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크리이프-피로 상호작용하의 균열성장속도 예측에 관한 연구
주원식(Won-Sik Joo),조석수(Seok-Swoo Cho) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.2
High temperature low cycle fatigue shows that cycle-dependent crack growth owing to cyclic plastic deformation occurred simultaneosly with-dependent crack growth owing to intergranular deformation. Consequently, to estimate crack growth rate uniquely, many investigators have proposed various kinds of parameters and theories but these could not investigators have proposed various kinds of parameters and theories but these could not produce satisfactory results. Therefore the goal of this study is focused on prediction of crack growth rate using predominant damage rule, linear cumulative damage rule and transitional parameter △Jc/△Jf. On the basis of these background, high temperature fatigue crack growth tests were carried out under sinusoidal loading waveform at 600℃ and 700℃.
역전파 신경회로망을 이용한 피로 균열성장 모델링에 관한 연구
주원식(Won-Sik Joo),조석수(Seok-Swoo Cho) 한국해양공학회 1996 韓國海洋工學會誌 Vol.10 No.1
Up to now, the existing crack growth modelling has used a mathematical approximation but an assumed function have a great influence on this method. Especially, crack growth behavior that shows very strong nonlinearity needed complicated function which has difficulty in setting parameter of it. The main characteristics of neural network modeling to engineering field are simple calculations and absence of assumed function. In this paper, after discussing learning and generalization of neural networks, we performed crack growth modelling on the basis of above learning algorithms. J'-da/dt relation predicted by neural networks shows that test condition with unlearned data is simulated well within estimated mean error(5%).
운전하중하의 레인플로집계법을 이용한 화차 대차의 피로누적손상과 수명예측
전주헌(Joo Heon Jeon),백석흠(Seok Heum Baek),이경영(Kyoung Young Lee),조석수(Seok Swoo Cho),주원식(Won Sik Joo) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Endbeam is an important structural member of freight bogie for the support of service loading. In general, more than 25 years' durability is necessary. However, endbeam occur fatigue fracture in dynamic stress concentration location because comparatively strength and stiffness are low. Therefore, structure analysis is performed to evaluate structural problem of endbeam and local strain range as durability analysis. The number of cycles is extracted concerning the bogie in operation by measurement dynamic stress time history on critical part which is crack initiation in actual fact. At this time rainflow cycle counting is used to consider change of stress for operating condition. Based on the fatigue life curves and the stress analysis, the fatigue life of the endbeam is predicted and compared with the experimentally determined fatigue life, resulting in a fairly good correlation.
2004-T3 AI합금의 표면미소균열 분포특성과 잔존수명평가법에 관한 연구
안원기(Won Kee An),주원식(Won Sik Joo),장득열(Deuk Yul Jang),박수열(Soo Young Park),조석수(Seok Swoo Cho) 한국자동차공학회 1996 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1996 No.11_1
The fracture of a structure, machine, machine part comes of surface micro-crack initiated and propagated at the root of notch, where the stress is high. Irregular distribution characteristics of micro-crack on the basis of elastic-plastic fracture mechanics doesn't predict exactly remaining life of them. It is thought that maximum micro-crack length represents the total fatigue damage because fatigue can be characterized as a progressive failure phenomenom that proceeds by the propagation and coalescence of micro-cracks to an unstable size. The maximum micro-crack length in an area larger than the sample area can be estimated by statistics of extremes. Therefore, the remaining life of components can be accurately predicted using the distribution of micro-crack length in critical areas and the fatigue damage model.<br/>
AFM과 FEH을 이용한 저압 터빈 블레이드의 파손해석에 관한 연구
홍순혁,조석수,주원식,Hong, Soon-Hyeok,Cho, Seok-Swoo,Joo, Won-Sik 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.11
Mechanical component has striation with constant width and SEM can estimate fracture type and loading condition. SEM has benefit to fatigue fracture analysis but striation can be observed according to the kind of material and range of crack growth rate and can't. In this case, it needs AFM that can measure 3-dimensional surface profile with resolution of atomic size. In this study. to find fracture reason of torsion-mounted blade in nuclear plant, we estimate the relation between stress intensity factor range and root mean square roughness in 12% Cr steel by AFM and predict in-service loading condition of turbine blade. failure analysis is performed by finite element method and Goodman diagram on torsion-mounted blade.
X선 잔류응력을 이용한 냉간압연강의 피로손상 모델링에 관한 연구
조석수(Seok-Swoo Cho),주원식(Won-Sik Joo) 한국해양공학회 1999 韓國海洋工學會誌 Vol.13 No.4
Cold rolled steel has much plastic strain in the material surface produced by manufacturing process. The strain causes the variation of surface residual stress, in which influences the fatigue behavior under repeated loading. As experimental results, it was confirmed that the behavior of residual stress σr with cycle N consisted of three stages except stress amplitude near fatigue limit in SPCC steel. On the first stage compressive residual stress decreased rapidly, on the second stage gradually, and on the last stage slightly. The relation between σr and log N appeared linear behavior except the early part of cycle ratio N/Nf. The average gradient of σr with respect to log N seemed to take a constant value without initial cycle ratio. On the other hand, the Nf line was regressed by the first-order polynomial equation on σr-log Nf diagram. Therefore, this study showed that both the gradient of σr with respect to log N and the Nf line was useful in predicting the cycle ratio N/Nf
창의적 문제해결 이론을 이용한 소성역깊이 측정에 관한 연구
이동우(Dong-Woo Lee),주원식(Won-Sik Joo) 한국기계가공학회 2008 한국기계가공학회지 Vol.7 No.1
Machine parts subjected to fluctuating or cyclic loads induce repeated stresses that often result in failure by fatigue. In such cases, the fatigue failures unfortunately sometimes occur. These may arise from a lack of knowledge with regard to the design, fabrication and operation of the machines or structures. The failure analysis provides valuable information regarding the prevention of similar failures. Furthermore, this information will be useful to improve or to develop new products. Failure stress analysis is classified into X-ray fractography. X-ray fractography has the limited applications because of material crystal size, difficult measurement method, electrolytic polishing precision, and long test time. Therefore, this study proposed the new method to improve the measurement precision of plastic zone depth and test time using TRIZ.
실험계획법과 수리적방법을 이용한 이산설계 공간에서의 다목적 최적설계
이동우,백석흠,이경영,조석수,주원식,Lee, Dong-Woo,Baek, Seok-Heum,Lee, Kyoung-Young,Cho, Seok-Swoo,Joo, Won-Sik 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.10
A recent research and development has the requirement for the optimization to shorten design time of modified or new product model and to obtain more precise engineering solution. General optimization problem must consider many conflicted objective functions simultaneously. Multi-objective optimization treats the multiple objective functions and constraints with design change. But, real engineering problem doesn't describe accurate constraint and objective function owing to the limit of representation. Therefore this study applies variance analysis on the basis of structure analysis and DOE to the vertical roller mill fur portland cement and proposed statistical design model to evaluate the effect of structural modification with design change by performing practical multi-objective optimization considering mass, stress and deflection.