• Transactions of Materials Processing
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• v.9 no.3
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• pp.233-241
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• 2000

It is well known that the quality and efficiency of the design of metal forming processes can be significantly improved with the aid of effective numerical simulations. In the present study, a two-and three-dimensional finite element simulation system, CAMP form, was developed for the analysis of metal forming processes in the PC environment. It is composed of a solver based on the thermo-rigid-viscoplastic approach and graphic user interface (GUI) based pre-and post-processors to be used for the effective description of forming conditions and graphic display of simulation results, respectively. In particular, in the case of CAMPform 2D (two-dimensional), as the solver contains an automatic remeshing module which determines the deformation step when remeshing is required and reconstructs the new mesh system, it is possible to carry out simulations automatically without any user intervention. Also, the forming analysis considers ductile fracture of the workpiece and wear of dies for better usage of the system. In the case of CAMPform 3D, general three-dimensional problems that involve complex die geometries and require remeshing can be analyzed, but full automation of simulations has yet to be achieved. In this paper, the overall structure and computational background of CAMPform will be briefly explained and analysis results of several forming processes will be shown. From the current results, it is construed that CAMPform can be used in providing useful information to assist the design of forming processes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.349-352
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• 2006

The plastic deformation of polycrystalline materials is induced by changes of the microstructure when the loading is beyond the critical state of stress. Constitutive models for the crystal plasticity have the common objective which relates microscopic single crystals in the crystallographic texture to the macroscopic continuum point. In this paper, a new consistent tangent stiffness for the anisotropic elasto-viscoplastic analysis of polycrystalline deformation is developed, which can be used in the finite element analysis for the slip-dominated large deformation of polycrystalline materials. In order to calculate the consistent tangent stiffness, the state function is defined based on the consistency condition between the elastic and plastic stress. The rate of shearing increment($\Delta{\gamma}^{\alpha}$) is calculated with satisfying the consistency condition. The consistency condition becomes zero when the trial resolved shear stress($\tau^{{\alpha}^*}$) becomes resolved shear stress($\tau^{\alpha}$) at every step. Iterative method is utilized to calculate the rate of shearing increment based on the implicit backward Euler method. The consistent tangent stiffness can be formulated by differentiating the rate of shearing increment with total strain increment after the instant rate of shearing increment converges. The proposed tangent stiffness is applied to the ABAQUS/Standard by implementing in the ABAQUS/UMAT.

• Journal of the Korean Geotechnical Society
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• v.36 no.7
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• pp.5-14
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• 2020

Kansai International Airport (KIX) was opened in September 1994. Although 26 years have passed since the completion of the first island, long-term settlement is still in progress. This settlement occurs in the Pleistocene layer. For it is not easy to determine the permeability of the Pleistocene sand layer because the thickness and the degree of fine content in the horizontal direction are constantly changing. In addition, it is also a difficult to predict the interactive behavior of the ground due to the construction of the second phase island adjacent to it. In order to solve this problem, a two-dimensional finite element analysis considering elasto-viscoplastic was performed to evaluate the long-term deformation, including the interactive behavior of the alternating Pleistocene foundation due to the construction of two adjacent reclaimed islands. In general, two-dimensional analysis can be used when a section can represent the entire sections. However, Kansai Airport is an artificial reclaimed island so two-dimensional analysis cannot solve the problem such as the stress deformation in the corners of the island. Additionally, the structure of the actual sub-ground through physical exploration is non-homogeneity and its thickness is also not constant. Therefore, there are limitations for the two-dimensional analysis to explain the phenomena. That is, three-dimensional analysis is strongly required. Due to these demands, the author extended the existing two-dimensional program capable of elasto-viscoplastic analysis to three-dimensional and completed the verification of the three-dimensional program developed through one-dimensional consolidation analysis. In order to demonstrate the validity of the developed 3D program that has been verified, an analysis is performed under the same analysis conditions as the existing research using a two-dimensional program. The effectiveness of the developed 3D numerical analysis program was demonstrated by comparing the analysis results with the 2D results and actual measurement data.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.365-366
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• 2007

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.362-375
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• 1991

