• Title/Summary/Keyword: Viscoplastic material

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Examination of 3D long-term viscoplastic behaviour of a CFR dam using special material models

  • Karalar, Memduh;Cavusli, Murat
    • Geomechanics and Engineering
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    • v.17 no.2
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    • pp.119-131
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    • 2019
  • Time dependent creep settlements are one of the most important causes of material deteriorations for the huge water structures such as concrete faced rockfill dams (CFRDs). For this reason, performing creep analyses of CFRDs is vital important for monitoring and evaluating of the future and safety of such dams. In this study, it is observed how changes viscoplastic behaviour of a CFR dam depending the time. Ilısu dam that is the longest concrete faced rockfill dam (1775 m) in the world is selected for the three dimensional (3D) analyses. 3D finite difference model of Ilısu dam is modelled using FLAC3D software based on the finite difference method. Two different special creep material models are considered in the numerical analyses. Wipp-creep viscoplastic material model and burger-creep viscoplastic material model were rarely used for the creep analyses of CFRDs in the last are taken into account for the concrete slab and rockfill materials-foundation, respectively. Moreover, interface elements are defined between the concrete slab-rockfill materials and rockfill materials-foundation to provide interaction condition for 3D model. Firstly, dam and foundation are collapsed under its self-weight and static behaviour of the dam is evaluated for the empty reservoir conditions. Then, reservoir water is modelled considering maximum water level of the dam and time-dependent creep analyses are performed for maximum reservoir condition. In this paper, maximum principal stresses, vertical-horizontal displacements and pore pressures that may occur on the dam body surface during 30 years (from 2017 to 2047) are evaluated in detail. According to numerical analyses, empty and maximum reservoir conditions of Ilısu dam are compared with each other in detail. 4 various nodal points are selected under the concrete slab to better seen viscoplastic behaviour changes of the dam and viscoplastic behaviour differences of these points during 30 years are graphically presented. It is clearly seen that horizontal-vertical displacements and principal stresses for maximum reservoir condition are more than the empty reservoir condition of the dam and significant pore pressures are observed during 30 years for maximum reservoir condition. In addition, horizontal-vertical displacements, principal stresses and pore pressures for 4 nodal points obviously increased until a certain time and changes decreased after this time.

Prediction of Material Behavior and Failure of Fresh Water Ice Based on Viscoplastic-Damage Model (점소성 손상모델 기반 담수빙 재료거동 및 파손 예측)

  • Choi, Hye-Yeon;Lee, Chi-Seung;Lee, Jong-Won;Ahn, Jae-Woo;Lee, Jae-Myung
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.3
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    • pp.275-280
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    • 2011
  • In the present study, a unified viscoplastic-damage model has been applied in order to describe the mechanical characteristics of fresh water ice such as nonlinear material behavior and volume fraction. The strain softening phenomenon of fresh water ice under quasi-static compressive loading has been evaluated based on unified viscoplastic model. The material degradation such as growth of slip/fraction has quite close relation with material inside damage. The volume fraction phenomenon of fresh water ice has been identified based on volume fraction (nucleation and growth of damage) model. The viscoplastic-damage model has been transformed to the fully implicit formulation and the discretized formulation has been implemented to ABAQUS user defined subroutine (User MATerial: UMAT) for the benefit of application of commercial finite element program. The proposed computational analysis method has been compared to uni-axial compression test of fresh water ice in order to validate the compatibilities, clarities and usefulness.

