• Title/Summary/Keyword: Visco-plastic constitutive equation

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Model for Flow Analysis of Fresh Concrete Using Particle Method with Visco-Plastic Flow Formulation (점소성 유동 입자법에 의한 굳지 않은 콘크리트의 유동해석 모델)

  • Cho, Chang-Geun;Kim, Wha-Jung;Choi, Yeol
    • Journal of the Korea Concrete Institute
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    • v.20 no.3
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    • pp.317-323
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    • 2008
  • In the current study, A model for the flow analysis of fresh and highly flowable concrete has been developed using a particle method, the moving particle semi-implicit (MPS) method. The phenomena on the flow of concrete has been considered as a visco-plastic flow problem, and the basic governing equation of concrete particle dynamics has been based on the Navier-Stokes equation in Lagrangian form and the conservation of mass. In order to formulate a visco-plastic flow constitutive law of fresh concrete, concrete is modeled as a highly viscous material in the state of non-flow and as a visco-plastic material in the state of flow after reaching the yield stress of fresh concrete. A flow test of fresh concrete in the L-box was simulated and the predicted flow was well matched with the experimental result. The developed method was well showed the flow motion of concrete particles because it was formulated to be based on the motion of visco-plastic fluid dynamics.

Finite Element Analysis with Viscoplastic Formulation in Open-Die RTP Process (개방형 RTP(Rapid Thermal Pressing)공정의 점소성 유한요소해석)

  • Son J. W.;Rhim S. H.;Oh S. I.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.10a
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    • pp.284-289
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    • 2004
  • Since polymer materials at elevated temperatures are usually rate-sensitive, the analysis of RTP process requires considering the effect of the rate-dependent. The material behavior that exhibits rate-sensitivity is called visco-plastic. A two-dimensional visco-plastic finite element formulation which constitutive equation is based on the formulation proposed by Perzyna is presented. This Paper is purposed to calcuate pressure distribution on PMMA in compression process and to predict the relationship with defects after demolding process. This paper analyzes, both analytically and numerically, the pressure distributions on the surface of PMMA during open-die RTP process. In this research, PMMA is used to be simulated at $110^{\circ}C$ near the transition temperature.

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Development of Temperature and Strain-Rate Dependent Unified Constitutive Equation for Ships and Offshore Structures (선박 및 해양구조물용 극저온 재료의 온도 및 변형률 속도 의존 통합 구성방정식 개발)

  • Park, Woong-Sup;Kim, Jeong-Hyeon;Chun, Min-Sung;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.200-206
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    • 2011
  • The mechanical properties of the most widely used cryogenic materials, i.e. austenitic stainless steel (ASS), aluminum alloy and invar steel, strongly depend on temperatures and strain rates. These phenomena show very complicated non-linear behaviors and cannot be expressed by general constitutive equation. In this study, an unified constitutive equation was proposed to represent the effect of temperature and strain rate on the materials. The proposed constitutive equation has been based on Tomita/Iwamoto and Bodner/Partom model for the expression of 2nd hardening due to martensite phase transformation of ASS. To simulate ductile fracture, modified Bodner/Chan damage model was additionally applied to the model and the model validity was verified by comparison of experimental and simulation results.

Implementation of Polycrystal Model in Rigid Plastic Finite Element Method (강소성 유한요소법에서의 다결정 모델의 구현)

  • Kang, G.P.;Lee, K.;Kim, Y.H.;Shin, K.S.
    • Transactions of Materials Processing
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    • v.26 no.5
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    • pp.286-292
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    • 2017
  • Magnesium alloy shows strong anisotropy and asymmetric behavior in tension and compression curve, especially at room temperature. These characteristics limit the application of finite element method (FEM) which is based on conventional continuum mechanics. To accurately predict the material behavior of magnesium alloy at microstructural level, a methodology of fully coupled multiscale simulation is presented and a crystal plasticity model as a constitutive equation in the simulation of metal forming process is introduced in this study. The existing constitutive equation for rigid plastic FEM is modified to accommodate deviatoric stress component and its derivatives with respect to strain rate components. Viscoplastic self-consistent (VPSC) polycrystal model was selected as a constitutive model because it was regarded as the most robust model compared to Taylor model or Sachs model. Stiffness matrix and load vector were derived based on the new approach and implemented into $DEFORM^{TM}-3D$ via a user subroutine handling stiffness matrix at an elemental level. The application to extrusion and rolling process of pure magnesium is presented in this study to assess the validity of the proposed multiscale process.

