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발전설비용 2.25Cr-1Mo 강의 시효에 의한 기계적 강도 특성 변화에 대한 연구
양현태,김상태,Yang, Hyeon-Tae,Kim, Sang-Tae 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.7
The purpose of this study is to investigate the thermal embrittlement and the mechanical properties of 2.25Cr-1Mo steel aged at high temperature for the extended periods. Original, aged artificiall y and used material were tested to obtain the tensile strength, hardness and impact absorbed energy. Tensile strength, hardness and impact absorbed energy decreased with the increasing aging time. The carbide morphology with the thermal embrittlement was found to contribute to the mechanical property change by X-Ray diffraction method.
SUS-304강 용접부의 잔류응력이 피로균열진전속도에 미치는 영향
이택순,양현태 대한용접접합학회 1997 대한용접·접합학회지 Vol.15 No.4
In the weldmentsm the crack propagation rate is changed due to the residual stress. The crack propagation rate is high in the region with the residual stress. However it shows rhw same behavior with the base metal in the region that does not include the residual stress. The fatigue crack growth rate for the material with residual stresses can be predicted more precisely by using the effective stress ratio. The difference between experimental results and prediction results in the initial stage seems to be due to the redistribution of residual stresses and microstructural change.
스테인리스강 용접부의 잔류응력이 피로특성에 미치는 영향
권종완,양현태 한국공작기계학회 2001 한국생산제조학회지 Vol.10 No.5
In the weldments, the crack propagation rate is changed due to the residual stress. The crack propagation rate is high in the region with the residual stress. However it shows the same behavior with the base metal in the region that does not include the residual stress. The fatigue crack growth rate for the material with residual stresses can be predicted more precisely by using the effective stress ratio. The difference between experimental results and prediction results seems to be due to the redistribution of the residual stresses and microstructural change.
이휘원,양현태,김상태,Lee, Hwi-Won,Yang, Hyun-Tae,Kim, Sang-Tae 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.6
This study presents the hydrogen emblittlement in the metal, which decreases the ductility and then induces the brittle fracture. The contribution deals with the effect of strain rate and notch geometry on hydrogen emblittlement of 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, which are in use at high pressure vessel. Smooth and notched specimens were examined to obtain the elongation and tensile strength. For charging the hydrogen in the metal, the cathodic electrolytic method was used. In this process, current density is maintained constant. The amount of hydrogen penetrated in the specimen was detected by the hydrogen determenator(LECO RH404) with the various charging time. The distribution of hydrogen concentration penetrated in the specimen was obtained by finite element analysis. The amount of hydrogen is high in smooth specimen and tends to concentrate in the vicinity of surface. The elongation and tensile strength decreased with the passage of charging time in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels. The elongation increased and tensile strength decreased as strain rate increased. As a result of this study, it is supposed that 1.25Cr-0.5Mo steel is more sensitive than 2.25Cr-lMo steel in hydrogen embrittlement. Hydrogen embrittlement susceptibility of notched specimen after hydrogen charging is more remarkable than that of smooth specimen.
초음파 시험에 의한 배관용 Cr-Mo강의 피로손상의 비파괴평가
김상태,이희동,양현태,최영근 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.1
재료의 손상을 평가하기 위하여 초음파법에 대한 많은 연구가 진행되었고 널리 사용되고 있으나 대부분 균열의 성장 또는 두께의 감소와 같은 문제에 집중되고 있다. 본 연구에서는 2.25Cr-1Mo 강을 이용하여 반복하중에 의해 재료내부에 발생하는 미시균열을 조기에 감지하고, 피로에 의한 파괴를 미연에 방지할 수 있도록 초음파 표면파의 감쇠와 속도변화를 이용하여 균열길이 측정의 정량적인 평가방법을 제시하였다. 중심주파수 5MHz의 탐촉자를 이용하여 파단수명비 약 60%, 균열길이 약 2mm 정도에서 표면파의 속도 및 감쇠 변화를 탐지할 수 있었다. 고주파 탐촉자를 이요함으로써 미시균열의 발생을 조기에 탐지할 수 있으며, 파단수명을 예측하는 기초자료로 활용할 수 있다. Although the ultrasonic method has been developed and used widely in the fields, it has been used only for measuring the defect size and thickness loss. In this study, the relationship between surface wave attenuation through micro-crack growth and variation of velocity under repeated cyclic loading has been investigated. The specimens are adopted from 2.25Cr-1Mo steel, which is used for power plant and pipeline system, and have dimensions of 200×40×4mm. The results of ultrasonic test with a 5MHz transducer show that surface wave velocity gradually decreases from the point of 60% of fatigue life and the crack length of 2mm with the increasing fatigue cycles. From the results of this study, it is found that the technique using the ultrasonic velocity change is one of very useful methods to evaluate the fatigue life nondestructively.
주원경(W. K. Joo),왕일기(Y. Q. Wang),양현태(H. T. Yang),심창영(C. Y. Sim),송정일(J. I. Song) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The microstructures and mechanical properties of OFHC copper/STKM 11A for D-tube joints brazed using BAg filler metal at 870℃ for 20 minutes in NH₃ atmospheres were performed. Interfacial microstructures were observed in reaction layer. A brazing strength causes of decline with defects of pin hole and base metal by lack of penetration. In tensile test, the properties of joints clearance of 0.01㎜ are better than other joints clearance that has yield strength of elasticity area with the brazing length of 2.5㎜, and also suitable for the case of brazing length of 5.0mm. According to the results of FEA (finite element analysis) on the tensile test, the maximum stress and strain were generated apart from the interface in large deformation. Diffused layer was formed by counter diffusion action of base metal and filler metal layer, and crack between two base metals was not discovered. This is the main reason that fracture of test piece does not appear in copper base metal, and brazing department forms good junctures.