• Title, Summary, Keyword: Modified Drucker-Prager 모델

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Dynamic Characteristics of Railway Structures under High-Speed Train Loading (고속열차 주행 시 동적하중을 받는 철도구조물의 진동 특성)

  • Rhee, Inkyu;Kim, Jae Min
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.33 no.2
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    • pp.121-128
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    • 2020
  • The purpose of this study is to investigate the distribution patterns of displacement and acceleration fields in a nonlinear soil ground based on the interaction of high-speed train, wheel, rail, and ground. For this purpose, a high-speed train in motion was modeled as the actual wheel, and the vertical contact of wheel and rail and the lateral contact, caused by meandering motion, were simulated; this simulation was based on the moving mass analysis. The soil ground part was given the nonlinear behavior of the upper ground part by using the modified the Drucker-Prager model, and the changes in displacement and acceleration were compared with the behavior of the elastic and inelastic grounds. Using this analysis, the displacement and acceleration ranges close to the actual ground behavior were addressed. Additionally, the von-Mises stress and equivalent plastic strain at the ground were examined. Further, the equivalent plastic and total volumetric strains at each failure surface were examined. The variation in stresses, such as vertical stress, transverse pressure, and longitudinal restraint pressure of wheel-rail contact, with the time history was investigated using moving mass. In the case of nonlinear ground model, the displacement difference obtained based on the train travel is not large when compared to that of the elastic ground model, while the acceleration is caused to generate a large decrease.

Constitutive Modeling of Magnesium Alloy Sheets (마그네슘 합금 판재의 비선형 항복.경화거동 모델링)

  • Lee, M.G.;Wagoner, R.H.;Lee, J.K.;Chung, K.;Kim, H.Y.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.298-301
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    • 2007
  • Magnesium alloy sheets have unique mechanical properties such as high in-plane anisotropy/asymmetry of yield stress and hardening response. The unusual mechanical behavior of magnesium alloys has been understood by the limited symmetry crystal structure of HCP metals or by deformation twinning. In the present study, the continuum plasticity models considering the unusual plastic behavior of magnesium alloy sheet were derived for a finite element analysis. A new hardening law based on two-surface model was developed to consider the general stress-strain response of metal sheets such as Bauschinger effect, transient behavior and the unusual asymmetry. Three deformation modes observed during the continuous tension/compression tests were mathematically formulated with simplified relations between the state of deformation and their histories. In terms of the anisotropy and asymmetry of the initial yield stress, the Drucker-Prager's pressure dependent yield surface was modified to include the anisotropy of magnesium alloys.

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Material Model and Thermal Response Analysis of Concrete at Elevated Temperatures (고온에서의 콘크리트 재료모델과 열거동해석)

  • 강석원;홍성걸
    • Journal of the Korea Concrete Institute
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    • v.13 no.3
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    • pp.268-276
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    • 2001
  • A numerical model for the thermal response analysis of concrete structures is suggested. The model includes the stress-strain relationship, constitutive relationship, and multiaxial failure criteria at elevated temperature conditions. Modified Saenz's model was used to describe the stress-strain relationship at high temperatures. Concrete subjected to elevated temperatures undergoes rapid strain increase and dimensional instability. In order to explain those changes in mechanical properties, a constitutive model of concrete subjected to elevated temperature is proposed. The model consists of four strain components; free thermal creep strain, stress-induced (mechanical) strain, thermal creep strain, and transient strain due to moisture effects. The failure model employs modified Drucker-Prager model in order to describe the temperature dependent multiaxial failure criteria. Some numerical analyses are performed and compared with the experimental results to verify the proposed model. According to the comparison, the suggested material model gives reliable analytical results.