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Reliability Improvement of Offshore Structural Steel F690 Using Surface Crack Nondamaging Technology
Weon-Gu Lee,Kyoung-Hee Gu,Cheol-Su Kim,Ki-Woo Nam 한국해양공학회 2021 韓國海洋工學會誌 Vol.35 No.5
Microcracks can rapidly grow and develop in high-strength steels used in offshore structures. It is important to render these microcracks harmless to ensure the safety and reliability of offshore structures. Here, the dependence of the aspect ratio (As) of the maximum depth of harmless crack (αhlm) was evaluated under three different conditions considering the threshold stress intensity factor (△Kth) and residual stress of offshore structural steel F690. The threshold stress intensity factor and fatigue limit of fatigue crack propagation, dependent on crack dimensions, were evaluated using Ando"s equation, which considers the plastic behavior of fatigue and the stress ratio. αhlm by peening was analyzed using the relationship between △Kth obtained by Ando"s equation and △Kth obtained by the sum of applied stress and residual stress. The plate specimen had a width 2W = 12 mm and thickness t = 20 mm, and four value of As were considered: 1.0, 0.6, 0.3, and 0.1. The αhlm was larger as the compressive residual stress distribution increased. Additionally, an increase in the values of As and △Kth(l) led to a larger αhlm. With a safety factor (N ) of 2.0, the long-term safety and reliability of structures constructed using F690 can be secured with needle peening. It is necessary to apply a more sensitive non-destructive inspection technique as a non-destructive inspection method for crack detection could not be used to observe fatigue cracks that reduced the fatigue limit of smooth specimens by 50% in the three types of residual stresses considered. The usefulness of non-destructive inspection and non-damaging techniques was reviewed based on the relationship between αhlm , αNDI (minimum crack depth detectable in non-destructive inspection), αcrN (crack depth that reduces the fatigue limit to 1/N ), and As.
Lee, Hong-Gu,Yin, Jin-Long,Xu, Cheng-Xiong,Hong, Zhong-Shan,Lee, Zhe-Hu,Jin, Yong-Cheng,Choi, Chang-Weon,Lee, Do-Hyeung,Kim, Kyoung-Hoon,Choi, Yun-Jaie Asian Australasian Association of Animal Productio 2011 Animal Bioscience Vol.24 No.12
This study was conducted to examine the effects of glucose, chromium picolinate (CrP), and vitamin C (Vit C) on lipid metabolism in Korean native steers fitted with indwelling catheters. A total of 12 Korean native steers were randomly allocated to the following treatments: 1) normal control diet, 2) same as 1) +250 g of glucose by intravenous (IV) infusion, 3) same as 2)+13.5 g CrP administered orally, and 4) same as 3)+2.52 g Vit C by IV infusion. Glucose, Vit C, and CrP treatments were administered for five days. At days 1 and 3, serum insulin was higher in treated animals than in those fed the control diet (p<0.05). Serum non-esterified fatty acid (NEFA) concentration in the steers on treatment 2), control+13.5 g CrP, was lower than those on other treatments at 90 min post-infusion on days 1 and 3 (p<0.05). The expression of peroxisome proliferator-activated receptor-${\gamma}$ (PPAR${\gamma}$)2, stearoyl-CoA desaturase-1 (SCD), fatty acid synthase (FAS), and glucose transporter type 4 (Glut 4) in the longissimus muscle of steers on treatment 2 was higher than those on other treatments. In conclusion, the results suggest that CrP is associated with the regulation of gene expression involved in adipogenesis.
( Kyoung-hee Gu ),( Gum-hwa Lee ),( Weon-gu Lee ),( Chang-seok Oh ),( Ki-woo Nam ) 한국산업융합학회 2022 한국산업융합학회 논문집 Vol.25 No.2
In this paper, the evaluation equations proposed by Tange et al. and Ando et al. were used to evaluate the threshold stress intensity factor △K(R/th(s)) and fatigue limit , △σ(R/WC) according to the small crack of offshore structural steel F690. Despite the differences in concept and shape of the two equations, the △K(R/th(s)) and △σ(R/WC) proved completely consistent. It is possible to use these equations to evaluate the dependence of the crack length on the △K(R/th(s)) and △σ(R/WC) of structures made of all steel grades. With these equations, the characteristics of microcracks can be quantitatively evaluated, and the safety and reliability of the structure can be secured.
이영한(Young-Han Lee),이성태(Seong-Tae Lee),허재영(Jae-Young Heo),김민근(Min-Geun Kim),홍광표(Kang-Pyo Hong),김은석(Eun-Seok Kim),송원두(Won-Doo Song),노치웅(Chi-Woong Rho),이진호(Jin-Ho Lee),전원태(Weon-Tai Jeon),고병구(Byong-Gu Ko) 한국토양비료학회 2010 한국토양비료학회지 Vol.43 No.3
Monitoring of the heavy metals at paddy rice agriculture is very important for environmental agriculture. A study was carried out of heavy metal concentrations in 260 paddy soil samples every four years from 1999 to 2007 in Gyeongnam Province. Heavy metals such as Cd, Cr, Cu, Ni, Pb, Zn, and As in paddy soils were analyzed. Average concentrations of heavy metal were Cd 0.426 (ranged 0.003-1.379) mg kg<SUP>-1</SUP> for Cd, 1.189 (0.003-3.264) mg kg<SUP>-1</SUP>, for Cr, 9.68 (0.05-22.38) mg kg<SUP>-1</SUP> for Cu, 2.64 (0.01-7.36) mg kg<SUP>-1</SUP> for Ni, 23.7 (0.7-54.1) mg kg-1 for Pb, 20.8 (0.7-131.2) mg kg<SUP>-1</SUP> for Zn, and 1.054 (0.001-2.110) mg kg<SUP>-1</SUP> for As, respectively . Long-term changes of heavy metals were showed that Cd, Ni, and Zn were significantly increased whereas Cr, Cu, and As were significantly decreased. Principle component analysis (PCA) of heavy metals in paddy soils was obtained with eigenvalues > 1 summing 34.3% of variance for PC1, 17.5% of variance for PC2, and 51.8% of the total variance in soil heavy metals.