• Structural Engineering and Mechanics
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• 제74권5호
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• pp.611-633
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• 2020

In this paper, a comprehensive review of nanostructures that exhibit piezoelectric behavior on all mechanical, buckling, vibrational, thermal and electrical properties is presented. It is firstly explained vast application of materials with their piezoelectric property and also introduction of other properties. Initially, more application of material which have piezoelectric property is introduced. Zinc oxide (ZnO), boron nitride (BN) and gallium nitride (GaN) respectively, are more application of piezoelectric materials. The nonlocal elasticity theory and piezoelectric constitutive relations are demonstrated to evaluate problems and analyses. Three different approaches consisting of atomistic modeling, continuum modeling and nano-scale continuum modeling in the investigation atomistic simulation of piezoelectric nanostructures are explained. Focusing on piezoelectric behavior, investigation of analyses is performed on fields of surface and small scale effects, buckling, vibration and wave propagation. Different investigations are available in literature focusing on the synthesis, applications and mechanical behaviors of piezoelectric nanostructures. In the study of vibration behavior, researches are studied on fields of linear and nonlinear, longitudinal and transverse, free and forced vibrations. This paper is intended to provide an introduction of the development of the piezoelectric nanostructures. The key issue is a very good understanding of mechanical and electrical behaviors and characteristics of piezoelectric structures to employ in electromechanical systems.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.171-177
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• 2000

It is essential to understand the creep behavior, which shows how long the characteristics of material maintains because press joined molding GMT-Sheet for recycle is usually used in the severe environment. In this study, we predict joining strength of GMT-Sheet for recycle, when lap length was changed. and we will investigate how compression ratio have an effect on creep behavior in press joined molding. The result of experiment of forming condition concerned with joining problem of GMT-Sheet is as followings joining efficiency. of GMT-Sheet, increases as lap joint length I, increases. Increase of compression ratio causes decrease o f joining efficiency after of GMT-Sheet joining. As the result of creep test, GMT-Sheet is easily damaged in high temperature range, because it is sensitive to the temperature

• 대한기계학회논문집A
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• 제20권12호
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• pp.3909-3916
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• 1996

Magnetic bearing is the machine element that supports the shaft without mechanical contact using the magnetic force induced by permanent magnet of electromagnet. Active magnetic bearing system is composed of sensor, controller, power amplifier, and electromagnet. If all the elements were dieal, shaft position could be controlled to sensor resolution, Because each elements inreal system have mechanical and electricla losses and nonlinearity, it is impossible to attain the desired performance using general control algorithm. So far it has been studied on improvement of the control algorithm of the electric characteristics of each elements. Another factors to affect shaft behavior are the manufacturing errors due to machine work, and assembling errors due to accumulate manufacturing errors of the radial magnetic bearing. This paper describes that the shaft behavior due to accumulate manufacturing errors and asymmetric bolting. This paper describes that the shaft behavior due to assembling errors of the radial bearings donot affect the rotaitonal accuracy of the shaft. But when the amplitude of the assembling errors increasees over the certain value, the bearing can not support the shaft properly.

• Advances in nano research
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• 제10권3호
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• pp.235-251
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• 2021

In the current study, the free vibrational behavior of a Porous Micro (PM) beam which is integrated with Functionally Graded Piezoelectric (FGP) layers with initial curvature is considered based on the two trigonometric shear deformation theories namely SSDBT and Tan-SDBT. The structure's mechanical properties are varied through its thicknesses following the given functions. The curved microbeam is exposed to electro-mechanical preload and also is rested on a Pasternak type of elastic foundation. Hamilton's principle is used to extract the motion equations and the MCST is used to capture the size effect. Navier's solution method is selected as an analytical method to solve the motion equations for a simply supported ends case and by validating the results for a simpler state with previously published works, effects of different important parameters on the behavior of the structure are considered. It is found that although increasing the porosity reduces the natural frequency, but enhancing the volume fraction of CNTs increasing it. Also, by increasing the central angle of the curved beam the vibrations of the structure increases. Designing and manufacturing more efficient smart structures such as sensors and actuators are of the aims of this study.

• 한국수소및신에너지학회논문집
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• 제33권2호
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• pp.158-163
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• 2022

The test method on the Type II high-pressure hydrogen storage tanks made of the metal wire hoop winding is a complex and high risk. Also closeup on the tank being test is difficult. In this study, we studied a mechanical test method for a high-pressure hydrogen tanks. This method must be simple, risk-free and possible to observe the change in microscopic behavior of a metal wire on a liner. As the results, it was possible to observe the microscopic behavior on the metal wire by the mechanical test method. Also, a simple and risk-free test was possible compared to the conventional test method for high pressure hydrogen tanks.

