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Gurson모델을 사용한 전자기성형의 성형성 개선에 대한 연구
김정(Jeong Kim),송우진(Woojin Song),강범수(Beomsoo Kang) 한국자동차공학회 2013 한국 자동차공학회논문집 Vol.21 No.3
The effect of the tool-sheet interaction on formability enhancement in electromagnetic forming is investigated using FEM. A free bulging and a conical forming die with 0.7㎜ AL1050 sheet are used to evaluate damage evolution based on Gurson-Tvergaard-Needleman plasticity material model. The impact between the tool and sheet results in complex stress states including compressive hydrostatic stresses, which leads to a suppression of void growth and restrain ascending void volume fraction of the sheet. Therefore, the damage suppression due to the tool-sheet interaction can be the main factor contributing to the increased formability in the electromagnetic forming process.
Model parameter identification of the Hansel-Spitttel flow stress equation by statistical regression
Kyunghoon Lee(이경훈),Woojin Song(송우진) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
For forming simulation flow stress modeling is imperative in emulating the mechanical behavior of a material of interest. Flow stress models are typically determined by model parameter identification via least squares methods. Instead, this research tackles the same problem of model parameters identification by statistical regression. To determine the parameters of a flow stress model, this research presumes an additive noise model for experimental strain and stress measurements in a log space. Based on a probabilistic formulation, this research draws on the method of maximum likelihood to derive the parameters of a flow stress model. For illustration, we used the Hansel-Spittel flow stress equation with strain and stress measurements of AA1070 aluminum alloys. We found that the fitted Hansel-Spittel flow stress model agrees well with the strain and stress measurements.
우민아(Mina Woo),노학곤(Hakgon Noh),송우진(WooJin Song),강범수(Beomsoo Kang),김정(Jeong Kim) 한국자동차공학회 2017 한국 자동차공학회논문집 Vol.25 No.2
Electrohydraulic forming is a high-speed forming process that deforms a blank using electric discharge in liquid. When high voltage is discharged in the water, a shock wave is propagated from the tip of the electrodes to the blank, causing the blank to be deformed into the die. Electrohydraulic forming has many advantages including improved formability and reduced bouncing effect and springback. The objective of this paper was to conduct a feasibility study to identify the electrohydraulic effect. An electrohydraulic forming apparatus was developed and experiments were carried out. The results of the experiment showed that the developed apparatus had sufficient energy to deform the blank into the die. Using the hole to emit residual air in the die was more effective than using the vacuum pump in terms of saving on experiment time.
Study on Performance Prediction of Electric Propulsion System for Multirotor UAVs
정진석(Jinseok Jeong),변영섭(Youngseop Byun),송우진(Woojin Song),강범수(Beomsoo Kang) Korean Society for Precision Engineering 2016 한국정밀공학회지 Vol.33 No.6
This paper describes a study of performance prediction of an electric propulsion system for multirotor UAVs. The electric propulsion system consists of motors, propellers, batteries and speed controllers, and significantly affects performance characteristics of the platform. The performance of the electric propulsion system for multirotor UAVs was predicted using an analytical model derived from the characteristics of each component, operation experiments and statistical analyses. Ground performance tests and endurance flights were performed to verify the reliability of the proposed performance prediction method. A quadrotor platform was designed to demonstrate the parcel delivery service used in the endurance flight. From the result of verification tests, it was confirmed that the proposed method has a good agreement.