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김대진(D. J. Kim),석창성(C. S. Seok),구재민(J. M. Koo),박재실(J. S. Park),서정원(J. W. Seo),구병춘(B. C. Goo) 한국철도학회 2004 한국철도학회 학술발표대회논문집 Vol.- No.-
Under cyclic loading, the fatigue failures of welded joints occur at weld toes which induce stress concentration by weld shape. So we need to obtain the peak stress and the S-N curve to assess the fatigue strength of welded joints. However the measurement of peak stress is of high uncertainty and low reproducibility, so we use nominal stress instead in fatigue tests of welded joints. In this study, fatigue tests to obtain S-N curves am FE analyses to obtain stress concentration factors were conducted for the two types of cruciform fillet welded joints, that is, load-carrying and non load-carrying types. Then we changed the obtained S-N curves to that based on peak stress using the bot-spot stress concept. From the analyses of the S-N curves obtained, we have concluded that there is a need to develop a new method to evaluate the fatigue life.
김대진(D. J. Kim),위우택(W. T. We),석창성(C. S. Seok),이근호(G. H. Lee),민제홍(J. H. Min) 한국정밀공학회 2006 한국정밀공학회 학술발표대회 논문집 Vol.2006 No.5월
To estimate the fatigue life of flange-shaft assembly, fatigue test for flange material and bending fatigue test for flange-shaft assembly were conducted. Also, finite element analysis for flange-shaft assembly was conducted. Then, we have changed the obtained P-N curve to S-N curve using the finite element analysis results which were stress values at the location of fracture. The S-N curve of flange material itself was almost consistent with that of flange-shaft assembly, so it seems that the fatigue life of flange-shaft assembly could be estimated by using S-N curve for flange material and the stress at the location of fracture calculated by finite element methods.
동적거동을 고려한 자동차용 엔진밸브의 피로특성 평가방법
전남규(N. G. Jun),박기범(K. B. Park),이종민(J. M. Lee),석창성(C. S. Seok) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
자동차용 엔진밸브는 엔진내부에서 배기가스에 의한 고온과 반복인장응력을 받아 피로파괴의 위험이 있으며, 특히 엔진 구조(설치 환경)에 따라 엔진밸브의 동적거동이 결정되는 특징을 가진다. 엔진밸브의 동적거동은 엔진밸브에 가해지는 응력의 양상과 밀접한 상관관계를 가지기 때문에 엔진(밸브트레인)개발 시 엔진밸브의 내구 안전성을 확보하기 위해서는 엔진구조에 따른 엔진밸브의 동적거동과 피로특성에 대한 연구가 필수적이다. 일반적으로 기계부품의 피로특성 평가는 제품의 안전성을 위한 중요한 요소이다. 주기적인 인장응력으로 인해 피로파괴의 위험이 있는 기계부품들의 경우, S-N 선도를 통한 피로수명 평가방법이 일반적이나 자동차용 엔진밸브는 주기적인 인장응력과 더불어 동적거동에 의한 동하중을 받기에 이를 고려한 피로수명평가방법이 요구된다. 이에 본 연구에서는 엔진밸브의 동적거동에 영향을 미치는 주요 설계인자를 도출하여 엔진 구조에 따른 엔진밸브의 동적거동을 운동방정식의 형태로 나타내였으며 밸브헤드와 밸브시트간의 충돌속도에 의해 엔진밸브의 최대충돌응력이 결정됨을 확인하였다. 또한 FEM 해석을 통해 엔진밸브의 운동방정식으로부터 최대충돌응력을 구하고 피로시험을 통해 최대충돌응력-피로수명 관계를 획득하였다. 엔진밸브 설치환경에 따른 엔진밸브의 피로특성을 평가할 수 있는 최대충돌응력-피로수명 모델을 제시하였으며 해당 모델 사용시 엔진밸브의 설치환경이 피로수명에 미치는 영향을 분석할 수 있을 것으로 판단된다. 이를 통해 엔진설계 시 엔진부품의 안전성을 확보하는데 활용될 수 있을 것으로 기대된다.
C.-S. Seok(석창성),D. H. Kim(김담현),J. M. Lee(이종민),N. G. Jun(전남규),K. B. Park(박기범),K. K. Kim(김기근) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
Thermal barrier coating (TBC) is technology applied to gas turbine blades to ensure high-temperature safety. When TBC is exposed to high temperature, thermally grown oxide (TGO) is formed due to degradation. TGO weakens the bonding strength between the top coating and bond coating of TBC and causes breakage. So, technology that can predict the growth behavior of TGO and secure durability of TBC is necessary. However, the prediction of the growth behavior of TGO uses an empirical method for each TBC. This method cannot be universally used due to the disadvantage that empirical formula cannot be used when microstructure of TBC is changed. In this study, an isothermal degradation test was performed under various degradation conditions to predict the growth of TGO of TBC manufactured by the Air Plasma Sprayed (APS) method. As a result of measuring the thickness of TGO, the exponential term of the growth equation was affected by the microstructure of the top coating. And the reaction rate constant k can be derived through the Arrhenius equation. Finally, using the two relationships, an equation for predicting the TGO thickness of TBC manufactured by the APS method was derived.
석창성(C. S. Seok),박홍선(H. S. Park),허용(Y. Huh),김재훈(J. H. Kim),이영민(Y. M. Lee) 한국정밀공학회 2006 한국정밀공학회 학술발표대회 논문집 Vol.2006 No.5월
A brake disk in railway vehicle is safety part. Requirements not only in performance but also in comfort, serviceability and working lifetime are high and rising. In this study , we carried out fatigue test and thermal stress analysis. To determine a pressure distribution, contact pressure analysis precede thermal stress analysis. Especially, characteristics of the brake disk were analyzed in considering intial velocity, and thickness of a frictional plate. Form the comparing the results of experiment and FEM analysis, fatigue characteristic and fatigue life assessment ofr a brake disk of railway vehicle were performed.
CF8M 주조 오스테나이트 스테인리스강의 열취화에 따른 재료물성치 평가
김철(C. Kim),방흥배(H. B. Park),진태은(T. E. Jin),정일석(I. S. Jeong),석창성(C. S. Seok),박재실(J. S. Park) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
CF8M cast austenitic stainless steel is used for several components such as primary coolant piping,<br/> elbow, pump casing, and valve bodies in light water reactors. These components are subject to thermal<br/> aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the<br/> delta-ferrite leading to increased strength and decreased toughness. In this study, three kinds of the<br/> aged CF8M specimen were prepared using an artificially simulated aging method. The objective of this<br/> study is to summarize the method of estimating ferrite contents, Charpy impact energy and J-R curve,<br/> and to evaluate the thermal embrittlement of the CF8M cast austenitic stainless steel piping used in the<br/> domestic nuclear power plants.