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하지웅(Jiwoong Ha),허훈(Hoon Huh),임승찬(Seung-Chan Lim),이홍우(Hongwoo Lee),남재복(Jae-Bok Nam) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
This paper is concerned with the failure characteristics and the failure criterion of spot welds of a dissimilar AHSS combination under combined axial and shear loading conditions. In order to keep the constant ratio of the axial load to the shear load acting on the spot weld during the failure test, the testing fixture and the specimen proposed by Song et al. for a loading angle ranging from 0° to 75° and the newly designed fixture and specimen for loading angle of 90° are used for the failure tests to obtain failure loads and to identify the failure behavior of spot weld of a dissimilar AHSS combination. The newly designed fixture and specimen can obtain more correct failure loads as preventing rotation of spot welds during the failure tests at a loading angle of 90°. The failure loads of spot welds were investigated with experiments for the spot weld of DP780 1.2t and DP980 1.2t steel sheet combination. The failure loads obtained at various loading angles are utilized to construct the failure criterion proposed Song and Huh for description of failure behavior of spot welds in the crash analysis or the strength analysis of an auto-body.
김기수,장래웅,남재복,최원집 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.5
No single test can accurately predict the press shop formability of sheet metal and provide reproducibility of measured data. However a Limiting Dome Height(LDH) test was developed to specifically rank sheet metals for forming operations. The dome height at plane-strain state, which is the typical failure condition in many automotive stamping process is used as the criterion for sheet metal formability. Moreover, the strain state at failure in the test can duplicate the various strain state at failure in actual stamping operations by oaring the sample width and lubrication condition. In this study the difference between the FLD and the LDH tests was investigated and the LDH curves of various low carbon steel sheets were compared to yield a ranking of materials used in press shop. It was found that lubrication(or friction) was no less important than material itself in LDH values and no significant differences in punch speed and blank holder force(BHF) during the test were observed. A high LDH value is therefore, resulted at low interface friction allowing uniform distribution of strains. The relevance of the plane-strain LDH values with real stamping was checked by material control limit obtained from statistical deformation control chart for wheel house inner blanks.
김기수,장래웅,남재복,최원집 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.2
In the steel D&I can-making industry, there has been a tendency of increasing the punch speed to meet the needs of high productivity. Owing to high punch speed, however, produced can occasionally shows dull and scratched surface which is called frosting phenomenon. In the present work, to investigate the effects of various factors on the frosting, steel D&I can-making was carried out with facilities of commercial line and ironing simulator of lavoratory scale. The frosting seemed to be influenced by the number of ironing steps and the characteristics of coating layer of tinplate. Tinplates resulting in lightly frosted cans were observed to have less surface oxides and Fe+Sn alloyed layers than those of heavily frosted cans. They had also developed preferred orientation of (101) plane. In laboratory scale experiments, it was found that the frosted area was decreased with decreasing thickness reduction ratio of final ironing die.