• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1185-1191
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• 2010

Aged aircraft have several cracks as a results of long-term service, and these cracks affect the safety and decrease the rate of operation of the aircraft. To solve these problems, crack propagation analysis should be performed to determine the service life at fatigue critical location(FCL). It is, however, almost impossible to obtain the stress spectrum, which is crucial for crack propagation analysis of the FCLs of wing structure of aged aircraft. In this study, to analyze the fatigue crack propagation behavior at the FCL of an aged aircraft, first finite element analysis is performed for a 3D geometry model of the aircraft wing structure, which is obtained using CATIA based on the paper drawings. Then, the transfer function and stress-spectrum of the FCL are derived using the load factor data and the FEA results. Finally, the crack propagation rates of the FCL are evaluated using the commercial software, NASGRO 6.0.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.11-17
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• 2016

Powder metallurgy nickel based superalloy has been used in a high temperature part of turbine engine for airplane. The fatigue crack growth behavior was investigated using CT specimens for the materials at room temperature(R.T.), $600^{\circ}C$ and $700^{\circ}C$. The direct current potential drop(DCPD) method suggested by ASTM E647 was used to measure the crack length during fatigue crack growth at various stress ratios. The fatigue crack growth rate at R=0.5 was faster than that at R=0.1 for all temperature conditions and increased with the increase of stress ratio and temperature. Fractography was conducted for analysis of fracture mechanism.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.62-68
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• 1997

In the first part of the paper, the crack growth process in rolling contact fatigue has been investigated on ring type plate specimens, in which crack growth is two dimensional and cracks are observed on the side surface of the specimens. The results have shown that cracks are initated from the contact surface in tensile mode in the direction approximately normal to the contact surface and after some short length of growth, shear mode growth occurs from the tip of the crack and it grows until the separation of the surface layer, namely flakung type failure, occurs. In the second part, mode U fatigue crack growth tests have been made by using an apparatus designed based on the concept that the subsurface fatigue crack growth in rolling contact fatigue is the mode U fatigue crack growth under the stress state where the tensile mode growth is suppressed by compression stress. The rest results have shown that the mode U fatigue crack growth occurs if the superposed compression stress is enough to suppress the tensile mode growth.

• Korean journal of applied entomology
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• v.25 no.1 s.66
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• pp.17-20
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• 1986

Based on the data of rice injury caused by the first generation of striped rice borer(Chilo suppressalis (Walker)), which were collected in the three years from 1974 to 1976 in Sweon area, progress of the injury in relation to Degree Days was studied. Increase in the number of infested stems was strongly related to the dispersal features of larvae. The increase ceased at about 400 DD after modal emergence date when the larval distribution pattern became stable. The regression of the number of infested stems per infested hill on Degree Days was significant and the coefficients of determaination were 0.84 and 0.95 for 1974 and 1976, respectively. The regression coefficients in the two years were not statistically significant, suggesting a possibility for pre- diction of the mean number of infested stems per infested hill through a simple model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.297-304
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• 2019

In this research, crack propagation in a silicon anode during two-phase lithiation was evaluated using a cohesive zone model. The phase transition from crystalline silicon to lithiated silicon causes compressive yielding due to the high volume expansion rate. Li-ion diffuses from the surface of the silicon to its core, and the complex deformation mechanisms during lithiation cause tensile hoop stress along the surface. The Park-Paulino-Roesler (PPR) potential-based cohesive zone model that guarantees consistent energy dissipation in mixed-mode fracture was adopted to simulate edge crack propagation. It was confirmed that the edge crack propagation characteristics during lithiation from the FEM simulation results coincided with the real experimental results. Crack turning observed from real experiments could also be predicted by evaluating the angles of maximum tensile stress directions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.129-136
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• 2018

The estimation of the fatigue design life for large welded structures is usually performed using the liner cumulative damage method such as Palmgren-Miner rule or the equivalent damage method. When a fatigue crack is detected in a welded steel structure, the residual service life has to be estimated base on S-N curve method and liner elastic fracture mechanics. In this study, to examine the 3D fatigue crack behavior and estimate the fatigue life of out-of-plane gusset fillet welded joint, the fatigue tests were carried out on the model specimens. Investigations of three-dimensional fatigue crack propagation on gusset welded joint was used the finite element analysis of FEMAP with NX NASTRAN and FRANC3D. Fatigue crack growth analysis was carried out to demonstrate the effects of aspect ratio, initial crack length and stress ratio on out-of-plane gusset welded joints. In addition, the crack behaviors of fatigue tests were compared with those of the 3D crack propagation analysis in terms of changes in crack length and aspect ratio. From this analysis result, SIFs behaviors and crack propagation rate of gusset welded joint were shown to be similar fatigue test results and the fatigue life can also be predicted.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.4
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• pp.529-537
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• 2021

