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Type 316LN 강의 크리프 수명예측 파라메타의 표준오차 분석
김우곤(Woo Gon Kim),윤송남(Song Nam Yoon),류우석(Woo Seog Ryu) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
A number of creep data were collected and filed for type 316LN stainless steels through literature survey and experimental data produced in KAERI. Using these data, polynomial equations for predicting creep life were obtained for Larson Miller (L-M), Qrr-Sherby-Dorn (O-S-D) and Manson-Haferd (M-H) parametric methods. In order to find out the suitability for them, the relative standard error (RSE) and standard error of estimate (SEE) values were obtained by statistical process of creep data. The O-S-D parameter showed better fitting to creep-rupture data than the L-M or the M-H parameters, and the three parametric methods did not generate the large difference in the SEE and the RSE values.
316LN 스테인리스강의 크리프 균열성장속도의 확률적 평가
김우곤(Woo-Gon Kim),윤송남(Song-Nan Yin),류우석(Woo-Seog Ryu),김선진(Seon-Jin Kim),이원(Won Yi) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3
This paper is to describe a probabilistic evaluation of the creep crack growth rate (CCGR) for type 316LN stainless steel. To logically obtain the Band q values in the CCGR equation of a = B(C<SUP>*</SUP>)<SUP>q</SUP>, three methods of the least square fitting method (LSFM), a mean value method (MVM) and a probabilistic distribution method (PDM) were adopted. The three methods did not show a large difference in the CCGR lines, but the PDM was most useful because the CCGR line can be evaluated with a probabilistic reliability. Both the Band q coefficients followed a lognormal distribution, even though the B ones were a little scattered for the points of the data. In the case of a standard deviation of I 0' for the probability variables, P (B, q), the results of the Monte Carlo simulation (MCS) and the PDM were compared for the distribution ranges of the CCGR lines.
김우곤(Woo Gon Kim),류우석(Woo Seog Ryu) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
In order to model a creep behavior of type 316LN stainless steel, the Kachanov-Rabotnov(K-R) damage equation was analyzed and its equation was reconstructed into the reference stress(RS) equation using a critical stress value σ. The RS equation was derived from the critical stress in failure time t<SUB>f</SUB> instead of material damage parameter ω. Cavity amount was measured in the crept specimen taken from interrupted creep test with time variation to quantify a damage parameter, and then the amount was reflected into the K-R damage equations. Master curve with λ = 3.0 was well coincided with an experimental one to the full lifetime. The value of creep constant r with stress levels was about 18 at 550℃ and 21 at 600℃. This value was almost similar with r = 24 in the K-R equation, which was obtained by using damage parameter ω. The RS equation was therefore more convenient than the generalized K-R equation, because the measuring process to quantify the damage parameter ω such as voids or micro cracks in crept materials was omitted.
고온가스로용 Hastelloy-X 강의 고온 인장 및 크리프 특성
김우곤(Woo-Gon Kim),윤송남(Song-Nam Yoon),류우석(Woo-Seog Ryu),장종화(Jonghwa Chang) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
The design of the metallic components for a high temperature gas cooled reactor (HTGR) such as hot gas ducts, intermediate heat exchanger (IHX) tube, and steam reformer tubes is principally carried out using the mechanical strength values of the tensile and creep properties. Elevated tensile and creep data for candidate alloys are needed to design the structural components operated at 900 to 1000℃. Hastelloy-X is a candidate heat-resistant alloy for the HTGR. In this study, the tensile and creep properties were investigated at the high temperature test conditions; 600 to 1000℃ in tensile and 950℃ in creep. A lot of data were collected through literature survey, and the data were analyzed in the viewpoint of the design of the HTGR structures. The fractured micrographs were also observed.
김우곤(Woo Gon Kim),류우석(Woo Seog Ryu),김현희(Hyun Hie Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
In order to predict stress intensity limit of high-temperature creep structures, creep work-time equation, defined as Wct^p=B, was used, and the results of the equation were compared with isochronous stress-strain curve(ISSC) ones of ASME BPV NH Code. For this purpose, the creep strain tests with time variations for commercial type 316 stainless steel were conducted with different stresses; 160 MPa150 MPa, 145 MPa, 140 MPa and 135 MPa at 593℃. The results of log Wc and log t plots showed a good linear relation up to 10^5 hr. The constants p, B and stress intensity limit values showed comparatively good agreement to those of ASME NH ISSC. It is believed that the relation can be simply obtained with only several short-term 1% strain data without ISSC which can be obtained by long-term creep data.
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.
변형 에너지를 이용한 크리프 한계응력강도(S<SUB>t</SUB>)의 결정
김우곤(Woo Gon Kim),이경용(Kyung Yong Lee),윤기봉(Kee Bong Yoon),류우석(Woo Seog Ryu) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
Creep stress intensity limit(S₁) value for 1% strain in 10? hr was determined using strain energy method based on the work done during creep. For this purpose, 1% creep strain tests for commercial type 316 (J316) and type 316LN (K316LN) stainless steels were conducted with various stress conditions at 550℃ or 593℃. The S₁ value of the K316LN stainless steel was 135 MPa at 550℃ and creep work was 87 KJ/m³. In order to identify reasonability of the strain energy method, the method of isochronus stress-strain curves(ISSC) for the J316 stainless steel was used comparatively. The S₁values for it showed good agreement between two methods. The strain energy method can be simply obtained using only three or four short-term 1% strain data without ISSC obtained by long-term creep data. Particularly, this method is useful in estimation of the stress intensity for new and emerging class of high-temperature materials where creep and tensile data for empirical extrapolation to design life is lacking.