주기하중을 받고 있는 금속의 시간의존적 소성 모델 비교

Dongkeon Kim,Gary Dargush 한국복합신소재구조학회 2013 복합신소재구조학회논문집 Vol.4 No.1

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. M any 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.

Unified Space-Time Finite Element Methods for Dissipative Continua Dynamics

Kim, Jinkyu,Dargush, Gary F.,Roh, Hwasung,Ryu, Jaeho,Kim, Dongkeon World Scientific Publishing Company 2017 International journal of applied mechanics Vol.9 No.2

<P>Based upon the extended framework of Hamilton’s principle, unified space-time finite element methods for viscoelastic and viscoplastic continuum dynamics are presented, respectively. For numerical efficiency, mixed time-step algorithm in time- and displacement-based algorithm in space are adopted. Through analytical investigation, we demonstrate that the Newmark’s constant average acceleration method and the present method are the same for viscoelasticity. With spatial eight-node brick elements, some numerical simulations are undertaken to validate and investigate the performance of the present non-iterative space-time finite element method for viscoplasticity.</P>

주기하중을 받고 있는 금속의 시간의존적 소성 모델 비교

김동건 ( Dong Keon Kim ),( Gary F. Dargush ) 한국복합신소재구조학회 2013 복합신소재구조학회논문집 Vol.4 No.1

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. M any 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.

A THERMO-ELASTO-VISCOPLASTIC MODEL FOR COMPOSITE MATERIALS AND ITS FINITE ELEMENT ANALYSIS

Shin, Eui-Sup The Korean Society for Energy 2002 Journal of Theoretical and Applied Mechanics Vol.3 No.1

A constitutive model on oorthotropic thermo-elasto-viscoplasticity for fiber-reinforced composite materials Is illustrated, and their thermomechanical responses are predicted with the fully-coupled finite element formulation. The unmixing-mixing scheme can be adopted with the multipartite matrix method as the constitutive model. Basic assumptions based upon the composite micromechanics are postulated, and the strain components of thermal expansion due to temperature change are included In the formulation. Also. more than two sets of mechanical variables, which represent the deformation states of multipartite matrix can be introduced arbitrarily. In particular, the unmixing-mixing scheme can be used with any well-known isotropic viscoplastic theory of the matrix material. The scheme unnecessitates the complex processes for developing an orthotropic viscoplastic theory. The governing equations based on fully-coupled thermomechanics are derived with constitutive arrangement by the unmixing-mixing concept. By considering some auxiliary conditions, the Initial-boundary value problem Is completely set up. As a tool of numerical analyses, the finite element method Is used with isoparametric Interpolation fer the displacement and the temperature fields. The equation of mutton and the energy conservation equation are spatially discretized, and then the time marching techniques such as the Newmark method and the Crank-Nicolson technique are applied. To solve the ultimate nonlinear simultaneous equations, a successive iteration algorithm is constructed with subincrementing technique. As a numerical study, a series of analyses are performed with the main focus on the thermomechanical coupling effect in composite materials. The progress of viscoplastic deformation, the stress-strain relation, and the temperature History are careful1y examined when composite laminates are subjected to repeated cyclic loading.

Viscoplastic Matrix Materials for Embedded 3D Printing

Grosskopf, Abigail K.,Truby, Ryan L.,Kim, Hyoungsoo,Perazzo, Antonio,Lewis, Jennifer A.,Stone, Howard A. American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.27

<P>Embedded three-dimensional (EMB3D) printing is an emerging technique that enables free-form fabrication of complex architectures. In this approach, a nozzle is translated omnidirectionally within a soft matrix that surrounds and supports the patterned material. To optimize print fidelity, we have investigated the effects of matrix viscoplasticity on the EMB3D printing process. Specifically, we determine how matrix composition, print path and speed, and nozzle diameter affect the yielded region within the matrix. By characterizing the velocity and strain fields and analyzing the dimensions of the yielded regions, we determine that scaling relationships based on the Oldroyd number, <I>Od</I>, exist between these dimensions and the rheological properties of the matrix materials and printing parameters. Finally, we use EMB3D printing to create complex architectures within an elastomeric silicone matrix. Our methods and findings will both facilitate future characterization of viscoplastic matrices and motivate the development of new materials for EMB3D printing.</P> [FIG OMISSION]</BR>

점소성 이론에 의한 변형률 속도 민감도에 대한 연구

호괄수 한국소성가공학회 2004 소성가공 : 한국소성가공학회지 Vol.13 No.7

This paper addresses a viscoplastic constitutive model that allows a consistent way of modeling positive and negative rate sensitivities of flow stress concerned with dynamic strain aging. Based on the concept of continuum mechanics, a phenomenological constitutive model includes the use of a yield surface within the framework of unified viscoplasticity theory. To model negative rate sensitivity, rate-dependent back stress is introduced and flow stress in fully developed inelastic deformation regime is thus decomposed into the plastic contribution of rate independency and the viscous one of rate dependency.

