• Journal of the Korean Society for Precision Engineering
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• v.19 no.9
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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.

• Composites Research
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• v.18 no.5
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• pp.15-20
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• 2005

In this paper, damage induced acoustic emission in the composite plate in numerically simulated by using the three dimensional finite element method and explicit time integration. Acoustic source is modeled by equivalent volume source. To verify the proposed method, dynamic displacements due to the elastic wave are compared with the experiment when the fiber is broken in the single fiber embedded isotropic plate. For the laminated composite plates, the results are compared between homogenized model and DNS approach which models fibers and matrix separately. To capture high frequencies in the elastic wave, small time step size and a large number of meshes are required. The parallel computing technology is introduced to solve a large scale problem efficiently.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.4 s.23
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• pp.5-13
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• 2005

The impact of a long-rod penetrator into oblique plates with combined obliquity and yaw is investigated. The study was done using a newly developed three dimensional dynamic and impact analysis code, which uses the explicit finite element method. Through the comparison of simulation result with experimental result and other code's result, the adaptability and accuracy of the developed code is evaluated under the complex situation in which yaw angle and oblique angle exist simultaneously. As a result of comparison, it has found that deformed shape, residual length and velocity, rotational velocity of long-rod show good agreement with experimental data. Through this study, the applicability and accuracy of the code as a metallic armour system design tool is verified.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.19 no.4
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• pp.51-57
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• 2011

The spin-up and the spring-back are most severe load cases in the aircraft landing gear design. These load cases are caused by reciprocal action of complex physical phenomenon such as the friction between a tire and ground, inertia of the rotation of a tire and the flexibility of a landing gear structure. Generally, the empirical formula or the theoretical formula is used to calculate the spin-up and spring-back load in the early stage of the development program of the aircraft landing gear. After the materialization of the design of a landing gear, spin-up and spring-back load are acquired by the free drop test. In this study, the spin-up and the spring-back load of the rubber shock absorber type KC-100 nose landing gear are calculated by the explicit finite element analysis. Through this analysis, more accurate and realistic spin-up and spring back loads could be applied to the early phase of the development of the aircraft landing gear.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.1
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• pp.21-26
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• 2005

In order to simulate the powder compaction process and to assess the effects of packing randomness and particle arrangement 2-dimensional model of rod array compaction using quasi-random multiparticle array is introduced. The elastic modulus of porous ceramics is computed by the homogenization method. With 3 Al₂O₃ and 3 Al particles the compaction processes associated with the porosities are simulated by the explicit finite element method, based on the elastic modulus found by the homogenization method. The simulation results are compared with both previous analytical ones and experimental measurements. Finally, in order to find the relationship between the friction coefficient of powder particles and the relative density, the sensitivity analysis is performed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.121-131
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• 1998

This paper applies the FE analysis procedure, developed in the Part I of the companion article, to the three-dimensional rubber pad deformation during rubber-pad forming process. Effects of different algorithms corresponding to incompressibility constraint and time integration methods on numerical solution responses are investigated. Laboratory scale experiments support the validity of the developed FE procedure an demonstrate the accuracy of the numerical models. Full scale model responses are also predicted using the reasonable method and parameters obtained in laboratory modeling.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.111-120
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• 1998

This paper is the first one of two-parted research efforts focusing on the modeling of rubber pad forming process. The rubber pad, driven by the pressurized fluid during the forming process, pushes the sheet metal to solid tool half and forms a part to final shape. In this part of the paper, a numerical procedure for the FE analysis of the rubber pad deformation is presented. The developed three-dimensional FE model is based on the total Lagrangian description of rubber maerial characterized by nearly incompressible hyper-elastic behavior under a large deformation assumption. Validity of the model as well as effects of different algorithms corresponding to incompresibility constraints and time integration methods on numerical solution responses are also demonstrated.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.3
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• pp.58-63
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• 2004

In the present work a finite element formulation using dynamic-explicit time integration scheme is used for numerical analysis of multi-stage stamping processes. The lumping scheme is employed for the diagonal mass matrix and dynamic explicit formulation Multi-Stage stamping is analyzed by using dynamic-explicit finite element method. Further, the simulated results for the panel stamping processes are shown and discussed. Its application is being increased especially in the stamping industrial area for the cost reduction, weight saving, and improvement of strength.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.4
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• pp.63-72
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• 2004

In this paper, a finite element formulation using dynamic-explicit time integration scheme is used for numerical analysis of auto-body panel stamping processes. The lumping scheme is employed for the diagonal mass matrix and dynamic explicit formulation. Auto-body panel forming is analyzed by using dynamic-explicit finite element method. Further, the simulated results of the auto-body panel stamping processes are shown and discussed. Its application is being increased especially in the stamping industrial area for the cost reduction, weight saving, and improvement of strength.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.1
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• pp.11-23
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• 2010

A sacrificial member with aluminum foam of excellent energy absorption capacity was proposed for the protection of significant structures. Parametric studies of explicit finite element analyses were performed to investigate the pressure mitigation of close-range air-blasts. The scaled distance of the blast had a range of Z=0.48~0.95 and an empirical blast load function was utilized. The analytical parameters of the aluminum foam were density, thickness and the existence of a cover sheet. Analytical results showed that the transmitted pressure can be controlled to have a similar level of yield values of the foam by using a foam with low density and higher thickness. As the blast load increased, the sacrificial member needed to have higher density and thickness. A cover sheet of the foam clearly showed its effect on the wider distribution of blast pressure. It is necessary to determine the design parameters of sacrificial foams considering different energy dissipation capacities according to the scaled distance.