• Steel and Composite Structures
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• v.21 no.1
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• pp.137-156
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• 2016

Due to excellent advantages such as better illuminative effects, considerable material savings and ease and rapidness of construction, the bolted ball-cylinder joint which is a new type joint system has been proposed in space truss structures. In order to reveal more information and understanding on the behaviour of bolted ball-cylinder joints, full-scale experiments on eight bolted ball-cylinder joint specimens were conducted. Five joint specimens were subjected to axial compressive force, while another three joint specimens were subjected to axial tensile force. The parameters investigated herein were the outside diameter of hollow cylinders, the height of hollow cylinders, the thickness of hollow cylinders, ribbed stiffener and axial force. These joint specimens were collapsed by excessive deformation of hollow cylinders, punching damage of hollow cylinders, evulsion of bolts, and weld cracking. The strain distributions on the hollow cylinder opening were mainly controlled by bending moments. To improve the ultimate bearing capacity and axial stiffness of bolted ball-cylinder joints, two effective measures were developed: (1) the thickness of the hollow cylinder needed to be thicker; (2) the ribbed stiffener should be adopted. In addition, the axial stiffness of bolted ball-cylinder joints exhibited significant non-linear characteristics.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.2
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• pp.85-91
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• 1998

In nuclear fuel manufacturing process, end-closure welding has long been recognized as requiring very high integrity. In this basic study, ECT(eddy current testing) method for end-closure welding has been developed to detect end cap weld discontinuities for nuclear fuel safety. In order to improve the inspection reliability, the maximum scanning speed and the maximum frequency is investigated for end-closure welding inspection. The bandpass filter(0-250Hz) is used for removing noise effects. This study shows that ECT method is effective and sensitive for the detection of small defect(0.35mm diameter).

• Steel and Composite Structures
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• v.37 no.4
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• pp.481-492
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• 2020

Twenty-two corrosion-damaged columns were simulated through accelerated steel corrosion tests. Eight specimens were directly tested to failure under axial load, and the remaining specimens were tested after concrete-filled steel tube (CFST) strengthening. This study aimed to investigate the damage of RC columns after corrosion and their restoration and enhancement after strengthening. The research parameters included different corrosion degrees of RC columns, diameter-to-thickness ratio of steel tube and the strengthening concrete strength. Experimental results showed that CFST strengthening method could change the failure mode of corrosion-damaged RC columns from brittleness to ductility. In addition to the bearing capacity provided by the strengthening materials, it can also provide an extra 26.7% amplification because of the effective confinement provided by steel tubes. The influence of corrosion on reinforcement and concrete was quantitatively analysed and considered in the design formula. The proposed formula accurately predicted the bearing capacity of the strengthened columns with a maximum error of only 7.68%.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.581-584
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• 2004

Currently, there are many subscriber access networks: PSTN, ADSL, Cellular Network, IMT200 and so on. To these service providers that provide above network service, it is important that they authenticate and authorize legal subscribers and account for their usage. At present, There exist the several protocols that Support AAA(Authentication, Authorization and Accounting) service : RADIUS, Diameter, TACACS+. Nowadays, RADIUS has used for AAA service widely. It has been extended to support other access network environment. So, we extend RADIUS to support environment of Mobile IPv6. Mobile IPv6 uses IPsec as a security mechanism, basically. But, IPsec is a heavy security technology for small, portable, mobile device. Especially, it is serious at IKE, the subset of IPsec. IKE is a key distribution protocol that distributes the key to the endpoints of IPsec. In t:lis paper, we extend RADIUS to support environment of Mobile IPv6 and simplify the IKE phase of IPsec by AAA system distributing the keys by using its security communication channel. Namely, we propose the key distribution method for IPsec SA establishment between mobile node and home agent. The suggested method was anticipated to be effective at low-power, low computing deyice. Finally, end users feel the faster authentication.

• Journal of the Korean Ceramic Society
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• v.45 no.9
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• pp.507-511
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• 2008

A "C-sphere" specimen geometry was used to determine the failure strength distributions of a commercially-available bearing-grade silicon nitride ($Si_3N_4$) with ball diameters of 12.7 and 25.4 mm. Strengths for both diameters were determined using the combination of failure load, C-sphere geometry, and finite element analysis and fitted using two-parameter Weibull distributions. Effective areas of both diameters were estimated as a function of Weibull modulus and used to explore whether the strength distributions predictably scaled between each size. They did not. That statistical observation suggested that the same flaw type did not limit the strength of both ball diameters indicating a lack of material homogeneity between the two sizes. Optical fractography confirmed that. It showed there were two distinct strength-limiting flaw types common to both ball diameters, that one flaw type was always associated with lower strength specimens, and that a significantly higher fraction of the 25.4-mm-diameter C-sphere specimens failed from it. Predictable strength-size-scaling would therefore not result as a consequence of this because these flaw types were not homogenously distributed and sampled in both C-sphere geometries.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.7
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• pp.644-649
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• 2006

