• 터널과지하공간
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• 제33권1호
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• pp.10-28
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• 2023

고준위방사성폐기물 처분장의 장기 안정성을 확보하기 위해서 암반 불연속면의 장기적인 전단 거동을 분석하고 그 안정성을 평가해야 한다. 암반 불연속면의 장기 전단 거동은 크리프 모델, RSF 모델로 모사될 수 있고, 전단 크리프 시험, 속도 단계 시험, 슬라이드-홀드-슬라이드 시험을 통해 모델에 필요한 파라미터를 결정하거나 여러 조건에서 전단 거동을 분석하는 실험을 수행할 수 있다. 기존 연구에 따르면 전단 실험을 위하여 직접전단시험기, 삼축압축시험기, 이축전단시험기가 주로 이용되었으며 현지 암반의 열-수리-역학적인 조건을 재현하기 위해 다양하게 개선된 장비가 이용되었고 그에 따라 다양한 양상의 전단 거동이 관찰되었다. 그러므로 국내 고준위방사성폐기물 처분장을 설계하기 위해서 처분장 부지의 암종, 열-수리-역학적 조건, 광물의 변성, 그리고 전단 저항의 회복 등을 고려하여 암반 불연속면의 장기 거동을 검토해야 한다.

• 마이크로전자및패키징학회지
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• 제20권2호
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• pp.33-38
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• 2013

In this study, both a finite element analysis and an experimental analysis are executed to investigate the mechanical characteristics of dielectric material effects on warpage. Also, viscoelastic material properties are measured by DMA and are considered in warpage simulation. A finite element analysis is done by using both thermal elastic analysis and a thermo-viscoelastic analysis to predict the nonlinear effects. For experimental study, specimens warpage of non-symmetric structure with body size of $22.5{\times}22.5$ mm, $37.5{\times}37.5$ mm and $42.5{\times}42.5$ mm are measured under the reflow temperature condition. From the analysis results, experimental warpage is not similar to FEA results using thermal elastic analysis but similar to FEA results using thermo-viscoelastic analysis. Also, its effect on substrate warpage is increased as core thickness is decreased and body size is getting larger. These FEA and the experimental results show that the nonlinear characteristics of dielectric material play an important role on substrate warpage. Therefore, it is strongly recommended that non-linear behavior characteristics of a dielectric material should be considered to control warpage of FCBGA substrate under conditions of geometry, structure and manufacturing process and so on.

• Journal of Welding and Joining
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• 제8권2호
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• pp.40-52
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• 1990

Fatigue behavior of the AH, DH and EH grade TMCP(Thermo-Mechanical Control Process) steels was studied. High cycle and low cycle fatigue tests were carried out for the weldment and base metal of each steel. The results showed that the fatigue limit at 2 * $10^6$ cycles was 33 to 37 kg/$mm^2$ for the base metal and 30 to 34 kg/$mm^2$ for the weldment. The ratio of fatigue limit to tensile strength for TMCP steels was 0.65 to 0.71, which was a value close to the upper limit for the ordinary steels. It was also found that the high cycle fatigue behavior of TMCP steels could be affected by the microstructures of base metal. It will be necessary to have fine structure for TMCP steels to increase the fatigue resistance. In low cycle fatigue test, the fatigue lifetime of AH and DH steels accorded well with the ASME best fit curve, while that of EH steel was considerably lower than the fatigue lifetime of the other steels. Fatigue resistance of the weldment made by high heat input(180kJ/cm) welding was not lower than that made by low heat input(80kJ/cm) welding in case of high cycle fatigue, but the high heat input welding decreased the fatigue resistance in case of low cycle fatigue.

• Smart Structures and Systems
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• 제18권4호
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• pp.755-786
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• 2016

The hygro-thermo-mechanical bending behavior of sigmoid functionally graded material (S-FGM) plate resting on variable two-parameter elastic foundations is discussed using a four-variable refined plate theory. The material characteristics are distributed within the thickness direction according to the two power law variation in terms of volume fractions of the constituents of the material. By employing a four variable refined plate model, both a trigonometric distribution of the transverse shear strains within the thickness and the zero traction boundary conditions on the top and bottom surfaces of the plate are respected without utilizing shear correction factors. The number of independent variables of the current formulation is four, as against five in other shear deformation models. The governing equations are deduced based on the four-variable refined plate theory incorporating the external load and hygro-thermal influences. The results of this work are compared with those of other shear deformation models. Various numerical examples introducing the influence of power-law index, plate aspect ratio, temperature difference, elastic foundation parameters, and side-to-thickness ratio on the static behavior of S-FGM plates are investigated.

• 터널과지하공간
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• 제11권3호
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• pp.257-269
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• 2001

지하 500 m의 화강암반내 단층지역에 위치한 지하 방사성폐기물 처분장의 구조거동을 이해하기 위하여 수치 해석을 수행하였다. 해석에는 2차원 해석코드인 UDEC을 사용하였다. 해석모델은 화강암반, 처분공내의 압축 벤토나이트로 둘러싸인 PWR 사용후 핵연료 처분용기 및 처분동굴내에 채워진 혼합 벤토나이트를 포함한다. 한 개의 단층이 처분동굴의 지붕과 벽이 만나는 지점을 33, 45, 및 $58^{\circ}$의 각도로 관통하는 세가지 다른 경우게 대한 구조거동을 비교, 분석하였다. 그리고 $45^{\circ}$단층의 경우에 대해서는 수리역학적, 열역학적, 및 열수리역학적 상호작용 거동을 해석하고 비교, 분석하였다. PWR 사용후 핵연료내의 방사성 물질로부터 나오는 시간의존 방사성 붕괴열에 의한 영향을 해석하였다. 지하수위는 지표면 아래 10 m로 가정하였고, 지하수해석은 정류 알고리즘을 사용하였다.

