• 대한기계학회논문집A
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• 제27권4호
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• pp.614-622
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• 2003

In this paper, the stress-strain curves of bearing steels at hot working conditions are obtained by hot compression test with a computer controlled servo-hydraulic Gleeble 3800 testing machine and elongations and reductions of area of the bearing steels are also obtained by hot tensile test with a Gleeble 1500 testing machine. Experiments are conducted under the various strain-rates and temperatures and their results are used to obtain the flow stress information. A rigid thermo-viscoplastic finite element method is applied to the multi-stage hot forging process in order to predict temperature distribution of workpiece. The experimental results and the analysis results are used to obtain an optimal hot forging condition.

• 한국지열·수열에너지학회논문집
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• 제11권2호
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• pp.12-18
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• 2015

The energy pile, used for both structural foundations and heat exchangers, brings about heat exchange with the ground formation by circulating a working fluid for heating and cooling buildings. As heat exchange occurs in the energy pile, thermal stress and strain is generated in the pile body and surrounding ground formation. In order to investigate the thermo-mechanical behavior of an energy pile, a comprehensive experimental program was conducted, monitoring the thermal stress of a cast-in place energy pile equipped with five pairs of U-type heat exchanger pipes. The heating and cooling simulation both continued for 30 days. The thermal strain in the longitudinal direction of the energy pile was monitored for a 15 operation days and another 15 days monitoring followed, without the application of heat exchange. In addition, a finite element model was developed to simulate the thermo-mechanical behavior of the energy pile. A non-linear contact model was adopted to interpret the interaction at the pile-soil interface, and thermal-induced structure mechanics was considered to handle the thermo-mechanical coupled multi-field problem.

• Advances in materials Research
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• 제6권3호
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• pp.279-301
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• 2017

Thermo-mechanical vibration characteristics of in homogeneousporous functionally graded (FG) micro/nanobeam subjected to various types of thermal loadings are investigated in the present paper based on modified couple stress theory with consideration of the exact position of neutral axis. The FG micro/nanobeam is modeled via a refined hyperbolic beam theory in which shear deformation effect is verified needless of shear correction factor. A modified power-law distribution which contains porosity volume fraction is used to describe the graded material properties of FG micro/nanobeam. Temperature field has uniform, linear and nonlinear distributions across the thickness. The governing equations and the related boundary conditions are derived by Extended Hamilton's principle and they are solved applying an analytical solution which satisfies various boundary conditions. A comparison study is performed to verify the present formulation with the known data in the literature and a good agreement is observed. The parametric study covered in this paper includes several parameters such as thermal loadings, porosity volume fraction, power-law exponents, slenderness ratio, scale parameter and various boundary conditions on natural frequencies of porous FG micro/nanobeams in detail.

• 터널과지하공간
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• 제29권1호
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• pp.38-51
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• 2019

Barcelona Basic Model(BBM)은 응력의 변화에 따른 부피변화뿐만 아니라 흡입력의 변화에 따른 팽윤거동을 설명할 수 있으며, 흡입력 변화에 따른 점착력과 선행압밀응력의 변화와 온도변화에 따른 선행압밀응력의 변화를 고려할 수 있다. 따라서, 고준위방사성폐기물 처분시스템에서 공학적방벽재로 고려되고 있는 벤토나이트 완충재의 열-수리-역학적 복합거동을 예측 및 분석하는 것에 많이 활용되고 있다. 그러나 우리나라의 암반 및 지반 공학자들에게 잘 알려져 있지 않기 때문에 BBM을 소개하고자 한다. BBM은 불포화 토질의 역학적 거동을 모사하기 위해 Modified Cam Clay(MCC) 모델을 확장하여 만들어 졌기 때문에 본 고에서는 먼저 MCC 모델을 간략하게 소개하고, 열-탄소성 모델인 BBM을 상세히 소개하였다.

• Steel and Composite Structures
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• 제16권1호
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• pp.77-96
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• 2014

In this paper, magneto-thermo-elastic problem of a thick truncated conical shell immersed in a uniform magnetic field and subjected to internal pressure is investigated. Material properties of the shell including the elastic modulus, magnetic permeability, coefficients of thermal expansion and conduction are assumed to be isotropic and graded through the thickness obeying the simple power law distribution, while the poison's ratio is assumed to be constant. The temperature distribution is assumed to be a function of the thickness direction. Governing equations of the truncated conical shell are derived in terms of components of displacement and thermal fields and discretised with the help of differential quadrature (DQ) method. Results are obtained for different values of power law index of material properties and effects of thermal load on displacement, stress, temperature and magnetic fields are studied. Results of the present method are compared with those of the finite element method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.365-366
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• 2015

This paper describes the analysis on thermo-mechanical characteristics of underground cable termination. Specially, the interface pressures between stress relief cone and XLPE insulation were analysed according to the change of conductor temperature and ambient temperature. This interface pressures were measured by real test with current transformer and chamber and the interface pressure was changed with conductor and ambient temperature. This paper will continue to perform the test with various cases, then the relation between low interface pressure and breakdown will prove with test results in the near future.

