• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 추계학술대회 논문집
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• pp.583-588
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• 1998

Large extrusions of aluminium alloy can be more general and useful as structural material of rolling stocks to reduce weight and labor cost than mild steel and stainless steel. Our company is studying aluminium coach body will be made of 6005A and A5083 alloy. In this paper, at first detailed finite element analysis is carried out to calculate the orthotropic material properties of aluminium extrusions. And then global strength evaluation of coach body is carried out according to UIC 566 OR code.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.259-264
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• 2000

This paper proposes a practical method for determining the most economical steel ratio in RC flexural members. The costs of individual material and labor are considered. Then, an equation for determining the optimal steel ratio is proposes. It was found that a relevant steel ratio is recommended to be 0.95~1.0% for designing singly reinforced rectangular beam.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.398-405
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• 1998

This study investigated to the stability of open car parks below $600^{\circ}C$, as to predict behavior of bare FR steel structure noosed to fire. Especially, This study evaluated deformation of steel structure members of open car parks, considering change of material property by temperature. From the numerical analysis, we know the fact that the deformations comparing of standard values are stable to use the FR steel below 600 $^{\circ}C$ in open car parks plan

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.206-213
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• 1999

The behavior of composite beams, which are composed of cold-formed steel sheeting and normal strength concrete, have been studied. An analytical method has been developed to trace the nonlinear behavior of composite beams. The nonlinear material properties of steel sheeting, reinforcing steel bar and concrete have been included in the analysis. The nonlinear moment-curvature relation of the composite beam has been described using a cross section analysis method and a simple power model, separately. The load-deflection behavior of the beams has been simulated by step-by-step numerical integration method and is compared with test results.

• 한국농공학회지
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• 제39권4호
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• pp.106-113
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• 1997

Dynamic loading of structures often causes excursions of stresses well into the inelastic range, and the influence of the geometric changes on the dynamic response is also significant in many cases. Therefore, both material and geometric nonlinearity effects should be considered in case that a dynamic load acts on the structure. A structure in a nuclear power plant is a structure of importance which puts emphasis on safety. A nuclear container is a pressure vessel subject to internal pressure and this structure is constructed by a reinforced concrete or a pre-stressed concrete. In this study, the material nonlinearity effect on the dynamic response is formulated by the elasto-viscoplastic model highly corresponding to the real behavior of the material. Also, the geometrically nonlinear behavior is taken into account using a total Lagrangian coordinate system, and the equilibrium equation of motion is numerically solved by a central difference scheme. The constitutive relation of concrete is modeled according to a Drucker-Prager yield criterion in compression. The reinforcing bars are modeled by a smeared layer at the location of reinforcements, and the steel layer model under Von Mises yield criteria is adopted to represent an elastic-plastic behavior. To investigate the dynamic response of a nuclear reinforced concrete containment structure, the steel-ratios of 0, 3, 5 and 10 percent, are considered. The results obtained from the analysis of an example were summarized as follows 1. As the steel-ratio increases, the amplitude and the period of the vertical displacements in apex of dome decreased. The Dynamic Magnification Factor(DMF) was some larger than that of the structure without steel. However, the regular trend was not found in the values of DMF. 2. The dynamic response of the vertical displacement and the radial displacement in the dome-wall junction were shown that the period of displacement in initial step decreased with the steel-ratio increases. Especially, the effect of the steel on the dynamic response of radial displacement disapeared almost. The values of DMF were 1.94, 2.5, 2.62 and 2.66, and the values increased with the steel-ratio. 3. The characteristics of the dynamic response of radial displacement in the mid-wall were similar to that of dome-wall junction. The values of DMF were 1.91, 2.11, 2.13 and 2.18, and the values increased with the steel-ratio. 4. The amplitude and the period of the hoop-stresses in the dome, the dome-wall junction, and the mid-wall were shown the decreased trend with the steel-ratio. The values of DMF were some larger than those of the structure without steel. However, the regular trend was not found in the values of DMF.

• Computers and Concrete
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• 제29권 6호
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• pp.393-405
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• 2022

