• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.61-66
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• 2011

According to recent figures, 35% of the world's blades are made using prepreg blades, by Vestas and Gamesa. They are the most advanced in the market today. In this study, we investigated the validity of the finite element method (FEM) applied to an FE analysis of a hybrid composite wind-turbine blade. Two methods were suggested for a composite FE analysis: using the equivalent properties of the composite or using stacking properties. FE analysis results using the stacking properties of the composite were in good agreement with results of using the equivalent properties. The difference between FE results was approximately 0.6~13.3%.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1187-1188
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• 2006

This paper compares the effect of using different types of iron powders for the preparation of $Sm_2Fe_{17}$ by calciothermic reduction-diffusion (CRD). Three types of iron powder were used: carbonyl, sponge and water atomized. The results show that, when immediately nitrogenated after the CRD process, $Sm_2Fe_{17}$ prepared from sponge and water atomized iron powders yield $Sm_2Fe_{17}N_3$-magnets with a high degree of texture. However, after a suitable treatment with hydrogen followed by nitrogenation, $Sm_2Fe_{17}$-powders made from Carbonyl iron produce magnets with the best quality regarding coercivity, remanence and degree of texture.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.128-134
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• 2013

A study on the corrosion behavior of Inconel alloys and Incoloy 800H in molten salt of LiCl-$Li_2O$ was investigated at $650^{\circ}C$ for 24-312 hours in an oxidation atmosphere. The order of the corrosion rate was Inconel 600 < Inconel 601 < Incoloy 800H < Inconel 690. Inconel 600 showed the best performance suggesting that the content of Fe, Cr and Ni are the important factor for corrosion resistance in hot molten salt oxidation conditions. The corrosion products of Inconel 600 and Inconel 601 were $Cr_2O_3$ and $NiFe_2O_4$, In case of Inconel 690, a single layer of $Cr_2O_3$ was formed in the early stage of corrosion and an outer layer of $NiFe_2O_4$ and inner layer of $Cr_2O_3$ were formed with an increase of corrosion time. In the case of Incoloy 800H, $Cr_2O_3$ and $FeCr_2O_4$ were observed. Most of the outer scale of the alloys was observed to be spalled from the results of the SEM analysis and the unspalled scale which adhered to the substrate was composed of three layers. The outer layer, the middle one, and the inner one were Fe, Cr, and Ni-rich, respectively. Inconel 600 showed localized corrosion behavior and Inconel 601, 690 and Incoloy 800H showed uniform corrosion behavior. Ni improves the corrosion resistance and too much Cr and/or Fe content deteriorates the corrosion resistance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.2
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• pp.90-94
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• 2016

In this work, [$Pb(Mg_{1/2}W_{1/2})_{0.03}(Ni_{1/3}Nb_{2/3})_x(Zr_{0.5}Ti_{0.5})_{0.97-x}O_3-BiFeO_3$] (x=0.02 to 0.12) composition ceramics were fabricated by the conventional soild state reaction method and their microstructure and piezoelectric properties were investigated according to PNN substitution. The addition of small amount of $BiFeO_3$, $Li_2CO_3$, and $CaCO_3$ were used in order to decrease the sintering temperature of the ceramics. The XRD (x-ray diffraction patterns) of all ceramics exhibited a perovskite structure. The sinterability of PMW-PNN-PZT-BF ceramics was remarkably improved using liquid phase sintering of $CaCO_3$, $Li_2CO_3$. However, it was identified from of the X-ray diffraction patterns that the secondary phase formed in grain boundaries decreased the piezoelectric properties. According to the substitution of PNN, the crystal structure of ceramics is transformed gradually from a tetragonal to rhombohedral phase. The x=0.10 mol PNN-substituted PMW-PNN-PZT-BF ceramics sintered at $920^{\circ}C$ showed the optimum values of piezoelectric constant($d_{33}$), piezoelectric figure of merit($d_{33{\cdot}}g_{33}$), planar piezoelectric coupling coefficient($k_p$) and density : $d_{33}=566$ [pC/N], $g_{33}=29.28[10^{-3}mV/N]$, $d_{33{\cdot}}g_{33}=16.57[pm^2/N]$, $k_p=0.61$, density=7.82 [$g/cm^3$], suitable for duplex ultrasonic sensor application.

• The Journal of Advanced Prosthodontics
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• v.11 no.6
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• pp.313-323
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• 2019

PURPOSE. Shear bond strength (SBS) test is the most commonly used method for evaluating resin bond strength of zirconia, but SBS results vary among different studies even when evaluating the same bonding strategy. The purpose of this study was to promote standardization of the SBS test in evaluating zirconia ceramic bonding and to investigate factors that may affect the SBS value of a zirconia/resin cement/composite resin bonding specimen. MATERIALS AND METHODS. The zirconia/resin cement/composite resin bonding specimens were used to simulate loading with a shear force by the three-dimensional finite element (3D FE) modeling, in which stress distribution under uniform/non-uniform load, and different resin cement thickness and different elastic modulus of resin composite were analyzed. In vitro SBS test was also performed to validate the results of 3D FE analysis. RESULTS. The loading flat width was an important affecting factor. 3D FE analysis also showed that differences in resin cement layer thickness and resin composite would lead to the variations of stress accumulation area. The SBS test result showed that the load for preparing a SBS specimen is negatively correlated with the resin cement thickness and positively correlated with SBS values. CONCLUSION. When preparing a SBS specimen for evaluating bond performance, the load flat width, the load applied during cementation, and the different composite resins used affect the SBS results and therefore should be standardized.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.567-568
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• 2009

