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미소 비커스경도에 의한 Cr-Mo-V강의 경년열화 평가
김정기,남승훈,김엄기 ( Jung Ki Kim,Seong Hoon Nahm,Am Kee Kim ) 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.1
Since Cr-Mo-V steel has excellent fracture and creep properties at elevated temperature, they are extensively used as steam turbine components such as the turbine rotor. However, the turbine rotor steel used to suffer material degradation during long term service. Therefore, the assessment of the safety and residual life of the turbine rotor is periodically required during service. One of the most convenient techniques for that is the hardness method mainly due to its simplicity and nondestructive characteristics. In this research, six specimens with different aging times of turbine rotor steel were artificially prepared by an isothermal heat treatment at 630℃. The micro Vickers hardnesses of specimens were measured at room temperature. The relationships between the fracture properties and the hardness ratio were investigated. And also an indirect method to evaluate the residual life of degraded turbine rotor was proposed based on the micro Vickers hardness measurement.
무한 평면체에 존재하는 복수 표면균열의 성장에 대한 수명예측용 시뮬레이션 개발에 관한 연구
황남성(Nam-Seong Hwang),서창민(Chang-Min Suh),남승훈(Seung-Hoon Nahm) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.4
The social demand urges us to use some equipments and structures in high temperature environment. By this occasion, the necessity of studying the fatigue crack growth is an important aspect of new materials. However, the present situation is rarely to accumulate the fatigue data. Especially, 1Cr-1Mo-0.25V steel and 304 stainless steel have been increased to be used under the severe condition of high temperature. And so, the fatigue estimation of those materials is important and appropriate.<br/> Fatigue tests have been carried out to examine the crack initiation, growth behaviour for the small fatigue crack of 1Cr-1Mo-0.25V steel and 304 stainless steel at room temperature and 538℃.<br/> The remote measurement system which has many merits of checking and saving the image for detailed examination was applied to closely detect the crack length.<br/> Generally, the fatigue crack initiated in the form of multiple cracks and grew each other. And then it coalesced to become a major crack. The major crack governed the rest of the fatigue life. In the growing process, each peripheral cracks interact and grow for a certain period. After then, it coalesced and fractured.<br/> On the basis of the above experimental data for the small crack, a simulation program was developed to predict the residual life time and to estimate the integrity of machine elements and structures. At the same time, the simulation was extended to 1Cr-1Mo-0.25V steel. The simulation results have shown a good agrement to those of the experimental ones for both materials of 1Cr-1Mo-0.25V steel and 304 stainless steel with small cracks. The NASCRAC has applied to compare the fatigue life with the experimental results. And so, it can be said that the simulation program is valuable tools to the industrial fields.
전기전도도를 이용한 Al-Si-Cu-Mg 합금 폼의 기계적 압축 특성 평가
이창훈(Chang-Hun Lee),김엄기(Amkee Kim),하산(Md Anwarul Hasan),남승훈(Seung-Hoon Nahm),조성석(Seong-Seock Cho) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Electrical conductivity of Al-Si-Cu-Mg alloy foams of various density produced in powder metallurgical method has been measured using two probe electrical conductivity measurement method. Compressive mechanical properties such as elastic modulus and plastic plateau stress of foams were evaluated from electrical conductivity using power law relation and scaling laws of foam properties. Uni-axial compression test was also performed. Experimentally measured elastic modulus and plastic plateau stress were compared with the values evaluated from electrical conductivity. The computed values were in good agreement with the experimental result.