• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.129-140
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• 2018

A residual stress generated in the steel structure is broadly categorized into initial residual stress during manufacturing steel material, welding residual stress caused by welding, and heat treatment residual stress by heat treatment. Initial residual stresses induced during the manufacturing process is combined with welding residual stress or heat treatment residual stress, and remained as a final residual stress. Because such final residual stress affects the safety and strength of the structure, it is of utmost importance to measure or predict the magnitude of residual stress, and to apply this point on the design of the structure. In this study, the initial residual stress of steel structures having thicknesses of 25 mm and 70 mm during manufacturing was measured in order to investigate initial residual stress (hereinafter, referred to as initial stress). In addition, thermal elastic plastic FEM analysis was performed with this initial condition, and the effect of initial stress on the welding residual stress was investigated. Further, the reliability of the FE analysis result, considering the initial stress and welding residual stress for the steel structures having two thicknesses, was validated by comparing it with the measured results. In the vicinity of the weld joint, the initial stress is released and finally controlled by the weld residual stress. On the other hand, the farther away from the weld joint, the greater the influence of the initial stress. The range in which the initial stress affects the weld residual stress was not changed by the initial stress. However, in the region where the initial stress occurs in the compressive stress, the magnitude of the weld residual compressive stress varies with the compression or tension of the initial stress. The effect of initial stress on the maximum compression residual stress was far larger when initial stress was considered in case of a thickness of 25 mm with a value of 180 MPa, while in case of thickness at 70 mm, it was 200 MPa. The increase in compressive residual stress is almost the same as the initial stress. However, if initial stress was tensile, there was no significant change in the maximum compression residual stress.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.6
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• pp.724-734
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• 2007

Statement of problem. Translucency and masking effect of provisional crown and fixed partial denture materials is an important esthetic consideration. But, provisional resin materials differ substantially in their ability to mask underlying colors. Purpose. The purpose of this study was to evaluate the translucency differences of provisional resin materials at various thicknesses and the correlation between the translucency and the masking efficiency. Material and methods. Two polymethyl methacrylate resins (Jet Tooth Shade, Alike) and three resin composites (Protemp 3 Garant, Luxatemp and Revotek LC) were used. Specimens (n=6) were fabricated from each material in 0.3, 0.5, 0.8, 1.0, 1.5, 2.0 and 3.0 mm thickness. The CIELAB parameters of each specimens were measured using a spectrophotometer. The translucency parameter (TP) values and the masking effect $({\Delta}ME^*{_{ab}})$ values were computed and all data were statistically analyzed by one-way ANOVA and the multiple comparisons Scheffe test. The correlation between the thickness and the TP values and the correlation between the thickness and the ${\Delta}ME^*{_{ab}}$ values were also evaluated by correlation analysis and regression analysis. Results. The TP values and the ${\Delta}ME^*{_{ab}}$ values were significantly related to the thickness in all specimens. The TP values were more sensitive to the change of thickness than the ${\Delta}ME^*{_{ab}}$ values. The order of the translucency by brand was different from the order of the masking effect by brand in all thickness groups. Conclusion. Within the limitations of this study, the translucency and masking effect of the provisional resin materials investigated were significantly related to their thickness. The masking effect of provisional resin was correlated with the translucency parameter, but the order of the masking effect by brand was different from the order of the translucency parameter.

• Tribology and Lubricants
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• v.19 no.3
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• pp.123-132
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• 2003

The effect of surface texture on elastohydrodynamic lubrication (EHL) point contact of a ball Joint mechanism in small reciprocating compressors is studied numerically by using multigrid method. Pressure and film thickness profiles have been calculated for surface roughness with waviness of different orientations and transverse ridge and dent at minimum and maximum Hoes M parameter conditions. The influence of the amplitude and the wavelength of the surface roughness was also studied. Results show that the oblique waviness with orientation angle of 30$^{\circ}$generates the smallest minimum film thickness as compared with those of longitudinal, transverse, and other oblique roughness. The influence of transverse waviness on the minimum film thickness is smaller than for the longitudinal waviness case.

• Journal of Integrative Natural Science
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• v.5 no.4
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• pp.211-215
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• 2012

Single-crystalline silicon nanowire arrays (SiNWAs) using electroless metal-assisted etchings of p-type silicon were successfully fabricated. Ag nanoparticle deposition on silicon wafers in HF solution acted as a localized micro-electrochemical redox reaction process in which both anodic and cathodic process took place simultaneously at the silicon surface to give SiNWAs. The growth effect of SiNWs was investigated by changing of etching times. The morphologies of SiNWAs were obtained by SEM observation. Well-aligned nanowire arrays perpendicular to the surface of the silicon substrate were produced. Optical characteristics of SiNWs were measured by FT-IR spectroscopy and indicated that the surface of SiNWs are terminated with hydrogen. The thicknesses and lengths of SiNWs are typically 150-250 nm and 2 to 5 microns, respectively.

