• 한국군사과학기술학회지
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• 제23권6호
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• pp.574-581
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• 2020

This paper describes the stacking effect for Ceramic Column Grid Array(CCGA) packages used for satellites. Reflow Soldering Process suitable for CCGA package with back structure was set as the process development goal to meet European Cooperation for Space Standardization(ECSS) standard. After analyzing the stacking effect according to the type of CCGA, it is verified by applying it to the CCGA Reflow Soldering Process. In order to confirm the validity of the staking effect analyzed in terms of vibration and thermal characteristics, it is verified through actual specimen production. It analyzes the cause of crack occurrence in the CCGA package and estimates the crack generation point using previously acquired inspection data.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2292-2306
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• 2024

This study addresses cracks and fracture problems in engineering structures that may cause significant challenges and safety concerns, with a focus on pressure vessels in nuclear power plants. Comprehensive parametric three-dimensional mixed mode fracture analyses for inclined and deflected nozzle corner cracks with various crack shape aspect ratios and depth ratios in nuclear reactor pressure vessels are carried out. Stress intensity factor (SIF) solutions are obtained using FRAC3D, which is part of Fracture and Crack Propagation Analysis System (FCPAS), employing enriched finite elements along the crack front. Also, improved empirical equations are developed to allow the determination of mixed mode SIFs, K_I, K_II, and K_III, for any values of the parameters considered in the study. This study provides practical solutions to assess the remaining life and fail-safe conditions of nuclear reactors by providing accurate SIF determination.

• 한국안전학회지
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• 제29권4호
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• pp.34-41
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• 2014

The goal of this study is to investigate some crack behaviors which affect the crack propagation angle at the planar solid oxide fuel cell with cracks under the fabricating and operating temperature and analyze the stresses by 3 steps processing on the solid oxide fuel cell. Currently, there are lots of researches of the performance improvement for fuel cells, and also for the more powerful efficiency. However, the planar solid oxide fuel cell has demerits which the electrode materials have much brittle properties and the thermal condition during the operating process. It brings some problems which have lower reliability owing to the deformation and cracks from the thermal expansion differences between the electrolyte, cathode and anode electrodes. Especially the crack in the corner of the electrodes gives rise to the fracture and deterioration of the fuel cells. Thus it is important to evaluate the behavior of the cracks in the solid oxide fuel cell for the performance and safety operation. From the results, we showed the stress distributions from the cathode to the anode and the effects of the edge crack in the electrolyte and the slant crack in the anode. Futhermore the crack propagation angle was expected according to the crack length and slant angle and the variation of the stress intensity factors for the each fracture mode was shown.

• Steel and Composite Structures
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• 제36권4호
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• pp.463-480
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• 2020

Although detailed shell analysis is suitable to predict the ductile crack initiation life of steel members, such detailed method adds time expense and complexity. In order to simply predict the ductile crack initiation life of stiffened steel bridge piers, a total of 33 cases are simulated to carry out the parametric analyses. In the analysis, the effects of the width-to-thickness ratio, slenderness ratio, plate thickness and so on are considered. Both shell analyses and beam analyses about these 33 cases are conducted. The plastic strain and damage index obtained from shell and beam analyses are compared. The modified factor β_s is determined based on the predicted results obtained from both shell and beam analyses in order to simulate the strain concentration at the base corner of the steel bridge piers. Finally, three experimental results are employed to verify the validity of the proposed method in this study.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 제7회 압연 심포지엄
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• pp.73-76
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• 2009

Increase in tensile strength of steel is important for fuel efficiency and $CO_2$ reduction. But the higher the strip strength, the more defect could be generated in hot strip mill. This study focuses on line-type edge scab. One of the causes for the defect is initial edge cracks commonly observed on a slab but their correlation has not been verified yet. Thus, the objective of this report is to verify if the edge crack is exactly the seed for edge scab. For this, we conducted pilot hot rolling test with cracked slab and compared the development of cracks and edge scabs on hot-rolled strip.

• KEPCO Journal on Electric Power and Energy
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• 제6권1호
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• pp.41-47
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• 2020

The contribution of damage mechanisms to failure of steam turbine casing made of Cr-Mo-V steel was investigated. Creep-fatigue interaction on the HP side corner of turbine casing was revealed as the root cause of the catastrophic failure performed by metallurgical analysis. The steady-state pressure and transient thermal stress were analyzed based on the actual operating condition of the thermal plant. Damage of creep-fatigue interaction to crack initiation was evaluated with multiaxial effects. The contribution ratio of creep and fatigue to the crack initiation was estimated to 3:1. Temporary geometrical correct action with repair weld was executed. For long-term operation, design improvement of casing equipment for creep resistance should be needed.

