• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.295-300
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• 2005

The freeplay, one of the concentrated structural nonlinearities, is inevitable for control surfaces of a real air vehicle due to normal wear of components and manufacturing mismatches. Also aerodynamic nonlinearities caused by a shock wave occur in transonic region. In practice, these nonlinearities induce the limit cycle oscillation (LCO) and decrease the transonic flutter speed. In this study, the fictitious mass method is used to apply a modal approach to nonlinear structural models due to freeplay. The transonic small-disturbance (TSD) equation is used to calculate unsteady aerodynamic forces in transonic region. Nonlinear aeroelastic time responses are predicted by the coupled time integration method (CTIM). This method was also applied to a 3D all-movable control wing to investigate its nonlinear aeroelastic responses. The angle of attack effect on the LCO characteristics has been found to be closely related with the initial pitching moment.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.16-21
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• 2002

Generally, Oxidization film are generated by friction and wear in lubricant oil. It is effect that the heat and pressure act on contact area. Because the electrons movement progress the oxidization, if the electrons movement be regulated, the thickness of oxidization film can be regulated and friction characteristics can be improved. But electronic current can deteriorate friction characteristics, so various characteristics must be investigated on transforming of electronic current. Therefor, using the Norton equation, short current were transformed between ball and disk. Also, an experiment was carried out using ball on disk type tester. So, we studied up on effect of current for friction characteristics.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.150-155
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• 2002

Generally, Oxidization film are generated by friction and wear in lubricant oil. It is effect that the heat and pressure act on contact area. Because the electrons movement progress the oxidization, if the electrons movement be regulated, the thickness of oxidization film can be regulated and friction characteristics can be improved. But electronic current can deteriorate friction characteristics, so various characteristics must be investigated on transforming of electronic current. Therefor, using the Norton equation, short current were transformed between ball and disk. Also, an experiment was carried out using ball on disk type tester. So, we studied up on effect of current for friction characteristics.

• Journal of the Korean Society of Safety
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• v.23 no.4
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• pp.25-29
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• 2008

Recently, new functionally graded material(FGM) that has a spatial variation in composition and properties is developed because of its good quality. This material yields the demands for resistance to corrosion and high temperature in turbine blade, wear resistance as in gears and high strength machine parts. Especially coating treatment in FGM surface brings forth a mechanical weak at the interface due to discontinuous stress resulting from a steep material change. It often, leads cracks or spallation in a coating area around an interface. The behavior of propagation cracks in FGMs was here investigated. The interface stresses were reduced because of graded material properties. Also graded material parameter with exponential equation was founded to influence the stress intensity factor. And the resistance curve with FGM coating was slightly increased.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.70-73
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• 2004

The approach in this thesis is for prediction of deformed strip profile in hot rolling mill. This approach shows how to make an expression as a mathematical form in predicting strip profile. This approach is based on the velocity field, shear stress and material flow on the strip edge along width direction and lateral displacement and stress along width are analytically calculated. Roll force is calculated in each section and then combined together to show roll force distribution along width. All the assumptions to make equation form for this approach are supported by FEM simulation result and the result of model is verified by FEM result. So, this model will supply very useful tool to the researcher and engineers which takes less time and has similar accuracy in predicting roll force profile comparing to FEM simulation. This model has to be combined with deformed roll profile model, which include thermal crown prediction and wear prediction model to predict deformed strip profile.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.234-238
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• 1999

This study suggests the design of the functionally gradient composite, [0/90/0/core]$_s$ cross-ply laminate, to prevent stress concentration induced from the difference of rigidity between the bone and the artificial hip joint and to reinforce the wear property of the surface and the expectation of their mechanical properties. First, the four-point bending test is done about wet bones and dry bones to know the mechanical properties of the cortical bones. In result, the wet bone shows the viscoelastic behavior and the dry bone shows the elastic behavior. Moreover, we expect the properties of the proposed gradient composites as a function of carbon fiber volume fraction in each layer to apply Halpin-Tsai equation, CLPT(classical laminate plate theory), and Bernoulli beam theory etc. and decide the thickness ratio of each lamina in order to match Young's modulus of the anisotropic cortical bone with the proposed gradient composites.

• Tribology and Lubricants
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• v.18 no.5
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• pp.339-344
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• 2002

Whenever moving surfaces of machine driving elements interact in air and lubricating oil, oxidization film on the surfaces are generated. It is effect to prevent friction and wear on contact area. Since the electronic current progress the oxidization of metal, if the electronic flow be regulated, the thickness of oxidization film can be regulated and friction characteristics can be improved. But the electronic current can deteriorate friction characteristics, so various characteristics must be investigated on transforming of electronic current. Therefor, using the Norton equation in this study, short current were transformed between frictional materials using ball on disk type tester. It was studied on effect of electronic current for friction characteristics.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.124-124
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• 2015

Acoustic microscopy and scanning electron microscopy were applied to non-destructively evaluate the hydrogen-induced cracking of API X-80 steels and to find the initiation time of the crack. The API X-80 steel had the average grain size of about $4-10{\mu}m$. The hardness was reduced from 240 to 202 [Hv] after exposing in HIC environment for 2-days. Friction coefficient and wear loss were 0.745 and 0.392 mm, respectively. Empirical equation of corrosion potential and corrosion rate of the steel with HIC time in $5%NaCl-0.5%CH_3COOH$ at $25^{\circ}C$ were $Eh\;(up)=0.06^*t[day]+0.2951$, $Eh(down)=0.376^*t[day]+0.5938$, respectively. HIC grew with micro-size after 1-day exposure. The HIC tended to propagate on the surface with Al, Si, Ti, and Mn.

• International journal of advanced smart convergence
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• v.11 no.4
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• pp.177-184
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• 2022

The purpose of this study is to provide implications by conducting research on brand benefits for skiwear brand customers. For this purpose, a structural equation model was established and empirical research was conducted by selecting brand convenience as a hygiene variable and brand emotion, brand satisfaction, and repurchase intention as endogenous variables. In order to analyze the general characteristics of the subjects, frequency analysis was conducted using SPSS 25 and Cronbach's alpha analysis was conducted using the same statistical program. Confirmatory factor analysis and path analysis were conducted using AMOS 21. In addition, the benefits of skiwear brand, which is an independent variable, were composed of two sub-dimensions, and psychological benefits rather than functional benefits were found to have a stronger impact on brand emotion, suggesting practical implications.

• Tribology and Lubricants
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• v.37 no.5
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• pp.172-178
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• 2021

An injector is a mechanical device present inside the engine. Its main function is to supply an appropriate volume of fuel into the combustion chamber, which is directly related to the overall engine efficiency of a car. During the operation of an injector, a magnetic force lifts the parts of the injector from closed position to open position which generates a horizontal force on the needle. The horizontal force acts on a different position from that of the center of mass of the needle. Therefore, this causes eccentricity in the needle and the generation of a tilting motion during the lifting operation which can result in wear. However, appropriate selection of clearances for these parts can prevent wear. In this study, lubrication analysis is conducted to determine the optimum clearance of parts with sliding motion inside the injector. The height functions are derived considering the dynamic behavior and relative velocity of the parts. Using the derived height function, the pressure profiles are calculated for the lubricated surfaces from the Reynolds' equation. Subsequently, the fluid reaction forces are calculated. The equations of motions are applied to the fluid reaction forces and external forces are solved to calculate the minimum film thickness between each part with variation in the clearances. Finally, the optimum clearances are determined. The effect of the clearances on the behavior of the moving parts is presented and discussed.