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김민철(M. C. Kim),정완진(W. J. Chung),김종호(J. H. Kim),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
In this paper, a finite element approach to analyzing a deep piercing process is presented. In the approach, the element deletion scheme after the element degradation scheme is employed to predict the piercing phenomenon because the time interval between the piercing initiation time and the final stroke is quite large. The normalized Cockcroft-Latham damage model is used and an assumed flow stress smoothing function is used to reflect the effect of cumulative damage on the flow stress. The approach is applied to a deep piercing process and the predictions are compared with experiments in terms of plastic deformation of the whole process. The comparison shows a good agreement with each other.
가정한 금형 온도를 이용한 소성가공 공정의 근사 비등온해석
김민철(M. C. Kim),김봉수(B. S. Kim),전만수(M. S. Joun) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.5
In this paper, an efficient and approximate approach to non-isothermal analysis of metal forming processes is presented. In the approach, nodal temperature at the point on a die is assumed as a function of temperature drop of the corresponding material point and thus the iteration between material and dies to obtain their temperature can be removed, which increases a lot of computational time. The approach is evaluated comparing the predictions of a 3D upsetting process obtained by the presented approach and the normal predictions obtained by the common capabilities of AFDEX 2D and 3D.
고온 및 상온에서의 소재 유동응력 획득 프로그램 AFDEX /MAT
김민철(M. C. Kim),전만수(M. S. Joun) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.10
In this study, AFDEX /MAT, an acquisition program of flow stress of material at the room or elevated temperature is presented. The flow stress at the room temperature is calculated from a simple tensile test of cylindrical specimen using an iterative algorithm of obtaining flow stress at the large strain which meets well with the experimental tensile test. The flow stress at the elevated temperature is obtained from hot compression tests at the sampled temperatures and strain rates using the least square approximation to minimize the difference between the experiments and fitted mathematical models. The improved user interface is introduced and application examples are given, which shows the applicability of the program for learned users.
전기자동차용 알루미늄 밧데리케이스 충격후방압출공정 해석을 위한 마찰에 관한 고찰
김민철(M. C. Kim),이민철(M. C. Lee),이민철(M. C. Lee),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
In this paper, appropriate frictional law and conditions for predicting the cold impact backward extrusion process of an aluminum battery case of electric vehicles are presented. Some limitations in simulating the battery case backward extrusion process using finite element method are explained with emphasis on mesh effects and frictional phenomena. A hybrid frictional law is proposed to simulate battery case backward extrusion, based on the investigation into the frictional flow marks on the internal bottom.
긴 단조품의 측방향 열간 단조공정 중 금형의 실용적 구조해석 기술에 관한 연구
김민철(M. C. Kim),엄재근(J. G. Eom),박건형(G. H. Park),강신길(S. G. Kang),정순종(S. J. Jung),전만수(M. S. Joun) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
In this paper, a useful two-dimensional finite element approach is applied to structural analysis of dies in hot lateral forging of long parts. Three-dimensional forging simulation and die structural analysis are conducted for an aluminum hot forging process of the front lower control arm of an automobile and their results are criticized in terms of application for improving designs of process or die. Two dimensional approach for engineering design is proposed especially for prediction of stress concentration with higher accuracy when the material is long compared to its diameter and it is applied to the process to solve the local problem. It is shown that the predictions of two dimensional approach is very close to those of three-dimensional approach if the velocity Component normal to the plane selected for two dimensional analysis is negligible.
냉간전방압출공정 중에 발생한 중심파괴 현상의 유한요소해석
김민철(M. C. Kim),이추실(Q. S. Li),손요헌(Y. H. Son),윤덕재(D. J. Yoon),전만수(M. S. Joun) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
In this paper, a new scheme for simulating the central bursting defect formation occurred during cold forward extrusion is presented. The scheme is implemented onto AFDEX 2D, based on a rigid-thermoviscoplastic finite element method. A element removal scheme after separating or cracking the damaged neighboring elements along the element boundary is proposed. Fracture model with fracture criterion are introduced considering both cumulative damage and the maximum principal stress. The results show that more realistic shape of the chevron crack was obtained with the new criterion.
역전파 신경회로망을 이용한 피로손상 모델링에 관한 연구
김민철(M.C.Kim),주원식(W.S.Joo),장득열(D.Y.Jang),조석수(S.S.Cho),김순호(S.H.Kim) 한국자동차공학회 1998 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1998 No.11_2
Back-propagation neural networks performs computer simulations that have the potential to find the same patterns that fatigue practitioners recognize to relate experimental results to fatigue life prediction. This potential was used to construct neural networks to recognize the relation between da/dN, N/Nf, X-ray diffraction half-value breadth ratio B/Bo, fractal dimension D_f and fracture mechanical parameters for Al 2024-T3 alloy. Learning and generalization of neural networks was optimized by floating rate method. This study shows that neural networks has ability to predict fatigue crack growth rate and life on data of unlearned experimental condition.<br/>