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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.
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.
외식산업 사회교육 프로그램 만족도와 선호도에 관한 탐색적 연구
김우곤(Kim Woo Gon),유영진(Yoo Young Jin) 한국외식경영학회 2000 외식경영연구 Vol.2 No.1
The propose of this study was to identify the problems of the social training program and to suggest the improving methods by analyzing the preference level and the satisfaction level of the social training program in dining industry while investigating the current statuses of the dining industry in Korea and the social training program at Korean colleges. A total of 338 valid responses ware analyzed after 15 questionnaires out of the total of 353 questionnaires collected did not meet the basic requirements for one month. In order to analyze the collected valid responses, SPSS / WIN 7.5 package program was utilized to employ the frequency analysis, the regression analysis, ANOVA, etc. In terms of the satisfaction level of the social training program in dining industry, the most influential factors were identified as the college social training centers, followed by private cooking schools in order; in terms of the preference level of the organizing body of each social training program, college professors, executive officers of social organization, and concurrent professors with practical experiences were identified as the most influential in order. In terms of the preference level of the training methods, the lecture was most influential.