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배기현(G. H. Bae),허훈(H. Huh),이준우(J. W. Lee),이병호(B. H. Lee) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
This paper deals with an evaluation method of a single-layer steel cord using the finite element analysis during the stranding process. The residual stress distribution of a drawn wire and the shape of a single-layer steel cord before the roller straightening process are investigated carefully for the accurate description of irregularities of a single-layer steel cord. Simulations of a twisting process and two roller straightening processes are performed with a simplified simulation method. From simulations, the steel cord shape and assessment items of the steel cord quality are measured before and after the roller straightening process. The simulation-based evaluation method developed can provide the specific information of the role of straightening devices to the steel cord quality. It also can be utilized for an optimum design of the stranding process for the reduction of the time and cost.
배기현(G. H. Bae) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.10
This paper evaluates performance of anisotropic yield function to approximate the uni-axial hardening behavior with respect to the loading angle from the rolling direction. Three yield functions, such as Hill48, YJd89 and Yld2000-2d, are selected to approximate the anisotropic hardening behavior. The test material is 340ES steel sheet with the thickness of 0.65 ㎜. The results show that more advanced material model is required to describe the anisotropy change with the increase of the plastic strain.
스틸코드 연선 시 주요공정에 따른 교정효과의 실험적 관찰
배기현(G. H. Bae),이종섭(J. S. Lee),허훈(H. Huh),이준우(J. W. Lee),이병호(B. H. Lee) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
This paper deals with the experimental investigation of the steel cord straightening during the stranding process. The over-twisting and roller straightening process are essential to improve the product quality during the stranding process. To investigate the effectiveness of two processes, four experimental cases are constructed according to the use of an over-twister and two roller straighteners. Three assessment items, such as the residual torsion, the arc-height and the preforming ratio, are measured in each experimental case for the quantitative evaluation of a steel cord. The steel cord shape is also measured to investigate the variation of the straightness efficiently after passing through each process. Finally, the effectiveness of the over-twisting and the roller straightening process is explained based on the experimental results.
변형를 속도에 따른 인장/압축 경화 거동의 근사를 위한 수정 Two-surface 모델
배기현(G. H. Bae),허훈(H. Huh) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
This paper suggests a modified two-surface model to describe the tension/compression hardening curves of auto-body steel sheets with the variation of the strain rate. Tension/compression tests of auto-body steel sheets were carried out by utilizing the simple clamping device developed by Bae et al. [~] in order to obtain tension/compression hardening curves. To consider the strain rate effect on the hardening behavior, a gap function used for the two-surface model was modified by inserting the strain rate hardening term. The approximation results show that the modified two-surface model can accurately describe the tension/compression hardening behavior with the variation of the strain rate.
대변형 유동응력선도를 이용한 초고강도강의 스프링백 예측 정확도 향상
배기현(G. H. Bae) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.10
This paper deals with a spring-back prediction method with Yoshida-Uemori model calibrated by using the large-deformation flow stress curve. Mechanical tests for YU model are performed for 780DP and 980DP. Two parameter sets for each material are calibrated with flow stress curves obtained from the tension test and the hydraulic bulge test. U-bending experiments and simulations are performed to evaluate the spring-back prediction accuracy. Simulation results show that the large-deformation flow stress curve can be effectively used to improve the spring-back prediction accuracy of ultra-high strength steels.