• Journal of the Korean Society for Precision Engineering
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• v.14 no.7
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• pp.82-90
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• 1997

When a structure is made by the process of forging, it has the different mechanical properties from those it has before the process. This study is based on the crack closure phenomenon of the crack growth behavior of forged AI7050-T7452. The specimens were prepared in three kinds of forging ratio in order to find out the effects of crack closure on the forged material and compare the crack growth behavior with not-forged aluminum. COD method and strain gage method were used in measuring the crack closure stress and the results from those methods were compared each other. FEM analysis was applied to verify the effective stress intensity factor range by the superposition of the crack closure load to the crack tip. In the result of this study, the crack closure stress decreased with increasing the forging ratio due to the finer grain size and the brittle manner.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.197-204
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• 2007

Fretting is a contact damage process that occurs between two contact surfaces. Fretting fatigue reduces fatigue strength of the material due to low amplitude oscillatory sliding and changes in the contact surfaces of strongly connected machine and structure such as bolt, key, pin, fixed rivet and connected shaft, which have relative slip of repeatedly extreme low frequency amplitude. In this research, the fretting fatigue behavior of 2024-T3511 and 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were experimentally estimated. Based on this experimental wort the following results were obtained: (1) A significant decrease of fatigue lift was observed in the fretting fatigue compared to the plain fatigue. The fatigue limit of 2024-T3511 aluminum alloy decreased about 59% while 7050-T7451 aluminum alloy decreased about 75%. (2) In 7050-T7451 specimen using ATSI4030 contact pad, crack was initiated more early stage than using 2024-T3511 contact pad. (3) In all specimens, oblique cracks were initiated at contact edge. (4) Tire tracks and rubbed scars were observed in the oblique crack region of fracture surface.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.123-126
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• 2003

A high strength aluminum alloy bolt (A7050, T7 temper treatment) has been developed by the authors. The bolt has a small grain size in the whole area of the bolt because of the large equivalent strain followed by thermo-mechanical treatment. As the bolt made of A 7050 has a risk of stress corrosion cracking, each grain should be strengthened the grain inside than the grain boundary in order to improve the stress corrosion cracking resistance. It has been confirmed that the nano-indentation hardness at each grain inside increased with the increasing equivalent strain by thermo-mechanical treatment processing.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.3
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• pp.200-206
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• 1998

The aim of this study is to investigate the effect of impurity level and fabrication processes on the strength, impact and fracture toughness of 7075, 7050 and 7175 aluminum alloy forgings. A specially processed 7175S-T74 aluminum forgings was superior to a conventionally processed 7075-T73, 7050-T74 and 7175-T74 aluminum forgings in both strength and toughness. The reduction of impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as $Al_7Cu_2Fe$ and $Mg_2Si$. A further reduction of the amount of second phase particles has been observed by applying a special fabrication process. This phenomena result from the application of intermediate soaking at higher temperature and more sufficiant hot working temperature than that of a conventional processing.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.4
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• pp.39-45
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• 2012

In this paper, process conditions are investigated for elimination of the grain coarsening and improved material flow during forging process by both of experiments and FEM analysis. Particular interest has been given to understand role of preform shape on the grain coarsening behavior and magnitude of the hammer forging load. As the results of FEM simulation by using DEFORM-3D, the simulated forging loads were 2,200ton in the case of a machined bar which is machined from 65mm to 60mm diameter, and below 1,900ton in the case of machined preform, respectively. The use of preform has been beneficial for reduction of the forging load and elimination of the grain coarsening. However, in the case of as received bar and the round bar, which was machined to 2.5mm thickness in surface layer, some degree of local grain coarsening behavior has been observed. The optimized preform shape could be properly designed by applying the FEM simulation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1995.11a
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• pp.195-203
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• 1995

본 연구는 강도와 인성이 우수한 7175Al 단조재의 국산화 개발을 위하여 기존 7XXX합금의 제조공정(일반공정)을 적용한 7075-T6/T73, 7050-774 및 7175-T74 단조재와 중간열처리, 용체화처리 등을 고온처리하는 특수제조 공정을 적용한 7175-T74 단조재의 강도, 파괴인성($K_IC$) 및 피로특성을 비교 평가하였다. 특수공정을 적용한 7175S-T74 단조재는 일반공정의 7075-T73, 7050-T74 및 7175-T74재보다 강도, 파괴 인성 및 피로특성이 향상되었다. 이것은 주조시 응고과정에서 형성되는 2차상입자의 감소와 특수공정의 적용효과에 기인하는 것으로 판단된다.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.123-128
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• 2022

