• Journal of Welding and Joining
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• 제21권5호
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• pp.540-546
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• 2003

Recently Al alloys are being used gradually for structural materials of transports. In welding of Al alloys used for transports, good weldabilities as well as adequate mechanical properties of the welds should be ensured as structural materials. In this study, the welds formation, macro and microstructural characteristics, generation of defects and hardness distribution in welds of Al alloys of 5083, 6N01 and 7N01 by DCSP- and AC-GTA welding process, were investigated. The deeper penetration was obtained in all welds of the alloys by DCSP-GTAW with He gas, compared with those by using AC-GTAW. The 6N01 alloy showed high susceptibilities to solidification cracking in weld metal and liquation cracking in HAZ of the welding beads of both DCSP- and AC-GTAW process. The cracking ratio of 6N01 alloy was increased with increasing of welding current. The porosity ratios in weld metal of all alloys used were extremely low including all welding conditions of DCSP-GTAW. However, in AC-GTAW process, the porosity ratios of the welds using Ar gas showed much higher values than those using He gas.

• Journal of Welding and Joining
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• 제22권5호
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• pp.65-72
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• 2004

The tendency and degree of hot cracking of high strength 5083, 6N01 and 7N01 Al alloy welds by using DCSP-GTAW through modified Varestraint test and autogenous butt welding were investigated. In hot cracking test, 6N01 alloy showed the highest susceptibility to hot cracking in the weld metal and HAZ. Cracking susceptibilities generally increased with increase of solidification temperature range of the base metal and bead penetration-to-width ratio of the weld metal. The cracks in welds of the alloys vertically formed to solid-liquid interface and propagated along with columnar grain boundaries. The fracture facets of cracks showed the typical morphology of solidification crack observed as dendritic structures. Especially, in 6N01 alloy, liquation cracks which were due to elements of Si, Fe and Mg also observed in HAZ near fusion boundary. In butt welding of different Al alloys, the bead crack was mainly occurred in the welds of 6N01, 7N01 and other Al alloys together with 6N01 or 7N01. In the butt welds of 7N01, it was found that the component of Cu had an effect on the higher susceptibility to the hot cracking.

• Steel and Composite Structures
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• 제24권2호
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• pp.151-176
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• 2017

This paper deals with general equations of motion for free vibration analysis response of thick three-layer doubly curved sandwich panels (DCSP) under simply supported boundary conditions (BCs) using higher order shear deformation theory. In this model, the face sheets are orthotropic laminated composite that follow the first order shear deformation theory (FSDT) based on Rissners-Mindlin (RM) kinematics field. The core is made of orthotropic material and its in-plane transverse displacements are modeled using the third order of the Taylor's series extension. It provides the potentiality for considering both compressible and incompressible cores. To find these equations and boundary conditions, Hamilton's principle is used. Also, the effect of trapezoidal shape factor for cross-section of curved panel element ($1{\pm}z/R$) is considered. The natural frequency parameters of DCSP are obtained using Galerkin Method. Convergence studies are performed with the appropriate formulas in general form for three-layer sandwich plate, cylindrical and spherical shells (both deep and shallow). The influences of core stiffness, ratio of core to face sheets thickness and radii of curvatures are investigated. Finally, for the first time, an optimum range for the core to face sheet stiffness ratio by considering the existence of in-plane stress which significantly affects the natural frequencies of DCSP are presented.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.89-93
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• 2002

A study of noticeable improvement in welding speed in thin-plate Type 304 stainless steels gas tungsten arc (GTA) welding was investigated. The welding speeds were increased to more than 3m/min, up to 8m/min. During the welding, Direct Current Straight Polarity (DCSP) and pulsed current GTA welding processes were carried out, respectively. The appropriate high speed welding parameters were established while achieving a high quality weld. After this, Erichsen test and tensile test were performed. The results obtained wert summarized as following: ultra high speed welding for thin-plate Type 304 could be satisfactorily welded with high speed from 3m/min to 8m/min in both DCSP and pulsed GTA welding; Increasing welding speed was found to decrease the ductility, tensile strength md elongation of welded joint; The optimal frequency would be 200Hz-500Hz for high speed welding in pulsed current welding; DCSP welding could obtain the better results of Erichsen test and tensile test than those of pulsed current welding obtained.

