http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
다양한 하중경로에서의 DP980 강판의 파단변형률 예측에 관한 연구
박남수(N. Park),허훈(H. Huh) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
This paper is concerned with prediction of fracture strains for DP980 steel sheets at a wide range of loading paths. The usage of DP980 steel is significantly increasing in automotive industries for enhanced safety and high fuel efficiency. The material behavior of advanced high-strength steels (AHSSs) sheets show unpredictable and sudden fracture in sheet metal forming processes. A modified Lou-Huh ductile fracture criterion is utilized to predict the formability of AHSSs because the conventional forming limit diagram (FLD) constructed based on necking is unable to evaluate the formability of AHSSs. Fracture loci were extracted from three dimensional fracture envelopes by assuming the plane stress condition to evaluate equivalent plastic strains at the onset of fracture at a wide range of loading paths. Three different types of specimens such as pure shear, dog-bone and plane strain grooved specimens were utilized for tensile tests to calibrate the fracture model of DP980 steel sheets. Fracture strains of each loading path were evaluated to show that there is little deviation between fracture strains predicted from the fracture model and experimentally acquired ones. Through the comparison, it is clearly shown that the three dimensional fracture envelopes can accurately predict the onset of the fracture of DP980 steel sheets in complicated loading conditions from compressive loading, and shear to equi-biaxial tension.
DP980의 트리밍 시 전단면 특성에 미치는 공정변수의 영향
최홍석(H. S. Choi),이지욱(J. W. Lee),김성귀(S. G. Kim),고대철(D. C. Ko),서판기(P. K. Seo),김병민(B. M. Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
Ultra high strength steels such as DP980, CP1180 and hot stamped boron steel are widely used in automotive industry for the light weight body. However, sheared edge of the trimmed part made of these steels is sensitive to edge cracking, which leads to unpredicted failure in the subsequent forming process such as bending and hole flanging. Furthermore, trimming tool life decreases due to their higher strength than mild steel. In this study, the effect of process variables on the sheared edge properties in trimming of DP980 sheet. Considered parameters are clearance and inclined angle of trimming die. Trimming load and sheared edge with respect to the parameters are investigated using finite element analysis. Maximum trimming load decreases with increasing clearance because of large bending moment resulting in tensile hydrostatic pressure in the sheared band. Also, tensile type burr occurs under the trimming clearance above 15%t. Inclined angle have better influence on sheared edge and trimming load.
FRACTURE LOCI OF DP980 STEEL SHEET FOR AUTO-BODY AT INTERMEDIATE STRAIN RATES
임성준,허훈 한국자동차공학회 2017 International journal of automotive technology Vol.18 No.4
This paper introduces the effect of the strain rate on the ductile fracture of DP980 1.2t steel sheet. Tensile tests of DP980 sheet are performed at a range of strain rates from 0.001 s−1 to 100 s−1 with three different shapes of specimens: the diagonally notched specimen for the in-plane shear test; the dog bone specimen for the uniaxial tension test; and grooved specimen for the plane strain tension test. To trace the strain on the surface of the specimen, 2-D digital image correlation (DIC) technique is adopted to encompass the remarkable transition of the fracture characteristics including the fracture strain, loading path and strain rate sensitivity. The negative stain rate sensitivity is observed on the equivalent strain to fracture which corresponds to the experimental results at low strain rate ranging from 0.001 s−1 to 0.1 s−1. The transition of thermal condition from isothermal to adiabatic comes into play to increase the equivalent strain to fracture at the intermediate strain rate from 0.01 s−1 to 1 s−1. The fracture loci incorporating with the Lou-Huh ductile fracture criterion are developed to identify the strain rate effect in the wide regime of triaxiality.
DP980 트리밍 시 전단 각도에 따른 금형 수명에 관한 연구
최홍석(Hongseok Choi),고대철(Daecheol Ko),김병민(Byungmin Kim) 한국자동차공학회 2012 한국자동차공학회 지부 학술대회 논문집 Vol.2012 No.5-1
Ultra high strength steels such as DP980 are widely used in automotive industry for the light weight body. However, cutting tool life decreases due to their extremely high strength when trimming or blanking these steels. Trimming angle is importance parameter for the reduction of contact pressure on tool edge resulting in premature tool failure. In this study, the effect of trimming angle on the burr formation and sheared edge in trimming of DP980 sheet Trimming load and sheared edge with respect to the trimming angle are investigated using finite element analysis. Furthermore, tool life on the basis of burr height of 0.1mm is estimated using burr height diagram during 30,000 strokes by trimming experiment As a result of FE-analysis and experiment, trimming angle of -10° provide better influence on sheared edge, trimming load and trimming tool life.
다양한 하중 조건에서 DP980 판재의 불안정성 및 파단점 결정시 DIC Frame Rate의 영향
노은솔,홍석무 한국소성∙가공학회 2019 소성가공 : 한국소성가공학회지 Vol.28 No.6
The past recent years have seen an increasing use of high-strength steel sheets in the automotive industry. However, the formability and damage prediction of these materials requires accurate acquisition of necking and fracture strains. Digital image correlation (DIC) is used to accurately capture the necking and fracture strains during testing. The fact that single time points of capturing vary with frame rate makes the need for an investigation necessary. For the high-strength steel DP980, the frame-rate dependences of the final necking and fracture strains values are analyzed here. To eliminate the influence of gauge length, the strains were measured locally by DIC. Results for three specimen shapes obtained with frame rates of 1 and 900 fps (frames per second) were considered and based on them, triaxiality failure diagrams (TFD) are established. It was observed that after diffuse necking, the deformation path departed from the initially linear one, and the stress triaxiality grew with ongoing deformation. It was further revealed that the frame rate-dependence of the necking strain was rather low (< 2%), whereas the fracture strain could be underestimated by up to 8% when the lower frame rate of 1 fps was used (compared with 900 fps). In this study, this issue is investigated while taking into consideration the three different triaxialities. These results demonstrate the importance of choosing an appropriate frame rate for the determination of necking and fracture strains in particular.