Dynamic instability of functionally graded material plates subjected to aero-thermo-mechanical loads

T. Prakash,M. Ganapathi 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.4

Here, the dynamic instability characteristics of aero-thermo-mechanically stressed functionally graded plates are investigated using finite element procedure. Temperature field is assumed to be a uniform distribution over the plate surface and varied in thickness direction only. Material properties are assumed to be temperature dependent and graded in the thickness direction according to simple power law distribution. For the numerical illustrations, silicon nitride/stainless steel is considered as functionally graded material. The aerodynamic pressure is evaluated based on first-order high Mach number approximation to the linear potential flow theory. The boundaries of the instability region are obtained using the principle of Bolotin’s method and are convenienty represented in the non-dimensional excitation frequency-load amplitude plane. The variation dynamic instability width is highlighted considering various parameters such as gradient index, temperature, aerodynamic and mechanical loads, thickness and aspect ratios, and boundary condition.

Unveiling the direct conversion X-ray sensing potential of Brucinium benzilate and N-acetylglcyine

Prakash T.,Karnan C.,Kanagathara N.,Karthieka R.R.,Ajith Kumar B.S.,Prabhaharan M. 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.6

The study investigates the dose-dependent direct X-ray sensing characteristics of Brucinium benzilate (BB) and Nacetylglycine (NAG) organic crystals. BB and NAG were prepared as a slurry and deposited as a thick film on a patterned metal electrode. The X-ray induced photocurrent response was examined for various exposure doses using an intraoral pulsed 70 keV X-ray machine connected to a source meter. Subsequently, the morphological properties and thickness of the thick films were analyzed using scanning electron microscopy (SEM). At a photon energy of 70 keV, the attenuation coefficient values for NAG and BB crystals were determined to be approximately 0.181 and 0.178 cm2/g, respectively. The X-ray stopping power of the crystals was measured using a suniray-2 X-ray imaging system. To evaluate the responsiveness of the sensors, the photocurrent sensitivity and noise equivalent dose rate (NED) were calculated for both thick films. The findings demonstrated a noteworthy capability of sensing low doses (mGy), thereby suggesting the potential application of these organic materials in X-ray sensor development.

Dynamic instability of functionally graded material plates subjected to aero-thermo-mechanical loads

Prakash, T.,Ganapathi, M. Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.4

Here, the dynamic instability characteristics of aero-thermo-mechanically stressed functionally graded plates are investigated using finite element procedure. Temperature field is assumed to be a uniform distribution over the plate surface and varied in thickness direction only. Material properties are assumed to be temperature dependent and graded in the thickness direction according to simple power law distribution. For the numerical illustrations, silicon nitride/stainless steel is considered as functionally graded material. The aerodynamic pressure is evaluated based on first-order high Mach number approximation to the linear potential flow theory. The boundaries of the instability region are obtained using the principle of Bolotin's method and are conveniently represented in the non-dimensional excitation frequency-load amplitude plane. The variation dynamic instability width is highlighted considering various parameters such as gradient index, temperature, aerodynamic and mechanical loads, thickness and aspect ratios, and boundary condition.

Application of Nanoparticles in Food Preservation and Food Processing

Prakash J.,Vignesh K.,Anusuya T.,Kalaivani T.,Ramachandran C.,Sudha Rani R.,RUBAB MOMNA,KHAN IMRAN,Fazle Elahi,DeogHwanOh,DevanandVenkatasubbu G. 한국식품위생안전성학회 2019 한국식품위생안전성학회지 Vol.34 No.4

This study focuses on the role of nanotechnology in the field of food industries. Bioactive components with antimicrobial activity against food pathogens are encapsulated into nanoparticles (NPs) to improve and extend their efficiency in food preservation. However, these NPs should be biocompatible and nontoxic for humans.Advancement in this field has resulted in the development of NPs for food packaging in some industries. The most commonly used group of NPs in the food industry is metal oxide. As metal oxide NPs such as zinc oxide and titanium dioxide exhibit antimicrobial activity in food materials, the NPs can be used for food preservation with enhanced functional properties. The application and effects of nanotechnology in correlation with the nutritional and sensory properties of foods were briefly discussed with a few insights into safety regulations on nano-based food formulation and preservation.

Review on Nanostructured Semiconductors for Dye Sensitized Solar Cells

T. Prakash 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.3

Nanostructured semiconductors with different morphologies are used widely in various applications in order to enhance their technological advancements compared with the bulk sample. This flourishing nanoscience field has enabled rapid developments that have created numerous opportunities for scienctific advancements with various devices. Considering large environmental impacts such as global warming, problems of nuclear waste storage and nuclear accidents, there is an urgent need for environmentally sustainable energy technologies such as solar cells and fuel cells. In the present paper, the role of nanostructured semiconductors in dyesensitized solar cells (DSSCs) is reviewed entensively. The review discusses the present developmental prospects of DSSCs and the problems associated with its layer materials and propose a method of overcoming these problems.

