• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.783-790
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• 2004

Adhesive-bonded joints are widely used in the industry. Recently, applications of adhesive bonding joints have been increased extensively in automobile and aircraft industry. The strength of adhesive joints is influenced by the surface roughness, adhesive shape, stress distribution, and etc. However, the magnitude of the influence has not yet been clarified because of the complexity of the phenomena. In this study, as the fundamental research of adhesive bonding joints, the effects of adhesive shape and loading speed on bonding strength properties and durability of aluminum to polycarbonate single-lap joints were studied. To evaluate the effect of adhesive shape, several modified shapes were used, and loading speeds were varied from 0.05 to 5 mm/min. As a result, the load-displacement distribution was shown a brittle fracture tendency. The trigonal edged single lap and bevelled lap joints showed the higher strength than the plain single lap, trigonal single lap, joggle lap and double lap joints in same adhesive area. The fractures of trigonal single lap and trigonal edged single lap joints that had the higher strength level were shown as the mixture type of the cohesive and interfacial-failure, mostly joggle lap joints that had the lower strength level were shown as the adhesive-failure.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.113-118
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• 2010

A straight pipe is used after complicated bending work in a mechanical system. In this work process, the plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the behavior of pipe fracture. For this reason, residual stress must be evaluated. Measuring the residual stress of a U-shaped pipe is difficult with existing destructive and nondestructive measurement methods. In this paper, the residual stress of a U-shaped aluminum pipe (99.7% pure aluminum) was evaluated from the Raman shift by Raman spectroscopy and FEM(Finite Element Method, FEM) analysis. The results of the stiffness test by FEM analysis are compared with those by experiments. The analyzed results of the Raman spectra showed a similar tendency with the results of the FEM analysis with respect to the residual stress distributions in U-shaped pipes. Also, the results of the bending tests showed resemblance to each other.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.315-318
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• 2003

Recently, condenser tube which is used for a cooling system of automobiles is mainly manufactured by the conform extrusion but this method is inferior as compared with direct extrusion in productivity per the unit time and in the equipment investment. Therefore, it is essential for the conversion of direct extrusion with porthole die. The direct extrusion with porthole die can produce condenser tube which has the competitive power in costs and qualities compared with the existing conform extrusion. This study is designed to evaluate metal flow, welding pressure, extrusion load tendency of mandrel deflection that is affected by variation of porthole shape in porthole die. Estimation is carried out using finite element method under the non-steady state. Also this study was examined into the cause of mandrel fracture through investigating elastic deformation of mandrel during the extrusion.

• Journal of Welding and Joining
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• v.4 no.1
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• pp.47-57
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• 1986

The elastic-plastic fracture toughness J_{Ic}$ of submerged arc welded structural steel $SB_{41}$ which has the properties of low strength and high ductility was discussed, especially paying attention to a comparison between two methods recommended by ASTM and JSME. $J_{IC}$ tests were carried out with compact specimens by means of R-curve, SZW, ultrasonic and electric potential methods. Based on the investigations in this study, the results obtained are as follows; (1) The JSME R-curve method gave the smallest $J_{IC}$ values which were physically closest to the crack initiation and seemed to be more practical and stable procedure between the two R-curve methods. (2) The JSME SZW method tended to slightly overestimate the $J_{IC}$ values at initiation of ductile tearing. (3) The ultrasonic and electric potential methods which also had a tendency to overestimate these $J_{IC}$ values were confirmed to be applicable and useful in determining these values. (4) The $J_{IC}$ values by the JSME R-curve method were 18.06 kgf/mm and 17.25kgf/ mm for the smooths and the side grooved CT specimen respectively.

• Journal of Welding and Joining
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• v.22 no.5
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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.