Membrane-type hull and cargo holds have been designed and built for large ship. However, there is a growing interest in applying the same technology to small and medium-sized Liquefied natural gas(LNG) carriers to meet the recent increase in demand for LNG as an ecofriendly fuel and for expanding LNG bunkering infrastructure. The purpose of this study is to apply the IMO Type-B tank to small and medium-sized LNG carriers and verify the safety and suitability of the design. Fatigue crack propagation analysis was performed to install a partial second drip tray installed at the lower part of the LNG cargo tank by calculating the amount of leaked gas in the support structure supporting the cargo tank. First, a program for fatigue crack propagation analysis was developed, in which Paris' law and British Standard 7910 (BS 79110) were applied based on the International Code for the Construction of Equipment and Ships Carrying Liquefied Gases in Bulk, an international standard for LNG carriers. In addition, a surface crack propagation analysis was performed. Next, a methodology for assuming the initial through-crack size was developed to determine the size of the partial second barrier. The analysis was performed for 15 days, which is a possible return time after cracks are detected. Finally, the safety and suitability of the IMO Type-B for LNG cargo tanks required by international regulations were verified. For the accurate analysis of fatigue crack propagation, it is necessary to develop and verify the analysis procedure based on direct analysis and international regulations.

• Restorative Dentistry and Endodontics
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• v.32 no.2
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• pp.138-150
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• 2007

The purpose of this study was to evaluate the difference of surface roughness of composite resin according to composite resin type, polishing methods, and use of resin sealant. Two hundred rectangular specimens, sized $8{\times}3{\times}2mm$, were made of Micro-new (Bisco, Inc., Schaumburg, IL, U.S.A) and Filtek Supreme (3M ESPE Dental Products, St. Paul, MN, U.S.A.), and divided into two groups; Micronew-M group, Filtek Supreme-S group. Specimens for each composite group were subdivided into five groups by finishing and polishing instruments used; M1 & S1(polyester strip), M2 & S2 (Sof-Lex disc), M3 & S3 (Enhance disc and polishing paste), M4 & S4(Astropol) and M5 & S5 (finishing bur), Polished groups were added letter B after the application of resin surface sealant (Biscover), eg, M1B and S1B. After specimens were stored with distilled water for 24hr, average surface roughness (Ra) was taken using a surface roughness tester. Representative specimens of each group were examined by FE-SEM (S-4700: Hitachi High Technologies Co., Tokyo, Japan). The data were analysed using paired t-test, ANOVA and Duncan's tests at the 0.05 probability level. The results of this study were as follows ; 1. The lowest Ra was achieved in all groups using polyester strip and the highest Ra was achieved in M5, S5 and M5B groups using finishing bur. On FE-SEM, M1 and S1 groups provided the smoothest surfaces, M5 and S5 groups were presented the roughest surfaces and voids by debonding of filler on the polished specimens. 2. There was no significant difference in Ra between Micronew and Filtek Supreme before the application of resin sealant, but Micronew was smoother than Filek Supreme after the application of resin sealant. 3. There was significant corelation between Ra of type of composite resin and polishing methods before the application of resin sealant (p=0.000), but no significant interaction between them after the application of resin sealant. On FE-SEM, most of composite resin surfaces were smooth after the application of resin sealant on the polished specimens. 4. Compared with before and after the application of resin sealant in group treated in the same composite and polishing methods, Ra of M4B and M5B was statistically lower than that of M4 and M5, and S5B was lower than that of S5, respectively (p<0.05). In conclusion, surface roughness by polishing instruments was different according to type of composite resin. Overall, polyester strip produced the smoothest surface, but finishing bur produced the roughest surface. Application of resin sealant provided the smooth surfaces in specimens polished with Enhance, Astropol and finishing bur, but not provided them in specimens polished with Sof-Lex disc.

• Nuclear industry
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• v.8 no.10 s.68
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• pp.72-74
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• 1988

경제협력개발기구$\cdot$원자력기관(OECD$\cdot$NEA)이 최근에 발표한 조사보고서에 의하면 OECD가맹국의 1987년도 원자력발전량은 전년도보다 $5.9\%$ 증가한 1조 3,126억kWh에 이르렀으며, OECD지역내의 원자력점유율도 전년보다 $0.4\%$ 증가한 $22.5\%$ 로서 점진적 진전을 보이고 있다.

• Fire Science and Engineering
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• v.33 no.2
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• pp.30-38
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• 2019

Tracking, which is one of the main causes of electrical fires, is perceived as a physical phenomenon of electrical discharge. Hence tracking should be explained based on electric field analysis, conduction path by electron generation, and gas discharge physics. However, few papers have considered these details. This paper proposes a tracking mechanism including their effects on tracking progress. In order to prove this mechanism, a tracking experiment, an electric field analysis for the carbonization evolution model, and an explanation of the tracking process by gas discharge physics were conducted. From the tracking experiment, the current waveforms were measured at each stage of the tracking progress from corona discharge to tracking breakdown. The electric field analysis was carried out in order to determine the electric field on the surface of a dry-band and the high electric field region for electron generation during the generation and progress of carbonization. In this paper, the proposed tracking mechanism consisted of six stages including electron avalanche by corona discharge, accumulation of positive ions, expansion of electron avalanche, secondary electron emission avalanche, streamer, and tracking by conductive path. The pulse current waveforms measured in the tracking experiment can be explained by the proposed tracking mechanism. The results of this study will be used as the technical data to detect tracking phenomenon, which is the cause of electric fire, and to improve the proof tracking index.