Multiscale modeling of elasto-viscoplastic polycrystals subjected to finite deformations

  • Matous, Karel;Maniatty, Antoinette M.
    • Interaction and multiscale mechanics
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    • v.2 no.4
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    • pp.375-396
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    • 2009
  • In the present work, the elasto-viscoplastic behavior, interactions between grains, and the texture evolution in polycrystalline materials subjected to finite deformations are modeled using a multiscale analysis procedure within a finite element framework. Computational homogenization is used to relate the grain (meso) scale to the macroscale. Specifically, a polycrystal is modeled by a material representative volume element (RVE) consisting of an aggregate of grains, and a periodic distribution of such unit cells is considered to describe material behavior locally on the macroscale. The elastic behavior is defined by a hyperelastic potential, and the viscoplastic response is modeled by a simple power law complemented by a work hardening equation. The finite element framework is based on a Lagrangian formulation, where a kinematic split of the deformation gradient into volume preserving and volumetric parts together with a three-field form of the Hu-Washizu variational principle is adopted to create a stable finite element method. Examples involving simple deformations of an aluminum alloy are modeled to predict inhomogeneous fields on the grain scale, and the macroscopic effective stress-strain curve and texture evolution are compared to those obtained using both upper and lower bound models.

A Compression Behavior of Semi-Solid Material and Finite Element Analysis Considering Flow of Liquid Phase (반응용재료의 압축거동 및 액상의 유동을 고려한 유한요소해석)

  • Gang, Chung-Gil;Yun, Jong-Hun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.12
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    • pp.3715-3727
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    • 1996
  • Compression behavior of semi-solid aluminum alloys with controlled solid fractions was investigated in the present study. The stress and strain relationships were obtained from the compression test. Variations of the solid fraction distribution and the material behaviour were investigated for various friction coeffieiants and die speedsd. For a finite element analysis, the semi-solid material was described by a compressible regid viscoplastic model for the solid region and darcy's law for the liquid region. The computed results were compared with experimental data for the validity of the yield criteria.

Analysis of Damaged Material Response Using Unified Viscoplastic Constitutive Equations (통합형 점소성구성식을 이용한 손상재료거동해석)

  • Ha Sang Yul;Kim Ki Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.2 s.233
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    • pp.253-261
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    • 2005
  • In decades, a substantial body of work on a unified viscoplastic model which considers the mechanism of plastic deformation and creep deformation has developed. The systematic scheme for numerical analysis of unified model is necessary because the dominant failure mechanism is the defect growth and coalescence in materials. In the present study, the unified viscoplastic model for materials with defects suggested by Suquet and Michel was employed for numerical analysis. The constitutive equations are integrated based on the generalized mid-point rule and implemented into a finite element program (ABAQUS) by means of user-defined subroutine (UMAT). To evaluate the validity of the developed UMAT code and the assessment of the adopted viscoplastic model, the results obtained from the UMAT code was compared with the numerical reference solution and experimental data. The unit cell analysis also has been investigated to study the effect of strain rate, temperature, stress triaxiality and initial defect volume fraction on the growth and coalescence of the defect.

Finite Element Analysis for Forming Process of Semi-Solid Material Considering Induction Heating (유도가열을 고려한 반용융 재료의 성형공정에 관한 유한요소 해석)

  • Park, W.D.;Ko, D.C.;Kim, B.M.;Park, J.C.
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.8
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    • pp.82-91
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    • 1997
  • The major objective of this study is to establish analytical technique in order to analyze the behaviour of semi-solid material considering induction heating of the billet. Induction heating process is analyzed by using commerical finite element software. ANSYS. The finite element program, SFAC2D, for the simulation of deformation in semi-solid state is developed in the present study. The semi-solid behaviour is described by a viscoplastic model for the solid phase, and by the Darcy's law for the liquid flow. Simple compression and closed-die compression process considering induction heating are analyzed, and also it is found that the distribution of initial solid fraction of the billet has an important effect on deformation behaviour of semi-solid material. In order to verify the effectiveness of proposed analytical technique the simulation result is compared with experimental result.

