• 소성∙가공
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• 제3권2호
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• pp.229-242
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• 1994

An approximate procedure based on a combination micro-macroscopic theories of plasticity for predicting the crystallographic texture during the plane strain forming of fcc metals has been developed. This procedure is divided into two steps. Firstly, we extract the history of the deformation gradient at all deformed elements with a elasto-plastic finite element method using isotropic plasticity model. Secondly, we use this deformation gradient history to predict the crystallographic deformation texture based on the Bishop-Hill theory. Renouard and Wintenberger' method is chosen for selecting the active slip systems. The predicted results have been compared with reported experimental results. The calculated results are in good agreement with their results.

• Elastomers and Composites
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• 제44권4호
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• pp.384-390
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• 2009

롤-롤(Roll to roll) 성형은 공정이 비교적 간단하고 생산 효율이 높은 중요한 금속 성형 공정이다. 이러한 이유로 롤-롤 성형 공정은 최근에 솔라셀 집전판, 디스플레이 격벽구조, 그리고 회로기판 성형 등 넓은 범위에서의 활용이 검토되고 있다. 본 연구에서는 솔라셀 집전판에 수십만 개의 홈을 성형하는 공정에 대해 유한요소해석을 수행하였다. 수백만 개 홈에 대한 성형을 해석하는 것은 컴퓨터 용량과 시간의 문제로 불가능하기 때문에 공정 설계를 가능하게 하는 최소의 문제 영역을 해석 결과를 바탕으로 설정하였다. 그리고, 홈의 형상과 온도에 따른 해석을 수행하여 그 결과를 분석함으로서 공정 설계의 방향성을 제시하였다.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.237-255
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• 2013

In this paper, a meshfree-enriched finite element method (ME-FEM) is introduced for the large deformation analysis of nonlinear path-dependent problems involving contact. In linear ME-FEM, the element formulation is established by introducing a meshfree convex approximation into the linear triangular element in 2D and linear tetrahedron element in 3D along with an enriched meshfree node. In nonlinear formulation, the area-weighted smoothing scheme for deformation gradient is then developed in conjunction with the meshfree-enriched element interpolation functions to yield a discrete divergence-free property at the integration points, which is essential to enhance the stress calculation in the stage of plastic deformation. A modified variational formulation using the smoothed deformation gradient is developed for path-dependent material analysis. In the industrial metal forming problems, the mortar contact algorithm is implemented in the explicit formulation. Since the meshfree-enriched element shape functions are constructed using the meshfree convex approximation, they pose the desired Kronecker-delta property at the element edge thus requires no special treatments in the enforcement of essential boundary condition as well as the contact conditions. As a result, this approach can be easily incorporated into a conventional displacement-based finite element code. Two elasto-plastic problems are studied and the numerical results indicated that ME-FEM is capable of delivering a volumetric locking-free and pressure oscillation-free solutions for the large deformation problems in metal forming analysis.

• 한국해양공학회지
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• 제25권2호
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• pp.67-72
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• 2011

This study had the goal of investigating the effect of the curvature along the heating line on the transverse angular distortion of plates having an initial curvature from line heating. A thermo-elasto-plastic analysis was carried out using 54 models with various radii of curvature, plate thicknesses, and heating speeds. The results show the effect of the curvature along the heating line on the angular distortion in relation to changes in the magnitudes of the curvature, heating speed, and plate thickness. The present numerical results show that the time history of the angular distortion after cooling and reaching the final deformed shape for a plate having an initial curvature is quite different from that of a flat plate. This emphasized the importance of considering the curvature effect on the transverse angular distortion. From the viewpoint of the curvature effect on the deformation, it has been seen that the curvature does not affect the transverse shrinkage. In this study the predicting formula for the transverse angular distortion was derived through a regression analysis. It showed that as the curvature increased, the angular distortion was reduced because of the higher bending rigidity at the same heat input parameter, and the peak points moved toward the origin as the curvature increased.

• Computers and Concrete
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• 제8권4호
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• pp.371-388
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• 2011

In this paper, time-continuous constitutive equations for strain rate-dependent materials are presented first, among which those for the overstress and the consistency viscoplastic models are considered. By allowing the stress states to be outside the yield surface, the overstress viscoplastic model directly defines the flow rule for viscoplastic strain rate. In comparison, a rate-dependent yield surface is defined in the consistency viscoplastic model, so that the standard Kuhn-Tucker loading/unloading condition still remains true for rate-dependent plasticity. Based on the formulation of the consistency viscoplasticity, a computational elasto-viscoplastic constitutive model is proposed for the short fiber-reinforced fresh cementitious paste for extrusion purpose. The proposed constitutive model adopts the von-Mises yield criterion, the associated flow rule and nonlinear strain rate-hardening law. It is found that the predicted flow stresses of the extrudable fresh cementitious paste agree well with experimental results. The rate-form constitutive equations are then integrated into an incremental formulation, which is implemented into a numerical framework based on ANSYS/LS-DYNA finite element code. Then, a series of upsetting and ram extrusion processes are simulated. It is found that the predicted forming load-time data are in good agreement with experimental results, suggesting that the proposed constitutive model could describe the elasto-viscoplastic behavior of the short fiber-reinforced extrudable fresh cementitious paste.

