• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.34-35
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• 2013

In this study, the ultra high strength concrete which have 80, 130, 180MPa took the heat from 20℃ to 700℃ and the 0, 20% stress in normal condition's to evaluate stress-strain, residual compressive strength and thermal expansion deformation were evaluated. The heating speed of specimen was 0.77℃/min 20~50℃, 50℃ before the target temperature, and the other interval's heating speed was 1℃/min. As a result, the stress-strain curve of non-load specimen showed the liner behavior at high temperature when the specimen's strength increased more. If ultra high strength concrete got loads, its compressive strength tended to decrease different from the normal strength concrete. The thermal expansion deformation was expanded from a vitrification of quartz over 500℃. however, over the 600℃, it was shrinked because of the dehydration of the combined water.

• Structural Engineering and Mechanics
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• v.55 no.6
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• pp.1087-1097
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• 2015

In this paper, the effect of functionally graded material (FGM) coatings on the fracture behavior of semi-elliptical cracks in cylinders is assessed. The objective is to calculate the stress intensity factor (SIF) of a longitudinal semi-elliptical crack on the wall of an aluminum cylinder with FGM coating. A three-dimensional finite element method (FEM) is used for constructing the mechanical models and analyzing the SIFs of cracks. The effect of many geometrical parameters such as relative depth, crack aspect ratio, FG coating thickness to liner thickness as well as the mechanical properties of the FG coating on the SIF of the cracks is discussed. For a special case, the validity of the FE model is examined. The results indicated that there is a particular crack aspect ratio in which the maximum value of SIFs changes from the deepest point to the surface point of the crack. Moreover, it was found that the SIFs decrease by increasing the thickness ratio of the cylinder. But, the cylinder length has no effect on the crack SIFs.

• Composites Research
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• v.37 no.1
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• pp.15-20
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• 2024

Since the residual stress of hydrogen tank is directly related to durability, it is very important to reduce it for safety. Type II~IV hydrogen tank are manufactured by the filament winding method, in which the fiber is impregnated with resin and wound around the liner. Residual stress in composite is affected by curing conditions and fiber tension etc. In this study, the effect of curing conditions on residual stress was analyzed when manufacturing a Type III hydrogen tank using carbon fiber filament winding process. First, the curing behavior of the epoxy resin was analyzed using a differential scanning calorimetry. Through this, the curing temperature was set to 140℃. During the same curing time, the specimens were cured under 2-stage curing condition that reached 140℃ earlier and a 4-stage curing condition that reached 140℃ later, respectively. After curing, the residual stress of the composite material was measured by the ring slitting method, and the experimental values were compared with numerical values. It was confirmed that there was a significant difference in residual stress according to the optimization of curing conditions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05b
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• pp.38-41
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• 2001

In this work, we have been studied the characteristics of each nitride film for the optimization of PMD(pre-metal dielectric) liner nitride process, which can applicable in the recent semiconductor manufacturing process. The deposition conditions of nitride film were splited by PO (protect overcoat) nitride, baseline, low hydrogen, high stress and low hydrogen, respectively. And also we tried to catch hold of correlation between BPSG(boro-phospho silicate glass) deposition and densification. Especially, we used FTIR area method for the analysis of density change of Si-H bonding and Si-NH-Si bonding, which decides the characteristics of nitride film. To judge whether the deposited films were safe or not, we investigated the crack generation of wafer edge after BPSG densification, and the changes of nitride film stress as a function of RF power variation.

• Journal of the Korean Geosynthetics Society
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• v.2 no.1
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• pp.57-68
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• 2003

Strain-softening model is developed to characterize the interface behavior of geomembrane with geotextile and geosynthetic clay liner(GCL). The model proposed in this research is calibrated by using data from direct shear tests conducted on smooth and textured geomembrane. The research is divided into two regions, pre-peak and post-peak, to take into account of strain-softening effect. Although slight difference between measured and back calculated data is observed under high normal stress, good agreements, in general, are found from back calculations. Especially, good consistency is observed in the case of low normal stress. Based on the results, it can be concluded that the proposed model can be a reasonable constitutive law to figure out the behavior of strain-softening between interfaces of geomembrane. In addition, DSC(Disturbed State Concept) model is also presented for further application in geosynthetic interfaces.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.25-31
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• 2005

