• 한국정밀공학회지
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• 제16권4호통권97호
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• pp.178-188
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• 1999

충격하중을 받는 시험편 높이의 1/4 길이의 notch를 가진 3점 굽힘시험편들의 기계적 거동에 관한 컴퓨터 시뮬레이션을 하고 이 시뮬레이션에 대한 실험적 검증도 하여 그 타당성을 입증하였다. 시험편들의 양쪽 가장자리(지지점)에서 작용되어지는 여러 가지의 하중속도에 대한 경우들과 탄소성 von Mises 재질인 모델들을 시뮬레이션에 포함시켰으며 이들에 대한 결과들을 간극 개구 변위, 반력, 크랙선단 개구 변위 및 변형률등이 속도에 의존되는 재질(점소성 재질)에 대한 시뮬레이션 결과와 비교하였다. 또한 여러가지의 동적 하중을 받는 상황하에서의 안정성이 본 연구의 시뮬레이션을 통하여 비교되었으며 그 차이점들이 규명되었다.

• 한국구조물진단유지관리공학회 논문집
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• 제8권2호
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• pp.195-204
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• 2004

본 연구에서는 약액주입 사질고결토에 대해 일정재하크리프시험과 반복재하크리프시험을 실시하여 점 탄소성 거동 규명과 크리프예측을 수행하였다. 일정재하크리프 시험결과 총 변형률은 탄성, 소성 그리고 점탄성변형률로 구분되었으며 이러한 변형률은 응력의 증가에 비례하여 증가하였고 회복된 변형률은 제하시간에 무관함을 알았다. 일정재하크리프시험 예측결과 일반화된 모델과 지수함수모델은 시험결과와 잘 일치하였다. 반복재하크리프시험에서 순간회복변형률은 반복횟수에 무관하였고 누적소성 변형률은 반복횟수에 따라 증가하였으며 응력레벨에 비례함을 알 수 있었다. 반복재하크리프시험의 예측결과 첫 사이클에서는 잘 일치하였으나 반복횟수가 증가함에 따라 약간의 오차가 발생되었다.

• 대한기계학회논문집
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• 제14권5호
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• pp.1043-1058
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• 1990

본 연구에서는 전자기 성형법에 의한 원통형상의 가공재의 자유 확관성형 가 공에 대해서 유한요소해석법을 이용한 변형 및 응력해석을 수행하였다. 탄소성 재료 모형을 확장하여 변형 경화율이 변형률 및 변형률 속도의 지배를 받는 변형률 속도 종 속 탄소성 재료 모형을 도입하였고, 1차 제하 이후까지 포함하여 고속 성형시 변형률 속도 효과에 의해 발생하는 현상들에 대해서 연구하였다.결과의 비교 및 논의를 위 하여, 해석대상과 성형조건, 그리고 가공재에 작용하는 자기압력은 Suzuki의 것과 동 일한 것을 사용하였다.

• 한국농공학회논문집
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• 제49권4호
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• pp.43-49
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• 2007

The reinforced concrete slab is one of main structure members in the construction industry sector. However, most of researches regarding to RC slabs have been focused on two-dimensional Mindlin-type plate element on the basis of laminated plate theory since three-dimensional solid element has a lot of difficulties in finite element formulation and costs in CPU time. In reality, the RC slabs are subjected to dynamic loads like a heavy traffic vehicle load, and thus should insure the safety from the static load as well as dynamic load. Once we can estimate the dynamic behaviour of RC slabs exactly, it will be very helpful for design of it. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The applicability of the proposed finite element has been tested for dynamic behaviour of RC slabs with respect to characteristics of concrete materials in terms of cracking stress, crushing strain, fracture energy and Poisson's ratio. The effect on dynamic behaviour is dependent on not crushing strain but cracking stress, fracture energy and Poisson's ratio. In addition to this, it is shown the damping phenomenon of RC slabs has been identified from the numerical results by using Rayleigh damping.

• 한국농공학회논문집
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• 제49권6호
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• pp.47-54
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• 2007

This paper is on the research of the special character of the dynamic response according to a design of the clamped reinforced concrete slab. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The design factor, which affect the dynamic response of the reinforced concrete slab, are the steel layer thickness, steel layer depth, steel layout method, steel layout angle and the slab thickness and span ratio. The main purpose of this study was to find out the dynamic response of the reinforced concrete slab according to above variables. The reduction of deflection/thickness ratio appeared less than 2% when the slab thickness between 20 and 21cm. It is desirable that the slab thickness must be above 20-21cm. The reduction ratio of deflection is appeared greatly when the value of the span/thickness ratio is between 25 and 30. In conclusion, the steel layer depth and thickness had a little effect on deflection of the dynamic response, but had no effect on the steel layout angle.

