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LIGA - like 공정으로 제작된 마이크로 터빈의 유한 요소 해석
오재근(J . G . Oh),최범규(B . K . Choi),김낙수(N . S . Kim) 한국센서학회 2000 센서학회지 Vol.9 No.5
N/A The finite element analysis of a micro turbine was made to investigate safety margin of its operating condition for the high aspect ratio nickel micro turbine blades fabricated by conventional LIGA-like method. From our study, we found that the fabricated turbine could not exceed its yield strength even if the pressure difference between inlet and outlet of turbine blade was about 44kPa, and the correlation of friction coefficient and the maximum stress, caused by contact friction between outer diameter of shaft and inner diameter of turbine blade, was somewhat reciprocal. The maximum stress was decreased with the increasing contact friction, when turbine blade was in its state of rotation. By the results of our study, we conclude that it is possible to fabricate metal micro turbine more easily than surface micromachining technology and to operate with no risk of metal structure`s damage, which is caused by yield strength, if the operating condition with the design of micro turbine itself are optimized. It is useful to adopt other applications which have the contact problems between a moving part and the faced one in micro structures.
Plastic Property Identification Using Surface Displacement Field from Vickers Indentation Testing
D. Park(박동휘),N. Kim(김낙수) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
An indentation testing is one of the methods to identify material properties. In this research, a method to identify plastic property of a material using surface displacement field generated from a Vickers indentation testing is proposed. The plastic property is defined using Swift type flow stress curve. Digital image correlation technique is adopted to measure the surface displacement field. Finite element simulations have been conducted to generate a database for the surface displacement field with Swift type flow stress coefficients and the Coulomb friction coefficient. Normalization of the displacement field using indentation load is developed which helps to reduce the size of the database and select the indentation load in the experiment. Al 6061 specimen is adopted to verify the plastic property identification method. Plastic property of Al 6061 is identified using tensile tests. Vickers indentation tests have been done on the same material and its plastic property is extracted from the measured surface displacement fields. The identified Swift flow stress coefficients are compared and the maximum difference is 5.4%.
쇼트피닝 잔류응력이 Leaf Spring의 피로강도에 미치는 영향
배동호(B. H. Bae),손일선(I. S. Sohn),정원석(W. S. Jung),김낙수(N. S. Kim),정원욱(W. W. Jung),박순철(S. C. Park) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Spring is one of major suspension pan of vehicle. Thus, in the process of manufacturing, it is shot-peened to improve its fatigue strength. In this paper, residual stresses by shot peening were calculated through finite element analysis, and the effects of these residual stresses on fatigue strength of leaf spring were evaluated. Fatigue tests were performed with two kinds of specimens, one is actual leaf spring assembly, and another is 3-point bending specimen simply simulated. And all fatigue tests were also performed under the loading condition that was measured on the proving ground. From the results, the maximum load-fatigue life relation of leaf spring was defined, and test results have good agreement between 3 point bending specimen and leaf spring assembly. The effects of residual stresses by shot peening on fatigue strength of leaf spring is not large in the high load range, however, in the low load range, its effects were revealed a little.<br/> <br/>
이승로(S. R. Lee),박준희(J. H. Park),김낙수(N. S. Kim),루카 콸리아토(L. Quagliato) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
본 연구는 링 롤링 공정에서 소요 에너지를 감소시키기 위한 공정 변수 선정 방법에 관한 연구이다. 링 롤링 공정은 이음매 없는 링 모양의 제품을 만드는 공정으로 자동차, 항공 우주 등의 다양한 산업 분야에서 제품 제작에 사용된다. 이때, 에너지 효율과 관리의 측면에서 링 롤링 공정에서 발생하는 에너지를 줄이기 위해 공정 변수를 선정하는 것은 중요하다. 따라서 다양한 공정 변수에 따라 공정에서 발생하는 에너지 값을 계산하기 위한 기계학습 모델을 구현하였다. 이를 최소화 기법의 목적 함수로 활용하여 최종 링 형상과 재료 물성치 변수가 입력되었을 때 에너지를 감소시킬 수 있는 예비성형체 형상 변수와 메인 롤 회전 속도, 만드릴 회전 속도의 공정 변수를 제안하는 알고리즘을 개발하였다. 평형 링 롤링에 개발 알고리즘을 적용하기 위해서, 상용 SW 인 Simufact Forming15를 통해 예비 성형체 형상, 물성, 공정 변수에 따른 하중 영향을 분석하였고 FIOT (Force Integral Over Time)을 정의하였다. 구성된 380 개의 학습 데이터에 대해 기계학습 기법 중 GB (Gradient Boosting) 모델은 평균 오차 3.2%로 FIOT 을 예측할 수 있었다. 구현된 GB 모델을 Differential Evolution 최소화 기법의 목적 함수로 활용하여 42CrMo₄ 소재 750 mm 외경 링 성형에서 FIOT을 감소시킬 수 있는 예비성형체 형상 및 공정 변수를 제안하였다. 다른 변수 조합을 사용 시 FEM에서 계산된 FIOT 과 비교하며 제안된 변수 조합을 검증하였다.