This paper presents a new disk-type piezoelectric transformer. The input side of the transformer has a crescent-shaped electrode and the output side has a focused poling direction. The piezoelectric transformers operated in each transformer's resonance vibration mode. The electrodes and poling directions on commercially available piezoelectric ceramic disks were designed so that the planar or shear mode coupling factor $(k_p\;k_{15})$ becomes effective rather than the transverse mode coupling factor $(k_{31})$. ANSYS finite element code was used to analyze transformer behavior and to optimize electrode and poling configurations. The voltage step-up ratio of the proposed transformer has been markedly improved in comparison with that of the equivalent rectangular(Rosen) type. A single layer prototype transformer, $20\sim30mm$ in diameter and $1.0\sim3.5mm$ thick, was fabricated, such as step-up ratio, power transformation efficiency, and temperature were measured. While the transformer was driving a Cold Cathode Fluorescent Lamp(CCFL), the temperature field of the transformer was also observed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.7 s.250
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• pp.773-778
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• 2006

High-aspect-ratio nano-hair or nano-pillar arrays have great potential in a variety of applications. In this study, we present a simple and cost-effective replication method of high-aspect-ratio polymer nano-hair arrays. Highly ordered nano-porous AAO (anodic aluminum oxide) template was utilized as a reusable nano-mold insert. The AAO nano-mold insert fabricated by the two-step anodization process in this study had close- packed straight nano-pores, which enabled us to replicate densely arranged nano-hairs. The diameter, depth and pore spacing of the nano-pores in the fabricated AAO nano-mold insert were about 200nm, $1{\mu}m$ and 450nm, respectively. For the replication of polymer nano-hair arrays, a UV nano embossing process was applied as a mass production method. The UV nano embossing machine was developed by our group for the purpose of replicating nano-structures by means of non-transparent nano-mold inserts. Densely arranged high-aspect-ratio nano-hair arrays have been successfully manufactured by means of the UV nano embossing process with the AAO nano-mold insert under the optimum processing condition.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.929-934
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• 2001

This study aimed to examine the cause of latent hydraulic property manifestation of ground granulated blast-furnace slag(GGBFS) using different alkali activators in pH, type and quantity. According to the experimental result, the higher pH value accelerated lastly latent hydraulic property and the early stage strength of GCBFS was ranked as activators with the higher pH, in an order of NaOH, $Ca(OH)_{2}$ and $Na_{2}$$Co_{3}$. Also, NaOH had accelerated latent hydraulic property of GGBFS, which had 40~50% of the 3 and 7 days compressive strength of base mortar in case of using 10% of powder-weight. In the case of 30% of GGBFS substitution with annexing 2.5% $Ca(OH)_{2}$, the compressive strength on the 3 and 7 days of the early-age, was increased to 5~10% than that of the same admixture with no activator. With annexing 5.0% $Ca(OH)_{2}$, the strength was increased to 10~20%. Although activator NaOH was effective on the manifestation of latent hydraulic property, it caused cement mortar compressive strength decrease by enlarging pore diameter.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.997-1002
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• 2012

Emission regulations have been strengthened step by step for marine engines. A noble measure is required both inside and outside of the combustion chamber. The combustion characteristics in cylinder have a very close relationship with the exhaust emission characteristics. Injection valve and nozzle hole geometry is an important factor for combustion. The study to improve the spray characteristics has concentrated on nozzle inlet geometry and nozzle hole diameter, but the exit geometry has not considered. In this study the nozzle exit angle variation was tested. The results show that the angle between $30^{\circ}$ and $60^{\circ}$ is more effective than the other cases.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.6
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• pp.57-62
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• 2015

A large variety of pipe flanges are required in the marine and construction industry. Pipe flanges are usually welded or screwed to the pipe end and are connected with bolts. This approach is very simple and has been widely used for a long time; however, it results in high development costs and low productivity, and the products made through this approach usually have safety problems in the welding area. In this research, a new approach for forming pipe flanges based on cold forging and the floating die concept is presented. This innovative approach increases the effectiveness of the material usage and saves time and costs compared with the conventional welding method. To ensure the dimensional accuracy of the final product, finite element analysis (FEA) was carried out to simulate the process of cold forging, and orthogonal experiment methods were used to investigate the influence of four manufacturing factors (stroke of distance, pin die angle, forming of pipe diameter, and speed of the die) and predict the best combination of them. The manufacturing factors were obtained through numerical and experimental studies, which show that the approach is very useful and effective for the forming of pipe flanges and could be widely used in the future.