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An ALE Finite Element Formulation for Rigid-Viscoplatic Materials and Its Application to Axisymmetric Extrusion through Square Dies (ALE 묘사에 근거한 강-점소성 유한요소 수식화와 축대칭 평금형 압출에의 적용)

  • 강연식;양동열
    • Transactions of Materials Processing
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    • v.3 no.2
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    • pp.156-166
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    • 1994
  • An arbitrary Lagrangian-Eulerian (ALE) finite element method has been developed. The finite element formation is derived and implemented for rigid-viscoplastic materials. The developed computer program is applied to the analysis of axisymmetric square die extrusion, which has many difficulties with updated Lagrangian approach. The results are compared with those from updated Largrangian approach. The results are compared with those from updated Lagrangian finite element program. Updating scheme of time dependent variables and mesh control are also examined.

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Anisotropic Constitutive Model at Large Viscoplastic Deformations (탄소성 대변형에 관한 비등방 구성방정식)

  • Cho, Han-Wook
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1995.10a
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    • pp.178-184
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    • 1995
  • A new combined isotropic/kinematic and orthotropic hardening viscoplastic model is proposed which can account for not only differential orientations but also preferred orientations of grains in n metal at finite plastic deformations with an introduction of multiple spin (rate of rotation) concept within the general framework of the model, the effects of anisotropy and constitutive spins will be discussed in conjunction with a closed-form solution for simple shear in n rigid-plastic material, which will be used to simulate experimental data of Montheillet, et al. (1984) for fixed-end tortion tests at finite plastic deformations.

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Structural Analysis of Liquid Rocket Thrust Chamber Regenerative Cooling Channel using Bodner-Partom Viscoplastic Model (Bodner-Partom 점소성 모델을 이용한 액체로켓 연소기 재생냉각 채널 구조해석)

  • Ryu, Chul-Sung;Baek, Un-Bong;Choi, Hwan-Seok
    • Journal of the Korean Society of Propulsion Engineers
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    • v.10 no.4
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    • pp.69-76
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    • 2006
  • Elastic-viscoplastic structural analysis has been performed for regenerative cooling chamber of liquid rocket thrust chamber using Bodner-Partom visco-plastic model. Strain rate test was conducted for a copper alloy at various temperatures in order to get material constants of visco-plastic model used in the structural analysis. Material constants of visco-plastic model were obtained from strain rate test results and visco-plastic model was incorporated into finite element program, Marc, by means of a user subroutine. The structural analysis results indicated that the deformation of cooling channel is mostly caused by thermal loading rather than pressure loading and confirmed structural stability of the cooling channel under the operating condition.

An Finite Element Analysis for Elasto-Plastic Thermal Stresses Considerating Strain Hysteresis at Quenching Process of Carbon Steel(II) - Analysis of elasto-viscoplastic thermal stress - (탄소강의 퀜칭처리 과정에서 변형율이력을 고려한 탄소성열응력의 유한요소 해석(II) - 탄점소성 열응력 해석 -)

  • Kim, Ok-Sam;Koo, Bon-Kwon
    • Journal of the Korean Society for Heat Treatment
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    • v.9 no.2
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    • pp.147-158
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    • 1996
  • Generally, analytical consideration on the behaviour of metallic structures during quenching process, and analysis on the thermal stress and deformation after heat treatment are very important in presumption of crack and distorsion of quenched material. In this study a set of constitute equations relevant to the analysis of thermo elasto-viscoplastic materials with strain hysteresis during quenching process way presented on the basis of contimuum thermo-dynamics mechanics. The thermal stresses were numerically calculated by finite element technique of weighted residual method and the principle of virtual work. In the calculation process, the temperature depandency of physical and mechaniclal properties of the material in consideration. On the distribution of elasto-viscoplastic thermal stresses according to radial direction, axial and tangential stress are tensile stress(50MPa, 1.5GPa and 300MPa) in surface and compressive stress(-1.2GPa, -1.14GPa and -750MPa) in the inner part on the other hand, radial stress is tensile stress(900MPa) in area of analysis. According to axial direction, tangential stress gradients are average 60MPa/mm on the whole. The reversion of stress takes place at 11.5 to 16.8mm from the center in area of analysing.

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