• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.2006-2010
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• 2005

This study is concerned with the relation between steelbelt and belt edge separation. Belt edge separation causes tire burst and threatens passenger's safety. For that reason, it is important to predict durability caused by belt edge separation first in tire structure design step. In this study, to predict belt edge separation, we suggest the prediction method of belt edge separation and evaluate the effect of steelbelt width on the belt edge separation using FEM. We study on analysis parameter also to do exact estimation about the shear behaviour of belt edge area.

• Structural Engineering and Mechanics
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• v.40 no.4
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• pp.501-515
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• 2011

Sandwich elements have high flexural rigidity and high strength per density. They also have excellent anti-vibration and anti-noise characteristics. Therefore, they are used for structures of airplanes and high speed ships that must be light, as well as strong. In this paper, the Reissner-Mindlin's plate theory is studied from a Hamilton's principle point of view. This theory is modified to include the influence of shear deformation and rotary inertia, and the equation of motion is derived using energy relationships. The theory is applied to a rectangular sandwich model which has isotropic, asymmetrical faces and an isotropic core. Investigations are conducted for five different plate thicknesses. These plates are identical to the sandwich plates currently used in various structural elements of surface effect ships (SES). The boundary conditions are set to simple supports and fixed supports. The elastic and shear moduli are obtained from the four-point bending tests on the sandwich beams.

• Structural Engineering and Mechanics
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• v.73 no.6
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• pp.685-698
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• 2020

The dynamic stability of a functionally graded polymer microbeam reinforced by graphene oxides subjected to a periodic axial force is investigated. The microbeam is assumed to rest on an elastic substrate and is subjected to various immovable boundary restraints. The weight fraction of graphene oxides nanofillers is graded across the beam thickness. The effective Young's modulus of the functionally graded graphene oxides reinforced composite (FG-GORC) was determined using modified Halpin-Tsai model, with the mixture rule used to evaluate the effective Poisson's ratio and the mass density. An improved third order shear deformation theory (TSDT) is used in conjunction with the Chebyshev polynomial-based Ritz method to derive the Mathieu-Hill equations for dynamic stability of the FG-GORC microbeam, in which the scale effect is taken into account based on modified couple stress theory. Then, the Mathieu-Hill equation was solved using Bolotin's method to predict the principle unstable regions of the FG-GORC microbeams. The numerical results show the effects of the small scale, the graphene oxides nanofillers as well as the elastic substrate on the dynamic stability behaviors of the FG-GORC microbeams.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.40.4-41
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• 2018

The current 'standard model' of cosmology provides a minimal theoretical framework that can explain the gaussian, nearly scale-invariant density perturbations observed in the CMB to the late time clustering of galaxies. However accepting this framework, requires that we include within our cosmic inventory a vacuum energy that is ~122 orders of magnitude lower than Quantum Mechanical predictions, or alternatively a new scalar field (dark energy) that has negative pressure. An alternative approach to adding extra components to the Universe would be to modify the equations of Gravity. Although GR is supported by many current observations there are still alternative models that can be considered. Recently there have been many works attempting to test for modified gravity using the large scale clustering of galaxies, ISW, cluster abundance, RSD, 21cm observations, and weak lensing. In this work, we compare various modified gravity models using cosmic shear data from the Deep Lens Survey as well as data from CMB, SNe Ia, and BAO. We use the Bayesian Evidence to quantify the comparison robustly, which naturally penalizes complex models with weak data support. In this talk we present our methodology and preliminary results that show f(R) gravity is mildly disfavoured by the data.

• Structural Engineering and Mechanics
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• v.42 no.4
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• pp.551-570
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• 2012

An experimental program was carried out to investigate the influence of fibre reinforcement on the mechanical behaviour of high strength reinforced concrete beams. Eighteen beams, loaded in four-point bending tests, were examined by applying monotonically increasing controlled displacements and recording the response in terms of load-deflection curves up to failure. The major test variables were the volume fraction of steel fibres and the transverse steel amount for two different values of shear span. The contribution of the stirrups to the shear strength was derived from the deformations of their vertical legs, measured by means of strain gauges. The structural response of the tested beams was analyzed to evaluate strength, stiffness, energy absorption capacity and failure mode. The experimental results and observed behaviour are in good agreement with those obtained by other authors, confirming that an adequate amount of steel fibres in the concrete can be an alternative solution for minimizing the density of transverse reinforcement. However, the paper shows that the use of different theoretical or semi-empirical models, available in literature, leads to different predictions of the ultimate load in the case of dominant shear failure mode.

