• KEPCO Journal on Electric Power and Energy
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• v.7 no.1
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• pp.129-135
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• 2021

Recently, additive manufacturing (AM) technology such as powder bed fusion (PBF) and directed energy deposition (DED) are actively attempted as consumers' needs for parts with complex shapes and expensive materials. In the present work, the effect of processing parameters on the mechanical properties of 316L stainless steel coupons fabricated by PBF and DED AM technology was investigated. Three major mechanical tests, including tension, impact, and fatigue, were performed on coupons extracted from the standard components at angles of 0, 45, 90 degrees for the build layers, and compared with those of investment casting and commercial wrought products. Austenitic 316L stainless steel additively manufactured have been well known to be generally stronger but highly vulnerable to impact and lack in elongation compared to casting and wrought materials. The process-induced pore density has been proved the most critical factor in determining the mechanical properties of AM-built metal parts. Therefore, it was strongly recommended to reduce those lack of fusion defects as much as possible by carefully control the energy density of the laser. For example, under the high energy density conditions, PBF-built parts showed 46% higher tensile strength but more than 75% lower impact strength than the wrought products. However, by optimizing the energy density of the laser of the metal AM system, it has been confirmed that it is possible to manufacture metal parts that can satisfy both strength and ductility, and thus it is expected to be actively applied in the field of electric power section soon.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1645-1651
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• 2015

This paper describes the changes of shape accuracy in workpiece materials depending on the turning clearance angle. The experiments started from choosing three workpiece materials, SM45C(machine structural carbon steel), STS303(stainless steel) and SCM415 (chrome-molybdenum steel). The experiments showed specifically how features of selected materials changed when they were processed with diverse machining depths, 0.1 mm, 0.2 mm and 0.3 mm, with various negative angles, $0.0^{\circ}(-6.0^{\circ})$, $0.3^{\circ}(-6.3^{\circ})$ and $0.9^{\circ}(-6.9^{\circ})$, and called cutting edge inclination starting from a fixed rotational speed, 2,500 rpm, focusing on the feed rate, 0.07 mm/rev and 0.10 mm/rev. The results of the accuracy of processing, cylindricity, deviation from coaxiality, etc. were compared using the graph and table. The accuracy of cylindricity in the order of degree $0.0^{\circ}{\rightarrow}0.3^{\circ}{\rightarrow}0.9^{\circ}$ depending on the workpiece materials showed the best cylindricity when it was $0.9^{\circ}$. In conclusion, the accuracy improved in specific degrees irrespective of the quality of the materials when the bite negative angles increased. This means that workability improved in these experiments. In addition, the processing shape changed depending on depth of the cut and feed rate.

• Journal of Adhesion and Interface
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• v.15 no.3
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• pp.116-122
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• 2014

This work deals with the effects of different oligomers, monomers, photoinitiators, and steel plates on the variation of gloss for UV coated steel plates at $20^{\circ}$ and $60^{\circ}$ (ASTM D523). The gloss value was more significantly varied with $20^{\circ}$ angle as compared with $60^{\circ}$. No substantial change in gloss was observed for the type of single oligomer; however, the gloss varied with the mixing ratios of oligomers, type and mixing ratio of monomers, type and concentration of photoinitiator, and type of steel plate. The maximum gloss value was observed when the mixing ratio of polyurethane acrylate (UA) to epoxy acrylate (EA) was 70 : 30, the mixing ratio of trimethylolpropantriacrylate (TMPTA) to tetrahydrofurfurylacrylate (THFA) was 5 : 5, the content of the mixed oligomer (UA : EA = 70 : 30) was 90 wt%, respectively. Darocur MBF of liquid type showed better gloss property than the solid type of Irgacure 184, and the gloss was decreased as the concentration of Darocur MBF increased from 1 to 4 wt%. Regarding the type of steel plate, GI steel plate showed better gloss property as compared with EG and primer-coated steel plates. The maximum gloss values of 95 GU and 120 GU, respectively, at $20^{\circ}$ and $60^{\circ}$ angles throughout the parametric study in the absence of leveling agents enhancing the gloss.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2130-2135
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• 2007

Operating characteristics of a loop heat pipe (LHP) having a bypass line was investigated experimentally. The LHP had a sintered metal wick as a capillary structure and methanol as a working fluid. The sintered metal wick was made of stainless steel of which the average pore size was 5 ${\mu}m$and porosity of 47%. A bypass line of a small diameter was attached between the vapor escape passage and the liquid reservoir. The dimension of the flat evaporator was $50(L){\times}40(W){\times}30(H)$ mm and that of the condenser was $50(L){\times}40(W){\times}11(H)$ mm. Wall and pipe material of the LHP was stainless steel and heating area was 35(W) mm${\times}$35(L) mm. The inner diameters of vapor and liquid transport lines were 4.0 mm and 2.0 mm, and the lengths of the two lines were both 0.5 m. The LHP was tested for three different tilt angles of horizontal, favorite tilt, and adverse tilt. The thermal load range was up to 290 W at the condenser above evaporation position. Furthermore, the effect of a bypass line on the start-up transient as well as steady-state operation was presented and discussed.

