• Journal of Platform Technology
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• v.10 no.4
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• pp.3-10
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• 2022

In this study, damage resulting from internal flaws was investigated by finite element analysis for the safety evaluation of a non-destructive testing platform for hydrogen pressure vessels. A specimen was modeled and calculated using finite element analysis to determine material properties in accordance with the parameters of the composite material in order to assess the safety of the Type 4 hydrogen pressure vessel. Through this, flaws in the hydrogen pressure vessel were modeled, and test conditions were provided in accordance with rules to look into whether there was safety. Delamination, foreign object, and vertical cracks were modeled for internal flaws, and damage was examined in accordance with failure criteria. As the delamination defect approached the interior of the hydrogen pressure tank, it became more likely to cause damage. Additionally, as the crack depth grew in the case of vertical cracks, the likelihood of crack propagation rose. On the other hand, it was anticipated that the foreign item defect would suffer more damage from the outside in. A non-destructive testing platform will be used to assess the safety of fuel cell vehicles that are already in operation in future research.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1230-1242
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• 1993

In a case of mushroom (Lentinus Edodes L.) , visual features are crucial for grading and the quantitative evaluation of the growth state. The extracted quantitative visual features can be used as a performance index for the drying process control or used for the automatic sorting and grading task. First, primary external features of the front and back sides of mushroom were analyzed. And computer vision based algorithm were developed for the extraction and measurement of those features. An automatic thresholding algorithm , which is the combined type of the window extension and maximum depth finding was developed. Freeman's chain coding was modified by gradually expanding the mask size from 3X3 to 9X9 to preserve the boundary connectivity. According to the side of mushroom determined from the automatic recognition algorithm size thickness, overall shape, and skin texture such as pattern, color (lightness) ,membrane state, and crack were quantified and measured. A portion of t e stalk was also identified and automatically removed , while reconstructing a new boundary using the Overhauser curve formulation . Algorithms applied and developed were coded using MS_C language Ver, 6.0, PC VISION Plus library functions, and VGA graphic function as a menu driven way.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.1051-1055
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• 1997

Hot forging is widely used in the manufacturing of automotive component. The mechanical, thermal load and thermal softening which is happened by the high temperature die in hot forging. Tool life of hot forging decreases considerably due to the softening of the surface layer of a tool caused by a high thermal load and long contact time between the tool and workpieces. The service life of tools in hot forging process is to a large extent limited by wear, heat crack, plastic deformation. These are one of the main factors affecting die accuracy and tool life. It is desired to predict tool life by developing life prediction method by FE-simulation. Lots of researches have been done into the life prediction of cold forming die, and the results of those researches were trustworthy, but there have been little applications of hot forming die. That is because hot forming process has many factors influencing tool life, and there was not accurate in-process data. In this research, life prediction of hot forming die by wear analysis and plastic deformation has been carried out. To predict tool life, by experiment of tempering of die, tempering curve was obtained and hardness express a function of main tempering curve.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.6
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• pp.356-364
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• 2004

The hydrides in cladding affect the corrosion and tensile properties. In this study corrosion and tensile properties were evaluated with varying the hydrogen concentration. The charged hydrogen contents were ranged from 200 to 1000 ppm. The corrosion rate in water and LiOH solution increases with the hydrogen concentration. The hydride did not affect the corrosion mechanism in the pre-transition region, but in the post-transition region the corrosion rate was accelerated. Cladding E contained higher Niobium content was slowly accelerated compared with other claddings. The yield and ultimate strengths were independent on the hydrogen content. However, the total elongation decreased gradually with increasing the hydrogen content. SEM observation of fracture surface showed that an average of depth of voids decreased with increasing the hydrogen content and small secondary crack are observed.

• Nuclear Engineering and Technology
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• v.36 no.4
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• pp.327-337
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• 2004

It is commonly required that tubes with defects exceeding $40\%$ of wall thickness in depth should be plugged; however, this criterion is too conservative for some locations and for some types of defects. Many studies have been done with the aim of developing an alternative plugging criteria, and these studies have shown that steam generator tubes with a certain range of axial through-wall cracks could remain in service without any safety or reliability problems. However, these studies have been limited, thus far, to consideration of single cracked tubes, necessitating a study on multiple cracks, which are commonly found. A crack coalescence model applicable to steam generator tubes with two collinear axial through-wall cracks was proposed in the previous study. In this paper, the investigation is extended to the parallel axial cracks spaced in a circumferential direction, because parallel axial cracks are more frequently detected during in-service inspections than collinear axial cracks. Interaction effects between two parallel cracks are evaluated by performing elastic and elastic-plastic finite element analyses.

