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송정한(Junghan Song),허훈(Hoon Huh),임지호(Jiho Lim),박성호(Sungho Park) 한국자동차공학회 2008 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
This paper is concerned with the evaluation of the dynamic failure load of the spot weld under combined axial and shear loading conditions. The testing fixture are designed to impose the combined axial and shear load on the spot weld. Using the proposed testing fixtures and specimens, quasi-static and dynamic failure tests of the spot weld are conducted with seven different combined loading conditions. The failure load and failure behavior of the spot weld are investigated with different loading conditions. Dynamic effects on the failure load of the spot weld, which is critical for structural crash worthiness, are also examined based on the experimental data. In order to evaluate the effect of the strain rate on the failure contour of the spot weld under combined axial and shear loads, the failure loads measured from the experiment are decomposed into the two components along the axial and shear directions. Experimental results indicate that the failure contour is expanded with increasing strain rates according to the rate sensitivity of the ultimate stress for welded material.
송정한(Junghan Song),허훈(Hoon Huh),김홍기(Honggee Kim),박성호(Sungho Park) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Simulation of vehicle crashes using the finite element method has made major advances in the last several years. Every major automotive company now uses CAE to perform virtual crash tests. Designers can mow quickly adjust the structural performance before performing a physical crash test. Compared to physical crash tests, the virtual simulation is less costly and faster which allows manufactures to reduce costs and vehicle development time. In order to produce more efficient and precise simulations, it is needed to adopt the dynamic property of materials and the failure modeling of resistance spot weld. The resistance spot weld in most current finite element crash models are characterized as a rigid beam at the location of the weld. The role of this rigid beam is simply to transfer the load across the welded component. The spot weld elements is design to be failed by some failure criteria which is function of axial and shear load at the rigid beam. For this reason, the calculation of the load at the rigid beam is important to predict the failure of the spot weld. In this paper, the numerical simulations are carried out to evaluate the calculation of the load at the rigid beam. The first study conducted is to examine the effect of mesh size on the load at the rigid beam. The effect of element shape on the welded components is, then, investigated. Finally, the location and the number of welded constrains is changed for the correct prediction of the load on the spot weld element. The analysis results demonstrate that the correct prediction of the load on the spot weld element is achieved by the change of the element shape on the welded component s and the location of welded constrains.
반응표면법을 이용한 차체용 프런트 사이드 멤버의 스프링백 저감
송정한(Junghan Song),허훈(Hoon Huh),김세호(Seho Kim),박성호(Sungho Park) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_3
Springback is a common phenomenon in sheet metal forming since the elastic recovery of the internal stresses is induced after removal of the tooling. The numerical analysis of spring back is a complicated time-consuming job and its result is greatly effected by a type of the yield function, finite elements used and the constraint condition for eliminating a rigid body motion. In this paper, optimization of the draw-bead force is carried out utilizing the response surface method in order to reduce springback and improve shape accuracy of a deep drawn product. In the optimization process, the tendency of springback is evaluated qualitatively without springback simulation usually done with the implicit solving scheme. Instead of springback simulation, the amount of stress deviation along the thickness direction in the deep drawn product is used as an indicator of springback. The stamping process is analyzed for a front side member formed with advanced high strength steel (AHSS) sheets such as DP60. The analysis procedure fully covers the binder-wrap, stamping, trimming and springback processes with the commercial elasto-plastic finite element code LS-DYNA 3D. The effect of the restraining force of draw-beads is con finned with the decreased stress deviation. The analysis result shown in the final springback simulation demonstrates that the present analysis provides a guideline for controlling the evolution of spring back based on the finite element simulation of complicated auto-body members.
디지털 이미지 상관관계를 이용한 알루미늄 합금 판재의 성형한계도 평가
김용배,박정수,송정한,Kim, Yongbae,Park, Jungsoo,Song, Junghan 한국교통대학교 융복합기술연구소 2015 융ㆍ복합기술연구소 논문집 Vol.5 No.1
Sheet metal formability can be defined as the ability of metal to deform without necking or fracture into desired shape. Every sheet metal can be deformed without failure only up to a certain limit, which is normally known as forming limit curve(FLC). In this paper, the dome stretching tests and tensile tests have been performed to obtain forming limit curve of aluminum alloy. During the experiment, failure strain is measured using digital image correlation(DIC) method. DIC method is a whole-field measurement technique that acquires surface displacements and strains from images information which characterized a random speckle as intensity grey levels. Recently years, this DIC method is being developed and used increasingly in various research. DIC results demonstrated the usefulness and ability to determine a strain.
배기현(Gihyun Bae),송정한(Junghan Song),허훈(Hoon Huh),김세호(Seho Kim),박성호(Sungho Park) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Draw-bead is applied to control the material flow in sheet metal forming process and improve the product quality by providing sufficient draw-bead restraining force (DBRF). However, actual die design depends mostly on the trial-and-error method without the accurate prediction of DBRF and the normal force. Die design with the predicted value of them can be utilized effectively to reduce the cost and time. In order to construct a prediction model, process parameters, which affects significantly to DBRF and the normal force, are selected as design variables. At first, the prediction model without considering the effect of BHF is constructed using the Box-Behnken design which is the most representative DOE method. Results obtained from finite element analysis are approximated with the second order regression model. It provides the maximum value of DBRF and the normal force because the male bead fully presses down the sheet. After that, the variation of DBRF with respect to the change of BHF is approximated with the first order regression model by adopting the fractional factorial design. It provides the equation for the scale factor with respect to the change of process parameters. Using two equations, DBRF can be obtained in general sheet metal forming process. To verify the reliability of the prediction model, results obtained from the prediction model are compared with them obtained from finite element analysis.