• Proceedings of the Korean Nuclear Society Conference
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• 2004.10a
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• pp.1047-1048
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• 2004

Simulation Coated layers of a nuclear fuel particle were evaluated by field emission scanning electron microscopy and nano-indentation method to give basic data to estimate 'Amoeba effect' and give an optimum fabrication condition and high quality control. Coated layers on the fuel kernel are in the order of buffer pyrolytic carbon, inner pyrolytic carbon, silicon carbide and outer pyrolytic carbon layers, which average thicknesses are 95, 25, 30 and 28 ${\mu}m$, respectively. Their densities and hardnesses are 1.08, 1.15, 3.18, 1.82 $g/cm^3$ and 0.522, 0.874, 9.641, and 2.726 GPa, respectively. Comparing theoretical density of pyrolytic carbon of 2.22 $g/cm^3$, the relative amount of porosity in each layer is about 52% for buffer, 48% for inner PyC and 18% for outer PyC.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.7
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• pp.602-609
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• 2008

This paper presents experimental optimization of process parameters for a newly developed SFF(Solid Freeform Fabrication) system. Two critical process parameters, layering thickness and curing period, which have a large effect on the quality of the product, are optimized through experiments. Specimens are produced using layering thicknesses of 60, 80, 100, 120, 140, and $160\;{\mu}m$ and curing periods of 0, 10, 20, and 30 minutes under the same processing conditions, i.e., build-room temperature, feed-room temperature, roller speed, laser power, scan speed, and scan spacing. The specimens are tested to compare and analyze performance indices such as thickness accuracy, flatness, stress-strain characteristics, and porosity. The experimental result indicates that layering thickness of $80{\sim}100\;{\mu}m$ and curing period of $20{\sim}30$ minutes are recommended for the developed industrial SFF system.

• Transactions on Electrical and Electronic Materials
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• v.14 no.1
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• pp.39-42
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• 2013

The effects of particle size on the mechanical and electrical properties of epoxy/spherical silica composites were studied. The silica particle sizes were varied from 5 to 30 ${\mu}m$ and the filler content was fixed to 60 wt%. Tensile and flexural tests were carried out and the interfacial morphology was observed by scanning electron microscopy (SEM). The electrical insulation breakdown strength was estimated using sphere-sphere electrodes with different insulation thicknesses of 1, 2 and 3 mm. The tensile strength and flexural strength increased with decreasing particle size, while electrical insulation breakdown strength increased with increasing particle size.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1738-1745
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• 2015

Radiation characteristics of a probe-fed rectangular microstrip patch antenna printed on a finite grounded high permittivity substrate are investigated systematically for various square grounded dielectric substrate sizes with several thicknesses and dielectric constants by experiment and full wave simulation. The effect of the substrate size on the radiation characteristics of a rectangular patch antenna is mainly determined by the effective dielectric constant of surface waves on a grounded dielectric substrate. As the effective dielectric constant of surface waves increases, the substrate sizes for the maximum broadside gain and the required onset for a large magnitude of squint angle decrease, while the variations of the broadside gain, the front-to-back ratio, and the magnitude of squint angle versus the substrate size increase due to the increase of the power of the surface wave.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2634-2645
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• 1993

Dome structures of pressure vessels subjected to internal pressure are usually analyzed by linear elastic theory assuming small deformation. Geometric and material nonlinear behaviors appear in actual dome structures because of large deformation and loads exceeding yield strength. In this paper, linear and nonlinear analyses were performed for various hemispherical and torispherical domes to check the effects of geometric and material nonliearity on the stress and displacement by the finite element method. The effect of the geometric nonlinearity decreased the stress levels a lot for very thin general torispherical domes, which enables more realistic and effective design. The material nonlinear effects are negligible for hemispherical and optimum torispherical domes, and those are large for most of the general torispherical domes.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1301-1309
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• 1994

A study of heat transfer and thermophoretic particle deposition has been carried out for the Modified Chemical Vapor Deposition(MCVD) process. A new concept utilizing two torches is suggested to simulate the heating effects from repeated traversing torches. Calculation results for the wall temperatures and deposition efficiency are in good agreement with experimental data. The effects of variable properties are included and heat flux boundary condition is used to simulate the moving torch heating. A conjugate heat transfer which includes heat conduction through solid layer and heat teansfer in a gas in a tube is analyzed. Of particular interests are the effects of torch speeds and solid layer thicknesses on the deposition efficiency, rate and the tapered entry length.