Finite Element Analysis of Extrusion Process in Semi-Solid State (반용융 재료의 압출공정에 관한 유한요소해석)

  • 황재호;고대철;민규식;김병민;최재찬
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1997.06a
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    • pp.5-15
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    • 1997
  • It is the objective of this study that by conducting the serni-solid extrusion using A12024, the effect of various process variables on the quality of extruded product and extrusion force is understood. The results of experiment are compared with those of finite element simulation in order to verify the effectiveness of the developed FE-simulation code. In order to simulate densification in the deformation of serni-solid material, the semi-solid material is assumed to be composed of solid region as porous skeleton following compressible visco-plastic model and liquid region following Darcy's equation for the liquid flow saturated in the interstitial space. Then the flow and deformation of the semi-solid alloy are analyzed by coupling the deformation of the porous skeleton and the flow of the eutectic liquid. It is assumed that initial solid fraction is homogeneous. Yield and plastic potential function presented by Kuhn and constitutive model developed by Gunasekera are used for solid skeleton.

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Numerical Fatigue Test Method Based on Continuum Damage Mechanics (연속체 손상역학을 이용한 수치 피로시험 기법)

  • Lee, Chi-Seung;Kim, Young-Hwan;Kim, Tae-Woo;Lee, Jae-Myung
    • Journal of Welding and Joining
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    • v.25 no.1
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    • pp.63-69
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    • 2007
  • Once assessment of material failure characteristics is captured precisely in a unified way, it can bedirectly incorporated into the structural failure assessment under various loading environments, based on the theoretical backgrounds so called Local Approach to Fracture. The aim of this study is to develop a numerical fatigue test method by continuum damage mechanics applicable for the assessment of structural integrity throughout crack initiation and structural failure based on the Local Approach to Fracture. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, is developed and employed in the 3-D FEA code in order to numerically evaluate the material and/or structural responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations for each material, are implemented in numerical fatigue test method. The material constants selected from constitutive equations are used directly in the failure assessment of material and/or structures. The performance of the developed system has been evaluated with assessing the S-N diagram of stainless steel materials.

Process Design on Fabrication of Large Sized Ring by Mandrel Forging of Hollow Cast Ingot (중공 잉곳을 이용한 대형 링 단조품 제조공정 설계 연구)

  • Lee, S.U.;Lee, Y.S.;Lee, M.W.;Lee, D.H.;Kim, S.S.
    • Transactions of Materials Processing
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    • v.19 no.6
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    • pp.329-336
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    • 2010
  • Ring forging process is more appropriate for high-length and thin walled ring, because it utilizes the forging press and hence does not require heavy-duty ring rolling mill. Although ring forging process is very simple and economic for facilities, the process is not efficient because of multi-forging-step and low material utilization. An effective ring forging process is developed using a hollow ingot. When a hollow ingot is used with a workpiece, the ingot can be forged into a final ring without multi-stage pre-forging process, such as, cogging, upsetting, and piercing, etc.. Finally it has advantages of the material utilization and process improvement because a few reheating and forging process are not necessary to make workpiece for ring forging. The important design variables are the applied plastic deformation energy to eliminate cast structure and make uniform properties. In this study, the mechanical properties after forging of hollow cast ingot were investigated from the experiment using circumferential sectional model. Also, the effects of process variables were studied by FEM simulation on the basis of thermo-visco-plastic constitutive equation. Applied strain is different at each position in length direction because diameter of hollow ingot is different in length direction. The different strain distribution become into a narrow gap by additional plastic deformation during diameter extension process.