• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.783-788
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• 2000

Hydroforming is a method for forming circular tubes. If this technology is to be applied economically, it is essential to have knowledge of the avoidance of failure cases as well as of the behavior of the tube in the tool under the compressive stress and forces that are exerted by the machine. A finite element simulation for manufacturing of lower arm from straight tubes, using the hydroforming method, was performed to investigate the effects of varying process parameters. Explicit method is used to simulate hydroforming in many cases, but that is not included flow rule. And then it needs simulation for implicit method. It was simulated by two methods, implicit and explicit, to compare the result of the hydroforming.

• 한국정밀공학회지
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• 제19권9호
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• pp.74-81
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• 2002

Recently tube hydroforming has been widely applied to the automotive industries due to its several advantages over conventional methods. In this paper, attention is paid to comparison of an implicit and an explicit finite element method widely used for numerical simulation of a hydroforming process. For an explicit FEM, a huge amount of computational time is required because of the very small time increment to solve a quasi-static problem. Hence, when an explicit FEM is used fDr a hydroforming process, it is general to convert the real problem to a virtual problem with a different processing time and mass density by appropriate scaling factor. However it is difficult to figure out how large the scaling should be adopted enough to ignore the dynamic effects and maintain the desired accuracy. In this paper, the comparison of the results obtained from both methods focus on the accuracy of the predicted geometrical shape and the stress with various scaling factors which are applied to analyze hydroforming process of an automobile lower arm.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.866-872
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• 2000

Superplastic forming processes by characteristic of low flow stress and high elongation have advantages to reducing on production cost and weight because of the product of complex form could be made in one part. However superplastically termed part has a characteristic of non-uniform thickness distribution along forming direction. Especially. since the thickness distribution affects on mechanical properties of product. the uniform thickness is very important. There are two solution procedure of implicit and explicit procedure to analyze the superplastic forming. In this study to analyze the thickness distribution two kinds of commercial programs of DEFORM and PAM-STAMP which implicit and explicit code are used respectly. The results from the two Programs were compared with eath other As a result implicit code were more suitable than explicit code for superplastic forming analysis.

• 소성∙가공
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• 제11권4호
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• pp.302-311
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• 2002

A generalized numerical approach based on the finite element method to analysis and design of hydroforming process is proposed in this paper. The special attention is focused on comparison of an implicit and an explicit finite element method widely used for hydroforming simulation. Furthermore, in order to meet the increasing real needs for prediction of forming limit, a ductile fracture criterion combined with finite element method is introduced and then applied to hydroforming process of an automobile lower m Consequently, the numerical analysis and design for hydroforming process presented here will facilitate the development and application of the tube hydrofoniung process to a new level.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.625-628
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• 1995

A static/implicit finite element code for sheet forming (ITAS3D) is parallelized on IBM SP 6000 multi-processor computer. Computing-load-balanced domain decomposition method and the direct solution method at each subdomain (and interface) equation are developed. The system of equations for each subdomain are constructed by condensation and calculated on each processor. Approximated operation counts are calculated to set up the nonlinear equation system for balancing the compute load on each subdomain. Th esquare cup tests with several numbers of elements are used in demonstrating the performance of this parallel implementation. This procedure are proved to be efficient for moderate number of processors, especially for large number of elements.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.136-140
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• 2000

It is desirable to predict springback quantitatively and accurately for the tool and process design in sheet stamping operations, however, it is blown very difficult. The result of springback analysis by the finite element method is sensitively influenced by numerical factors such as blank element size, number of integration point, punch velocity, contact algorithm etc. In the present work, a parametric study by Taguchi method is performed in order to evaluate the influence of numerical factors on springback Quantitatively and to obtain the combination of numerical factors which yields the best approximation to experimental data. Since springback is determined by the residual stress after forming process, it is important to evaluate stress distribution accurately. The oscillation in the time history curve of stress obtained by explicit FEM says that the stress solution at termination time is in very unstable state. Therefore, a variability study is also carried out in this study in order to assess the stability of implicit springback analysis starting from the stress solution by explicit forming simulation. The 2D draw bending process, one of the NUMISHEET '93 benchmark problems, is adopted as an application model.

