Presence Of Dielectric Medium Research Articles

A study on material removal rate of Cu-Al-Mn shape memory alloys in WEDM

Wire Electric discharge Machining (WEDM) is a non-traditional machining process and considered as an important machining method in case of manufacturing of tools, to produce dies and molds. The material is removed from the workpiece only when the spark is generated by electric pulse generators at short intervals between the wire electrode and the workpiece in the presence of dielectric medium. In recent years the use of copper based shape memory alloys is high because it plays a major role in manufacturing industries due to its low cost and ease of manufacturing. The present study is to determine machining parameters of Cu-Al-Mn(CAM) Shape Memory Alloys (SMA’s) in WEDM to achieve good machinability and to know the effect of input parameters on material removal rate (MRR). If the percentage of manganese is more in Cu-Al-Mn SMA’s then the ductility of that alloy will also be more. The rolled samples were subjected to a bend test to determine its shape memory effect (SME). The cylindrical specimens of size 100 mm (L) × 12 mm (D) were used to determine its machinability parameters in WEDM. The specimens exhibiting shape memory effect will be subject to machining in WEDM. The input parameters considered were Pulse off time (Toff), Pulse on time (Ton), and peak current (A) and the output parameter was Material Removal Rate (MRR). The Taguchi method has been selected to reduce the number of experiments to be carried out and to determine the machining parameters of Cu-Al-Mn SMA’s in WEDM. It was found that as Ton and peak current increases, the MRR also increase, but decreases with an increase in Toff.

Measuring the influence of discharge energy on white layer thickness in electrical discharge machining process

In electrical discharge machining, the performance measures are mainly influenced by the discharge energy developed during the machining process. Owing to its higher strength, stainless steel can be easily machined by electrical discharge machining under the presence of dielectric medium. Since the surface quality of high strength workpiece is influenced by white layer formation, it is very essential to analyze the effects of discharge energy distribution and process parameters on white layer formation in machining process. In the present study, an endeavor has been attempted to analyze the influence of a modified pulse energy generator system on performance measures. From the experimental results, it has been observed iso energy pulse generator has created thinner and more symmetrical white layer thickness on the machined workpiece owing to its ability to produce lower discharge energy pulses with nearly uniform energy distribution. Peak current has been observed as significant factor on determining white layer formation in the EDM process.

Cationic cyanine dyes: impact of symmetry-breaking on optical absorption and third-order polarizabilities

A systematic study is carried out to find the exact crossover point from symmetric to asymmetric configurations (symmetry-breaking) in a series of cationic cyanine dyes. Hybrid density functional with varying exact-exchange admixture has been used to understand the impact of HF exchange both in the gas phase and in the presence of dielectric medium. This approach provides a basis for understanding the electronic structure and photophysical properties of cyanine dyes. The crossover points predicted using this method are in good agreement with the experiment. The SAC-CI method is used to evaluate the lowest S0 → S1 transition energies in the gas phase. These transitions are preferably dominated by the promotion of an electron from HOMO → LUMO. The average static third-order polarizabilities, [γ], are obtained within the three-state model approximation. The analysis showed that for symmetric cyanines, the calculated [γ] values are large and negative, mainly originated from the large S0 → S1 transition moments and small S0 → S1 transition energies. For asymmetric cyanines, the [γ] values are positive and mainly originate from the large change in the ground and first excited state dipole moments. However, both configurations do not include contributions from the two-photon absorption. Further, the localization of charge densities in the HOMO and LUMO indicates that the symmetric and asymmetric cyanines act as promising materials for molecular wires and molecular switches which are fundamental building blocks for molecular electronic devices.

Scattering properties of metallic carbon nanotubes in the presence of dielectric media

Scattering properties of a metallic single-walled carbon nanotube that encapsulates a nanowire is studied within the framework of classical electrodynamics. The system is assumed to be illuminated by either a transverse magnetic (TM) or a transverse electric (TE) wave. Electronic excitations on the nanotube's surface are modeled as an infinitesimally thin cylindrical layer of the π-electrons, whose dynamics are described by means of the fluid hydrodynamic theory. The problem is two-dimensional and the solution to both TM and TE uniform plane waves by the system at normal incidences is presented.

Effects of the local environment on plasmonic coupling of metallic nanotube arrays

We have theoretically investigated the effect of the dielectric core and the dielectric embedding medium separately on the transmission spectra and plasmonic properties of coupled metallic nanotube arrays. It is found that the plasmonic properties of the nanotube arrays are strongly influenced by the presence of the dielectric which induces additional screening charges. We show that instead of one single photonic bandgap for the hollow nanotube arrays placed in air, an additional photonic bandgap arises from the presence of dielectric media in the transmission spectra. Based on the localized nature of the electric field distributions, we also clearly show the presence of the local plasmonic resonant modes that originate from multipolar plasmon polaritons in the cross section of these nanotube arrays, and that a large amount of opposing surface charges are built up in the gap between adjacent nanotubes.

English

Electrical discharge machining is considered as one of the main non-conventional machining processes used for manufacturing geometrically complex or hard material parts that are extremely difficult to machine by conventional machining processes. The process involves a controlled erosion of electrically conductive materials by the initiation of rapid and repetitive spark discharges between the tool and work piece in the presence of dielectric medium. The most important process parameters in EDM are material removal rate, electrode wear and surface roughness. The present work is focused to obtain a comprehensive study of surface roughness parameters (Ra, Rz, Rzmax & Rsm) of work materials at different currents in sink EDM process. The experiments were carried out on Al & Die steel components at different currents using cu as a common tool material. The surface roughness parameters under study included average roughness (Ra), average maximum height of the profile (Rz), maximum roughness depth (Rzmax) and the mean spacing of the asperities (Rsm). Machining time of each component and micro hardness of the work pieces before and after machining ware also obtained. In this work the Surface integrity was characterized by roughness parameters and micro hardness values. The results of this investigation revealed that the surface roughness parameters, machining time and micro hardness of work pieces were influenced by current and could be utilized to achieve desired quality of surface finishing thereby increasing the EDM efficiency.

Guided dispersion characteristics of metallic single-walled carbon nanotubes in the presence of dielectric media

Propagation of surface plasma waves in a metallic single-walled carbon nanotube that either is encapsulated in a solid metallic channel or encapsulates a metallic nanowire are studied within the framework of the classical electrodynamics. The linearized hydrodynamic theory is used to describe the electronic excitations on the nanotube’s surface, while the dielectric function of dielectric media is modeled on the basis of the Drude approximation. It is shown that for all wavelengths, only the transverse magnetic wave with no angular dependence can propagate in these systems and the dispersion relations of this mode are obtained.

Photon-graviphoton mixing in a dielectric medium

If photons are mixed with graviphotons, as suggested by supersymmetry and multidimensional unification schemes, then the presence of dielectric medium can affect in a significant way the mixing coefficient and the frequency splitting between the energy eigenstates. It is shown, in particular, that photon-graviphoton conversion processes may occur, and the possibility of their detection is discussed.

Reaction field effects on the electron distribution and chemical reactivity of molecules

We examine the effects of macroscopic solvation using the self-consistent reaction field technique. On the basis of ab initio, INDO SCF, and INDO/CI calculations we conclude that the introduction of a dielectric media seems to have little effect on calculated geometries. However, the charge distribution is effected: the presence of dielectric media allows greater local charge to develop. The dissociation of hydrogen fluoride is examined. With electron correlation, HF dissociates homolytically in the “gas” phase, but heterolytically in a “solvent” of dielectric constant of 80.