• Nuclear Engineering and Technology
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• v.42 no.5
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• pp.546-551
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• 2010

The objective of this research is to estimate the crack location and size of a carbon steel pipe by using a laser ultrasound guided wave for the wall thinning evaluation of an elbow. The wall thinning of the carbon steel pipe is one of the most serious problems in nuclear power plants, especially the wall thinning of the carbon steel elbow caused by Flow-Accelerated Corrosion (FAC). Therefore, a non-destructive inspection method of elbow is essential for the nuclear power plants to operate safely. The specimens used in this study were carbon steel elbows, which represented the main elements of real nuclear power plants. The shape of the wall thinning was an oval with a width of 120mm, a length of 80mm, and a depth of 5mm. The L(0,1) and L(0,2) modes variation of the ultrasound guided wave signal is obtained from the response of the laser generation/air-coupled detection ultrasonic hybrid system represent the characteristics of the defect. The trends of these characteristics and signal processing were used to estimate the size and location of wall thinning.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.354-359
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• 2015

Stainless steel has poor corrosion resistance in marine environment due to the breakdown of a passive film caused by chloride. It suffers electrochemical corrosion like pitting corrosion, crevice corrosion, and stress corrosion crack (SCC) in marine environment. In general, it indicates that the passive film of $Al_2O_3$ has better corrosion resistance than that of $Cr_2O_3$ in seawater. This paper investigated the damage behavior 304 stainless steel and hot-dip aluminized 304 stainless steel in seawater solution. Various electrochemical experiments were carried out including potential measurement, potentiodynaimic experiment, Tafel analysis and galvanostatic experiment. As a result of anodic polarization experiment, higher pitting damage depth was indicated at 304 stainless steel than hot-dip aluminized 304 stainless steel. In addition, relatively higher corrosion current density was shown at hot-dip aluminized stainless steel as a result of Tafel analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.653-659
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• 2002

This paper describes a probabilistic fracture mechanics(PFM) analysis based on Monte Carlo(MC) simulation. In the analysis of CANDU pressure tube, the depth and aspect ratio of an initial semi-elliptical surface crack, a fracture toughness value and delayed hydride cracking(DHC) velocity are assumed to be probabilistic variables. As an example, some failure probabilities of piping and CANDU pressure tube are calculated using MC method with the stratified sampling MC technique, taking analysis conditions of normal operations. In the stratified MC simulation, a sampling space of probabilistic variables is divided into a number of small cells. For the verification of analysis results, a comparison study of the PFM analysis using other commercial code is carried out and a good agreement was observed between those results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.731-738
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• 2002

To understand failure behavior of pipe thinned by flow accelerated corrosion, in this study, the pipe failure tests were performed on 102mm-Sch.80 carbon steel pipe with various local wall thinning shapes, and the failure mode, load carrying capacity, and deformability were investigated. The tests were conducted under loading conditions of 4-points bending and internal pressure. The experimental results showed that the failure mode of thinned pipe depended on magnitude of internal pressure and thinning length as well as loading direction and thinning depth and angle. The variation in load carrying capacity and deformability of thinned pipe with thinning length was determined by stress type appled to the thinning area and circumferential thinning angle. Also, the effect of internal pressure on failure behavior was dependent on failure mode of thinned pipe, and it promoted crack occurrence and mitigated local buckling at thinned area.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.384-390
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• 2021

In this paper, durability evaluation and surface damage mechanism were investigated through solid particle erosion (SPE) test after applying hot-dip aluminizing (HDA) technology for the purpose of maintenance of marine economizer tube. Damaged surface shape was analyzed using SEM and 3D microscope. Compositional changes and microstructure of the HDA layer were analyzed through EDS and XRD. Durability was evaluated by analyzing weight loss and surface damage depth after SPE. HDA was confirmed to have a two-layer structure of Al and Al₅Fe₂. HDA+HT was made into a single alloy layer of Al₅Fe₂ by diffusion treatment. In the microstructure of HDA+HT, void and crack defect were induced during the crystal phase transformation process. The SPE damage mechanism depends on material properties. Plastic deformation occurred in the substrate and HDA due to ductility, whereas weight loss due to brittleness occurred significantly in HDA+HT. As a result, the substrate and HDA showed better SPE resistance than HDA+HT.