• 복합신소재구조학회 논문집
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• 제4권1호
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• pp.25-32
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• 2013

In real world applications, the response of structures may be dependent on the rate of loading and thus can be affected by transient loading, especially when the rate of loading is significant. In such situations, the rate of loading may become a major issue to understand structures during earthquake excitation or under blast or high velocity impact. In some cases, the rate effect on structures under strong earthquake excitation cannot be ignored when attempting to understand inelastic behavior of structures. Many researchers developed the constitutive theories in cyclic plasticity and viscoplasticity. In this study, numerical simulation by cyclic visocoplasticity models is introduced and analyzed. Finally, the analytical results are compared with experimental results as a means to evaluate and verify the model.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.309-312
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• 2001

FEM simulating system of the cross-rolling texture formation offers a systematic and efficient way of exploring the relationship between the process variables and the state of plastic anisotropy of sheet product. Cross-rolled sheets possess higher average plastic strain ratios and lower planer anisotropy than those of the straight-rolled sheets. The employed model is a finite-element polycrystal model which each element used in FEM is assumed to be a crystal having different orientation by Takahashi. Texture development, deformation textures due to cross-rolling are predicted for face-centered cubic sheet metal. Crystal orientations are assigned on the basis of the pole figures obtained by X-ray diffraction. Development of anisotropy during cross rolling of an fcc sheet material is predicted theoretically with respected to flow stress and R-value in tensile test.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.62-65
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• 1999

To reduce the cost of finite element analyses for sheet forming a 3D hybrid membrance/sheel method has been developed to study the springback of anisotropic sheet metals. in the hybrid method the bending strains and stresses were analytically calculated as post-processing using incremental shapes of the sheet obtained previously from the membrane finite element analysis. To calculate springback a shell finite element model was used to unload the final shape of the sheet obtained from the membran code and the stresses and strains that were calculated analytically. For verification the hybrid method was applied to predict the springback of a 2036-T4 aluminum square blank formed into a cylindrical cup. the springback predictions obtained with the hybrid method was in good agreement with results obtained using a full shell model to simulateboth loading an unloading and the experimentally measured data. The CPU time saving with the hybrid method over the full shell model was 75% for the punch stretching problem.

• Steel and Composite Structures
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• 제35권6호
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• pp.739-752
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• 2020

This paper aims to investigate cyclic plasticity of a new type of high-performance austenitic stainless steel with both high strength and high ductility. The new stainless steel termed as QN1803 has high nitrogen and low nickel, which leads to reduction of cost ranging from 15% to 20%. Another virtue of the new material is its high initial yield strength and tensile strength. Its initial yield strength can be 40% to 50% higher than conventional stainless steel S30408. Elongation of QN1803 can also achieve approximately 50%, which is equivalent to the conventional one. QN1803 also has a corrosion resistance as good as that of S30408. In this paper, both experimental and numerical studies on the new material were conducted. Full-range true stress-true strain relationships under both monotonic and cyclic loading were obtained. A cyclic plasticity model based on the Chaboche model was developed, where a memory surface was newly added and the isotropic hardening rule was modified. A user-defined material subroutine was written, and the proposed cyclic plasticity model can well evaluate full-range hysteretic properties of the material under various loading histories.

• 한국지진공학회논문집
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• 제8권1호
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• pp.59-65
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• 2004

최근 강구조물의 고층화 및 장경간화로 인하여 SM570강재와 같은 고강도 강재의 적용을 필요로 하고 있다. 강구조물의 정확한 내진설계를 위한 내진구조해석시 비선형 반복하중을 받는 강재의 특성을 명확히 포현할 수 있는 구성식이 필요하다. SM570는 최근 그 사용이 증가하고 있으나 아직 반복소성거동의 구현 및 정식화에 관한 연구는 아직 미진하다. 본 연구에서는 인장 및 저싸이클 피로 실험을 통하여 SM570 강재의 반복소성모델을 제안하였다. 제안된 반복소성모델을 3차원 유한요소에 적용하여 SM570이 사용된 원형 강교각의 내진해석을 수행하였다. 실험결과와 내진해석을 통하여 본 연구에서 제안한 구성식은 SM570이 사용된 강구조물의 복잡한 소성거동을 정도 높게 구현함을 알 수 있었다.