• Journal of Korea Foundry Society
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• v.8 no.3
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• pp.296-309
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• 1988

In this study the mechanical properties of ferritic ductile cast iron in as-cast are discussed by metallographic considering the effect of phosphorus content(about 0 - 0.8wt.%). In ferritic S.G. cast iron containing about 4.2wt.% Si, 0.5wt.% Ni, 0.02wt.%B, these samples are investigated for castability, microstructure, machinability, wear resistance, mechanical and thermal properties. The main results are summarized as follows. 1) The chill depth increased greatly with P addition up to about 0.6wt.% but the tensile strength and the elongation are decreased smoothly. 2) The size of S.G. and the amount of steadite increase with increasing P content. This means the tendency of increasing the number of S.G. 3) The maximum value of wear by mechanical fracture was appeared at the abrasion speed of 1.14m/sec and the plastic Flow layers are stretched longly on the wear surface with decreasing P content. 4) Although the coefficient of thermal expansion increased with P addition, the cast iron growth was slowing down extremely at 0.6w.% P or more.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.853-855
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• 1998

The electrical resistivity and mechanical properties of the hot-pressed and annealed ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_{3}$(6:4wt%). In this microstructures. no reactions were observed between $\beta$-SiC and $ZrB_2$, and the relative density is over 97.6% of the theoretical density. Phase analysis of composites by XRD revealed mostly of a $\alpha$-SiC(6H, 4H), $ZrB_2$ and weakly $\beta$-SiC(15R) phase. The fracture toughness decreased with increased $Al_{2}O_{3}+Y_{2}O_{3}$ contents and showed the highest for composite added with 4wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives. The electrical resistivity increased with increased $Al_{2}O_{3}+Y_{2}O_{3}$ contents because of the increasing tendency of pore formation according to amount of liquid forming additives $Al_{2}O_{3}+Y_{2}O_{3}$. The electrical resistivity of composites is all positive temperature coefficient resistance(PTCR) against temperature up to $700^{\circ}C$.

• Journal of Korean Association for Spatial Structures
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• v.20 no.3
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• pp.91-98
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• 2020

For form stability of membrane structures, membrane material is required to be in tension. Therefore, in planning and maintenance management, the engineer should consider enough about introduction of stress during construction and re-introduction of stress after completion. Clamping part is an important portion with the function for introducing tension into membrane materials, and the function to transmit stress to boundary structures, such as steel frames. Then, the purpose of this research is to clarify stress condition and stress transfer mechanism including clamping part of membrane structures, and to grasp the changing tendency of membrane structures with the passage of time. In this research, following previous one, we perform well-balanced evaluation by conducting tensile fractured tests of clamping part's specimens, and by measuring individually the amount of displacement of not only overall specimen's length but membrane material and clamping part. Thereby, we consider the influence the difference in the hardness of edge rope and the difference in the direction of thread affect modification and fracture load.

• Journal of the Korean Ceramic Society
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• v.43 no.1 s.284
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• pp.48-54
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• 2006

Hydroxyapatite $(HAp,\;Ca_{10}(PO_4)_6(OH)_2)$/alumina composites were fabricated with the addition of fluorides, such as $MgF_2$ and $CaF_2$. In this study, the effect of fluorides on the inhibition of phase decomposition and the mechanical properties of HAp was investigated. Due to the higher solubility of F ion in HAp structure, $MgF_2$ additive was more effective compared to $CaF_2$ additive in the lowering decomposition temperature of HAp. Therefore, the dissociation tendency of HAp was fully inhibited below $1400^{\circ}C$. The mechanical properties of HAp composites with $MgF_2$ additive showed higher value (flexural strength: $\~170MPa$, Vickers hardness: $\~7\;GPa$, fracture toughness: $\~1.5\;MPam^{1/2}$) compared to $MgF_2-free$ composites. The linear thermal expansion coefficient of HAp composites with $MgF_2$ showed the value of $16.4\times10^{-6}/^{\circ}C\;at\;20\~400^{\circ}C $.

• Journal of Ocean Engineering and Technology
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• v.23 no.5
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• pp.79-84
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• 2009

Super duplex stainless steel has long life in severe environments by showing the enough strength and corrosion resistance. Therefore, the fracture mechanics approach needs to support the structural strength integrity for the used material. In this study, fatigue crack propagation behavior was investigated to super duplex stainless steel with 0.2% nitrogen. The various volume fraction and distribution of austenite structure for applied specimen in test were obtained by changing the heat treatment temperature and cycle. From test results, fatigue crack propagation rate showed two kinds of tendency between da/dN and ${\Delta}K$ according to distribution of austenite structure and structure anisotropy.