• 대한조선학회지
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• 제27권3호
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• pp.107-116
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• 1990

구조물의 탄성을 고려한 탱크내 유동은 자유수면을 갖는 유체와 탄성변형하는 구조물이 연성된 시스템으로서 유체유동으로 인한 과도한 구조물변형, 유체의 부가질량 및 부가감쇠력에 의한 구조물의 동특성변화, 구조물 진동으로 인한 유체유동의 왜곡 등이 복합된 비선형 해석이 요구된다. 본 논문에서는 탱크 벽을 1자유도 수평운동하는 강체로 가정하였으며 Lagrangian 유한요소법을 이용하여 유동해석을 수행하였고 유체-구조물 연성문제의 수치적분을 위하여 조합된 implicit-explicit 알고리듬을 도입하였다. 탱크벽의 동특성 변화에 따른 유체-구조물연성 탱크의 동특성변화를 관찰하였으며 파도생성 문제에 관한 수치계산을 수행하였다.

• Computers and Concrete
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• 제25권1호
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• pp.67-73
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• 2020

Traditionally used analytical approach to predict the fatigue failure of reinforced concrete (RC) structure is generally conservative and has certain limitations. The nonlinear finite element method (FEM) offers less expensive solution for fatigue analysis with sufficient accuracy. However, the conventional implicit dynamic analysis is very expensive for high level computation. Whereas, an explicit dynamic analysis approach offers a computationally operative modelling to predict true responses of a structural element under periodic loading and might be perfectly matched to accomplish long life fatigue computations. Hence, this study simulates the fatigue behaviour of RC beams with finite element (FE) assemblage presenting a simplified explicit dynamic numerical solution to show computer aided fatigue behaviour of RC beam. A commercial FEM package, ABAQUS has been chosen for this complex modelling. The concrete has been modelled as a 8-node solid element providing competent compression hardening and tension stiffening. The steel reinforcements are simulated as two-node truss elements comprising elasto-plastic stress-strain behaviour. All the possible nonlinearities are duly incorporated. Time domain analysis has been adopted through an automatic Newmark-β time incremental technique. The program consists of twelve RC beams to visualize the real behaviour during fatigue process and to obtain the reliability of the study. Both the numerical and experimental results indicate a redistribution of stresses along the time and damage accumulation of beam which severely affect the serviceability and ultimate capacity of RC beam. The output of the FEM analysis demonstrates good match with the experimental consequences which affirm the efficacy of the computer aided model. The controlled fatigue damage evolution at service fatigue load limits makes the FE model an efficient tool in predicting high cycle fatigue behaviour of RC structures.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1992년도 춘계학술대회 논문집 92
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• pp.201-212
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• 1992

The plane strain analysis for simulating the stretch/draw forming operation of arbitrarily-shaped tool profiles and arbitrarily draw-in conditions is introduced. An implicit, incremental, updated Lagrangian formulation is employed, introducing a rigid-viscoplastic constitutive equation. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshe without depending on the explicit spatial derivatives of tool surfaces. The FEM formulation is tested in the sections automotive inner panel and two-side draw-in. Not only the excellent agreement between measured and computed strains in the stretched section is obtained, but also the numerical stability of current formulation is verified in the two-side draw-in section.

• 소성∙가공
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• 제1권1호
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• pp.95-103
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• 1992

The plane strain analysis for simulating the stretch/draw forming operation with an arbitrarily-shaped tool profile 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 linear line elements are used for depicting the formed sheet, based on membrane approximation. The FEM formulation is tested in the sections of automotive inner panel and two-side draw-in. Not only the excellent agreement between measured and computed strains is obtained in the stretched section, but also the numerical stability of formulation is verified in the draw-in section.