• 콘크리트학회논문집
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• 제19권5호
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• pp.655-664
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• 2007

콘크리트의 인장균열에 따른 방향적 비국소 손상이라는 특징은 인장-압축을 받는 철근콘크리트 전단 부재에서 회전인장균열 특성 및 압축강도 감소 현상을 일으킨다. 본 연구에서는 인장과 압축거동에 대하여 다른 손상 모델을 사용하는 기존의 방법과는 달리, 동일한 인장균열 손상 모델을 사용하여, 인장균열거동과 압축연화거동을 나타낸다. 이러한 비국소 균열 손상의 영향을 나타낼 수 있는 소성모델을 개발하기 위하여 미소면 모델의 개념을 도입한다. 기존의 소성모델과 달리, 비국소 균열 손상을 나타내기 위하여 인장과 압축의 소성파괴면은 각 미소면에서 정의하며, 각 미소파괴면의 조합에 의하여 대표파괴면을 정의한다. 이때, 방향적 비국소 균열 손상을 나타내는 소성인장변형률의 영향에 의하여 각 미소면의 인장과 압축 소성변형률의 크기가 결정된다. 본 연구에서 개발된 소성모델은 유한요소해석에 적용되며, 다양한 전단패널의 기존 실험 결과들과 비교하여 제안된 재료 모델의 유효성을 검증한다.

• Computers and Concrete
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• 제7권4호
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• pp.365-386
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• 2010

This paper presents the physical formulation of a 1D material model suitable for seismic applications. It is written within the framework of thermodynamics with internal variables that is, especially, very efficient for the phenomenological representation of material behaviors at macroscale: those of the representative elementary volume. The model can reproduce the main characteristics observed for concrete, that is nonsymetric loading rate-dependent (viscoelasticity) behavior with appearance of permanent deformations and local hysteresis (continuum plasticity), stiffness degradation (continuum damage), cracking due to displacement localization (discrete plasticity or damage). The parameters have a clear physical meaning and can thus be easily identified. Although this point is not detailed in the paper, this material model is developed to be implemented in a finite element computer program. Therefore, for the benefit of the robustness of the numerical implementation, (i) linear state equations (no local iteration required) are defined whenever possible and (ii) the conditions in which the presented model can enter the generalized standard materials class - whose elements benefit from good global and local stability properties - are clearly established. To illustrate the capabilities of this model - among them for Earthquake Engineering applications - results of some numerical applications are presented.

• Interaction and multiscale mechanics
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• 제4권3호
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• pp.187-206
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• 2011

Accurate estimations of pre-failure deformations and post-failure responses of geostructures require that the simulation tool possesses at least three main ingredients: 1) a constitutive model that is able to describe the macroscopic stress-strain-strength behavior of soils subjected to complex stress/strain paths over a wide range of confining pressures and densities, 2) an embedded length scale that accounts for the intricate physical phenomena that occur at the grain size scale in the soil, and 3) a computational platform that allows the analysis to be carried out beyond the development of an initially "contained" failure zone in the soil. In this paper, a two-scale micropolar plasticity model will be used to incorporate all these ingredients. The model is implemented in a finite element platform that is based on the mechanics of micropolar continua. Appropriate finite elements are developed to couple displacement, micro-rotations, and pore-water pressure in form of $u_n-{\phi}_m$ and $u_n-p_m-{\phi}_m$ (n > m) elements for analysis of dry and saturated soils. Performance of the model is assessed in a biaxial compression test on a slightly heterogeneous specimen of sand. The role of micropolar component of the model on capturing the post-failure response of the soil is demonstrated.

• 콘크리트학회논문집
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• 제16권3호
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• pp.345-356
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• 2004

다양한 압축 응력 상태에서의 콘크리트의 거동 특성을 나타내기 위한 소성 모델을 개발하였다. 응력 성분은 압축 상태에서 각각의 거동특성을 갖는 세 개의 직교 성분으로 분리하였다. 각 성분의 거동 특성을 독립적으로 나타내기 위하여 각 성분에 대한 독립적인 다중 파괴기.준을 이용하는 소성모델을 적용하였다. 각 파괴면은 실험결과에 근거하여 각 파괴기준에 대한 등가 소성 변형률에 의하여 정의하였다. 또한, 압축손상에 의한 체적팽창을 나타내기 위한 간단한 비상관 소성흐름법칙을 제안하였다. 제안된 모델은 다양한 재료 특성 및 응력 상태를 갖는 기존의 실험 결과들과 비교를 통하여 검증되었다. 이 비교는 기존의 소성모델보다 제안된 모델의 적용성이 우수함을 입증하고 있다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.301-308
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• 2004

The present study mainly focuses on the inelastic stress analysis of the 1/4 scale prestressed concrete containment vessel model(PCCV) under internal pressure and evaluates not only failure mode but also ultimate pressure capacity of the PCCV. Inelastic analysis is carried out 2D axisymmertic FE model and 3D FE model using four concrete material models which are Drucker-Prager Model, Chen-Chen Model, Damaged Plasticity Model and Menetrey-Willam Model. The uplift phenomenon of the basemat is considered in the 2D axisymmetric FE models. It is found from the 2D axisymmetric analysis results that both of Drucker-Prager model and Damaged Plasticity Model have a good performance and the uplift of the basemat is too small to influence on the global behavior of the PCCV. The FE analysis results on the ultimate pressure and failure mode have a good agreement with experimental results.