• International Journal of Korean Welding Society
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• 제3권1호
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• pp.29-33
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• 2003

The ferritic stainless steels are generally considered to have poor weldability compared with that of the austenitic stainless steels. However the primary advantages of ferritic stainless steels include lower material cost than the more commonly used austenitic stainless steels and a greater resistance to stress corrosion cracking. Thus, the weldability of ferritic stainless steels was investigated in this study. In concerning the weldability, Grain size measurement test, Erichsen test and Varestraint test were involved. full penetration welds were produced by autogeneous direct current straight polarity (DCSP) and pulsed currents gas tungsten arc welding (GIAW) and the effect of pulsed currents welding on the welds was compared to that of DCSP welding. The results showed that pulsed current was effective to refine grain size in the weld metal and the finest grain size was obtained at the frequency of 150Hz. In addition, the ductility of welds was lower than that of base metal. Finally, autogeneous type 444 welds were less susceptible to macro solidification cracks, but more sensitive to micro cracks; SEM/EDS analysis indicated that all the inclusions in the crack showed enrichment of Mn, Si, O and S.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.107-112
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• 2002

Ferritic stainless steels would be the most important alloys under the chloride environment. They are a cheaper alternative to austenitic stainless steels [1]. The present study is related to gas tungsten arc welding (GTAW) characteristics of Type 444 stainless steels. The heat of welding leads to grain coarsening in the HAZ and in the weld metal of ferritic stainless steels because they solidify directly from the liquid to the ferritc phase without any intermediate phase transformation. It is therefore recommended that these alloys be welded with a low heat input and at high welding speeds. Attempts to improve weldability were made by using of direct current straight polarity (DCSP) and pulsed current GTAW processes in this study. Measuring weld bead, grain size and Erichsen test were performed and the effects of heat input, pulse frequency on the weld metal and HAZ were studied. The main results were obtained as followings: decreasing heat input was effective to control the width of weld both in DCSP welding and in pulsed current welding; pulsed current welding was found to refine the grain size effectively and the finest grain size was found at the frequency of 150Hz in pulsed current welding; it was found that decreasing heat input also refine the HAZs effectively and the frequency had no different effect on HAZ at the same heat input; the ductility could be improved effectively in pulsed current welding.

• 한국미생물·생명공학회지
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• 제36권1호
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• pp.43-48
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• 2008

함초(Salicornia herbacea)는 염습 지대에서 자생하는 명아주과에 속하는 일년초 식물로서 우리말로는 퉁퉁마디라고 불리우며, 식용과 약용으로 이용되고 있다. 건조된 함초로부터 열수 추출을 하여 조추출물(CSP)을 얻었으며 조추출물을 한외 여과하여 다당체(SP1)를 얻었다. 이렇게 얻은 조추출물과 다당체에 대해 streptozotocin (55 mg/mL/kg)으로 유발한 당뇨 쥐를 이용하여 정상 대조군(NC)과 당뇨 대조군(DC), 당뇨 조추출물군(DCSP), 당뇨 다당체군(DSP1)으로 분류하고 각각 조추출물과 다당체 2%를 6주간 공급하여 실험한 결과, DCSP군과 DSP1군에서는 대조군과 비교하여 혈당은 10%, 25%씩 감소하고, 중성 지방은 13%, 20%씩 감소하여 유의적인 수치를 나타내었다. 즉, 함초로부터 조추출물과 다당체를 획득하여 이들에 대한 항당뇨 실험을 한 결과, 조추출물과 다당체에서 혈당 저하와 중성 지방 저하의 효과를 보였는데, 조추출물보다 다당체에서 더 높은 활성을 보였다. 따라서 함초 다당체는 항당뇨 활성을 가진 바이오헬스 소재로 개발될 수 있을 것으로 기대된다.

• 산업경영시스템학회지
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• 제23권61호
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• pp.33-39
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• 2000

In this paper, we present an algorithm for the multicast routing problem when there exit the cell replication limits of ATM switching nodes. This problem can be formulated as a Degree Constrained Minimum Steiner Tree Problem(DCSP). The proposed algorithm is a modification of the shortest path heuristic originally devised for minimum Steiner tree problem. From the experimental results, it can be seen that our algorithm is efficient to obtain a near optimal solution with comparatively low computational time.

• International Journal of Korean Welding Society
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• 제3권1호
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• pp.23-28
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• 2003

The effect of the welding speeds on the weld bead shape, microstructure, and mechanical properties in type 304 austenitic stainless steels was investigated by microscopic test, Erichsen test and tensile test. In this study welds were produced using autogeneous Direct Current Straight Polarity (DCSP) and pulsed current GTA welding. This study shows the ferrite content, ductility, tensile strength and elongation of high speed welds are decreased with increasing welding speed. The high speed welds exhibits satisfactory tensile strength, though the ductility is not good as that of the base metal.

• International Journal of Contents
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• 제1권1호
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• pp.29-34
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• 2005

In this paper, we proposed an advanced authentication structure for reducing the certificate acquisition time which is one of the factors that should be improved in a conventional wireless PKI. A conventional key exchange method simply performs the key exchange setup step based on discrete algebraic subjects. But the mutual-authentication procedure of wireless PKI for reducing authentication time uses an elliptical curve for a key exchange setup step. We simulated and compared the authentication structure proposed by Sufatrio, K. Lam[4] and proposed authentication structure in terms of the authentication time. Simulation results show that the proposed method reduces the authentication time compared to the conventional wireless PKI authentication method.