• Transactions of the Korean Society of Automotive Engineers
• /
• v.11 no.1
• /
• pp.185-192
• /
• 2003

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to Dow the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, three kinds of spring steel (JISG4081-SUP7, SAE 9254, DON 50CrV4) are made. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) Decreasing the surface roughness (2) Unchanging the surface hardness (3) Increasing the compressive residual stress. But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of hish hardness.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2002.10a
• /
• pp.366-372
• /
• 2002

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface deject as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to know tile influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, three kinds of spring steel (JISG4081-SUP7,SAE 9254, DIN 50CrV4, ) are made. This study shows the outstanding improvement of fatigue properties at tire case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) Decreasing the surface roughness (2) Unchanging the surface hardness (3) Increasing the compressive residual stress But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.

• Proceedings of the KIEE Conference
• /
• summer
• /
• pp.1067-1069
• /
• 2004

22.9[kV]/50[MVA]/30[m] HTS transmission power cable has been developed and tested at Korea Electrotechnology Research Institute and LG Cable Company by 21 century center for applied superconductivity technology. It is necessary to measure of critical current degradations, AC loss, insulation test and etc at the HTS cable development. This paper is analyzed characteristics that critical current of HTS cable bending condition according to this paper. We will be able to decide the diameter of drum which HTS cable is wound around and minimum curvature radius of HTS cable from results of this research.

• Structural Engineering and Mechanics
• /
• v.71 no.5
• /
• pp.485-502
• /
• 2019

In this research, the nonlinear static, buckling and vibration analysis of viscoelastic micro-composite beam reinforced by various distributions of boron nitrid nanotube (BNNT) with initial geometrical imperfection by modified strain gradient theory (MSGT) using finite element method (FEM) are presented. The various distributions of BNNT are considered as UD, FG-V and FG-X and also, the extended rule of mixture is used to estimate the properties of micro-composite beam. The components of stress are dependent to mechanical, electrical and thermal terms and calculated using piezoelasticity theory. Then, the kinematic equations of micro-composite beam using the displacement fields are obtained. The governing equations of motion are derived using energy method and Hamilton's principle based on MSGT. Then, using FEM, these equations are solved. Finally the effects of different parameters such as initial geometrical imperfection, various distributions of nanotube, damping coefficient, piezoelectric constant, slenderness ratio, Winkler spring constant, Pasternak shear constant, various boundary conditions and three material length scale parameters on the behavior of nonlinear static, buckling and vibration of micro-composite beam are investigated. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of micro-composite beam increases and thus the non-dimensional nonlinear frequency of the micro structure reduces gradually.

• Advances in nano research
• /
• v.11 no.6
• /
• pp.621-640
• /
• 2021

Effect of thickness stretching on mechanical behavior of functionally graded (FG) carbon nanotubes reinforced composite (CNTRC) laminated nanoplates resting on elastic foundation is analyzed in this paper using a novel quasi 3D higher-order shear deformation theory. The key feature of this theoretical formulation is that, in addition to considering the thickness stretching effect, the number of unknowns of the displacement field is reduced to four, and which is more than five in the other models. Single-walled carbon nanotubes (SWCNTs) are the reinforced elements and are distributed with four power-law functions which are, uniform distribution, V-distribution, O-distribution and X-distribution. To cover various boundary conditions, an analytical solution is developed based on Galerkin method to solve the governing equilibrium equations by considering the nonlocal strain gradient theory. A modified two-dimensional variable Winkler elastic foundation is proposed in this study for the first time. A parametric study is executed to determine the influence of the reinforcement patterns, power-law index, nonlocal parameter, length scale parameter, thickness and aspect ratios, elastic foundation, thermal environments, and various boundary conditions on stresses, displacements, buckling loads and frequencies of the CNTRC laminated nanoplate.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.7
• /
• pp.2051-2055
• /
• 2013

Existing theoretical calculations predict that infrared spectra of the two most fundamental reactive carbo-ions, methyl cation $CH{_3}^+$ with $D_{3h}$ symmetry and protonated methyl cation $CH{_5}^+$ with $C_s(I)$, $C_s(II)$, and $C_{2v}$ symmetries, appear together in the 7-${\mu}m$ region corresponding to the C-H bending modes. Vibrational band profiles of $CH{_3}^+$ and $CH{_5}^+$ have been compared by ab initio calculation methods that use the basis sets of MP2/aug-cc-pVTZ and CCSD(T)/cc-pVTZ. Our results indicate that the bands of rotation-vibration transitions of $CH{_3}^+$ and $CH{_5}^+$ should overlap not only in the 3-${\mu}m$ region corresponding to the C-H stretching modes but also in the 7-${\mu}m$ region corresponding to the C-H bending modes. Five band intensities of $CH{_5}^+$ among fifteen vibrational transitions between 6 and 8 ${\mu}m$ region are stronger than those of the ${\nu}_2$ and ${\nu}_4$ bands in $CH{_3}^+$. Ultimate near degeneracy of the two bending vibrations ${\nu}_2$ and ${\nu}_4$ of $CH{_3}^+$along with the stronger intensities of $CH{_5}^+$ in the three hydrogen scrambling structures may cause extreme complications in the analysis of the high-resolution carbo-ion spectra in the 7-${\mu}m$ region.