This paper proposes a non-explosive separation device for the deployable SAR antenna. This device utilises a Ni-Cr wire to restrain the antenna's belt mechanism, and joule-heating is used to minimise the impact of deployment. After the Ni-Cr wire has been cut, the device is deployed through the preload of the belt mechanism. Considering the design load(99g) and preload conditions, FEM analysis for AL7050 and Ti was performed. This analysis revealed that the amount of deformation for AL7050 was 0.256 mm with a margin of +0.09. In addition, by performing orbital thermal analysis, the temperature distribution for AL7050 in the worst cold case is confirmed as -50 to +2℃ and -10 to +90℃ in the worst hot case. This analysis confirmed that the separation device would remain stable even in the worst environment.

• Microbiology and Biotechnology Letters
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• v.4 no.4
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• pp.166-178
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• 1976

Taxonomic study of 11 strains of Bacillus coagulans and 14 strains of 13 spccies of Bacillus by deoxyribonucleic acid (DNA)-DNA hybridization were conducted. Among the 11 strains of B. coagulans, 6 were isolated from soil and the rest were the authentic strains obtained from American Type culture collection (ATCC) or the Institute for Fermentation, Osaka (IFO). All strains were examined to confirm as they are expected species of B. coagulans by the methods of Cordon et al. according to Bergey's Manual (8th ed.). The intraspecific DNA homology indexes among the 11 strains of B. coagulans using strain ATCC 7050 as the standard ($^3$H labeled input DNA) showed 76％ or, more, respectively. These findings accorded well with the results of the conventional taxonomic study according to the Bergey's Manual. The interspecific DNA homology indexes between B. coagulant strain ATCC 7050 and the type cultures of B. subtilis (168), B. licheniformis (IFO 12107), B. pumilus (IFO 12110), B. firmus (ATCC 14575), B. lentus (ATCC 10840), B. circulans (ATCC 4513), B. macelans (ATCC 8244), B. polymyxa (ATCC 842), B. sphaericus (ATCC 14577), B. brevis (ATCC 8246, IFO 12334), B. laterosporus (ATCC 64), and B. pantothenticus (ATCC 14576) respectively, showed 2 to 4％, while that of between B. coagulans ATCC 7050 and Escherichia coli K-12 was less than 1 ％.

• Korean Journal of Materials Research
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• v.10 no.7
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• pp.493-498
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• 2000

The effects of RRA treatment on the microstructures and mechanical properties of 7050 Al alloy were investigated by differential scanning calolimetry, transmission electron microscopy, microhardness measurement and electrical conductivity. The hardness of 2nd-step aged specimen at $175^{\circ}C$ was decreased to mimimum value and increased to a peak hardness, and then re-decreased with retrogression treatment. It was found that the hardness of 2nd-step aged specimen was further increased by 3rd step aging treatment($120^{\circ}C$x24h). The initial decrease in hardness during 2nd-step aging was due to the partial dissolution of pre-existing GP zone, the major precipitation hardening phase at T6 condition. It was confirmed that the major precipitation hardening phase at 3rd-step aging was GP zone and η' phase. The electrical conductivity increased continually through 2nd-step and 3rd-step aging treatment. It was conclude that the optium 2nd-step aging condition was at $175^{\circ}C$ for 50min by considering the hardness and electrical conductivity.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.3
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• pp.161-168
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• 1996

The purpose of this study is to investigate the effect of impurity level and fabrication processes on the strength, fracture toughness and fatigue resistance of 7075, 7050 and 7175 high strength aluminum forgings. It has been verified that plane strain fracture toughness and fatigue characteristics of a specially processed 7175S-T74 alloy is superior to a conventionally processed 7075-T6/T73, 7050-T74 and 7175-T74 alloys. These beneficial effects primarily arise from two view points, i.e., the effect of reducing the impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as $Al_7Cu_2Fe$ and $Mg_2Si$. Futher reduction of the amount of nonequilibrium second phase particles has been observed by applying a special fabrication process.