Lightweight concrete is a superior material due to its light weight and high strength. There however remain significant lacunae in engineering knowledge with regards to shear failure of lightweight fiber reinforced concrete beams. The main aim of the present study is to investigate the optimum usage of steel fibers in lightweight fiber reinforced concrete (LWFRC). Multi-scale finite element model calibrated with experimental results is developed to study the effect of steel fibers on the mechanical properties of LWFRC beams. To decrease the amount of steel fibers, it is preferred to reinforce only the middle section of the LWFRC beams, where the flexural stresses are higher. For numerical simulation, a multi-scale finite element model was developed. The cement matrix was modeled as homogeneous and uniform material and both steel fibers and lightweight coarse aggregates were randomly distributed within the matrix. Considering more realistic assumptions, the bonding between fibers and cement matrix was considered with the Cohesive Zone Model (CZM) and its parameters were determined using the model update method. Furthermore, conformity of Load-Crack Mouth Opening Displacement (CMOD) curves obtained from numerical modeling and experimental test results of notched beams under center-point loading tests were investigated. Validating the finite element model results with experimental tests, the effects of fibers' volume fraction, and the length of the reinforced middle section, on flexural and residual strengths of LWFRC, were studied. Results indicate that using steel fibers in a specified length of the concrete beam with high flexural stresses, and considerable savings can be achieved in using steel fibers. Reducing the length of the reinforced middle section from 50 to 30 cm in specimens containing 10 kg/m3 of steel fibers, resulting in a considerable decrease of the used steel fibers by four times, whereas only a 7% reduction in bearing capacity was observed. Therefore, determining an appropriate length of the reinforced middle section is an essential parameter in reducing fibers, usage leading to more affordable construction costs.

• 한국기계가공학회지
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• 제6권2호
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• pp.34-40
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• 2007

Antifatigue failure technology take an important part of current industries. Currently, the shot peening is used for removing the defect from the surface of steel and improving the fatigue strength on surface. Therefore, this paper the effect of compressive residual stress and corrosion of spring steel(SAE 5155)by shot-peening on fatigue crack growth characteristics in stress ratio(R=0.05)was investigated with considering fracture mechanics. By using the methods mentioned above, We arrived at the following conclusions. The fatigue crack growth rate(da/dN) of the shot-peening material was lower than that of the un-peening material. And in stage I, ${\Delta}Kth$, the threshold stress intensity factor, of the shot-peen processed material is high in critical parts unlike the un-peening material. Also m, fatigue crack growth exponent and number of cycle of the shot-peening material was higher than that of the un-peening material. That is concluded from effect of da/dN. Finally fracture of shot-peening material and un-peening material was identified and discussed in this study.

• 한국소음진동공학회논문집
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• 제23권4호
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• pp.332-337
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• 2013

This paper presents a subsequent research work on the roller design of IRB(isolation roller bearing) seismic isolation device presented in Part 1 by focusing on heat treatment. The hardness and friction factor are very important factors of material and after-treatment process selection. Normally, roller bearing consists of roller and retainer. The roller gets high pressure constantly, while the retainer gets tensile and compressive stress. Therefore, sensitive material selection and heat treatment of each part is quite important. In this experimental evaluation, carbon steel, chrome special steel and others are employed and their characteristics after heat treatment are identified. Each material is prepared by refining high frequency heat treatment. The friction factor and static load capacity of manufactured material are experimentally identified and destructive test of material is processed. Optimal material and heat treatment conditions for IRB roller bearing are determined based on experiment results.

• 대한기계학회논문집A
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• 제24권7호
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• pp.1673-1680
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• 2000

The degradation of a boiler header constructed by a material, 1Cr-0.5Mo steel in a fossil power plant is observed when the header is exposed for a long period to the high temperature and pressure. The present investigations are for evaluating the effect of the degradation on the material, such as its strength changes. Reheat-treated metal is used to compare the mechanical properties of the degraded and that of reheat-treated materials. Through the investigation, following results are obtained 1) the area ratio of ferrite in the reheat-treated material is larger than that of the degraded material, 2) the hardness and tensile strength of the degraded material are lower than that of the reheat-treated material, 3) the ductile-brittle transition temperature(DBTT) increased toward high temperature region, 4) the fatigue crack growth rate(FCGR) of the degraded material is higher than that of the reheat-treated material in the region of low ΔK value while FCGR of the both materials are similar in high ΔK region.

• Journal of Welding and Joining
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• 제24권1호
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• pp.56-63
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• 2006

The characteristics of $CO_2$ or Nd:YAG laser welded 600MPa ade TRIP steel was investigated. He or Ar gas was used as a shield gas in case of $CO_2$ laser welding, but the shield gas was not used in case of Nd:YAG laser welding. Bead on plate welding was performed with various welding conditions. Defects in the joints of both welding type occurred at 1.8m/min but were not observed over the welding speed of 2.1m/min in case of Nd:YAG laser welding. However, porosity occurred in $CO_2$ laser welding and the tendency of decreasing with the increase of welding speed. The hardness was the highest at heat affected zone near fusion zone as well as at the fusion zone and decreased on approaching the base metal. In a perpendicular tensile test to the weld line, all specimens that have been welded at optimum conditions were fractured at the base metal, and the tensile properties showed the rather higher than those of raw material. In a parallel tensile test, the strength of the joints was higher than that of the base metal. Elongation was found to be lower than that of the raw material. Forming height by Erichsen test and elongation were deeply related with the ratio of base metal/weld metal and the maximum hardness of the weld metal. Also porosity induced to decrease the strength and the elongation. The maximum formability was recorded at approximately 80% as compared with that of the raw material with the optimum condition.