• The Journal of Advanced Prosthodontics
• /
• v.10 no.1
• /
• pp.43-49
• /
• 2018

PURPOSE. The purpose of this in vitro study is to examine the effects of a nano-structured alumina coating on the adhesion between resin cements and zirconia ceramics using a four-point bending test. MATERIALS AND METHODS. 100 pairs of zirconium bar specimens were prepared with dimensions of $25mm{\times}2mm{\times}5mm$ and cementation surfaces of $5mm{\times}2mm$. The samples were divided into 5 groups of 20 pairs each. The groups are as follows: Group I (C) - Control with no surface modification, Group II (APA) - airborne-particle-abrasion with $110{\mu}m$ high-purity aluminum oxide ($Al_2O_3$) particles, Group III (ROC) - airborne-particle-abrasion with $110{\mu}m$ silica modified aluminum oxide ($Al_2O_3+SiO_2$) particles, Group IV (TCS) - tribochemical silica coated with $Al_2O_3$ particles, and Group V (AlC) - nano alumina coating. The surface modifications were assessed on two samples selected from each group by atomic force microscopy and scanning electron microscopy. The samples were cemented with two different self-adhesive resin cements. The bending bond strength was evaluated by mechanical testing. RESULTS. According to the ANOVA results, surface treatments, different cement types, and their interactions were statistically significant (P<.05). The highest flexural bond strengths were obtained in nano-structured alumina coated zirconia surfaces (50.4 MPa) and the lowest values were obtained in the control group (12.00 MPa), both of which were cemented using a self-adhesive resin cement. CONCLUSION. The surface modifications tested in the current study affected the surface roughness and flexural bond strength of zirconia. The nano alumina coating method significantly increased the flexural bond strength of zirconia ceramics.

• Korean Journal of Materials Research
• /
• v.21 no.2
• /
• pp.115-119
• /
• 2011

Si Nanowire (NW) field effect transistors (FETs) were fabricated on hard Si and flexible polyimide (PI) substrates, and their electrical characteristics were compared. Si NWs used as channels were synthesized by electroless etching method at low temperature, and these NWs were refined using a centrifugation method to get the NWs to have an optimal diameter and length for FETs. The gate insulator was poly(4-vinylphenol) (PVP), prepared using a spin-coating method on the PI substrate. Gold was used as electrodes whose gap was 8 ${\mu}m$. These gold electrodes were deposited using a thermal evaporator. Current-voltage (I-V) characteristics of the device were measured using a semiconductor analyzer, HP-4145B. The electrical properties of the device were characterized through hole mobility, $I_{on}/I_{off}$ ratio and threshold voltage. The results showed that the electrical properties of the TFTs on PVP were similar to those of TFTs on $SiO_2$. The bending durability of SiNWs TFTs on PI substrate was also studied with increasing bending times. The results showed that the electrical properties were maintained until the sample was folded about 500 times. But, after more than 1000 bending tests, drain current showed a rapid decrease due to the defects caused by the roughness of the surface of the Si NWs and mismatches of the Si NWs with electrodes.

• Journal of the Korean Chemical Society
• /
• v.21 no.5
• /
• pp.379-383
• /
• 1977

Since the organophilic bentonite disperses well in polymer matrix, a composite material of polymer and bentonite was studied for its mechanical properties. To increase the degree of dispersion and the bond in forces to the polymer matrix, bentonite, encapsulated by imidazoline, was used as a filler. Polyethylene powder of particle size of 100 mesh was used, and organophilic bentonite, so-called bentone, whose particle size was 250 mesh was also used in this experiment. V-type mixer was used for mixing and Banbury mixer was used for melt-blending. The sample specimen were made by heating the mixture in the plate press, and the specimen were formed as a sheet, exactly the same as the mold on the plate. Tensile strength, bending strength and compressive strength were studied specially. Tensile strength, elongation rate, bending strength and bending rate at constant pressure were decreased as the filler content increased. Compressive strength was increased as the filler content increased.

• The Journal of Advanced Prosthodontics
• /
• v.8 no.6
• /
• pp.433-438
• /
• 2016

PURPOSE. The aim of this in vitro study was to evaluate the mechanical properties (bending strength and hardness) of seven different fiber reinforced composite posts, in relation to their microstructural characteristics. MATERIALS AND METHODS. Two hundred eighty posts were divided into seven groups of 40, one group for each type of post analyzed. Within each group, 15 posts were subjected to three-point bending strength test, 15 to a microhardess meter for the Knoop hardness, and 10 to Scanning Electron Microscope in order to determine the diameter of the fibers and the percentage of fibers embedded in the matrix. To compare the flexural strength in relation to the type of fiber, matrix, and the hardness of the posts, a Kruskal-Wallis H test was used. The Jonckheere-Terpstra test was used to determine if the volume percent of fibers in the post influenced the bending strength. RESULTS. The flexural strength and the hardness depended on the type of fibers that formed the post. The lower flexural strength of a post could be due to deficient bonding between the fiber and the resin matrix. CONCLUSION. According to the results, other factors, besides the microstructural characteristics, may also influence the mechanical properties of the post. The feature that has more influence on the mechanical properties of the posts is the type of fiber.