• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.428-432
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• 2010

연소기 챔버 노즐확장부 외피구조물의 성형특성에 대한 연구를 수행하였다. 노즐확장부 외피구조물의 제작에 사용되는 냉간압연 판재가 갖는 이방성 특성을 확인하기 위하여 세 가지 방향의 시편을 제작하여 인장시험을 수행하였으며, 그 결과를 이용하여 Lankford 값을 얻어 구조해석에 적용하였다. 실물형 연소기에 사용될 노즐확장부 외피구조물의 제작 및 성형공정을 통하여 외피구조물의 성형특성을 확인하였으며, 성형으로 얻은 변형률들을 구조해석 결과들과 비교하였다. 본 연구에서 얻은 결과들은 확대비가 더 큰 노즐확장부 제작을 위한 치구 및 성형공정의 설계에 활용될 예정이다.

• 한국재료학회지
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• 제26권11호
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• pp.628-634
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• 2016

The cold rolling workability and mechanical properties of two new alloys, designed and cast Al-5.5Mg-2.9Si and Al-7Mg-0.9Zn alloys, were investigated in detail. The two alloy sheets of 4 mm thickness, 30 mm width and 100 mm length were reduced to a thickness of 1 mm by multi-pass rolling at ambient temperature. The rolling workability was better for the Al-7Mg-0.9Zn alloy than for the Al-5.5Mg-2.9Si alloy; in case of the former alloy, edge cracks began to occur at 50% rolling reduction, and their number and length increased with rolling reduction; however, in the latter alloy, the sheets did not have any cracks even at higher rolling reduction. The mechanical properties of tensile strength and elongation were also better in the Al-7Mg-0.9Zn alloy than in Al-5.5Mg-2.9Si alloy. Work hardening ability after cold rolling was also higher in the Al-7Mg-0.9Zn alloy than in the Al-5.5Mg-2.9Si alloy. At the same time, the texture development was very similar for both alloys; typical rolling texture developed in both alloys. These differences in the two alloys can primarily be explained by the existence of precipitates of $Mg_2Si$. It is concluded that the Al-7Mg-0.9Zn alloy is better than the Al-5.5Mg-2.9Si alloy in terms of mechanical properties.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.99-101
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• 2008

At 21st century, material development concepts were changed to fulfill the environmental friendly demands. This study is to study the effect of pressurized nitrogen gas and manganese in high nitrogen austenitic stainless steel(HNS) in which N and Mn elements substitute the nickel element. 100kg HNS ingots were made by Pressurized Vacuum Induction Melting(P-VIM) and were forged according to free forging process. As forged HNS were hot and cold rolled by pilot scale rolling machine. Depending on the rolling condition, the mechanical properties of HNS were changed. The roll thrust and sheet folding showed asymmetry condition between work and drive side during cold and hot rolling. The purpose of this study are to improve workability the hot and cold rolling machine and to set the conditions for establishing the rolling process.

• 한국해양공학회지
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• 제13권4호통권35호
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• pp.55-62
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• 1999

Cold rolled steel has much plastic strain in the material surface produced by manufacturing process. The strain causes the variation of surface residual stress, in which influences the fatigue behavior under repeated loading. As experimental results, it was confirmed that the behavior of residual stress ${\sigma}_r$, with cycle N consisted of three stages except stress amplitude near fatigue limit in SPCC steel. On the first stage compressive residual stress decreased rapidly, on the second stage gradually, and on the last stage slightly. The relation between ${\sigma}_r$, and log N appeared linear behavior except the early part of cycle ratio $N/N_f$. The average gradient of ${\sigma}_r$, with respect to log N seemed to take a constant value without initial cycle ratio. On the other hand, the $N_f$ line was regressed by the first-order polynomial equation on ${\sigma}_r-log\;N_f$ diagram. Therefore, this study showed that both the gradient of ${\sigma}_r$, with respect to log N and the $N_f$ line was useful in predicting the cycle ratio $N/N_f$.