• 대한조선학회논문집
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• 제48권3호
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• pp.200-206
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• 2011

The mechanical properties of the most widely used cryogenic materials, i.e. austenitic stainless steel (ASS), aluminum alloy and invar steel, strongly depend on temperatures and strain rates. These phenomena show very complicated non-linear behaviors and cannot be expressed by general constitutive equation. In this study, an unified constitutive equation was proposed to represent the effect of temperature and strain rate on the materials. The proposed constitutive equation has been based on Tomita/Iwamoto and Bodner/Partom model for the expression of 2nd hardening due to martensite phase transformation of ASS. To simulate ductile fracture, modified Bodner/Chan damage model was additionally applied to the model and the model validity was verified by comparison of experimental and simulation results.

• 대한기계학회논문집A
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• 제30권11호
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• pp.1494-1501
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• 2006

Mechanical and physical properties of a copper alloy for a liquid rocket engine(LRE) combustion chamber liner application were tested at various temperatures. All test specimens were heat treated with the condition they might experience during actual fabrication process of the LRE combustion chamber. Physical properties measured include thermal conductivity, specific heat and thermal expansion data. Uniaxial tension tests were preformed to get mechanical properties at several temperatures ranging from room temperature to 600$^{\circ}C$. The result demonstrated that yield stress and ultimate tensile stress of the copper alloy decreases considerably and strain hardening increases as the result of the heat treatment. Since the LRE combustion chamber operates at higher temperature over 400$^{\circ}C$, the copper alloy can exhibit time-dependent behavior. Strain rate, creep and stress relaxation tests were performed to check the time-dependent behavior of the copper alloy. Strain rate tests revealed that strain rate effect is negligible up to 400$^{\circ}C$ while stress-strain curve is changed at 500$^{\circ}C$ as the strain rate is changed. Creep tests were conducted at 250$^{\circ}C$ and 500$^{\circ}C$ and the secondary creep rate was found to be very small at both temperatures implying that creep effect is negligible for the combustion chamber liner because its operating time is quite short.

• 한국농공학회논문집
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• 제50권2호
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• pp.19-26
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• 2008

This study has been carried out to investigate the dynamic characteristics of RC slabs. For this purpose, the 20-node solid element has been used to discretize the RC slabs into two parts of concrete and rebar. The material non-linearity considering elasto-visco plastic model and the smeared crack model have been adopted in the finite element formulation. The applied load can handle step load, load intensity of harmonic load, area of distributed load and frequency. The frequency of harmonic load has an significant effect on dynamic behaviour in terms of displacement. As the frequency is increased, the effect of load amplitude is more serious. Especially, if the frequency of harmonic load exceeds 30 Hz, it is noted that the displacement by harmonic load is greater than that by step load. In case of harmonic load, the damping effect shows no certain tendency with respect to frequency of load. In details, the damping is effective when the frequency of harmonic load is 2 Hz, but there is no consistent tendency according to damping ratio. The dynamic response when the frequency of harmonic load is 3 Hz shows same result for undamped case as well as for damped case with 5% damping ratio. It is also noted that we can get the largest deflection for damped case with 1% damping ratio. However, there is not any damping effect when the frequency of harmonic load is greater than 4 Hz.

• 한국전산구조공학회논문집
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• 제15권4호
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• pp.567-578
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• 2002

본 논문은 8절점 고체요소를 이용하여 항공기 충돌에 의한 원전 격납건물의 동적 거동을 분석하고 그 결과를 기술하였다. 콘크리트의 재료적 특성을 표현하기 위하여 Drucker-Prager항복기준을 바탕으로 항복면과 파괴면을 형성하였다. 이때 항복면과 파괴면은 콘크리트의 소성변형이 누적되면 가변하는 것으로 가정하였다. 철근의 재료특성은 변형도에 의존적인 탄성/점소성모델을 이용하여 표현하였다. 표준고체요소의 성능저하를 방지하기 위하여 Hughes가 제시한 B bar법을 바탕으로 변형도-변위관계 행렬을 형성하였다. 동적 시간이력해석을 수행하기 위하여 안정적인 수렴성을 가지는 암시적인 Newmark법을 도입하였다. 마지막으로 시간이력해석을 통하여 콘크리트 균열변형도의 수준과 충돌하는 항공기의 종류에 따른 격납건물의 동적거동변화를 조사하고 이를 정량적으로 기술하였다.