• 한국정밀공학회지
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• 제27권5호
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• pp.75-84
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• 2010

The aim of this paper is to design the blank shape of SPFH 590 high strength steel for stamping of the center hinge of automotive via numerical analyses and experiments for multi-stages transfer forming process. Three-dimensional elasto-plastic finite element analyses for the transfer forming process with six stages were performed using a commercial code AUTOFORM V4.2. The influence of the blank shape on the formability and the shape conformity were quantitatively examined through the FE analyses. From the results of the FE analysis, a feasible shape of the blank and the forming load were estimated. Stamping experiments were carried out using the proposed blank shape. The results of experiments were shown that the center hinge parts with the desired shapes can be manufactured successfully as the proposed blank shape is used. Through the comparison of the results of the experiments with those of the analyses, it was shown that the estimation of blank shape using the FE analysis is a proper methodology to create a feasible shape of the blank for the center hinge of automotive.

• 대한기계학회논문집
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• 제15권1호
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• pp.1-10
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• 1991

본 연구에서는 고속 대변형 탄소성 변형 과정을 해석할 수 있는 프로그램(NET )을 개발하고 이것을 실린더 및 링 성형 문제에 적용하여 마찰 및 관성 효과가 변형 거동에 미치는 영향을 규명하여 보았다.

• 한국기계가공학회지
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• 제8권2호
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• pp.60-68
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• 2009

The objective of this paper is to design stamping die of inner reinforcement panel with DL 950 advanced high strength steel as stamping materials through numerical analyses and experiments. The stamping process was designed as bending dominant process consisting of 1 step of notching and 4 steps of bending processes. In order to obtain a proper design of the stamping die, various three-dimensional elasto-plastic finite element analyses were performed using a commercial code AUTOFORM V4.2. Design parameter of stamping die was chosen as the corner radius of the stamping die for each step. From the results of the FE analysis, feasible corner radii of the stamping die, which can minimize the deviation of corner angle of the stamped part from design data, and forming load for each part were estimated. Stamping experiments were carried out using the manufactured stamping die according to the proposed die design. The results of experiments were shown that the stamping die can successfully manufacture the inner reinforcement panel with DL 950 advanced high strength steel as base stamping material.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.160-163
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• 2004

The hub hole in a wheel of vehicles usually formed with hole expansion process. Formability of material, especially the hole expansion ratio, is important to produce a fine hub hole. The hub hole expansion process is different from general forming process or bore expansion process in the viewpoint of forming a thick plate. In the hole expansion process of the plate with a hole, as the hole being expanded, the crack is occurred to outward direction at the boundary of a hole. Therefore, it is need to apply the fracture criterion in the hub hole expansion process. In this paper, the hub hole expansion process is simulated with commercial elasto-plastic finite element code, LS-DYNA3D considering some ductile fracture criteria. Fracture mode and hole expansion ratio is compared with respect to the fracture criteria. Analysis results demonstrate that only the effective plastic strain is not adequate to predict the fracture mode in the hub hole. And the analysis results also indicate that the ductile fracture criteria properly predict the fracture mode but hole expansion ratio is different with the result of each other because of their different characteristics.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.334-336
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• 2009

An elastic-plasticity model during the austenitic decomposition was derived and implemented to incorporate the two important deformation behaviors observed during the phase transformations: the volumetric strain and transformation induced plasticity due to the temperature change and phase transformation. To obtain transformed phase volume fractions during cooling, the fourth order Runge-Kutta method was used to solve the Kirkaldy's phase kinetics model which is function of temperature, austenitic grain size and chemical composition. The volumetric strain was calculated by considering the densities of constituent phases, while the transformation induced plasticity was based on the micro-plasticity due to the volume mismatch between soft austenitic phase and other harder phases. The constitutive equations were implemented into the implicit finite element software and a simple boundary value problem was chosen as a model problem to validate the effect of transformation plasticity on the deformation behavior of steel under cooling from high temperature. It was preliminary concluded that the transformation plasticity plays a critical role in relaxing the developed stress during forming and thus reducing the magnitude of springback.