Identification of inelastic material parameters for modified 9Cr-1Mo steel applicable to the plastic and viscoplastic constitutive equations

Koo, G.H.,Kwon, J.H. Applied Science Publishers ; Elsevier Science Ltd 2011 The International journal of pressure vessels and Vol.88 No.1

In this paper, the material parameters of plastic and viscoplastic constitutive equations for modified 9Cr-1Mo steel are developed for various isothermal conditions to support inelastic analysis for a sodium-cooled fast reactor. To do this, the material parameters related with the elastoplastic behaviour are identified with uniaxial cyclic test data by performing computer simulations, which use the combined Chaboche model including the kinematic hardening rule and the isotropic softening rule. The viscous parameters are identified from uniaxial stress relaxation test data through computer simulations with the pre-determined elastoplastic material parameters. Sensitivity studies are performed for the material parameters to investigate cyclic inelastic behaviour and stress relaxation during a hold time. From the comparison between the tests and the simulations, it is expected that the identified material parameters of the plastic and viscoplastic constitutive equations can accurately express the material characteristics of modified 9Cr-1Mo steel sufficiently well to be used for inelastic analysis.

Time-dependent and inelastic behaviors of fiber- and particle hybrid composites

Jeongsik Kim,Anastasia Muliana 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

Polymer matrix composites are widely used in many engineering applications as they can be customized to meet a desired performance while not only maintaining low cost but also reducing weight. Polymers can experience viscoelastic-viscoplastic response when subjected to external loadings. Various reinforcements and fillers are added to polymers which bring out more complexity in analyzing the timedependent response. This study formulates an integrated micromechanical model and finite element (FE) analysis for predicting effective viscoelastic-viscoplastic response of polymer based hybrid composites. The studied hybrid system consists of unidirectional short-fiber reinforcements and a matrix system which is composed of solid spherical particle fillers dispersed in a homogeneous polymer constituent. The goal is to predict effective performance of hybrid systems having different compositions and properties of the fiber, particle, and matrix constituents. A combined Schapery’s viscoelastic integral model and Valanis’s endochronic viscoplastic model is used for the polymer constituent. The particle and fiber constituents are assumed linear elastic. A previously developed micromechanical model of particle reinforced composite is first used to obtain effective mechanical properties of the matrix systems. The effective properties of the matrix are then integrated to a unit-cell model of short-fiber reinforced composites, which is generated using the FE. The effective properties of the matrix are implemented using a user material subroutine in the FE framework. Limited experimental data and analytical solutions available in the literatures are used for comparisons.

Time-dependent and inelastic behaviors of fiber- and particle hybrid composites

Kim, Jeong-Sik,Muliana, Anastasia Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

Polymer matrix composites are widely used in many engineering applications as they can be customized to meet a desired performance while not only maintaining low cost but also reducing weight. Polymers can experience viscoelastic-viscoplastic response when subjected to external loadings. Various reinforcements and fillers are added to polymers which bring out more complexity in analyzing the timedependent response. This study formulates an integrated micromechanical model and finite element (FE) analysis for predicting effective viscoelastic-viscoplastic response of polymer based hybrid composites. The studied hybrid system consists of unidirectional short-fiber reinforcements and a matrix system which is composed of solid spherical particle fillers dispersed in a homogeneous polymer constituent. The goal is to predict effective performance of hybrid systems having different compositions and properties of the fiber, particle, and matrix constituents. A combined Schapery's viscoelastic integral model and Valanis's endochronic viscoplastic model is used for the polymer constituent. The particle and fiber constituents are assumed linear elastic. A previously developed micromechanical model of particle reinforced composite is first used to obtain effective mechanical properties of the matrix systems. The effective properties of the matrix are then integrated to a unit-cell model of short-fiber reinforced composites, which is generated using the FE. The effective properties of the matrix are implemented using a user material subroutine in the FE framework. Limited experimental data and analytical solutions available in the literatures are used for comparisons.

Room-temperature anelasticity and viscoplasticity of Cu-Zr bulk metallic glasses evaluated using nanoindentation

Yoo, B.G.,Choi, I.C.,Kim, Y.J.,Ramamurty, U.,Jang, J.i. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.577 No.-

Anelastic and viscoplastic characteristics of Cu<SUB>50</SUB>Zr<SUB>50</SUB> and Cu<SUB>65</SUB>Zr<SUB>35</SUB> binary bulk metallic glasses at room temperature were examined through nanoindentation creep experiments. Results show that both the deformations are relatively more pronounced in Cu<SUB>50</SUB>Zr<SUB>50</SUB> than in Cu<SUB>65</SUB>Zr<SUB>35</SUB>, and their amount increases with the loading rate. The results are analyzed in terms of the influences of structural defects and loading rate on the room temperature indentation creep.