Background and Necessity of the study : For more than 20 years, the soil engineering reserach group of Chonnam National University has been performing the deformation analysis of soft clayey foundation, since the University is located near the south-western coast of Korean Peninsulla, along which tide reclamation works have been under proaressing. Associsted with the fact mentioned above, the researchers have been developing a computer program in order to carry out deformation analysis of soft foundation since early 1980. Case-studies : In this research, the Biot's equation was selected as the governing equation coupled with several constitutive models including original and modified Cam-clay models, elasto-viscoplastic model, Lade's model etc. The anisotropy of soi1 can be considered in this program. To validate the accuracy of the computer program developed a couple of case-studies were performed. These include the pilot banking, sand drain considering smear effect and compound foundation reinforced with sheet pile into soft foundation.i) The pilot banking Good results could be acquired by assuming banking load as the body force composed of finite element mesh rather than equivalent concentrated load.ii) The sand drain Due to smear, the delay of consolidation was remarkable at the early stsge. so safety for the failure of foundation should be checked for the initial step of consolidation. iii) The compound foundation Accurate results were obtained by introducing the joint element method for the soft foundation reinforced with sheet pile into soiㅣ.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.190-200
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• 1991

Certain structural components are exposed to high temperatures. At high temperature, under thermal and mechanical loading, metal components exhibit both creep and plastic behavior. The unified constitutive theory is to model both the time-dependent behavior(creep) and the time-independent behavior(plasticity) in one set of equations. Microscopically both creep and plasticity are controlled by the motion of dislocations. A finite element method is presented encorporating a unified constitutive model for the transient analysis of viscoplastic behavior of structures exposed to high temperature.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2113-2122
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• 1994

The 3-D FEM analysis for simulating the stamping operation of planar anisotropic sheet metals with arbitrarily-shaped tools is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshes without depending on the explicit spatial derivatives of tool surfaces. The consistent full set of governing relations, comprising equilibrium equation and mesh-normal geometric constraints, is appropriately linearized. The linear triangular elements are used for depicting the formed sheet, based on membrane approximation. Barlat's non-quadratic anisotropic yield criterion(strain-rate potential) is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and non-quadratic function parameter. The planar anisotropic finite element formulation is tested with the numerical simulations of the stamping of an automotive hood inner panel and the drawing of a hemispherical punch. The in-plane anisotropic effects on the formability of both mild steel and aluminum alloy sheet metals are examined.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.1
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• pp.97-106
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• 2011

In this study, viscoplastic material properties of solder alloy which is used in the electronics packages are inversely estimated. A specimen is fabricated to this end, and an experiment is conducted to examine deformation by Moir$\acute{e}$ interferometry. As a result of the experiment, bending displacement of the specimen and shear strain of the solder are obtained. A viscoplastic finite element analysis procedure is established, and the material parameters are determined to match closely with the experiments. The uncertainties which include inherent experimental error and insufficient data of experiments are addressed by using the method of computer model calibration. As a result, material parameters are identified in the form of confidence interval, and the displacements and strains using these parameters are predicted in the form the prediction interval.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2003.10a
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• pp.187-190
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• 2003

In order to apply a cyclic elasto-plastic and a viscoelastic-viscoplastic constitutive model to actual multi-layered ground conditions during large earthquake, numerica simulations were performed by a liquefaction analysis in the present study. From the liquefaction analysis, it was verified that the models can give a good description of the damping characteristics and liquefaction phenomena of ground accurately during large event which induces plastic deformation in large strain range.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.21-28
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• 2010

Creep behaviors of the solder balls in a flip chip package assembly during thermal cycling test is investigated.. A material models used in the finite element analysis are viscoplastic model introduced by Anand and creep model called partitioned model. Experiment of two temperature cycles using moir$\acute{e}$ interferometry is conducted to verify the reliability of material models for the analysis of thermo-mechanical behavior. Bending deformations of the assemblies and average strains of the solder balls due to temperature change and dwell time are investigated. The results show that time-dependent shear strain of solder by the partitioned model is in excellent agreement with those by moir$\acute{e}$ interferometry, while there is considerable difference between results by Anand model and experiment. In this paper, the partitioned model is employed for the time-dependent creep analysis of the FC-PBGA package. It is also shown that the thermo-mechanical stress becomes relaxed by creep behavior at high temperature during temperature cycles.