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RISS 인기검색어
- 검색키워드
- 저자 : Woo Gon Kim(김우곤) (검색결과 165 건)
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참조응력을 이용한 316LN 스테인리스강의 크리프 해석
김우곤,류우석,Kim, Woo-Gon,Ryu, Woo-Seog 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.10
Creep damage using a reference stress(RS) was analyzed for type 316LN stainless steel. The generalized K-R equation was reconstructed into the RS equation using a critical stress value $\sigma$. The RS equation was derived from the critical stress in failure time $t_f$ instead of material damage parameter $\omega$, which indicates the critical condition of collapse or approach to gross instability of materials during creep. For obtaining the reference stress, a series of creep tests and tensile tests were conducted with at 55$0^{\circ}C$ and $600^{\circ}C$. The stress-time data obtained from creep tests were applied to the RS equations to characterize the creep damage of type 316LN stainless steel. The value of creep constant r with stress levels was about 18 at 55$0^{\circ}C$ and 21 at $600^{\circ}C$. This value was almost similar with r = 24 in the K-R equation, which was obtained by using damage parameter $\omega$. Relationship plots of creep failure strain and life fraction $(t_f /t_r)$ were also obtained with different λ values. The RS equation was therefore more convenient than the generalized K-R equation, because the measuring process to quantify the damage parameter $\omega$ such as voids or micro cracks in crept materials was omitted. The RS method can be easily used by designers and plant operator as a creep design tool.
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UNS N06690 제1열 시제전열관의 U-굽힘성형에서 형상변화와 표면잔류응력
김우곤,장진성,국일현,주진원,김성청,Kim, Woo-Gon,Jang, Jin-Sung,Kuk, Il-Hiun,Joo, Jin-Won,Kim, Sung-Chung 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.1
Surface residual stresses as well as wall thickness and ovality changes after U-bending process on UNS N06690 row-1 heat exchanger tubes, were estimated. Surface residual stresses were measured by Hole Drilling Method(HDM), calculating the stresses from relieved strains of 3 rosette strain gages. After bending of the tubes, dimensional tolerances for wall thickness and ovality were satisfied with ASTM requirements. Residual stresses at the extrados were introduced with compressive stress(-) by bending operations, and its maximum value reached-319 MPa in axial direction at ${\phi}=0^{\circ}$ in position. Tensile residual stresses(+) of ${\sigma}_zz=45$ MPa,${\sigma}_zz=25$ MPa were introduced in the intrados surface at position of ${\phi}=0^{\circ}$ Maximum tensile residual stress of 170 MPa was detected on the flank side at position of ,${\phi}=95^{\circ}$i.e., at apex region. It appeared that higher stress gradients were generated at the irregular transition regions. In the trend of residual stress changes with U-bend position, the extrados is related with the changes of ovality and the intrados is related with the changes of wall thickness.
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김우곤(Woo-Gon Kim),박재영(Jae-Young Park),박진솔(Jin-Sol Park),장진성(Jinsung Jang) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
This study is to model high-temperature stress relaxation curves for Grade 91 steel, which is used for major structural material of a sodium-cooled fast reactor (SFR) system. A series of stress relaxation data was obtained through stress relaxation tests (SRT) conducted under a constant strain of 1.0% at 500, 550, 600, and 650℃. Herein, two models of exponential model and Peleg’s model were considered to describe the stress relaxation curves of Grade 91 steel. Each parameter value used for the two models was optimized through the nonlinear least square fit (NLSF) method to experimental stress relaxation data. In the results, the exponential model was not in accordance with the experimental stress relaxation curves for all temperatures of 500, 550, 600, and 650℃. Meanwhile, Peleg’s model was found to be in good accordance with all curve data of four temperatures, and its each parameter followed the temperature dependence well. It is suggested that Peleg’s model is reasonable for describing the stress relaxation curves of Grade 91 steel.
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