• 한국해양공학회지
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• 제6권2호
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• pp.76-84
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• 1992

In this study, corrosion fatigue test of SAPH45 steel was performed by the use of plane behavior of base metal (BM) and heat affected zone (HAZ) of SAPH45. The main results obtained are as follows: 1) The more aspect ratio (b/t) of corner crack decreases, the more aspect ratio (b/a) takes greatly effect by corrosion. 2) The correlation between the stress intensity factor range ($\Delta$k) and crack growth rate (da/dN) for weldment in seawater is given by Paris rule as follow: da/dN=C($\Delta$K) super(m). Where m is constant, and the value is 3.82-3.84. 3) The accelerative factor ($\alpha$) of BM and HAZ under seawater is about 1.1-1.9, and ($\alpha$) of HAZ increases more and more under the low $\Delta$K region. 4) HAZ is more susceptible to corrowion than BM because of potential of electrode (E sub(c)) of HAZ becomes more less noble potential than that of BM.

• Design & Manufacturing
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• 제12권1호
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• pp.13-17
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• 2018

It was analyzed and experimented on the change of the material thickness according to the size of the "R" of the punch and die corners using the material of SCP-1 0.25mm As a result, the following conclusions were obtained. Tensile strength analysis and safety analysis of materials are very important process for each process in strip layout, and Through this, the Influx of material and the deformation of the material were found. As a result of safety analysis and tensile thickness analysis, when the corner R of the punch was 0.3 mm and the edge R of the die was 1.0 mm The inflow of the material was not smooth, and the thickness of the corner part became 0.2 mm, causing cracks. when the corner R of the punch was 0.5 mm and the edge R of the die was 1.5 mm The inflow of the material was smooth, The thickness of the corners of the product is 0.21mm and It was considered that cracks do not occur when the thickness of the bottom surface and the body part becomes thin. The results obtained by applying the results obtained from the analysis, In Experimental Condition 1, a crack occurred in the same part of the analysis In Experimental Condition 2, the flow of the material was smooth and the drawing processing could be performed without generating cracks.

• Journal of Welding and Joining
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• 제35권3호
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• pp.7-14
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• 2017

The effect of high temperature-moisture on corrosion and mechanical properties for Sn-0.7Cu, Sn-3.0Ag-0.5Cu (SAC305) solders on flexible substrate was studied using Highly Accelerated Temperature/Humidity Stress Test (HAST) followed by three-point bending test. Both Sn-0.7Cu and SAC305 solders produced the internal $SnO_2$ oxides. Corrosion occurred between the solder and water film near flexible circuit board/copper component. For the SAC305 solder with Ag content, furthermore, octahedral corrosion products were formed near Ag3Sn. For the SAC305 and Sn-0.7Cu solders, the amount of internal oxide increased with the HAST time and the amount of internal oxides was mostly constant regardless of Ag content. The size of the internal oxide was larger for the Sn-0.7Cu solder. Despite of different size of the internal oxide, the fracture time during three-point bending test was not significantly changed. It was because the bending crack was always initiated from the three-point corner of the chip. However, the crack propagation depended on the oxides between the flexible circuit board and the Cu chip. The fracture time of the three-point bending test was dependent more on the crack initiation than on the crack propagation.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.235-243
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• 2002

Ni-base superalloys are used extensively in industry, both in aeroengines and land based turbines. About 60% by weight of most modern gas turbine engine structural components are made of Ni-base superalloys. To satisfy practical demands, the efficiency of gas turbine engines has been steadily and systematically increased by design modifications to handle higher turbine inlet or firing temperatures. However, the increase in operating temperatures has lead to a decrease in the life of components and increase in costs of replacement. Moreover, around 80% of the large frame size industrial/utility gas turbines operating in the world today were installed in the mid-sixties to early seventies and are now 25 to 30 years old. Consequently, there are greater opportunities now to repair and refurbish the older models. Basically, there are two major factors influencing the weldability of the cast alloys: strain-age cracking and liquation cracking. Susceptibility to strain-age cracking is due to the total Ti plus AI content of the alloy; Liquation cracking is due either to the presence of low melting constituents or constitutional liquation of constituents. Though Rene 41 superalloy has 4.5wt.% total Ti and Al content and falls just below the safe limit proposed by Prager et al., controlled grain size and special heat treatments are needed to obtain crack-free welds. Varying heat treatments and filler materials were used in a laboratory study, then the actual welding of service parts was carried out to verity the possibility of crack-tree weld of components fabricated from Rene 41 superalloy. The microstructural observations indicated that there were two kinds of carbides in the FCC matrix. MC carbides were located along the grain boundaries, while M$_{23}$C$_{6}$ carbide was located both inter and intra granularly. Two kinds of filler materials, Rene 41 and Hastelloy X were used to gas tungsten arc weld a patch into the sheet metal, along with varying pre-weld heat treatments. The microstructure, hardness and tensile tests were determined. The service distressed parts were categorized into three classes: with large cracks, with medium cracks and with small or no visible cracks. No significant difference in microstructure among the specimens was observed. Specimens were cut from the corner and the straight edge of the patch repair, away from the corner. The only cracks present were found to be associated with inadequate surface preparation to remove oxidation. Guidelines for oxide removal and the welding procedures developed in the research enabled crack-free welds to be produced.d.