• Computers and Concrete
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• 제7권2호
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• pp.145-158
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• 2010

In this work the implementation of a production-level port of the Microplane constitutive model for concrete into the EPIC code is described. The port follows guidelines outlined in the Material Model Module (MMM) standard used in EPIC to insure a seamless interface with the existing code. Certain features of the model were not implemented using the MMM interface due to compatibility reasons; for example, a separate module was developed to initialize, store and update internal state variables. Objective strain and deformation measures for use in the material model were also implemented into the code. Example calculations were performed and illustrate the veracity of this new implementation.

• Coupled systems mechanics
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• 제10권6호
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• pp.521-544
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• 2021

In this work, we present the development of a 3D lattice-type model at microscale based upon the Voronoi-cell representation of material microstructure. This model can capture the coupling between mechanic and electric fields with non-linear constitutive behavior for both. More precisely, for electric part we consider the ferroelectric constitutive behavior with the possibility of domain switching polarization, which can be handled in the same fashion as deformation theory of plasticity. For mechanics part, we introduce the constitutive model of plasticity with the Armstrong-Frederick kinematic hardening. This model is used to simulate a complete coupling of the chosen electric and mechanics behavior with a multiscale approach implemented within the same computational architecture.

• 한국지반공학회지:지반
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• 제10권1호
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• pp.7-18
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• 1994

본 연구에서는 단조하중과 반복하중에 대한 점토지반의 거동을 표현할 수 있는 새로운 구성모델을 제안하였다. 제안된 모델은 과압밀상태에서의 응력-변형률 관계를 쌍곡선식으로 가정하고 한계상태이론과 결합시켜 비배수 응력경로를 예측한다. 에너지분산식을 이용하여 개발된 이 구성모델은 단조하중 작용시에 미약한 과압밀상태 및 과다한 과압밀상태의 점성토거동을 표현할 수 있다. 또한 반복하중하에서의 거동을 나타내기 위하여 단조하중에 대하여 개발된 구성모델에 비배수 경로간격비 이동함수를 도입하였다. 이를 위하여 한개의 추가적인 모델계수가 필요하며 그 값은 합리적 방법으로 실험결과로부터 산정될 수 있다. 본 구성모델은 비교적 쉽고 정확하게 반복하중을 받는 점성토지반의 비배수 거동에 대한 실험결과를 예측한다.

• 한국지반공학회지:지반
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• 제8권4호
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• pp.17-30
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• 1992

연약한 점토지반에서는, 정규압밀상태와 더불어 미약한 과압밀상태에서의 구성관계가 실제 지반구조물의 거동을 해석하는 데 중요한 역할을 한다. 미약한 과압밀상태의 거동에 실용적으로 적용될 수 있는 구성모델은 비교적 간편한 계수만을 사용하여 실제의 다양한 거동을 정확하게 예측할 수 있도록 개발되어야 한다. 이러한 연유로 본 연구에서는 등가응력 (자)으로규준화하였을 때 나타나는 지반의 비 배수거동을 재현하여 미약한 과압밀상태에 적용할 수 있는 구성모델을 제안하였다. 제안된 모델은 단지 정규압밀상태의 거동으로 도출할 수 있는 모델계수만을 사용하여 초기항복면내부에서 발생하는 항복현상을 표현할 수 있다. 뿐만아니라 제안된 모델은 과압밀상태, 2차압밀, 응력이완등의 영향에 따른 실제의 거동을 기존의 모델들에 비하여 더욱 간편하고 정확하게 예측할 수 있다.

• 열처리공학회지
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• 제31권4호
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• pp.180-186
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• 2018

High temperature flow behaviors of Fe-Cr-Mo-V-W-C tool steel were investigated using isothermal compression tests on a Gleeble simulator. The compressive test temperature was varied from 850 to $1,150^{\circ}C$ with the strain rate ranges of 0.05 and $10s^{-1}$. The maximum height reduction was 45%. The dynamic softening related to the dynamic recrystallization was observed during hot deformation. The constitutive model based on Arrhenius-typed equation with the Zener-Hollomon parameter was proposed to simulate the hot deformation behavior of Fe-Cr-Mo-V-W-C steel. An artificial neural network (ANN) model was also developed to compare with the constitutive model. It was concluded that the ANN model showed more accurate prediction compared with the constitutive model for describing the hot compressive behavior of Fe-Cr-Mo-V-W-C steel.