• 대한기계학회논문집A
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• 제26권2호
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• pp.340-348
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• 2002

Deformation analysis of injection molded articles whose geometry is considered as the assembly of thin flat plates has been conducted. For the in-mold analysis, thermo-viscoelastic stress calculation of thermo-rheologically simple amorphous polymer and in-mold deformation calculation considering the in-plane mold constraint have been done. Free volume theory has been used to represent the non-equilibrium density state during the fast cooling. At ejection, instantaneous deformation takes place due to the redistribution of in-mold residual stress. During out-of-mold cooling after ejection, thermoelastic model based on the effective temperature has been adopted for the calculation of out-of-mold deformation. In this study, emphasis is also made on the treatment with regard to lateral constraint types during molding process. Two typical mold geometries are used to test the numerical simulation modeling developed in this study.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.218-221
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• 2008

Hot Press Forming (HPF), an advanced sheet forming method in which a high strength part can be produced by forming at high temperature and rapid cooling in dies, is one of the most successful forming process in producing components with complex geometric shape, high strength and a minimum of springback. In order to obtain effectively and accurately numerical finite element simulations of the actual HPF process, the flow stress of a boron steel in the austenitic state at elevated temperatures has been investigated with Gleeble system. To evaluate the formability of the thermo- mechanical material characteristics in the HPF process, the FLDo defined at the lowest point in the forming limit diagrams of a boron steel has been investigated. In addition, the simulation results of thermo-mechanical coupled analysis of an automobile one-piece lower-arm part are compared with the experimental ones to confirm the validity of the proposed simulations.

• Geomechanics and Engineering
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• 제23권6호
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• pp.561-573
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• 2020

The creep and consolidation behaviors of clays subjected to thermal cycles are of fundamental importance in the application of energy geostructures. This study aims to numerically investigate the physical mechanisms for the temperature-triggered volume change of saturated clays. A recently developed thermodynamic framework is used to derive the thermo-mechanical constitutive model for clays. Based on the model, a fully coupled thermo-hydro-mechanical (THM) finite element (FE) code is developed. Comparison with experimental observations shows that the proposed FE code can well reproduce the irreversible thermal contraction of normally consolidated and lightly overconsolidated clays, as well as the thermal expansion of heavily overconsolidated clays under drained heating. Simulations reveal that excess pore pressure may accumulate in clay samples under triaxial drained conditions due to low permeability and high heating rate, resulting in thermally induced primary consolidation. Results show that four major mechanisms contribute to the thermal volume change of clays: (i) the principle of thermal expansion, (ii) the decrease of effective stress due to the accumulation of excess pore pressure, (iii) the thermal creep, and (iv) the thermally induced primary consolidation. The former two mechanisms mainly contribute to the thermal expansion of heavily overconsolidated clays, whereas the latter two contribute to the noticeable thermal contraction of normally consolidated and lightly overconsolidated clays. Consideration of the four physical mechanisms is important for the settlement prediction of energy geostructures, especially in soft soils.

• Composites Research
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• 제36권2호
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• pp.117-125
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• 2023

본 논문에서는 복합소재 적층 구조물의 열-기계적 거동을 효과적으로 예측할 수 있는 8절점 판 요소 기반 전산해석 기법을 제안하고자 한다. 횡방향 수직 변형이 고려된 개선된 일차전단변형이론을 바탕으로 유한요소 정식화를 수행하였으며, 독립적으로 가정되는 변위장 및 응력장 사이의 타당한 수학적 관계식을 도출함으로써 해석 결과의 정확도와 계산 과정의 효율성을 동시에 향상시키고자 하였다. 또한, 횡 방향 변위장의 개선을 통해 횡 방향 수직 변형을 효과적으로 고려함으로써, 복합소재 적층 구조물의 열적 거동 예측 과정에서의 신뢰성을 확보하고자 하였다. 수치 예제로써 열-기계 하중을 받는 2차원 복합소재 적층평판을 고려하였으며, 3차원 탄성해 및 참고문헌에서 활용 가능한 해석 결과와의 비교, 검토를 통해 제안된 유한요소 해석 기법의 성능을 검증하였다.