HuL and inhibit its fibrillization by binding with weak to moderate affinity to the conformations populated at the early stages of the pathway with concomitant stabilization of these initial conformations. The marginal decrease in the lifetime of HuL in the presence of resveratrol by time‐resolved fluorescence measurements indicated the involvement of a static quenching mechanism in the interaction between HuL and resveratrol. Docking studies predicted the binding of resveratrol to aggregation‐prone regions in HuL, and structure and activity analyses demonstrated the retention of much of the α‐helical structure and activity of HuL in the presence of resveratrol. Resveratrol modulated the fibrillization pathway towards less‐hydrophobic, less‐toxic, off‐pathway aggregates. These results demonstrate that binding of resveratrol to HuL could protect against the formation of pathogenic, cytotoxic aggregates formed in amyloidogenic disorders, such as systemic amyloidosis; thus suggesting its potential as a plausible therapeutic agent against lysozyme amyloidosis.     

Tuned vibration absorber for suppression of hand-arm vibration in electric grass trimmer

Prolonged use of electric grass trimmer exposes the user to the risk of hand-arm vibration syndrome. A simple approach for the suppression of hand-arm vibration in electric grass trimmer is presented. The proposed system is a tuned vibration absorber (TVA). Modal analysis and operating deflection shape analysis of the electric grass trimmer were carried out and a TVA was designed and fabricated for testing. The results indicated that minimum vibration level was related to the position of the TVA on the shaft of electric grass trimmer. The TVA was found to have best performance with 95% reduction on the acceleration level at position 0.025L. The results from modal analysis and operating deflection shape revealed that the presence of TVA has successfully reduced the large deformations of the handle where the node was shifted nearer to the handle location. The effect of TVA was also evaluated during field test involving grass trimming operation and subjective rating. The results indicated that average reduction of frequency-weighted rms acceleration in the Z_h- axis was 84% and 72% in X_h- axis for the cutting operation. For the no cutting operation, the reduction is 82% in Z_h- axis and 67% in X_h- axis. The presence of TVA in the electric grass trimmer has amplified the vibration level in Y_h- axis by 19% (no cutting) and 21% (cutting). From the field test, subjective rating of vibration perception consistently rate better for controlled electric grass trimmer.

Relevance to industry

The tuned vibration absorber when installed to the electric grass trimmer attenuated the vibration total value by 67%. This significantly reduces the risk of hand-arm vibration syndrome.     

Quantifying the surface roughness effect in microindentation using a proportional specimen resistance model

The influence of the surface roughness on the indentation size effect in microindentation was examined using the proportional specimen resistance model. Stainless steel, aluminium, and copper surfaces were polished to different levels of roughness and subjected to microindentation. The results showed that the indentation size effect increases with increasing surface roughness, according to the proportional specimen resistance model. A normalized hardness equation H/H ₀ = (c ₀ + c ₁ R _a)/(a ₂ d) + 1 was established, and the value of c ₁ can be used to quantify the effect of surface roughness on the severity of the indentation size effect; this value was found to be highest for stainless steel, followed by copper and aluminium.     

Three dimensional numerical investigations for the effects of gas diffusion layer on PEM fuel cell performance

Gas diffusion layer (GDL) is an important component of a proton exchange membrane fuel cell (PEMFC) to take part in the interplay of the transport of different species. It has been found that the performance of a PEMFC depends upon the morphology of the GDL. The performance of PEM fuel cell varies with different porosity and thickness of the GDL. Hence, a three dimensional model is simulated to find out the effects of porosity and thickness of GDL on PEMFC performance using a commercial code CFD-ACE+. It was observed that high porosity gave high current density by allowing more reactants to reach the reaction site. Similarly greater thickness of the GDL gives reactant species to increase the consumption rate at the GDL/catalyst layer interface. The simulation results showed that the connection of bipolar plate with the GDL played an important role for reducing the amount of reactants to reach the catalyst layer especially under the land area of the bipolar plate. However, this effect seems to decrease with an increase of overall porosity and the thickness of the GDL.