The CAMUS 2000-1 experimental program were performed in France to investigate of the 1/3-scaled reinforced concrete bearing walls behavior on the shaking table under biaxial earthquake loading. The nonlinear 3D finite element analysis of push over test and linear dynamic analysis under biaxial earthquake loading are investigated with the concrete damaged plasticity model using ABAQUS.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.47 no.3
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• pp.86-94
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• 2024

In this study, an attempt was made to approximate the main characteristic values of Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (= BNKT) depending on the content of Fe₂O₃ additives, aiming to approach the values of lead(Pb) piezoelectric ceramic materials (PZT). Specifically, when the piezoelectric coefficient (d₃₃) value of lead(Pb) piezoelectric ceramic material (PZT polycrystalline ceramic powder) is 300[pC/N] or higher, it is applied for hard purposes such as ultrasonic welding machines and cleaning machines, and when it exceeds 330[pC/N], it is applied for soft purposes like piezoelectric sensors. In this study, research and development were conducted for devices with a piezoelectric coefficient (d₃₃) of 300[pC/N] or more for actuators. For this purpose, K⁺ exceeding 0.02 to 0.12 mol% was added to (Na_0.78K_0.22)_0.5Bi_0.5TiO₃ to analyze structural changes due to K⁺ excess, and (Na_0.78K_0.22)_0.5Bi_0.5TiO₃ + 8mol% K₂CO₃ Ti⁴⁺ was substituted with Fe³⁺ to manufacture lead-free piezoelectric materials. As a result, ceramics with Fe³⁺ substitution at x = 0.0075 yielded an average value of d₃₃ = 315[pC/N]. Furthermore, for ceramics with Fe³⁺ substitution at x = 0.0075, the average values of maximum polarization (P_max), residual polarization (P_rem), and coercive field (E_c) were found to be 39.63 μC/cm², 30.45 μC/cm², and 2.50 kV/mm, respectively. The reliable characteristic values obtained from the research results can be applied to linear actuator components (such as the zoom function of mobile cameras, LDM for skin care, etc.) and ultrasonic vibration components.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.234-238
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• 2007

Highly conducting Polypyrroles soluble in organic solvents were synthesized using functional doping agents, such as mixed dopants [sodium di(2-ethylhexyl)sulfosuccinate (DEHSNa) Naphthalenesulfonic acid (NSA), DEHSNa Toluenesulfonic acid (TSA), DEHSNa Dodecylbenzensulfonic acid (DBSA)] and mixed oxidants [$(NH_4)_2S_2O_8{\cdot}FeCl_3$, $(NH_4)_2S_2O_8{\cdot}Fe_2(SO_4)_3$]. Ppy-DEHS powder using an oxidant, such as $(NH_4)_2S_2O_8$ (10 wt%/vol.) showed higher solubility than the mixed dopant (DEHSNa NSA, 3 wt%/vol.) and mixed oxidant [$(NH_4)_2S_2O_8{\cdot}Fe_2(SO_4)_3$, 4 wt%/vol.] in DMF solvent. But Ppy-DEHS free standing film using a mixed dopant, such as DEHSNa NSA (16 S/cm) and a mixed oxidant, such as $(NH_4)_2S_2O_8{\cdot}Fe_2(SO_4)_3$ (13 S/cm) cast from DMF solvent showed higher electrical conductivity than $(NH_4)_2S_2O_8$ (2 S/cm). For the Ppy-DEHS films using various condition cast from DMF solvent, three dimensional various range hopping model (3D VRH ; $\{{\sigma}_{dc}(T)={\sigma}_oexp[-(T_o/T)^{1/4}]\}$) provided fit to the results of temperature dependence of electrical conductivity measurement.

• Journal of Powder Materials
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• v.19 no.4
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• pp.247-252
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• 2012

Effect of Cu and $DyF_3$ powder mixing with Cu-free (Nd, Dy)-Fe-B jet-milled powder on the magnetic properties of sintered magnets was investigated. The coercivity of a magnet prepared from the Cu-free (Nd, Dy)-Fe-B powder was about 10 kOe even though the alloy powder already contained some Dy (3.5 wt%). When small copper powder was blended, however, the coercivity of the magnet increased almost 100%, exhibiting about 20 kOe. On the contrary, the coercivity enhancement was moderate, about 4 kOe, when dysprosium content in the sintered magnet was simply increased to 4.9 wt% by the addition of small $DyF_3$3 powder.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.6
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• pp.250-255
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• 2018

The CoCrMo as-built alloys prepared by 3D-printing process are studied on tensile strength, wear resistance, crystal structure and microstructure after complex heat-treatment including HIP. In this study, HIP treatment for removing micropores, ambient heat-treatment for formation of metal carbides, and solution heat-treatment for homogenization of the created metal carbides were tried and characterized for applying to artificial joint. The complex heat-treatment effects of the CoCrMo as-built alloys prepared by 3D-printing process were owing to the densification during HIP, formation of metal carbides and homogenization of the created metal carbides. The effects of the complex heat-treatment were confirmed by XRD, FE-SEM and EDS.