• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2008년도 추계학술대회 논문집
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• pp.605-606
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• 2008

• Structural Engineering and Mechanics
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• 제61권3호
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• pp.317-323
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• 2017

This work presents a new strategy to model stress dependent relaxation process in large deformation. The strategy is relied on the fact that in some particular soft materials undergoing large deformation, e.g., elastomers, rubbers and soft tissues, the relaxation time depends strongly on stress levels. To simplify the viscoelastic model, we consider that the relaxation time is the function of previous elastic deviatoric stress state experienced by materials during loading. Using the General Maxwell Model (GMM), we simulate numerically conditions with the constant and the stress dependent relaxation time for uniaxial tension and compression loading. Hence, it can be shown that the proposed model herein not only can represent different relaxation time for different stress level but also maintain the capability of the GMM to model hysteresis phenomena.

• Geomechanics and Engineering
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• 제12권3호
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• pp.347-360
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• 2017

The problem of cylindrical cavity expansion incorporating deformation dependent of intermediate principal stress in rock or soil mass is investigated in the paper. Assumptions that the initial axial total strain is a non-zero constant and the axial plastic strain is not zero are defined to obtain the numerical solution of strain which incorporates deformation-dependent intermediate principal stress. The numerical solution of plastic strains are achieved by the 3-D plastic potential functions based on the M-C and generalized H-B failure criteria, respectively. The intermediate principal stress is derived with the Hook's law and plastic strains. Solution of limited expansion pressure, stress and strain during cylindrical cavity expanding are given and the corresponding calculation approaches are also presented, which the axial stress and strain are incorporated. Validation of the proposed approach is conducted by the published results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.647-650
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• 2003

Under sustained loads, the deformation of a structure gradually increase with time and eventually may be much greater than its instantaneous value, This inelastic and time-dependent deformation causes increase in deflection and curvature, redistribution of stress and internal action, In this paper, time-dependent analysis with creep and shrinkage of uncracked and cracked partially prestressed concrete flexural members is presented.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
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• pp.313-319
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• 1999

The development of deformation texture in FCC polycystalline metals during rolling was simulated by the finite element analysis using a large-deformation, elaatic-plastic, rate-dependent polycrystalline model of crystal plasticity. Different plastic anisotropy due to different orientation of each crystal makes inhomogeneous deformation. Assuming plane strain compression condition, the simulation with a high rate sensitivity resulted in main component change from Dillamore at low rate sensitivity to Brass component.

• 지질공학
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• 제18권2호
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• pp.207-214
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• 2008

점토함량에 따른 미고결 이암의 시간 의존적 변형을 비교하기 위해 측방변형이 구속된 상태에서의 일축압밀시험을 수행하였다. 미고결 이암의 변형은 응력의 증가에 따른 즉각적인 변형과 일정한 응력 하의 크리프 변형으로 구분되었다. 응력 증가분이 동일한 경우에 시간 의존적 변형은 거의 일정한 크기로 발생하였으며 응력 증가분이 증가할수록 크리프변형의 크기도 증가하여 선형점성변형의 특성을 보였다. 점토함량이 증가함에 따라 시간 의존적 변형은 증가하는 경향을 보여 점토가 이암의 시간 의존적 변형 발생에 중요한 역할을 하는 것으로 사료된다. 크리프 변형은 시간에 따라 지수함수 형태를 보여 크립 모델 중 하나인 power-law 모델로 잘 예측될 수 있었다.

• 한국지반공학회논문집
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• 제23권3호
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• pp.15-24
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• 2007

본 논문은 도로기초 입상재료의 응력의존적인 특성을 고려한 응력의존적 재료 상수의 적용을 통하여 층 변형예측을 수행하는 간편한 방식을 소개한다. 이 방법은 Unbound지반재료에 대하여 회복변형과 영구변형을 구분하여 고려하며 두 변형의 상호작용을 적용하지 않는 방식이다. 그 결과 회복변형 탄성계수와 포와송비를 포함한 해석모형은 상호작용이 고려되지 않아도 현장에서의 도로기초 변형을 예측할 수 있음을 잘 보여주고 있다. 또한 응력의존 탄성계수와 응력의존 포와송 비 모형에서 가장 영향을 많이 미치는 계수를 찾기 위하여 민감도분석을 실시하였다. 이러한 분석결과를 토대로 응력의존에 의하여 변형 예측시 나타나는 경향을 살펴보았다.

• 소성∙가공
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• 제22권4호
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• pp.216-222
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• 2013

Solid polymers exhibit rate-dependent deformation behavior such as nonlinear strain rate sensitivity and stress relaxation like metallic materials. Despite the different microstructures of polymeric and metallic materials, they have common properties with respect to inelastic deformation. Unlike most metallic materials, solid polymers and shape memory alloys (SMAs) exhibit highly nonlinear stress-strain behavior upon unloading. The present work employs the viscoplasticity theory [K. Ho, 2011, Trans. Mater. Process. 20, 350-356] developed for the pseudoelastic behavior of SMAs, which is based on unified state variable theory for the rate-dependent inelastic deformation behavior of typical metallic materials, to depict the curved unloading behavior of polyphenylene oxide (PPO). The constitutive equations are characterized by the evolution laws of two state variables that are related to the elastic modulus and the back stress. The simulation results are compared with the experimental data obtained by Krempl and Khan [2003, Int. J. Plasticity 19, 1069-1095].

• 국제초고층학회논문집
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• 제6권1호
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• pp.83-89
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• 2017

Due to the time-dependent properties of materials, structures, and loads, accurate time-dependent effects analysis and precise construction controls are very significant for rational analysis and design and saving project cost. Elevation control is an important part of the time-dependent construction control in supertall structures. Since supertall structures have numerous floors, heavy loads, long construction times, demanding processes, and are typically located in the soft coastal soil areas, both the time-dependent features of superstructure and settlement are very obvious. By using the time-dependent coupling effect analysis method, this paper compares Shanghai Tower's vertical deformation calculation and elevation control scheme, considering foundation differential settlement. The results show that the foundation differential settlement cannot be ignored in vertical deformation calculations and elevation control for supertall structures. The impact of foundation differential settlement for elevation compensation and pre-adjustment length can be divided into direct and indirect effects. Meanwhile, in the engineering practice of elevation control for supertall structures, it is recommended to adopt the multi-level elevation control method with relative elevation control and design elevation control, without considering the overall settlement in the construction process.

• 한국지반공학회지:지반
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• 제5권2호
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• pp.57-77
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• 1989

본고는 팽장성 암석들의 시간의존적변형의 측정을 위한 실험장치와 실험고과에 관해서 설명한다. 새로운 실험장치들은 개선된 일축벽축하의 팽난시험, 일축 인장하의 인창시험과 이축 응력하의 팽 복시험을 위해서 제작하였다. 본 실험장치들은 암반파착시 지반에 작용하는 단순화된 헌력상태하에 있는 암반의 시간의존적 변형을 제 수직방향에서 측정한다. 지난 몇년간에 걸쳐서 얻은 실험결과에 의하면 본 실험장치들은 세공적으로 작동하는 것으로 나타났다. 실험결과로 보면, 퀸스톤 체일(Queenston shale)의 자유변형조건하에서의 시간의존적 변형 거동은 층리면과 수직인 방향에서는 층리면과 평행인 방향에서보다 약간 더 많은 역접이 일어나는 이방성적 거동을 보인다. 한 방향에 응력을 받을 때에는 응력이 작용하는 방향은 물론 그와 수직되는 방향의 역장성변형이 억제된다.