• Polymer(Korea)
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• v.38 no.3
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• pp.397-405
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• 2014

To manufacture of high-performance semi-structural double-sided adhesive tape, 2-ethylhexyl acrylate (2-EHA) and acrylic acid (AAC) were used, and the syrup was prepared by UV irradiation in this study. The effects of the thickness, various inorganic filler contents, and filler types on the semi-structural properties of acrylic double-sided adhesive tape were investigated. The peel strength increased with increasing thickness and wetting time. In case of the thin thickness (under $250{\mu}m$) with decreasing true density of inorganic filler, the peel strength increased with increasing wetting time. The initial peel strength showed a higher value at a big size of inorganic filler, and the filler's size in adhesive tapes was confirmed by SEM images. The peel strength and dynamic shear strength increased as a proportional relationship with various inorganic fillers and contents, and these inorganic fillers in $0.1{\mu}m$ thickness indicated more effect on the dynamic shear strength of double-sided adhesive tape. From these results the thin acrylic double-sided adhesive tape determined to be use for applications as a high-performance semi-structural.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.73.1-73.1
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• 2010

We use three-dimensional hydrodynamic simulations to investigate the characteristics of turbulence driven in rotating, vertically-stratified disk. Our models are isothermal, and local in the in-plane direction while global in the vertical direction. We allow localized regions with density larger than the threshold value to explode and inject kinetic energy to the surrounding medium in the real space rather than Fourier space, mimicking supernova explosions thought to be the dominant turbulence source. This work extends our previous study where we studied turbulence in a non-rotating, uniform environment. We find that the galaxy rotation does not make a significant difference in the turbulence level at saturation, since the associated shear velocity is much smaller than the explosion velocity. We analyze the properties of turbulence in our models and compare them with those from the uniform-density models. We also discuss the astrophysical implication of our findings.

• Proceedings of the KACD Conference
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• 2008.05a
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• pp.213-223
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• 2008

The objective of this study was to compare dentin shear bond strength (DSBS) of dentin bonding agents (DBAs) cured with a plasma arc (PAC) light curing unit (LCU) and those cured with a light emitting diode (LED) LCU. Optical properties were also analyzed for Elipar freelight 2 (3M ESPE); LED LCU, Apollo 95E (DMT Systems); PAC LCU and VIP Junior (Bisco); Halogen LCU. The DBAs used for DSBS test were Scotchbond Multipurpose (3M ESPE), Singlebond 2 (3M ESPE) and Clearfil SE Bond (Kuraray). After DSBS testing, fractured specimens were analyzed for failure modes with SEM. The total irradiance and irradiance between 450 nm and 490 nm of the LCUs were different. LED LCU showed narrow spectral distribution around its peak at 462 nm whereas PAC and Halogen LCU showed a broad spectrum. There were no significant differences in mean shear bond strength among different LCUs (P > 0.05) but were significant differences among different DBAs (P < 0.001).

• Restorative Dentistry and Endodontics
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• v.33 no.3
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• pp.213-223
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• 2008

The objective of this study was to compare dentin shear bond strength (DSBS) of dentin bonding agents (DBAs) cured with a plasma arc (PAC) light curing unit (LCU) and those cured with a light emitting diode (LED) LCU. Optical properties were also analyzed for Elipar freelight 2 (3M ESPE); LED LCU, Apollo 95E (DMT Systems); PAC LCU and VIP Junior (Bisco); Halogen LCU. The DBAs used for DSBS test were Scotchbond Multipurpose (3M ESPE), Singlebond 2 (3M ESPE) and Clearfil SE Bond (Kuraray). After DSBS testing, fractured specimens were analyzed for failure modes with SEM. The total irradiance and irradiance between 450 nm and 490 nm of the LCUs were different. LED LCU showed narrow spectral distribution around its peak at 462 nm whereas PAC and Halogen LCU showed a broad spectrum. There were no significant differences in mean shear bond strength among different LCUs (P > 0.05) but were significant differences among different DBAs (P < 0.001)

• Journal of the Korean Society for Precision Engineering
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• v.12 no.3
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• pp.101-109
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• 1995

Axisymmetric and quasi-static finite element analysis of an inflated tire rotating with constant angular velocity and contact to road has been performed. Centrifugal force effect was added to load stiffness matrix and equation of effective material properties were calculated by the Halpin-Tsai formulation. In this report, radial truck/bus tire was analyzed. It was inflated and rotated at speeds up to 140 km/h. Then, contact problem was performed to calculate stress-strain field of tire wiht flat rigid road under the load due to the self-weight of a vehicle. Significant changes of stress-strain field of tire were observed in the finite element analysis. Shear stress, strain and strain energy density were rapidly increased at the dege of #2 belt at freely rotating state. This concentrated stress and strain made belt edge sparation. Under the condition of flat riged road contact, strain energy density of #2 belt, carcass turn-up part were concentrated and bigger values than only freely rotation state. Therefore, dynamic behaivor of tire has to considered as design factors which are affected to belt edge separation and bead breakage.