• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.301-306
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• 2009

High strength steels are widely used for lightweight automobile parts and the control of springback is very important in sheet metal forming. The object of this study is to develop the forming process for stair type side sill made of high strength steel, DP780. Stair type side sill with local formed area and geometry change area can improve stiffness and design freedom but there are a few studies for forming process. The forming technology considered in this paper is form type process, which have many advantages for farming of high strength steel compared with draw type process. Finite element analysis is carried out to predict formability and springback. It is shown that angle calibration of die is essential for reducing springback, and local forming involving bead is effective to control springback also. The effectiveness of local forming and angle calibration is verified by experimental.

• Transactions of Materials Processing
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• v.18 no.8
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• pp.601-606
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• 2009

High strength steels are widely used for lightweight automobile parts and the control of springback is very important in sheet metal forming. The object of this study is to develop the forming process for stair type side sill made of high strength steel, DP780. Stair type side sill with local formed area and geometry change area can improve stiffness and design freedom but there are few studies for forming process. The forming technology considered in this paper is form type process, which has many advantages for forming of high strength steel compared with draw type process. Finite element analysis is carried out to predict formability and springback. It is shown that angle calibration of die is essential for reducing springback, and local forming involving bead is effective to control springback also. The effectiveness of local forming and angle calibration is verified by experimental.

• Wind and Structures
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• v.16 no.2
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• pp.213-224
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• 2013

One of the key issues affecting the promotion of solar water heaters in Taiwan is the severe impact of typhoon each year. An experimental study was conducted to investigate the wind uplift characteristic of a solar collector model with and without a guide plate. The guide plate with different lengths and orientations with respect to wind direction was adopted. It is found that the wind uplift of a solar collector is associated with the tilt angle of the flat panel as expected. A cavity formed between the guide plate and the flat panel has a significant effect on the distributions of streamwsie and lateral pressure. Reduction in uplift is essentially coupled with the projected area of a guide plate on the lower surface of the tilt flat panel.

• Journal of Photoscience
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• v.4 no.2
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• pp.61-67
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• 1997

The model based on the idea that the p$_y$-orbital of the carbonyl oxygen is responsible to receiving hydrogen was devised for simulation of intramolecular hydrogen transfer. A Monte Carlo method was applied to free rotation of a molecular chain performed by changing the dihedral angles, and a "hit" was defined as the case when the migrating hydrogen comes within the region defined as the p$_y$-orbital and satisfies all the geometrical requirements for abstraction. A set of parameters was employed for defining the region and the requirements; $\tau$ was defined as the angle formed between O...H vector and its projection on the mean plane of the carbonyl group (- 43$\circ$ < $\tau$ < + 43$\circ$), $\Delta$ as the C=O...H angle (90 -15$\circ$ < $\Delta$ < 90 + 15$\circ$), $\theta$ as the O...H - C angle ( 180 - 80$\circ$< 0 < 180 + 80$\circ$), d as the distance from the center of the lobe of the p$_y$-orbital to hydrogen (0 < d < 1.04 ${\AA}$). The minimum value for the distance between carbonyl oxygen (O$_1$) and the migrating hydrogen (H$_i$) and for that between non-bonded atoms except the pair of O$_1$ and H$_i$ were assumed to be 0.52 ${\AA}$ and 1.54 ${\AA}$, respectively. The apphcation of this model to intramolecular $\beta$-, $\gamma$-, $\delta$-, $\epsilon$-, and $\zeta$-hydrogen abstraction in ketones and $\eta$- and $\theta$- proton transfer in oxoesters gave good results reflecting their photochemical behavior. The model was also used for prediction of photoreactivities of 2-(N,N-dibenzylamino)ethyl 2-, 3- and 4-benzoylbenzoate (1a - c). (1a - c).

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.454-461
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• 1997

Heat transfer and pressure drop for single phase flow of water in circular smooth and micro-fin tubes are measured. Copper tubes of 9.52 and 7mm outer diameter were used. The internal roughness in micro-fin tubes was formed by spiral grooves having $25^{\circ}$ helx angle, 0. 12mm fin height and 0.454mm pitch in 9.52mm tubes; $18^{\circ}$ helix angle, 0.15mm fin height and 0.322mm pitch in 7mm tubes. The measured friction factor and heat transfer coefficient are compared with relevant previous works, and the correlations for micro-fin tube are developed.

• Fire Science and Engineering
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• v.22 no.2
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• pp.44-48
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• 2008

In this paper, we measured a contact angle, surface resistivity and XPS to study the thermal aging characteristics of the epoxy resin for cast resin transformer. As a result of this experiment, we found that the contact angle increases up to $200^{\circ}C$ as it causes a re-crosslinking on the surface, but starts decreasing at $250^{\circ}C$ as it causes heat condensation. As a result of examining the oxygen/carbon peaks through the XPS analysis, we obtained a higher oxygen peak vs. carbon in the first untreated sample, but it showed the opposite trend after heat treatment. That rise in the carbon peak continued up to $200^{\circ}C$, but decreased again at the temperatures above. That's because it kept forming a stable surface structure up to $200^{\circ}C$ but its carbon combination got destroyed due to a rapid oxidization at $250^{\circ}C$. And a conduction path was formed easily with the hydrophile property caused by rapid surface activation.

