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분자동역학을 이용한 고변형률하에서 결함으로 인한 저장에너지 계산에 관한 연구
유한규(Han-Kyu Ryu),최덕기(Deok-Kee Choi) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
This psper addresses a theoretical study to calculate the amount of the stored energy due to vacancies during high-stain-rate deformation. The study concerns the role of excess vacancies, which can play an important role to increase the amount of stored energy. Molecular dynamics simulation using a 3D model is carred out and the result clearly shows that the excess vacancies are are credited to generation of the stored stored energy.
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고변형률 변형하에서 재료 내부의 온도상승 계산을 위한 재료 모델링
최덕기(Deok-Kee Choi),유한규(Han-Kyu Ryu) 한국항공우주학회 2004 한국항공우주학회지 Vol.32 No.7
고속으로 비행하는 물체가 다른 물체와 충돌하는 경우에는 극히 짧은 시간에 커다란 변형이 일어나게 된다. 고변형률 변형(high-strain-rate deformation)에서는 소성변형이 일어나면서 상당한 열을 발생시키고 재료의 온도를 상승시킨다. 온도의 상승은 재료의 동적인 물성에 많은 영향을 미치게 되므로, 변형 시의 온도상승을 예측하는 것은 매우 중요하다. 변형시의 온도상승은 주로 전위( dislocation)의 움직임과 공공(vacancy)으로 인한 재료내의 저장에너지와 밀접한 관계를 갖게되므로, 저장 에너지의 양을 파악하는 것은 매우 중요하다. 고변형률 변형시 전위가 빠르게 움직이면서 평형상태에서의 경우보다 많은 과공공(excess vacancies)을 발생시키게 된다. 본 논문에서는 과공공을 포함하는 미시적 재료 모델을 구성하고 분자동역학(molecular dynamics, MD) 기법을 사용하여 면심입방격자(fcc) 구조를 가지는 재료(구리)에 대한 저장 에너지를 계산하였다. High velocity impacts are accompanied with large deformations, which generate a large amount of heat due to plastic works, resulting in a significant temperature rise of the material. Because the elevated temperature affects the dynamic properties of materials, it is important to predict the temperature rise during high-strain-rate deformations. Both existing vacancies and excess vacancies are credited to the stored energy, yet it is difficult to distinguish one from another in contribution to the stored energy using macroscopic level materials models. In this study, an atomistic material model for fcc materials such as copper is set up to calculate the stored energy using molecular dynamics (MD) simulations. It is concluded that excess vacancies play an important role for the stored energy during a high-strain-rate deformation.
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정상 척추체 모델을 이용한 척추측만증 모델 자동 생성 프로그램 개발
김영은(Young Eun Kim),유한규(Han Kyu Ryu) Korean Society for Precision Engineering 2006 한국정밀공학회지 Vol.23 No.3
Unexpected postoperative changes, such as growth in rib hump and shoulder unbalance, have been occasionally reported after corrective surgery for scoliosis. However there has been neither experimental data for explanation of these changes, nor the suggestion of optimal correction method. Therefore, the numerical study was designed to investigate the post-operative changes of vertebral rotation and rib cage deformation after the corrective surgery of scoliosis. A mathematical finite element model of normal spine including rib cage, sternum, both clavicles, and pelvis was developed with anatomical details. In this study, we also developed a special program which could convert a normal spine model to a desired scoliotic spine model automatically. A personalized skeletal deformity of scoliosis model was reconstructed with X-ray images of a scoliosis patient from the normal spine structures and rib cage model. The geometric mapping was performed by translating and rotating the spinal column with an amount analyzed from the digitized 12 built-in coordinate axes in each vertebral image. By utilizing this program, problems generated in mapping procedure such as facet joint overlapping, vertebral body deformity could be automatically resolved.
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3차원 분자 모델을 사용한 재료내의 저장 에너지 계산에 관한 연구
최덕기,유한규 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.5
This paper addresses a theoretical approach to calculate the amount of the stored energy during a deformation using atomistic level simulation. During a deformation, only a small percent of the energy input is stored in the material, and most of input energy is converted into heat. The cause of the temperature rise within materials is traditionally credited to dislocations, vacancies and other defects. An atomistic material model for fcc such as copper is used to calculated the stored elastic energy. The potential energy is obtained by a molecular dynamics (MD) simulation. Two different states are considered for comparison: one is a perfect state and the other is a state with dislocations. The calculated potential energies in these two states are compared. The difference in the potential energies is considered the amount of the stored elastic energy of dislocations. The conversion factor, i.e., the fraction of the input energy that is stored as elastic energy within a material is then calculated. (Received December 22, 2003)
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