• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.75-82
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• 2005

Recently the needs of high reliable substances of high strength and high ductility are gradually increased with the development of aerospace industry. The characteristics of maraging steel has high ductililty, formability, corrosion resistant and high temperature strength and is easy to fabricate, weld and treat with heat, and maintain an invariable size even after heat treatment. e steels are furnished in the solution annealed condition and they achieve full properties through martensitic precipitation aging a relatively simple, low temperature heat treatment. As is true of the heat treating procedures, aging is a time/temperature dependent reaction. Therefore, the objective of this stud)'was consideration of fatigue characteristics according as Nb(niobium) content and time/temperature of heat treatment change. Also the stress analysis, fatigue lift, and stress intensity factor were compared with experiment results and FEA(finite element analysis) result. The maximum ftresses of)( Y, and Z axis direction showed about $2.12\times$10$^{2}$MPa, $4.40\times$10$^{2}$MPa and $1.32\times$10$^{2}$MPa respectively. The fatigue lives showed about $7\%$ lower FEA result than experiment result showing almost invariable error every analyzed cycle. Stress intensity factor of the FEA result was lower about $3.5~ 10\%$ than that of the experiment result showing that the longer fatigue crack ten添 the hi인or error. It considered that the cause for the difference was the modeled crack tip having always the same shape and condition regardless of the crack growth.

• Archives of Plastic Surgery
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• v.40 no.4
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• pp.330-334
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• 2013

Background Ultrasound-aided fixation is a recently developed alternative method of treatment of zygomatico-maxillary (ZM) fracture, and it can resolve the problems of excessive torsion force and subsequent fractures of screws. We conducted this study to evaluate the clinical usefulness of ultrasound-aided fixation as compared with the conventional fixation method using a drill and an expander in patients with ZM fracture. Methods We conducted a retrospective study in 35 patients with ZM fracture who had been treated at our hospital during a period ranging from March of 2008 to December of 2010. We divided them into two groups: an ultrasound-aided fixation group, comprising 13 patients who underwent ultrasound-aided fixation (SonicWeld Rx, KLS Martin), and a conventional group, comprising 22 patients who underwent conventional fixation (Biosorb FX, Linvatec Biomaterials Ltd.). We compared such variables as sex, direction, age at operation, follow-up period, operation duration, number of fixed holes, and time to discharge between the two groups. Results The ultrasound-aided fixation reduced the operation duration by about 30 minutes as compared with that of conventional fixation. There was no significant difference in follow-up period, number of fixed holes, or time to discharge between the two groups. Furthermore, there were no complications in either group. Conclusions The ultrasound-aided fixation of fractured ZM bone using an absorbable implant system is safe and effective in promptly reducing the bone fracture and providing satisfactory cosmetic outcomes over time.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.8
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• pp.28-37
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• 1999

This investigation is the result of the structural analysis by finite element method and test for considering stress distribution and stress concentration to be generated according to the change of attached shape and method of the bracket to pipe in welding structure. Generally, members that consist structures are subjected to various forces and are jointed each other with a number of bracket. In this case, circular pipe was adapted in order to weld these members easily and to study the optimal design which is used a beam with shape section as main components of the structure, According to attached shape and method, distributed stress on circular pipe is appeared so differently. This may result deeply effects with respect to thickness, material properties. So a study on attaching shape and method of bracket to circular pipe is needed. In this paper, to obtain the maximum equivalent stress or stress concentration was used experimental and F.E.M. analysis. First five parameter was defined with respect to attached a shape and method to circular pipe i.e. the variation of the attached area, the variation of the attached shape, the variation of the attached length, the variation of both directin angles, the variation of the upper angle. Afterward the experimental analysis was practiced as the variation of the both direction angel and the finite element analysis was practiced as each parameters. We can discover stress distribution and stress concentration according to the change of form of bracket. And the result can be referenced for a design of similar structure.

• Journal of Welding and Joining
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• v.26 no.4
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• pp.79-84
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• 2008

Use of sheet metal structure is increased in various fields such as automobile, aerospace and communication equipment industry. When this structure is welded, welding distortion is generated due to the non-uniformity of temperature distribution. Recently welding distortion becomes a matter of great importance in the structure manufacture industry because it deteriorates the product's quality by bringing about shape error. Accordingly many studies for solving the problems by controlling the welding distortion are being performed. However, it is difficult to remove all kinds of distortion by welding process, though various kinds of methods for reducing distortion are applied to production. Consequently, straightening process is operated if the high precision quality is requested after welding. The local heating method induces compression plastic deformation by thermal expansion in the heating stage and then leaves constriction of length direction in the cooling stage. Accordingly, in the case of sheet metal structure, straightening effect is expected by heating for the part of distortion. This study includes numerical analysis of straightening effect by the local heating method in distortion comes from production of welded sheet metal structure. Particularly straightening effect followed by dimensions of heating area is analyzed according to the numerical analysis. The numerical analysis is performed by constructing 3-dimensional finite element model for 0.4mm stainless steel-sheet metal. Results of this study confirm that straightening effect changes as heating area increases and the optimum value of heating area that proves the maximum straightening effect exists.

