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- 저자 : 최민국(M. K. Choi) (검색결과 5 건)
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최민국(M. K. Choi),허훈(H. Huh) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.5
Sheet metal forming processes induce residual stress in the final product due to the plastic deformation. The residual stress leads elastic recovery of the formed part called springback which causes shape error in final product. Evaluation of the amount of springback becomes important for high strength steels since the amount of springback becomes significant. Strain rate is known to be an important parameter to influence the hardening behavior of sheet metals. A blank sheet experiences a wide range of strain rates during the forming process since the punch progresses with the velocity of several m/s to form the product. This paper deals with the experimental investigation of the effect of the forming speed on the amount of springback in U-bending process of high strength steel sheets. U-bending tests were conducted for springback evaluation at different forming speeds with the geometry adopted from the NUMISHEET ‘93 benchmark problem. For the U-bending tests, INSTRON8801 dynamic materials testing machine and a newly designed U-bending jig were used to conduct U-bending tests at different forming speeds. Experimental results show that the amount of springback increases as the forming speed increases.
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상관관계를 고려한 AZ31 합금 판재의 동적인장물성 측정불확도평가
최민국(M. K. Choi),허훈(H. Huh),김창근(C. G. Kim),채균식(K. S. Chae) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
In the last years, a growing interest of lightweight vehicle design could be observed in the automotive industry. This trend is related to an increasing interest in substituting steel parts by lightweight material such as magnesium alloy. However, evaluation of the crashworthiness should be considered for lightweight vehicle as crash safety becomes more stringent. In order to evaluate the crashworthiness of auto-body structure, finite element methods has been conducted for crash analysis. Generally, strain rates distribution of auto-body structure in the car crash is ranging from 0.001/s to 500/s. Since the material properties depend on the strain rates, the dynamic behavior of magnesium alloy sheet must be examined and applied to the finite element model appropriately. This paper is concerned with the evaluation of standard uncertainty of high speed tensile properties of AZ31 sheet considering correlation effect during the measurement. Standard uncertainty of the true stress is evaluated considering sources of uncertainties of input quantities and their associated sensitivity coefficients using modified uncertainty evaluation model considering correlation. The results show that the standard uncertainty decreases when correlation is applied to uncertainty evaluation procedure.
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U-bending에서의 DP780 강판의 스프링백 거동 연구
최민국(M. K. Choi),허훈(H. Huh) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
Sheet metal forming processes induce residual stress in the final product due to the plastic deformation. The residual stress leads elastic recovery of the formed part called springback which causes shape errors in final product. This error becomes serious especially for high strength steels which are widely used in auto-body structures, then the evaluation of the amount of springback becomes important for high strength steels. This paper investigates the spring back behavior of DP780 steel sheets after the U-bending process using the geometry of the standard U-shape from NUMISHEET’93. The amounts of springback were measured with the variation of the blank holding force, forming speed and material anisotropy.
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영상 프레임 분석을 통한 대용량 캡슐내시경 영상의 지능형 판독보조 시스템
이현규(H. G. Lee),최민국(M. K. Choi),이돈행(D. H. Lee),이상철(S. C. Lee) 한국지능정보시스템학회 2009 지능정보연구 Vol.15 No.2
Capsule endoscopy is one of the most remarkable inventions in last ten years. Causing less pain for patients, diagnosis for entire digestive system has been considered as a most convenience method over a normal endoscope. However, it is known that the diagnosis process typically requires very long inspection time for clinical experts because of considerably many duplicate images of same areas in human digestive system due to uncontrollable movement of a capsule endoscope. In this paper, we propose a method for clinical diagnosticians to get highly valuable information from capsule-endoscopy video. Our software system consists of three global maps, such as movement map, characteristic map, and brightness map, in temporal domain for entire sequence of the input video. The movement map can be used for effectively removing duplicated adjacent images. The characteristic and brightness maps provide frame content analyses that can be quickly used for segmenting regions or locating some features(such as blood) in the stream. Our experiments show the results of four patients having different health conditions. The result maps clearly capture the movements and characteristics from the image frames. Our method may help the diagnosticians quickly search the locations of lesion, bleeding, or some other interesting areas.
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