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316L(N)스테인리스강의 Monkman-Grant 크리프 수명식의 적용성
김우곤,김대환,류우석,Kim, U-Gon,Kim, Dae-Hwan,Ryu, U-Seok 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.9
Creep tests for type 316L(N) stainless steel were carried out using constant-load creep machines at 55$0^{\circ}C$, 575$^{\circ}C$ and $600^{\circ}C$. Material constants necessary to predict creep rupture time were obtained from the experimental creep data. And the applicability of Monkman-Grant(M-G) and modified M-G relationships was discussed. The log-log plot of M-G relationship between the rupture time($t_r$,) and the minimum creep rate ($ $\varepsilon$ _m$) was dependent on test temperatures. The slope of m was 1,05 at 55$0^{\circ}C$ and m was 1.30 at $600^{\circ}C$. On the other hand, the log-log plot of modified M-G relationship between $t_r/$\varepsilon$_r$, and $ $\varepsilon$ _m$ was independent on stresses and temperatures. That is, the slope of m' was approximately 1.35 in all the data. Thus, modified M-G relationship for creep life prediction could be utilized more reasonably than that of M-G relationship for type 316L(N) stainless steel. It was analyzed that the constant slopes regardless of temperatures or applied stresses in the modified relationship were due to an intergranular fracture grown by wedge-type cavities.
Creep Characterization of Type 316LN and HT-9 Stainless Steels by the K-R Creep Damage Model
김우곤,김성호,류우석,Kim, U-Gon,Kim, Seong-Ho,Ryu, U-Seok 대한기계학회 2001 KSME International Journal Vol.15 No.11
The Kachanov and Rabotnov (K-R) creep damage model was interpreted and applied to type 316LN and HT-9 stainless steels. Seven creep constants of the model, A, B, $textsc{k}$, m, λ, ${\gamma}$, and q were determine d for type 316LN stainless steel. In order to quantify a damage parameter, the cavity was interruptedly traced during creep for measuring cavity area to be reflected into the damage equation. For type 316LN stainless steel, λ= $\varepsilon$R/$\varepsilon$* and λf=$\varepsilon$/$\varepsilon$R were 3.1 and increased with creep strain. The creep curve with λ=3.1 depleted well the experimental data to the full lifetime and its damage curve showed a good agreement when r=24. However for the HT-9 stainless steel, the values of λ and λf were different as λ=6.2 and λf=8.5, and their K-R creep curves did not agree with the experimental data. This mismatch in the HT-9 steel was due to the ductile fracture by softening of materials rather than the brittle fracture by cavity growth. The differences of the values in the above steels were attributed to creep ductilities at the secondary and the tertiary creep stages.
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.
연구논문 / 호텔환경변화가 투숙객에에 미치는 영향에 관한 연구 : 부산 경주지역 일본인 관광객을 중심으로
김우곤,윤우희 대한관광경영학회 2000 觀光硏究 Vol.15 No.1
Luxury Hotel room supply in Pusan has increased more than 25% in 199? since Lone Hotel and Grand Hotel opened. The room supply increase is considered to be a major environmental change. After the environmental change, this study investigates whether the number of room nights of Japanese tourists in Kyongju and Pusan have increased. The findings of this study showed that more Japanese tourists who used to stay at Kyongju now would prefer to stay overnight in Pusan. Overall, additional demand has been generated after the additional hotel room supply in Pusan area. According to the survey results, Pusan needs to improve the development of tourism resources and a high priority should be given to Kyongju for the development of night entertainment and duty free shops. This study implies that more cooperative marketing effort should be made to increase the number of Japanese tourists into both Pusan and Kyongju area since the market is regarded as a unified market rather than a separate market. The findings of this study would be used as a useful input for the development plan of attraction, the analysis of current problems of the tourism industry of both Pusan and Kyongju, the development policy of tourism industry.