• 한국기계가공학회지
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• 제14권4호
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• pp.21-27
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• 2015

Induction bending is a method that allows the bending of any material that conducts electricity. This technology applies a bending force to a material that has been locally heated by an eddy current induced by a fluctuating electromagnetic field. Induction bending uses an inductor to locally heat steel through induction. This results in a narrow heat band in the shape to be bent. In general, the reduction of thickness attenuation of a large-diameter steel pipe is not allowed to exceed 12.5%. In this paper, in order to meet the standard of thickness attenuation reduction, a non-uniform heating temperature jump-bending process was investigated. As a result, the developed bending technique meets the requirements of thickness attenuation reduction for large-diameter steel pipes.

• 동력기계공학회지
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• 제14권1호
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• pp.59-64
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• 2010

Ferritic stainless steel is currently increasingly used for automotive exhaust material. The material for exhaust manifold is used in the temperature range of 500∼$850^{\circ}C$. Therefore, high temperature characteristic is an important one that affects it's life span. It has been investigated the effect of alloying elements of Cr, Mo, Nb, Ti in the ferritic stainless steel for exhaust manifold on the high temperature tensile strength. There was a few difference in the tensile strength at $600^{\circ}C$ with the exception of low Cr steel, but the steels containing higher Cr, Mo or Nb elements showed significantly higher tensile strength at the temperature of $800^{\circ}C$. The precipitates of the specimens after heat treating at the test temperature were electrolytic extracted, and quantitatively analysed using by SEM-EDS and TEM. The alloying elements of Cr and Mo increased the tensile strength as a solid solution strengthener, and on the other hand Nb element enhanced the strength by forming the fine intermetallic compounds such as NbC or $Fe_2Nb$.

• 소성∙가공
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• 제18권5호
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• pp.410-415
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• 2009

Experimental and numerical studies were performed to examine the effect of material temperature and reduction ratio on friction coefficient during hot flat rolling. We carried out a single pass pilot hot flat rolling test at the temperatures range of $900{\sim}1200^{\circ}C$ and measured the spread of deformed material while reduction ratio varied from 20% to 40%. Materials used in this study were a high carbon steel and two alloy steels. The dimension of specimen used in hot rolling experiment was $50mm{\times}50mm{\times}300mm$. We performed a series of finite element simulation of the hot rolling process to compute the friction coefficient change in terms of steel grade and reduction ratio. Results showed that temperature dependency of friction coefficient is not noteworthy but the effect of reduction ratio on friction coefficient is quite large. For high carbon steel, friction coefficient at reduction ratio of 30% is lower than that at that of 20%. Meanwhile friction coefficient at reduction ratio of 40% was one and half times large compared with that at that of 20%. The effect of steel grade on friction coefficient was significant when reduction ration was large, e.g., 40%.

• 비파괴검사학회지
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• 제15권1호
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• pp.310-317
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• 1995

원자력 발전소의 주요 계통 재료로 사용되는 오스테나이트계 스텐레스강에 대한 초음파탐상은 초음파 에너지가 전파될 경우 재질 자체가 갖는 여러 문제점으로 인하여 결함 위치나 크기 측정에 많은 문제점을 야기한다. 본 연구에서는 이러한 문제점을 이해하기 위하여 여러가지 경우를 가정하여 선 추적(ray tracing) 기법을 사용한 컴퓨터 모의(simulation)를 실시하였다. 우선 종파를 사용하여 모재에 초음파가 입사하여 진행할 시 어느정도의 휘어짐이 발생하는지를 계산하였으며 재질 특성상 용접부와 모재가 큰 차이를 보이지 않는 경우와 원자로 노즐 부위와 같이 서로 다른 금속으로 용접된 경우에 결함이 존재한 경우를 가정하여 계산하였다.

• 대한기계학회논문집A
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• 제25권2호
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• pp.296-303
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• 2001

Kachanov-Rabotnov(K-R) creep damage theory was reviewed, and applied to design a creep curve for type 316LN stainless steel. Seven coefficients used in the theory, i.e., A, B, k, m, λ, r, and q were determined, and their physical meanings were analyzed clearly. In order to quantify a damage parameter ($\omega$), cavity amount was measured in the crept specimen taken from interrupted creep test with time variation, and then the amount was reflected into K-R damage equations. Coefficient λ, which is regarded as a creep tolerance feature of a material, increased with creep strain. Mater curve with λ=2.8 was well coincided with an experimental one to the full lifetime. The relationship between damage parameter and life fraction was matched with the theory at exponent ${\gamma}$=24 value. It is concluded that K-R damage equation was reliable as the modelling equation for type 316LN stainless steel. Coefficient data obtained from type 316LN stainless steel can be utilized for life prediction of operating material.