• 터널과지하공간
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• 제31권6호
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• pp.610-622
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• 2021

DECOVALEX 프로젝트는 고준위방사성폐기물 처분 시스템에서 발생하는 복잡한 열-수리-역학-화학적(THMC) 복합거동에 대해 수치해석을 통해 보다 더 깊이 이해하기 위해 수행되고 있는 대표적 국제공동 연구이다. 현재 DECOVALEX-2023이 7개 task를 기반으로 진행 중이며, 이 중 Task C는 Mont-Terri 지하연구시설에서 수행된 실규모 정치(FE) 시험을 대상으로 처분시스템 내 THM 복합거동을 모사하는 것을 목표로 하고 있다. 본 연구에서는 자체개발 해석 코드인 OGS-FLAC을 활용하여 수치해석 연구를 수행하였다. 수치모델에서는 FE 시험과 같이 일정 출력의 히터를 수평으로 위치시켰으며, 주어진 계측지점에서 압력 분포, 온도 변화, 역학적 변형을 계측하였다. 완충재 내부로 유입되는 유체 흐름은 완충재의 흡입력으로 인해 발생하였으며, 주변 영역에서는 열 팽창 및 열 압력이 지배적으로 작용함을 확인하였다. 해석 결과는 향후 타 참여 그룹 및 실험 결과와 비교 검증을 수행할 계획이다.

• 대한기계학회논문집A
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• 제31권2호
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• pp.174-181
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• 2007

This paper is concerned with the thermo-mechanical behavior of steel sheet for an auto-body including temperature dependent strain rate sensitivity. In order to identify the temperature-dependent strain rate sensitivity of SPRC35R, SPRC45E and TRIP60, uniaxial tensile tests are performed with the variation of the strain rates from 0.001/sec to 200/sec and the variation of environmental temperatures from $-40^{\circ}C$ to $200^{\circ}C$. The thermo-mechanical response at the quasi-static state is obtained from the static tensile test and that at the intermediate strain rate is obtained from the high speed tensile test. Experimental results show that the variation of the flow stress and fracture elongation becomes sensitive to the temperature as the strain rate increases. It is observed that the dynamic strain aging occurs with TRIP60 at the temperature above $150^{\circ}C$. Results also indicate that the flow stress and tincture elongation of SPRC35R are more dependent on the changes of strain rates and temperature than those of SPRC45E and TRIP60.

• 열처리공학회지
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• 제10권1호
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• pp.20-29
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• 1997

Pure copper is widely used for base material for electrical and electronic parts because of its good electrical conductivity. However, it has such a low strength that various alloying elements are added to copper to increase its strength. Nevertheless, alloying elements which exist as solid solution elements in copper matrix severely reduce the electrical conductivity. The reduction of electrical conductivity can be minimized and the strengthening can be maximized by TMT(Thermo-Mechanical Treatment) in copper alloys. In this research, the effects of TMT on mechanical and electrical properties of Cu-Ni-Al-Si-P, Cu-Ni-Al-Si-P-Zr and Cu-Ni-Si-P-Ti alloys aged at various temperatures were investigated. The Cu alloy with Ti showed the hardness of Hv 225, electrical conductivity of 59.8%IACS, tensile strength of 572MPa and elongation of 6.4%.

• Advances in nano research
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• 제10권4호
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• pp.385-395
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• 2021

This research concentrates on the effects of distributions and volume fractions of carbon nanotubes (CNT) on the nonlinear bending behavior of deep cylindrical panels reinforced by functionally graded carbon nanotubes under thermo-mechanical loading, hitherto not reported in the literature. Assuming the effects of shear deformation and moderately high value of the radius-to-side ratio (R/a), based on the first-order shear deformation theory (FSDT) and von Karman type of geometric nonlinearity, the governing system of equations is obtained. The analytical solution of field equations is carried out using the Ritz method together with the Newton-Raphson iterative scheme. The effects of radius-to-side ratio, temperature change, and boundary conditions on the nonlinear response of the functionally graded carbon nanotubes reinforced composite deep cylindrical panel (FG-CNTRC) are investigated. It is concluded that, among the five possible distribution patterns of CNT, FG-V CNTRC deep cylindrical panel is strongest with the highest bending moment and followed by UD, X, O, and Ʌ-ones. Also, considering the present deep cylindrical panel formulation increases the accuracy of the results. Hence, according to the noticeable amount of R/a in FG-CNTRC cylindrical panels, it is mandatory to apply strain-displacement relations of deep cylindrical panels for bending analysis of FG-CNTRC which certainly is desirable for industrial application.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
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• pp.175-183
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• 2004

In hot strip rolling, a capability for precisely predicting roll force is crucial for sound process control. In the past, on-line prediction models have been developed mostly on the basis of Orowan's theory and its variation. However, the range of process conditions in which desired prediction accuracy could be achieved was rather limited, mainly due to many simplifying assumptions inherent to Orowan's theory. As far as the prediction accuracy is concerned, a rigorously formulated finite element(FE) process model is perhaps the best choice. However, a FE process model in general requires a large CPU time, rendering itself inadequate for on-line purpose. In this report, we present a FE-based on-line prediction model applicable to precision process control in a finishing mill(FM). Described was an integrated FE process model capable of revealing the detailed aspects of the thermo-mechanical behavior of the roll-strip system. Using the FE process model, a series of process simulation was conducted to investigate the effect of diverse process variables on some selected non-dimensional parameters characterizing the thermo-mechanical behavior of the strip. Then, it was shown that an on-line model for the prediction of roll force could be derived on the basis of these parameters. The prediction accuracy of the proposed model was examined through comparison with measurements from the hot strip mill.