• 대한기계학회논문집
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• 제7권4호
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• pp.355-360
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• 1983

This paper deals with fatigue behavior of ion-nitrided coil spring. It is found that fatigue limit can be significantly increased by ion-nitriding. Ion-nitribed specimen which is treated at 550.deg. C for 5 hours improves in the fatigue limit by 30 percent in comparison with that of non-nitrided specimen. On the other hand, the value of spring constant K has nothing to do with nitriding time and temperature in this experimental range. Besides fatigue behavior, the following effects are discussed such as compound layer, diffusion layer, hardness distribution and their relations.

• 한국기계가공학회지
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• 제2권4호
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• pp.53-60
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• 2003

Large sized marine structures are used under corrosion environment of seawater and applied by severe service loading such as an ocean current, a billow and a tempest. Marine structures are usually constructed by lots of thick wall steel pipes joining welded joints. The thickness of such as steel pipes is usually more than 40mm. The such as steels are called "Thermo-Mechanical Control Process steel (TMCP steel)" strengthened by a heat treatment in process of steel manufactures. The failure, especially crack initiation, of marine structures was starting at weld joints under service condition. Then they should be designed by basis of the fatigue strength under seawater corrosion environment of weld joints. To clarity the fatigue crack initiation behavior is important more than to clarify the crack propagation behavior on the strength design of marine structures, because it is very difficult to find out the crack initiation and propagation phenomena and then even if it will be able to find out, it is considered that the refit of the damaged parts of welded joints have a technical difficulty under the sea. Therefore, it is most important to clarify the corrosion fatigue crack initiation behavior under the seawater condition. But, there is one big difficulty to make a test for thick plate specimen, for example thicker than 40mm. Because, it is need large capacity loading apparatus to test such as thick plate specimen. In this research, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the fatigue clack initiation tests with relatively low cyclic loading and to observe a fatigue crack initiation behavior.

• Advances in nano research
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• 제15권1호
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• pp.59-65
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• 2023

In this present article, the mechanical behavior of single-walled black phosphorene nanotubes (SW-αPNTs) is simulated using molecular dynamics (MD). The proposed model is subjected to the axial loading and the effects of morphological parameters, such as the mono-vacancy defect and strain rate on the tensile behavior of the zigzag and armchair SW-αPNTs are studied as a pioneering work. In order to assess the accuracy of the MD simulations, the stress-strain response of the current MD model is successfully verified with the efficient quantum mechanical approach of the density functional theory (DFT). Along with reproducing the DFT results, the accurate MD simulations successfully anticipate a significant variation in the stress-strain curve of the zigzag SW-αPNTs, namely the knick point. Predicting such mechanical behavior of SW-αPNTs may be an important design factor for lithium-ion batteries, supercapacitors, and energy storage devices. The simulations show that the ultimate stress is increased by increasing the diameter of the pristine SW-αPNTs. The trend is identical for the ultimate strain and stress-strain slope as the diameter of the pristine zigzag SW-αPNTs enlarges. The obtained results denote that by increasing the strain rate, the ultimate stress/ultimate strain are respectively increased/declined. The stress-strain slope keeps increasing as the strain rate grows. It is worth noting that the existence of mono-atomic vacancy defects in the (12,0) zigzag and (0,10) armchair SW-αPNT structures leads to a drop in the tensile strength by amounts of 11.1% and 12.5%, respectively. Also, the ultimate strain is considerably altered by mono-atomic vacancy defects.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.234-237
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• 2008

It was reported that the semi-solid forming process has many advantages over the conventional forming process, such as a long die life, good mechanical properties and energy savings. It is very important, however, to control liquid segregation to gain mechanical property improvement of materials. During forming process, Rheology material has complex characteristics, thixotropic behavior. Also, difference of velocity between solid and liquid in the semi-solid state material makes a liquid segregation and specific stress variation. Therefore, it is difficult for a numerical simulation of the rheology Process to be Performed. General Plastic or fluid dynamic analysis is not suitable for the behavior of rheology material. The behavior and stress of solid particle in the rheology material during forging process is affected by viscosity, temperature and solid fraction. In this study, compression experiments of aluminum alloy were performed under each other tool shape. In addition, the dynamics behavior compare with Okano equation to Power law model which is viscosity equation.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.325-330
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• 1999

The dynamic behavior analysis of air-lubricated tilting pad journal bearing which considers start-up, running and shutdown Process were performed. By carrying out the experiment of shaft vibration, measurement of the vibration amplitudes supported by air lubricated tilting pad bearing and analysis of the result, we found more accurate dynamic behavior of the system. There were many investigations in these bearings, but dynamic behavior of startup, shutdown and running process were lacked. By using the experimental data we found the accurate dynamic behavior of the system.