• Corrosion Science and Technology
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• v.19 no.6
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• pp.296-301
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• 2020

Failure analysis on the welded type 304 pipe used for cooling water piping in the district heating primary side was conducted. Inorganic elements and bacteria in the cooling water and in corrosion products were analyzed, and the weldment was inspected by microscopy and a sensitization test. Corrosion damages were observed in the heat-affected zone, on weld defects such as incomplete fusion or excessive penetration caused by improper welding, or/and at the 6 o'clock position along the pipe axial direction. However, the level of concentration of chloride in the cooling water as low as 80 ppm has been reported to be not enough for even a sensitized type 304 steel, meaning that the additional corrosive factor was required for these corrosion damages. The factor leading to these corrosion damages was drawn to be the metabolisms of the types of bacteria, which is proved by the detection of proton, sulfur containing species, biofilms, and both bacteria and corrosion product analyses.

• Corrosion Science and Technology
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• v.22 no.6
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• pp.435-446
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• 2023

Corrosion behaviors of laser-welded super duplex stainless steel (SDSS) tubes after exposure to an actual power plant environment for one year and those of fin-tube welded SDSS were evaluated. Results showed that corrosion damage on the back side of the SDSS tube in the direction of hot air was higher than that on the front side regardless of weldment location. However, corrosion damage showed no difference between weldment and base metal due to recovery of phase fraction in the weldment through post weld heat treatment (PWHT). Nevertheless, the SDSS tube showed severe corrosion damage along grain boundary due to surface phase transformation (δ → γ) and Cr₂N precipitation caused by PWHT with a high N₂ atmosphere. Corrosion resistance of the SDSS tube was recovered when degraded surface was removed. Corrosion sensitivity of a fin-tube increased significantly due to pre-existing crevice, unbalanced phase fraction, and σ phase precipitation adjacent to the fusion line. Although corrosion resistance was improved by recovered phase fraction and sufficient dissolution of σ phase during PWHT, corrosion reaction was concentrated at the pre-existing crevice. These results suggest that welding conditions for fin-tube steel should be optimized to improve corrosion resistance by removing pre-existing crevice in the weldment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.706-713
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• 2016

In this study, the welding characteristics of friction stir welding were investigated in accordance with the tool plunge position and cooling to the base materials for the joining of dissimilar materials (A6005-AZ61). Other different welding conditions, such as the tool rotation speed and welding speed, were fixed to 500rpm-30mm/min, respectively, and welding was then carried out by placing the Mg alloy (AZ61) on the advancing side and Al alloy(A6005) on the retreating side. Welding was conducted under six different conditions. To investigate the welding characteristic, tensile test and microstructure observations using an optical microscope were carried out. As the tensile test result, the maximum strength appeared under the condition in which the tool is moved 1 mm to the Mg alloy direction and cooling to the base materials. Under the same welding conditions, the strength with cooling was approximately two times higher than that without cooling. The tool was located in each direction of 1.7 mm from the weld line. Therefore, in the excessive off-set of tool position, the welding integrity was in an extremely poor condition due to the lack of stirring. This study was confirmed by the A6005-AZ61 dissimilar friction stir welding the welding speed and the tool rotation speed. In addition, the temperature control and tool plunge position are important welding parameters.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.280-288
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• 2016

This study proposes improved welding tools for magnesium alloys. Two types of tools were used for friction stir welding (FSW). The effect of the welding tools on the FSW joints was investigated with a fixed welding speed of 200mm/min and various rotation speeds of 400 to 800 rpm. After FSW, the joints were cross-sectioned perpendicular to the welding direction to investigate the defects. A tensile test and Vickers hardness test were conducted to identity the mechanical properties of the joints. Defects were observed when the rotation speed was 400 rpm, regardless of the welding tool, and the amount of defects tended to decrease with increases in rotational speed. Defect-free welds were obtained when the rotation speed was 800 rpm. The best weld quality was acquired using the C type welding tool. The rotation speed of 800 rpm and welding speed of 200 mm/min produced the best joining properties. The ultimate tensile strength, yield strength, and elongation of the welded region were 90.0%, 69.1%, and 83.2% those of the base metal, respectively.