• 대한기계학회논문집
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• 제18권5호
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• pp.1227-1234
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• 1994

A cold spot temperature control system for the batch annealing furnace has been established in order to reduce energy consumption which is essential to improve productivity and stabilize the properties of products. A relationship between annealing cycle time and gas flow rate is developed and also for the variation of coil cold spot temperature with time during heating, and actual temperature measurements at mid-width of each coil during soaking. The results of the temperature variation effect on the cold rolled steel sheet batch annealing are as follows. (1) Cooling rate increasing gradually with increasing atmospheric gas flow, but heating rate is hardly increasing without atmospheric gas component change. (2) In case of short time heating, the slowest heating part is the center of B coil and in case of ling time heating, the low temperature point moves from the center of coil to inside coil. (3) The outside of top coil is the highest temperature point under heating, which becomes the lowest temperature point under cooling. (4) Soaking time determination depends on the input coil width, and soaking time for quality homogenization of 1214 mm width coil must be 2 hours longer than that of 914 mm width coil.

• 한국공작기계학회논문집
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• 제13권4호
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• pp.44-55
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• 2004

In order to meet the requirement for higher thickness accuracy in tandem cold rolling processes, it is strongly necessary to have good performance in control units. To meet this requirement, this paper suggested an output regulating control system with a roll-eccentricity estimator for each rolling stand of tandem cold mills. Considering entry thickness variation and roll eccentricity simultaneously as the major disturbances, a synthesis of multivariable control systems was presented based on H$\infty$ control theory, which could reflect the knowledge of input direction and spectrum of disturbance signals on design. Then, to effectively reject roll eccentricity, a weight function having some poles on the imaginary axis was introduced. This lead to a non-standard H$\infty$ control problem, and the design procedures for solving this problem were analytically presented. The effectiveness of the proposed control method was evaluated through computer simulations and compared to that of the conventional linear quardratic control and feedforward control methods for roll eccentricity.

• 한국안전학회지
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• 제27권5호
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• pp.42-48
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• 2012

Peel-tension fatigue experiments were conducted for investigating on fatigue strength of mechanical press joints of SPCC steel sheet used in the field of the automobile industry. In addition, finite element method analysis on the peel-tension specimen was conducted using HyperMesh and ABAQUS softwares. The cold rolled mild steel was used to join the T-shaped peel-tension specimen with a button diameter of 5.4 mm and a punch diameter of 8.3 mm. The fatigue limit load amplitude was found to be 112.4 N at the number of cycles 106, indicating that the ratio of fatigue limit load to static peel-tension strength was about 8%. This value suggests that the mechanical press joint is highly vulnerable to peel-tension load rather than to tensile-shear load, considering that the ratio of fatigue limit load to static tensile-shear strength was about 43%. Fatigue failure mode was found to be interface-failure mode.

• 대한기계학회논문집
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• 제8권5호
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• pp.435-441
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• 1984

본 연구에서는 반경 방항으로 균일하게 잡아당기는 문제에 대하여 등방성, 직 교 이방경, 평면 이방성의 해를 비교하고, 성형성에 중요한 의미를 갖는 두께방항 변 형도와 원주방항 응력의 분포에 대하여 해석한다. 또 냉간 압연된 철판을 사용하여 평저 펀치(flat punch)에 의한 스트레칭(stretching) 실험을 하고, 실험과 같은 경계 조건으로 시뮬레이션(simulation)하여 결과를 비교한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1521-1524
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• 2003

Currently the plates used for the various structures has a tendency to being slim to the degree of the sheet metal vis-a-vis the overall measurements of the structure, and the conditions of their usage and load have been getting diverse. As the structure material has been used more and more under the various conditions, the necessity of the strength analysis is to be required. While most of these methods are simply based on the strain gaging method; that is, directly attaching most of the material to the gage, using the non-contact method is still in the early stage. One of the non-contact methods is by the use of the laser that has high-level of the accuracy for the measurement, and this laser also has excellent characteristics on which many studies for its applications are focused throughout the many fields. Therefore, this dissertation is on the measurement of the strain caused by the characteristics of the TIG welded zone which is used with 3D ESPI system that is functionally modified through the laser ESPI system.

• 대한기계학회논문집A
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• 제24권11호
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• pp.2845-2852
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• 2000

When welding a car frame with one spot welding there are same limitations because many parts of it cannot be simplified by one spot welding alone. It is presented two spot welding model for the description of the spot welding which is usually used in a car frame structure. This study primarily covers fatigue behavior taking spot welded SPCC(Steel plate carbon C) with different ungget intervals as a tension shear specimen. It was prepared that intervals between two nuggets are varied as 9mm, 14mm, and 20mm respectively. The tensile tests and fatigue tests were executed to know the mechanical properties under static and fatigue load condition. In addition, the relationship between fatigue life and nugget intervals was illustrated by finite element method.