• Earthquakes and Structures
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• 제25권1호
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• pp.57-67
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• 2023

The buckling of longitudinal reinforcements under seismic loading accelerates the degradation of the bearing capacity of reinforced concrete columns. The traditional hysteretic constitutive model of reinforcement, which does not consider buckling, usually overestimates the seismic performance of pier columns. Subsequent researchers have also proposed many models including the buckling effects. However, the accuracy of these hysteretic constitutive models proposed for simulating the buckling behavior is inadequate. In this study, based on their works, the influence of historical events on buckling is considered, the path of the re-tensioning phase is corrected by adjusting the boundary lines, and the positions of the onset buckling point and compressive buckling path during each buckling deformation are corrected by introducing correction parameters and a boundary line. A modified hysteretic constitutive model is obtained, that can more accurately reflect the buckling behavior of reinforcements. Finally, a series of hysteresis tests of reinforcements with different slenderness ratios were then conducted. The experimental results verify the effectiveness of the proposed modified model. Indicating that the modified model can more accurately simulate the equivalent stress-strain relationship of the buckling reinforcement segment.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.190-193
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• 2009

A recently reported simple phenomenological constitutive model (SK) demonstrated comparable or better data description capability to/than one of the rigorous and physics-based models, the PTW model. The simple SK model is believed to be an efficient model for practical applications where an extensive computation is needed, and can serve as a rigorous comparison standard for the development of a physics-based model.

• 소성∙가공
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• 제9권1호
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• pp.59-65
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• 2000

Most studies of failure analysis in ductile metals have been based on the classical plasticity theory using the local constitutive relations. These frequently yields a physically unrealistic solution, in which a numerical prediction of the onset of a deformation localization shows an inherent mesh-size sensitivity. A one way to remedy the spurious mesh sensitivity resulted in the unreasonable results is to incorporate the non-local plasticity into the simulation model, which introduce an internal (material) length-scale parameter into the classical constitutive relations. In this paper, a non-local version of the modified Gurson constitutive relation has been introduced into the finite element formulation of the simulation for plane strain compression of the visco elastic-plastic void material. By introducing the non-local constitutive relations we could successfully removed the inherent mesh-size sensitivity for the prediction of the deformation localization. The effects of non-local constitutive relation are discussed in terms of the load-stroke curve and the strain distributions accross the shear band.

• 대한기계학회논문집A
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• 제31권2호
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• pp.182-189
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• 2007

This paper is concerned with the empirical flow stress constitutive equation of steel sheets for an auto-body with the variation of temperature and strain rate. In order to represent the strain rate and temperature dependent behavior of the flow stress at the intermediate strain rates accurately, an empirical hardening equation is suggested by modifying the well-known Khan-Huang-Liang model. The temperature and strain rate dependent sensitivity of the flow stress at the intermediate strain rate is considered in the hardening equation by coupling the strain, the strain rate and the temperature. The hardening equation suggested gives good correlation with experimental results at various intermediate strain rates and temperatures. In order to verify the effectiveness and accuracy of the suggested model quantitatively, the standard deviation of the fitted result from the experimental one is compared with those of the other two well-known empirical constitutive models such as the Johnson-Cook and the Khan-Huang-Liang models. The comparison demonstrates that the suggested model gives relatively well description of experimental results at various strain rates and temperatures.

• Computers and Concrete
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• 제25권2호
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• pp.181-192
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• 2020

Nowadays, steel fiber reinforced concretes (SFRCs) are widely used in practical applications. Significant experimental research has thus been carried out to determine the constitutive equations that represent the behavior of SFRCs under multiaxial loadings. However, numerical modelling of SFRCs via FEM has been challenging due to the complexities of the implementation of these constitutive equations. In this study, following the literature, a plasticity model is constructed for the behavior of SFRCs that involves the Willam-Warnke failure surface with the relevant evolution laws and a non-associated flow rule for determining the plastic deformations. For the precise (yet rapid) integration of the constitutive equations, an explicit substepping scheme consisting of yield intersection and drift correction algorithms is employed and thus implemented in ABAQUS via UMAT. The FEM model includes various material parameters that are determined from the experimental data. Three sets of parameters are used in the numerical simulations. While the first set is from the experiments that are conducted in this study on SFRC specimens with various contents of steel fibers, the other two sets are from the experiments reported in the literature. The response of SFRCs under multiaxial compression obtained from various numerical simulations are compared with the experimental data. The good agreement between numerical results and the experimental data indicates that not only the adopted plasticity model represents the behavior of SFRCs very well but also the implemented integration scheme can be employed in practical applications of SFRCs.