• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05a
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• pp.185-188
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• 2004

A diode structure of field emission lamps based upon carbon-nanotube is studied. The single-walled carbon nanotubes(SWNTs) were produced by arc discharge method. We made the 1-inch diode type flat lamp using CNTs. We applied anode voltage gradually to refine the field emission behavior of emitter in dynamic vacuum system to study the emission current. the brightness and efficiency, etc. The field emission properties was estimated by varying gaps between the cathode and anode, contents of the glass frit. The good luminous efficiency is showed in the gap $900{\mu}m$, $1200{\mu}m$ and contents of the proper glass frit. For the upper conditions, the luminous efficiencies were respectively 23.30, 11.12 1m/W.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1533-1538
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• 2008

The development of new material systems like Carbon Fiber Reinforced Polymer (CFRP) places ever higher demands on the techniques for non-destructive material characterisation. Image-producing eddy current methods also need to satisfy these demands. Eddy-current imaging of FRP is based on the anisotropic electrical properties of the material investigated. Significant differences in conductivity between carbon fibres, polymer matrix and integrated functional components can be found. The availability of high-resolution sensors enables access to the local distribution of the electromagnetic properties. The static and dynamic procedures for isolating influential characteristics, already in use in eddy-current technology, can now be supplemented by topographical images. The precondition for a successful implementation of the eddy-current procedure is a deeper understanding of the image-generating process which allows correct interpretation of the images obtained.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.649-652
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• 2005

It is reported that semi-solid forming process takes many advantages over the conventional forming process, such as long die lift, good mechanical properties and energy saves. Rheology material has a thixotropic, pseudo-plastic and shear-thinning characteristic. Therefore, general plastic or fluid dynamic analysis is not suitable for the behavior of rheology material. So it is difficult for a numerical simulation of the rheology process to be performed because complicated processes such as the filling to include the state of the free surface and solidification in the phase transformation must be considered. Moreover, it is important to predict the deformation behavior for optimization of net shape forging process with semi-solid materials and to control liquid segregation for mechanical properties of materials. In this study, so, molecular dynamics simulation was performed for the control of liquid segregation in compression experiment as a part of study on analysis of rheology forming process.

• Steel and Composite Structures
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• v.49 no.6
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• pp.633-643
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• 2023

In this study, the natural frequencies of Functional Graded Materials (FGM) plates are predicted using Artificial Neural Network (ANN). A model based on Third-order Shear Deformation Theory (TSDT) and FEM is used to train the ANN model. Different training methods are tested to simulate input and output dependency. As this is a parametric model, several architectures and optimization algorithms were tested. The proposed model allows us to minimize the CPU time to evaluate candidate material properties for FGM plate material selection and demonstrate their influence on dynamic behavior. Consequently, the time required for the FGM design process (candidate materials for material selection) and the geometric optimization of the FGM structure would remain reasonable. The ANN model can help industries to produce FGM plates with good mechanical properties of the selected materials. I addition, this model can be used to directly predict vibration behavior by testing a large number of FGM plates, representing all possible combinations of metals and ceramics in today's industry, without having to solve any eigenvalue problems.

• Computers and Concrete
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• v.21 no.6
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• pp.717-726
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• 2018

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that $SiO_2$ nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as $SiO_2$ nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of $SiO_2$ nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

• Computers and Concrete
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• v.24 no.2
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• pp.125-135
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• 2019

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that SiO2 nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as SiO2 nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of SiO2 nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.35-35
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• 2009

Capacitorless one transistor dynamic random access memory (1T-DRAM) cells were fabricated on the fully depleted strained-silicon-on-insulator (FD sSOI) and the effects of silicon back interface state on buried oxide (BOX) layer on the memory properties were evaluated. As a result, the fabricated 1T-DRAM cells showed superior electrical characteristics and a large sensing current margin (${\Delta}I_s$) between "1" state and "0" state. The back interface of SOI based capacitorless 1T-DRAM memory cell plays an important role on the memory performance. As the back interface properties were degraded by increase rapid thermal annealing (RTA) process, the performance of 1T-DRAM was also degraded. On the other hand, the properties of back interface and the performance of 1T-DRAM were considerably improved by post RTA annealing process at $450^{\circ}C$ for 30 min in a 2% $H_2/N_2$ ambient.

• Corrosion Science and Technology
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• v.7 no.3
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• pp.145-151
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• 2008

Material degradation such as high temperature oxidation of metallic material is a severe problem in energy generation systems or manufacturing industries. The metallic materials are oxidized to form oxide films in high temperature environments. The oxide films act as diffusion barriers of oxygen and metal ions and thereafter decrease oxidation rates of metals. The metal oxidation is, however, accelerated by mechanical fracture and spalling of the oxide films caused by thermal stresses by repetition of temperature change, vibration and by the impact of solid particles. It is therefore very important to investigate mechanical properties and adhesion of oxide films in high temperature environments, as well as the properties in a room temperature environment. The oxidation tests were conducted for Ni and Ni-Co alloy under high temperature corrosive environments. The hardness distributions against the indentation depth from the top surface were examined at room temperature. Dynamic indentation tests were performed on Ni oxide films formed on Ni surfaces at room and high temperature to observe fractures or cracks generated around impact craters. As a result, it was found that the mechanical property as hardness of the oxide films were different between Ni and Ni-Co alloy, and between room and high temperatures, and that the adhesion of Ni oxide films was relatively stronger than that of Co oxide films.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.22-32
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• 1998

Many of steel structures having little internal damping consist of stiffened plates. In case that viscoelastic materials are adhered to the stiffened plates for the reduction of structure-borne noise, their effects are varied by the adhered position and dynamic characteristics of the structures as well as their material properties and adhered amount. In this paper, sound reduction effects of viscoelastic materials partially adhered to the different positions of a stiffened steel plate have been investigated by the measurement of vibratory velocity and sound intensity. The results show that optimal adherent positions of viscoelastic materials to reduce sound radiation power are the loop areas of modes.

• Smart Structures and Systems
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• v.26 no.2
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• pp.185-193
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• 2020

Nonlinear vibration of sandwich plate with functionally graded material (FGM) core and carbon nano tubes reinforced (CNTs) nano-composite layers by considering temperature-dependent material properties are studied in this paper. Base on Classical plate theory (CPT), the governing partial differential equations of motion for sandwich plate are derived using Hamilton principle. The Galerkin procedure and multiple scales perturbation method are used to find relation between nonlinear frequency and amplitude of vibration response. The dynamic responses of the sandwich plate are also investigated in both time and frequency domains. Then, the effects of nonlinearity, excitation, power law index of FG core, volume fraction of carbon nanotube, the function of material variations of FG core, temperature changes, scale transformation parameter and damping factor on the frequency responses are investigated.