• Steel and Composite Structures
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• 제1권1호
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• pp.97-110
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• 2001

Architectural steel structures with visible tension and compression members are becoming more prevalent as a popular form of construction that reflects the nature of the resistance to the applied loads. These members require the use of structural steel pins at their ends to ensure either axial tension or axial compression in the members. Structural pins have been used as a means of connection for centuries and it would appear that their behaviour is relatively well understood. However, the rules for the design of pins vary quite considerably from code to code and this has caused some confusion amongst consulting structural engineers operating internationally. To provide some insight into this problem, a comprehensive testing program has been carried to examine the influence of parameters such as pin diameter, material properties of the pin, thickness of the loading plates, material properties of the loading plates and the distance of the pin to the edge of the loading plates. The modes of failure have been carefully examined. Based on this study, modifications to current design procedures are proposed that properly take into account the different possible modes of failure.

• Corrosion Science and Technology
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• 제11권6호
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• pp.232-241
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• 2012

This work focused on corrosion of carbon steel bolted GECM/Al parts in tap water and NaCl solutions. In tap water and NaCl solutions, open circuit potential of GECM and its potentials in a series of carbon steel bolt>Ti>Al became active. Regardless of test materials, open circuit potentials in tap water were noble, and increasing NaCl concentration, its potentials became active. Immersion test of single specimen showed that no corrosion occur in Ti and GECM. In tap water, carbon steel bolt didn't show red corrosion product and in chloride solutions, corrosion rate in 1% NaCl solution was greater than its rate in 3.5% NaCl solution and red corrosion product in 1% NaCl solution was earlier observed than that in 3.5% NaCl solution. It seems that this behavior would be related to zinc-coatings on the surface of carbon stee l bolt. On the other hand, aluminium was corroded in tap water and chloride solutions. Corrosion of aluminium in tap water was due to the presence of chloride ion in tap water by sterilizing process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.360-363
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• 2007

This paper deals with the dynamic tensile characteristics of the steel sheets for structural members of a train. Train accidents occurs rarely but lead to many casualties and economical loss. Therefore the safety of the train becomes important during the train crash. The dynamic tensile characteristics of the steel sheets are indispensable to analyze the structural crashworthiness. Current research reports the stress-strain curves, fracture elongation and strain rate sensitivities evaluated at the various strain rates especially for SUS304L-ST and SUS304L-LT steel sheets. The results include the difference in the dynamic tensile characteristics of both rolling and transverse directions. Dynamic tensile tests were performed at the strain rates ranging from 0.003/sec to 200/sec using High Speed Material Testing Machine. The materials tested in this research shows interesting behavior at the low strain rates. The strain hardening exponent decreases remarkably while the yield strength increases.

• Steel and Composite Structures
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• 제12권6호
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• pp.523-540
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• 2012

It was clear from the former researches on reinforced concrete filled tubular steel (RCFT) structures that RCFT structures have different performance than concrete filled steel tubular (CFT) structures. However, despite of that, load-sharing ratio of RCFT is evaluating by the formula and range of CFT given by JSCE. Therefore, the aim of this investigation is to study the load-sharing ratio of RCFT columns subjected to axial compressive load by performing numerical simulations of RCFT columns with the nonlinear finite element analysis (FEA) program - ADINA. To achieve this goal, firstly proper material constitutive models for concrete, steel tube and reinforcement are proposed. Then axial compression tests of concrete, RC, CFT, and RCFT columns are carried out to verify proposed material constitutive models. Finally, by the plenty of numerical analysis with small-sized and big-sized columns, load-sharing ratio of RCFT columns was studied, the evaluation formulas and range were proposed, application of the formula was demonstrated, and following conclusions were drawn: The FEA model introduced in this paper can be applied to nonlinear analysis of RCFT columns with reliable results; the load-sharing ratio evaluation formula and range of CFT should not be applied to RCFT; The lower limit for the range of load-sharing ratio of RCFT can be smaller than that of CFT; the proposed formulas for load-sharing ratio of RCFT have practical mean in design of RCFT columns.

• 한국전기전자재료학회논문지
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• 제21권11호
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• pp.1036-1041
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• 2008

According to previous report, aged sleeves of old transmission line showed several defaulted installation patterns, which was biased or corrosive-fractured of steel sleeve installed cases. These defects can cause serious accidents such as rapid increasing of sag or falling out of overhead conductor from sleeves. Consequently, the defects lead to the major power outage. Corrosion of steel sleeve is a typical defect by aging of sleeves. And it occupied almost 25 percent of investigated aged sleeves. This paper studied thermal properties and tension for ACSR conductor in case of fractured steel sleeve model by corrosion. The temperature distribution within overhead conductor has a specific gradient. Thermal properties of splice connectors(sleeve and clamp) showed normal behavior. However, mechanical properties were worse than normal sleeves. The detailed results were presented in the text.