• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.3
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• pp.276-282
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• 2009

Wrinkling in the flange and wall of a deep-drawn part is one of the major defects in sheet metal processes. Wrinkling is influenced by many factors, such as material properties, shape of the body, forming conditions, stress state and thickness, etc. It is difficult to analyze the wrinkling initiation and growth according to the factors because the effects of the factors are very complex and the wrinkling behavior may show wide variation even though small deviation of factors. In this study, the influence of wrinkling parameters, such as material properties (Al1050, Al5052), the blank holding force and the drawing depth on the wrinkling initiation and growth is investigated by using the experimental method and the dynamic explicit finite element analysis. From the results, it is shown that the dynamic explicit finite element method can be used effectively to prevent the wrinkling problems advancely in the deep drawing process. Also, there is a good agreement between the experimental result and the dynamic explicit finite element analysis.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.3
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• pp.201-209
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• 2015

The deformed degree of car body varies largely with the collision part from side collision of car-to-car. In case of deformation of car body caused by collision, the movement is different as speed energy changes to strain energy. Generally, in the analysis of traffic accident, the movement of car after the collision is analyzed by law of conservation of motion and the error of energy absorption rate along the deformation of car body can be calibrated by inputting coefficient of restitution, but it is current situation that coefficient of restitution applied by referring to the research results of forward collision and backward collision because the research results of side collision is rare. Vehicle model of finite element method applied by structure of car body and materials of each component was analyzed by explicit finite element method, and coefficient of restitution and collision detection time along contact part of side collision was drawn by analyzing the results. Analysis result acquired through the law of conservation momentum by applying finally-computed coefficient of restitution and crash detection time compared to collision result of actual vehicle. As a result, the reliability of analysis was higher than the existing analysis method were acquired when applying the drawn initial input value that used finite element method analysis model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.345-351
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• 2003

Due to increasing legal and market demands for safety in the automotive design process, the design of integrated seat is important more and mote because it should satisfy the conflict between stronger and lower weight for safety and environmental demands. In this study for crash simulations, the numerical simulations have been carried out using the explicit finite element program LS-Dyna according to the FMVSS 210 standard for safety test of seat. Since crash simulations are very time-consuming and a series of simulations that does not lead to a better result is very costly, the optimization method must be both efficient and reliable. As a result of that, statistical approaches such as design of experiments and response surface model have been successfully implemented to reduce time-consuming LS-Dyna simulations and optimize the safety and environmental demands together with nonlinear optimization algorithm. Design of experiments is used lot exploring the design space of maximum displacement and total weight and for building response surface models in order to minimize the maximum displacement and total weight of integrated seat.

• Transactions of the KSME C: Technology and Education
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• v.3 no.3
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• pp.183-191
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• 2015

In this study, the finite element analysis was carried out to investigate dynamic characteristics of the AGF(Active Gurney Flap) which is under development for reducing vibration and noise of the helicopter rotor system. The Gurney flap is a kind of small flat plate, mounted normal to the lower surface of the airfoil near to the trailing edge. An electric motor, L-shaped linkages and flap parts were integrated into a rotor bade, and 3~5/rev control was given to the AGF to reduce the vibration in the fixed frame. Thus, an explicit time integration method was adopted to investigate the dynamic response of the AGF with considering both centrifugal force due to the rotor rotation and active control input, and it can be seen that the vertical displacement of the AGF was satisfied to meet the design requirement.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.172-175
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• 2005

The numerical simulation is performed for the acoustic emission and the wave propagation due to fiber breakage in single fiber composite plates by the finite element transient analysis. The acoustic emission and the following wave motions from a fiber breakage under a static loading is simulated to investigate the applicability of the explicit finite element method and the equivalent volume force model as a simulation tool of wave propagation and a modeling technique of an acoustic emission. For such a simple case of the damage event under static loading, various parameters affecting the wave motion are investigated for reliable simulations of the impact damage event. The high velocity and the small wave length of the acoustic emission require a refined analysis with dense distribution of the finite element and a small time step. In order to fulfill the requirement for capturing the exact wave propagation and to cover the 3-D simulation, we utilize the parallel FE transient analysis code and the parallel computing technology.

• Composites Research
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• v.24 no.5
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• pp.9-16
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• 2011

This paper describes the crashworthiness evaluation and performance improvement of tilting train made of sandwich composites. The applied sandwich composite of carbody structure was composed of aluminum honeycomb core and glass/epoxy & carbon/epoxy laminate composite facesheet. Crashworthiness analysis of tilting train was carried out using explicit finite element analysis code LS-DYNA 3D. The 3D finite element model and 1D equivalent model were applied to save the finite element modeling and calculation time for crash analysis. The crash conditions of tilting train were conducted according to four crash scenarios of the Korean railway safety law. It found that the crashworthiness analysis results were satisfied with the performance requirements except the crash scenario-2. In order to meet the crashworthiness requirements for crash scenario-2, the stiffness reinforcement for the laminate composite cover and metal frames of cabmask structure was proposed. Consequentially, it has satisfied the requirement for crash scenario-2.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.576-585
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• 2002

A three-dimensional Lagrangian explicit time-integration finite element code for analyzing the dynamic impact phenomena was developed. It uses four node tetrahedral elements. In order to consider the effects of strain rate hardening, strain hardening and thermal softening, which are frequently observed in high-velocity deformation phenomena, Johnson-Cook model is used as constitutive model. For more accurate and robust contact force computation, the defense node contact algorithm was adopted and implemented. In order to evaluate the performance of the newly developed three-dimensional hydrocode NET3D, numerical simulations of the oblique impact of mild steel plate by mild steel sphere were carried out. Ballistic limit about various oblique angle between 0 degree and 80 degree was estimated through a series of simulations with different initial velocities of sphere. Element eroding by equivalent plastic strain was applied to mild steel spheres and targets. Ballistic limits and fracture characteristics obtained from simulation were compared with experimental results conducted by Finnegan et al. From numerical studies, the following conclusions were reached. (1) Simulations could successfully reproduce the key features observed in experiment such as tensile failure termed "disking"at normal impacts and outwards bending of partially formed plus segments termed "hinge-mode"at oblique impacts. (2) Simulation results fur 60 degrees oblique impact at 0.70 km/s and 0.91 km/s were compared with experimental results and Eulerian hydrocode CTH simulation results. The Lagrangian code NET3D is superior to Eulerian code CTH in the computational accuracy. Agreement with the experimentally obtained final deformed cross-sections of the projectile is excellent. (3) Agreement with the experimental ballistic limit data, particularly at the high-obliquity impacts, is reasonably good. (4) The simulation result is not very sensitive to eroding condition but slightly influenced by friction coefficient.