• Steel and Composite Structures
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• v.17 no.1
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• pp.47-67
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• 2014

Due to thermal expansion, the structural behaviour of beams in steel structures subjected to temperature increase will be affected. This may result in the failure of the structural members or connection due to extra internal force in the beam induced by the thermal increase. A method to release some of the thermally generated internal force in the members is to allow for some movements at the end supports of the member. This can be achieved by making the plane of the end-plate of the connection slanted instead of vertical as in conventional design. The present paper discusses the mechanical behaviour of beams with bolted slant end-plate connection under symmetrical gravity loads, subjected to temperature increase. Analyses have been carried out to investigate the reduction in internal force with various angles of slanting, friction factor at the surface of the connection, and allowable temperature increase in the beam. The main conclusion is that higher thermal increase is tolerable when slanting connection is used, which means the risk of failure of structures can be reduced.

• Steel and Composite Structures
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• v.20 no.4
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• pp.913-930
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• 2016

It is common practice to use Reduced Web Beam Sections (RWBS) in steel moment resisting frames. Perforation of beam web in these members may cause stress and strain concentration around the opening area and facilitate ductile fracture under cyclic loading. This paper presents a numerical study on the cyclic fracture of these structural components. The considered connections are configured as T-shaped assemblies with beams of elongated circular perforations. The failure of specimens under Ultra Low Cycle Fatigue (ULCF) condition is simulated using Cyclic Void Growth Model (CVGM) which is a micromechanics based fracture model. In each model, CVGM fracture index is calculated based on the stress and strain time histories and then models with different opening configurations are compared based on the calculated fracture index. In addition to the global models, sub-models with refined mesh are used to evaluate fracture index around the beam to column weldment. Modeling techniques are validated using data from previous experiments. Results show that as the perforation size increases, opening corners experience greater fracture index. This is while as the opening size increases the maximum observed fracture index at the connection welds decreases. However, the initiation of fracture at connection welds occurs at lower drift angles compared to opening corners. Finally, a probabilistic framework is applied to CVGM in order to account for the uncertainties existing in the prediction of ductile fracture and results are discussed.

• Structural Engineering and Mechanics
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• v.68 no.2
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• pp.193-201
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• 2018

This paper describes an experimental study on the seismic performance of steel reinforced concrete (SRC) T-shaped columns. The lateral loads were applied along the web of the column with different loading histories, such as monotonic loading, mixed loading of variable amplitude cyclic loading and monotonic loading, constant amplitude cyclic loading and variable amplitude cyclic loading. The failure modes, load-displacement curves, characteristic loads and displacements, ductility, strength and stiffness degradations and energy dissipation capacity of the column were analyzed. The effects of loading history on the seismic performance were focused on. The test results show that the specimens behaved differently in the aspects of the failure mode subject to different loading history, although all the failure modes can be summarized as flexural failure. The hysteretic loops of specimens are plump, and minimum values of the failure drift angles and ductility coefficients are 1/24 and 4.64, respectively, which reflect good seismic performance of SRC T-shaped column. With the increasing numbers of loading cycles, the column reveals lower bearing capacity and ductility. The strength and stiffness of the column with variable amplitude cyclic loading degrades more rapidly than that with constant amplitude cyclic loading, and the total cumulative dissipated energy of the former is less.

• Journal of Korean Society of Steel Construction
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• v.24 no.2
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• pp.199-206
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• 2012

Unstiffened seated connections (USC) ensure easy installation and safety during erection, thereby making the process more economical. USCs consist of a seat angle for carrying the beam's reactions and a top angle to provide beam stability. These angles are bolted or welded to the beam and supporting member. This paper sought to propose a design table for the weld strength of such connections obtained from the elastic vector method (EVM) and the instantaneous center-of-rotation method (ICM) in terms of calculating the eccentricity. Also, the proposed design table is compared with both AISC and KBC specifications.

• Steel and Composite Structures
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• v.33 no.6
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• pp.767-776
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• 2019

In this article, a simple and robust multi-objective assessment method to control design angles and node positions connected among steel outrigger truss members is proposed to approve both structural safety and economical cost. For given outrigger member layouts, the present method utilizes general-purpose prototypes of outrigger members, having resistance to withstand lateral load effects directly applied to tall buildings, which conform to variable connecting node and design space deposition. Outrigger layouts are set into several initial design conditions of height to width of an arbitrary given design space, i.e., variable design space. And then they are assessed in terms of a proposed multi-objective function optimizing both minimal total displacement and material quantity subjected to design impact factor indicating the importance of objectives. To evaluate the proposed multi-objective function, an analysis model uses a modified Maxwell-Mohr method, and an optimization model is defined by a ground structure assuming arbitrary discrete straight members. It provides a new robust assessment model from a local design point of view, as it may produce specific optimal prototypes of outrigger layouts corresponding to arbitrary height and width ratio of design space. Numerical examples verify the validity and robustness of the present assessment method for controlling prototypes of outrigger truss members considering a multi-objective optimization achieving structural safety and material cost.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4_1
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• pp.23-32
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• 1992

The objective of this study is to identify the quantitative relationships among the important physical factors associated with failure of steel members under strong seismic excitations through very low-cycle fatigue tests. Very low-cycle fatigue is meant to be structural fatigue causing cracks and rupture in about 5~30 cycle ranges. The angle specimen was subjected to repeated axial Ioad after undergoing inelastic buckling. The test results reveal that the energy absorption capacities vary heavily with the history of loading and the failure mode. The maximum values of residual local strain at the initiation of a visible crack due to the very low-cycle fatigue were of the order of 25~40%, regardless of loading patterns, deflection modes, and width-to-thickness ratios.