The theory developed in a preceding paper [1] for poroelastic composite material behavior under thermal and gas diffusion is applied to thermo-chemical decomposition of a carbon-phenolic composite rocket nozzle liner under typical operating conditions. Specifically, the structural component simulated is the cowl ring for which distributions of pressure in the material pores, temperature and across-ply stress are presented. The results for particular composite designs show that across-ply failure occurs due to tensile stress in the material which is indicative of plylift. This prediction corroborates observations of plylift in a nozzle cowl. Simulations suggest designs to avoid plylift in the cowl zone.

• Journal of the Korean Institute of Gas
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• v.6 no.4 s.18
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• pp.33-39
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• 2002

[ $9\%$ ] nickel steel LNG storage tank have double containments that can store cryogenic LNG independently. Inner tank material is used as $9\%$ nickel steel and outer tank is constructed by concrete. Comer protection which is installed on inner surface of concrete corner is consist of $9\%$ nickel steel liner and form glass insulator that make reduce tension at corner when LNG is leaked from inner tank. It is very difficult to design corner protection because expansion and contraction of liner make stress state complex. Corner protections of operating tank in KOGAS are designed by Japanese engineering company such as TKK, KHI and England company of WHESSOE. This paper is mainly focused on the integrity comparison of them according to requirements of Appendix 4 in ASME Section VIII Div. 2 by using FEM.

• Journal of the Korean Society of Safety
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• v.34 no.5
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• pp.7-14
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• 2019

The type III vessel, which is used to store high-pressure hydrogen gas, is made by wrapping the vessel's liner with carbon fiber composite materials for strength performance and lightening. The liner seals the internal gas and the composite resists the internal pressure. The properties of the fiber composite material depends on the angle and thickness of the fiber. Thus, engineers should consider these various design variables. However, it significantly increases the design cost due to the trial and error under designing based on experience or experiments. And, for aluminum liners, fatigue loads due to using and charging could give a huge impact on the performance of the structure. However, fatigue failure does not necessarily occur in the position under the highest load in use. Therefore, for hydrogen storage vessel, fatigue evaluation according to design patterns is essential because stress distribution varies depend on composite layer patterns. This study performed an optimization analysis and evaluated a high-pressure hydrogen storage vessel to minimize these trial and error and improve the reliability of the structure, while simultaneously conducting fatigue assessment of all patterns derived from the optimization analysis process. The results of this study are thought to be useful in the strength improvement and life design of composite reinforced high-pressure storage vessels.

• Journal of Convergence for Information Technology
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• v.7 no.5
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• pp.103-109
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• 2017

A pressure vessel is a cylindrical container that accommodates a pressurized fluid. In real life, there are propane canisters and butane canisters. According to data from the Korea Gas Safety Corporation, The number of domestic gas accidents is average 33 cases of domestic gas accidents occurred per year and 20.8 for mobile butane gases. The purpose of this study was to investigate a method to prevent this kind of explosion. Common studies include forced drain through safe holes, forced separation of butane canisters, and manufacturing of high-strength steel. This paper uses a concept that reduces stress inside the cylinder using prestressed method that precede compression. In other words, install a long liner in both ends of the pressure vessel. I want to develop a safety device that acts like a gas intermediate valve.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.5
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• pp.13-20
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• 2012

In order to clarify the effect of overload on crack growth behaviors, fatigue tests for overload were carried out for round plain specimens of SM45C steel. In the experiment, typical semi-elliptical crack shape was found and further crack growth behaviors were tested. Using three types of single overload fatigue tests, Crack growth retardation phenomenon were examined. The growth rate of surface crack(da/dN) during retardation period was analyzed in terms of ${\Delta}K$ and ${\Delta}K_{eff}$. On the growth rate of surface crack analyzed by ${\Delta}K$, the dependence of overload stress levels appears. However, on the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a non-liner relationship between da/dN and ${\Delta}K_{eff}$ with narrow scatter band.