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Application of Ductile Fracture Criteria for the FLD Prediction of Steel Sheets
Yanshan Lou,Soekbong Kim,Younki Ko,Hoon Huh 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
This paper applies ductile fracture criteria for the formability prediction of various types of steel sheets to evaluate the accuracy of ductile fracture criteria on the prediction of forming limit diagrams (FLDs). The ductile fracture criteria studied in this paper include the Cockcroft criterion (1968), the Brozzo criterion (1972), the Oh criterion (1979), the Oyane-Sato criterion (1980), the Clift criterion (1990) and the Ko-Huh criterion (2007). The material properties and the experimental FLDs of 24 kinds of steel sheets are collected from researchers. Hosford79 yield function with normal anisotropy is utilized to model the yield surfaces of these steel sheets. The Hollomon equation is employed to describe the strain hardening behaviors. The material constants in the ductile fracture criteria are evaluated with the limited strains in the uniaxial tension state for Cockcroft criterion, Brozzo criterion, Oh criterion, Clift criterion and Ko-Huh criterion while the limit strains in both the uniaxial tension and plane strain tension conditions are used for the material constant evaluation in Oyane-Sato criterion. The FLDs are predicted with these ductile fracture criteria with linear strain paths. The predicted FLDs are compared with experimental data. The results show that the FLDs predicted from Oyane-Sato and Ko-Huh ductile fracture criteria match the experimental data well for the LHS FLDs while other ductile fracture criteria overestimate the limited strain in plane strain tension conditions. For the right hand side FLDs, all these ductile fracture criteria do not perform well compared with experimental FLDs.
Comparative Study of the Ductile Fracture criteria on the Prediction of FLDs for Aluminum Alloys
Yanshan Lou,Hoon Huh,Younki Ko,Jiwoong Ha 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
This paper evaluates the performance of ductile fracture criteria on the prediction of forming limit diagrams (FLDs) of aluminum alloys. The ductile fracture criteria in this study include Cockcroft-Latham criterion (1968), Brozzo criterion (1972), Oh criterion (1979), Oyane-Sato criterion (1980), Clift criterion (1990) and Ko-Huh criterion (2007). The material properties and the experimental FLDs of 30 kinds of aluminum alloys are collected from researchers. Hosford79 yield function with normal anisotropy is applied. The Hollomon equation is utilized to describe the stress-strain relation of aluminum alloys. The experimental FLDs on the left hand side (LHS) are fitted linearly and the fitted straight line is applied to determine the limited strains of uniaxial tension and plane strain conditions. The material constants in the ductile fracture criteria are evaluated with the limited strains of uniaxial tension and plane strain tension conditions. The FLDs are predicted with these ductile fracture criteria with linear strain increment. The predicted FLDs are compared with experimental data. The results show that the FLDs predicted from Oyane-Sato and Ko-Huh ductile fracture criteria match the experimental data well for the LHS FLDs while other ductile fracture criteria overestimate the limited strain of LHS FLDs. For the right hand side FLDs, all these ductile fracture criteria do not perform well compared with experimental FLDs.
PAB 모듈 적용 고분자소재의 내환경 물성 특성 변화에 관한 연구
고윤기(Younki Ko),정선경(Sunkyoung Jeoung),유승을(Seungeul Yoo),곽성복(Sungbok Kwak),김정현(Jeounghyun Kim) 한국자동차공학회 2012 한국자동차공학회 부문종합 학술대회 Vol.2012 No.5
In the interior parts of the vehicle, the plastic material is popularly used in the economical and emotional aspects of passengers. The plastic component lies in the harsh environment such as high temperature, humidity variation and direct sun light. These environmental factors affect to the material characteristics and life time of plastic components in the vehicle. In this paper, the material test for the specimens made from the plastic used in the dash board in the vehicle, is carried out after aging in the various condition of temperature, humidity and ultraviolet rays. In order to investigate the aging effect on the environmental factors, the elastic modulus and stress-strain curve are obtained from the tensile tests.
철도 차량용 티어링 튜브의 충돌 에너지 흡수 능력 예측 기법
고윤기(Younki Ko),안광현(Kwanghyun Ahn),허훈(Hoon Huh),최원목(Wonmok Choi),정현승(Hyunseung Jung),권태수(Taesoo Kwon) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
This paper deals with the numerical prediction of energy absorbing capacity of a tearing tube, which can absorb the crash energy through expanding and axial splitting process. It is important to consider the dynamic material behavior and fracture characteristics of tube material in order to simulate accurately the deformation behavior of tearing tube. Therefore, uniaxial tensile tests are performed in order to obtain the flow stress curve and fracture strain of tube material according to strain rate. Quasi-static tensile tests were conducted at the strain rate ranged from 0.001/sec to 0.01/sec using the static tensile machine(Instron 5583). Dynamic tensile tests were conducted at the strain rate ranged from 0.1/sec to 300/sec using the high speed material testing machine. These dynamic material properties are applied to finite element analysis through user material subroutine. Especially, ductile fracture criterion is applied in order to describe the fracture characteristics of tube material during axial splitting process. Dynamic tearing process is simulated and the simulated result is compared with the experimental result in dynamic tearing test. The simulated results predict accurately the onset of fracture in axial splitting process and the energy absorption capacity has a good agreement with experimental result.
충격 및 바운스 특성 양상을 위한 HEV-Relay의 설계
고윤기(Younki Ko),조상순(Sangsoon Cho),허훈(Hoon Huh),이상엽(Sangyoeb Lee),박홍태(Hongtae Park),오일성(Ilsung Oh) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
A HEV-relay plays a significant role as a mechanical switch which determines the operation of a gasoline engine or an electric motor in a hybrid electric vehicle (HEV). The HEV-relay has critical two problems in the operating process. First, the unstable current can occur in the operating process of the HEV-relay due to the severe bounce between moving and fixed electrode. Second, noises occur due to impact between electrodes in HEV-relay. In this research, spring properties such as stiffness and initial compression force, and electrode shape are designed to reduce the bounce time and noises caused by impact between moving and fixed electrode. The operating process of HEV-relay is simulated using LS-DY□A3D as explicit finite element code. The optimum spring properties are determined using the response surface method (RSM) as the design methodology, and the electrode shape is newly designed through the modifying the stiffness of moving and fixed electrode.