Crystallite Size Effect on Voltage Tunable Giant Dielectric Permittivity of Nanocrystalline CuO

T. Prakash,B.S. Murty,A.R. Kaskhedikar,P.D. Peshwe 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.1

The effect of crystallite size and applied DC bias voltage on dielectric permittivity of CuO was studied using impedance spectroscopy. The measurements were performed at room temperature in a wide frequency range of 1 Hz to 1 MHz under applied DC bias voltages from 0 to 3 V in the periodic increment of 0.2 V. The observed applied DC bias voltage effect on giant dielectric constant (ε' = 104) were analyzed with ‘grain boundary double Schottky potential barrier height model’. The percentage of tunability (T %) at the frequency 100 Hz is found to be 45.5% for the case of nanocrystalline CuO in contrast to 0% tunability in bulk CuO.

Effect of DC Bias on Dielectric Properties of Nanocrystalline CuAlO2

T. Prakash,S. Ramasamy,B.S. Murty 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.2

Grain boundary effect on the room temperature dielectric behavior in mechanically alloyed nanocrystalline CuAlO2 has been investigated using impedance spectroscopy under the applied DC bias voltages 0 V to 4.8 V in a periodic interval of 0.2 V. Analysis of impedance data confirms the existence of double Schottky potential barrier heights (Φb) between two adjacent grains (left and right side) with grain boundary and its influences in dielectric relaxation time (τ), dielectric constant (ε') and dielectric loss (tan δ) factor. Also, clear evidence on the suppression of Φb was demonstrated in the higher applied bias voltages with the parameter τ. At equilibrium state, τ is 0.63 ms and it was reduced to 0.13 ms after the 3.2 V applied DC bias. These observed DC bias voltage effects are obeying ‘brick layer model’ and also elucidates Φb is playing a crucial role in controlling dielectric properties of nanomaterials.

Effect of Applied Bias Voltage on Grain Boundary Potential Barrier Height (Φb) in Semiconductor Nanocrystals

T. Prakash,S. Ramasamy 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.2

Carrier transport through electrically active grain boundaries was studied under biased condition using impedance spectroscopy in the frequency range 1 Hz to 1 MHz for a model system nanocrystalline CuSCN. Since,grain boundaries of semiconductors contain defects which often trap charge carriers and cause to form a potential barrier around them also plays a crucial role in the electrical properties of nanomaterials. The influence of bias voltage on relaxation times of grain (τg) and grain boundary (τgb) for our wet chemically prepared nanocrystalline CuSCN was estimated at a periodic increment of 0.35 V from 0 V to −4.2 V. In the static case with no applied bias voltage the grain boundary potential barrier height was found to be 0.144 eV. During each periodic increment of applied bias voltages, both the grain and grain boundary relaxation times are decreases it gives direct and unambiguous evidence on the suppression of grain boundary potential barrier height (Φb).

Vibrations and thermal stability of functionally graded spherical caps

Prakash, T.,Singh, M.K.,Ganapathi, M. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.24 No.4

Here, the axisymmetric free flexural vibrations and thermal stability behaviors of functionally graded spherical caps are investigated employing a three-noded axisymmetric curved shell element based on field consistency approach. The formulation is based on first-order shear deformation theory and it includes the in-plane and rotary inertia effects. The material properties are graded in the thickness direction according to the power-law distribution in terms of volume fractions of the constituents of the material. The effective material properties are evaluated using homogenization method. A detailed numerical study is carried out to bring out the effects of shell geometries, power law index of functionally graded material and base radius-to-thickness on the vibrations and buckling characteristics of spherical shells.

Effect of tension stiffening on the behaviour of square RC column under torsion

T. Ghosh Mondal,S. Suriya Prakash 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.3

Presence of torsional loadings can significantly affect the flow of internal forces and deformation capacity of reinforced concrete (RC) columns. It increases the possibility of brittle shear failure leading to catastrophic collapse of structural members. This necessitates accurate prediction of the torsional behaviour of RC members for their safe design. However, a review of previously published studies indicates that the torsional behaviour of RC members has not been studied in as much depth as the behaviour under flexure and shear in spite of its frequent occurrence in bridge columns. Very few analytical models are available to predict the response of RC members under torsional loads. Softened truss model (STM) developed in the University of Houston is one of them, which is widely used for this purpose. The present study shows that STM prediction is not sufficiently accurate particularly in the post cracking region when compared to test results. An improved analytical model for RC square columns subjected to torsion with and without axial compression is developed. Since concrete is weak in tension, its contribution to torsional capacity of RC members was neglected in the original STM. The present investigation revealed that, disregard to tensilestrength of concrete is the main reason behind the discrepancies in the STM predictions. The existing STM is extended in this paper to include the effect of tension stiffening for better prediction of behaviour of square RC columns under torsion. Three different tension stiffening models comprising a linear, a quadratic and an exponential relationship have been considered in this study. The predictions of these models arevalidated through comparison with test data on local and global behaviour. It was observed that tension stiffening has significant influence on torsional behaviour of square RC members. The exponential and parabolic tension stiffening models were found to yield the most accurate predictions.