• Journal of Korean Dental Science
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• v.10 no.1
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• pp.10-21
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• 2017

Purpose: The purpose of this study was to investigate the electrochemical characteristics of nanotubular Ti-25Nb-xZr ternary alloys for dental implant materials. Materials and Methods: Ti-25Nb-xZr alloys with different Zr contents (0, 3, 7, and 15 wt.%) were manufactured using commercially pure titanium (CP-Ti), niobium (Nb), and zirconium (Zr) (99.95 wt.% purity). The alloys were prepared by arc melting in argon (Ar) atmosphere. The Ti-25Nb-xZr alloys were homogenized in Ar atmosphere at $1,000^{\circ}C$ for 12 hours followed by quenching into ice water. The microstructure of the Ti-25Nb-xZr alloys was examined by a field emission scanning electron microscope. The phases in the alloys were identified by an X-ray diffractometer. The chemical composition of the nanotube-formed surfaces was determined by energy-dispersive X-ray spectroscopy. Self-organized $TiO_2$ was prepared by electrochemical oxidation of the samples in a $1.0M\;H_3PO_4+0.8wt.%$ NaF electrolyte. The anodization potential was 30 V and time was 1 hour by DC supplier. Surface wettability was evaluated for both the metallographically polished and nanotube-formed surfaces using a contact-angle goniometer. The corrosion properties of the specimens were investigated using a 0.9 wt.% aqueous solution of NaCl at $36^{\circ}C{\pm}5^{\circ}C$ using a potentiodynamic polarization test. Result: Needle-like structure of Ti-25Nb-xZr alloys was transform to equiaxed structure as Zr content increased. Nanotube formed on Ti-25Nb-xZr alloys show two sizes of nanotube structure. The diameters of the large tubes decreased and small tubes increased as Zr content increased. The lower contact angles for nanotube formed Ti-25NbxZr alloys surfaces showed compare to non-nanotube formed surface. The corrosion resistance of alloy increased as Zr content increased, and nanotube formed surface showed longer the passive regions compared to non-treatment surface. Conclusion: It is confirmed that corrosion resistance of alloy increased as Zr content increased, and nanotube formed surface has longer passive region compared to without treatment surface.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.1
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• pp.41-47
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• 1992

In SFB Process, after 110$0^{\circ}C$ annealing in wet OS12T(95$^{\circ}C$ HS12TO bubbling) atmosphere, the existence of the interfacial oxide film in micro-gap at Si-Si bonding interface was identified. The angle lapping/staining and SEM morphologies of bonding interface showed that the growing behavior of interfacial oxide made a contribution to eliminate the micro-gaps having a width of 200-300$\AA$. In case of the diodes composed of p-n wafer pairs made by SFB processes, the annealed one in wet OS12T atmosphere exhibited a dielectric breakdown phenomena of interfacial oxide at 37-40 volts d.c.

• Bulletin of the Korean Chemical Society
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• v.22 no.7
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• pp.748-752
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• 2001

Alkanethiols (CH3(CH2)n-1SH) based self-assembled monolayers (SAMs) on the clean copper surfaces have been examined for n = 4, 8, and 16. Using X-ray photoelectron spectroscopy (XPS) and contact angle analysis, it is found that alkanethiolate monolayers similar to those on gold are formed on clean copper surfaces. The monolayers are stable in air up to about 140 $^{\circ}C.$ Above 160 $^{\circ}C$ the monolayers begin to desorb through the oxidation reaction of the thiolate to sulfonate, with the alkyl chains remaining intact. Following this desorption step, the copper surface has begun to oxidize to CuO at about 180 $^{\circ}C$.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.7 no.4
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• pp.155-160
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• 2008

End part of the brake tube formed with the shape of snake head is important for the braking of automobile in safety because it has to prevent crack, fracture and defects occurred during the forming process. Especially, the shape of tube end has influence on the ability of brake. Based on the procedure of process design, in this paper, the forming operation is done by finite element method and the design variables are analyzed by Taguchi method. Design variables such as the outer angle of tube end with the shape of snake head(A), the inner angle to make a hole at tube end with the shape of snake head(B) and the forming distance at tube end(C) are used. Optimization of design variables is performed to minimize the damage factor of the tube end occurred during the forming process. The value of damage factor of 0.327 was obtained under the optimal condition like $A=114^{\circ},\;B=80^{\circ}$ and C=5.3mm, respectively.