• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.1
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• pp.38-44
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• 2003

Performance demonstration with real flawed specimens has been strongly required for nondestructive evaluation of safety class components in nuclear power plant. Mechanical or thermal fatigue crack and intergranular stress corrosion cracking could be occured in the in-service nuclear power plant and mechanical fatigue crack was selected to study in this paper. Specimen was designed to produce mechanical fatigue flaw under tensile stress. The number of cycles and the level of stress were controlled to obtain the desired flaw roughness. After the accurate physical measurement of the flaw size and location, fracture surface was seal-welded in place to ensure the designed location and site. The remaining weld groove was then filled by using gas-tungsten are welding(GTAW) and flux-cored arc welding(FCAW). Results of radio graphic and ultrasonic testing showed that fatigue cracks were consistent with the designed size and location in the final specimens.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.6.2-6.2
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• 2010

Stainless steel is widely known to have superior corrosion properties. However, in some harsh conditions it still suffers various kinds of corrosions such as galvanic corrosion, pitting corrosion, intergranular corrosion, chloride stress corrosion cracking, and etc. For the corrosion protection of stainless steel, the ceramic coatings such as protective silica film can be used. The sol-gel coating technique for the silica film has been extensively studied especially because of the cost effectiveness. It has been proved that silica can improve the oxidation and the acidic corrosion resistance of metal surface in a wide range of temperatures due to its high heat and chemical resistance. However, in the sol-gel coating process there used to engage a heat treatment at an elevated temperature like $500^{\circ}C{\sim}600^{\circ}C$ where cracks in the silica film would be formed because of the thermal expansion mismatch with the metal. The cracks and pores of the film would deteriorate the corrosion resistance. When the heat treatment temperature is reduced while keeping the adhesion and the density of the film, it could possibly give the enhanced corrosion resistance. In this respect, inorganic protective silica film was tried on the surface of stainless steel using a sol-gel chemical route where silica nanoparticles, tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) were used. Silica nanoparticles with different sizes were mixed and then the film was deposited on the stainless steel substrate. It was intended by mixing the small and the large particles at the same time a sufficient consolidation of the film is possible because of the high surface activity of the small nanoparticles and a modest silica film is obtained with a low temperature heat treatment at as low as $200^{\circ}C$. The prepared film showed enhanced adhesion when compared with a silica film without nanoparticle addition. The films also showed improved protect ability against corrosion.

• Tribology and Lubricants
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• v.32 no.4
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• pp.113-118
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• 2016

As an economic, high quality, and highly reliable gear with low noise and low vibration is demanded, an overall finite element analysis regarding a gear is required. Also, an infrared thermography test, which is a quantitative testing technique, is demanded for safety and longer lifespan of gear products. In order to manufacture a gear product or to determine safety of a gear being used, it is necessary to precisely determine ingredients of a material constituting a gear and detect any internal defect. This study aims to realize a design that minimizes the spur gear displacement with respect to power during its rotation and ensures the spur gear control capacity by using a 3D model and the midasNFX program. This facilitates the assessment of the possibility of cracking by evaluating the stress intensity and focusing on the integrity of the spur gear. We prepare the specimen of the spur gear based on the possibility of cranking as per the result of the structural interpretation from an infrared ray thermal measuring technique. After cooling the spur gear, we perform experiments using thermography and halogen lamps and analyze the temperature data according to the results of the experiment. In the experiment which we use thermography after cooling, we find a rise in the temperature of the room. As a result, the defective part show temperatures lower than their surroundings while the normal parts have temperatures higher than the defective parts. Therefore, it possible to precisely identify defective part owing to its low temperature.

• Transactions of Materials Processing
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• v.17 no.4
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• pp.240-248
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• 2008

The effect of alloying elements(Mn, S, Mo, B) on the high temperature deformation behavior of Fe-29%Ni-17%Co (Kovar) alloy were investigated. And the effect of high temperature oxidation on the hot ductility was also studied. The hot ductility of Kovar alloy was drastically increased with the addition of Mn and lowering of S content. It has been found that the brittle intergranular fracture at high temperature cracking is closely associated with the FeS sulfide along the grain boundary. When Mn was added, the type of sulfide was changed to MnS from FeS and ductile intergranular fracture and transgranular fracture were promoted. The formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation. Hot ductility was remarkably improved by the addition of Boron. The improvement of hot ductility results from the grain boundary migration mainly due to the dynamic recrystallization at lower temperature range ($900{\sim}1000^{\circ}C$).

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.33-36
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• 2007

In order to select the optimum mix for the required fluidity and strength of mass concrete which is applied to transfer girder and to choose the optimum curing method depending on circumstances through hydration heat analysis of mass concrete, this study examined slump flow, air content and elapsed variation (0, 30, 60, 90) in unhardened concrete properties and reviewed compressive strength characteristics in hardening properties. And hydration heat analysis results through simulation are as follows; 1) Fluidity changes of unhardened concrete showed no significant difference, and those of elapsed variation also showed no difference but a bit of tendency to increase in comparison with the initial properties. 2) The higher the water-binder ratio was, the lower the compressive strength properties were, and the higher the fly ash replacement rate was, the lower the compressive strength development was. 3) In case of $Fc=40N/mm^2$, the optimum mix was fly ash replacement rate of 15% from water-binder ratio of 33.0%. 4) Hydration heat analysis results showed that in case of bundle cast, concrete temperature profile characteristics around transfer girder was unfavorable, and in case of separate cast, constant curing for at least seven days guaranteed thermal cracking index of 1.2.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.2
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• pp.20-27
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• 2010

In order to prevent the corrosion of component contacted primary water designed alloy 600 material in the nuclear power plant. But the primary water stress corrosion cracking(PWSCC) of alloy 600 and weld area occurs continuously due to the residual stress. The leakage accident resulted from PWSCC in the drain nozzle of the steam generator of domestic power plants. Heater sleeves of the pressurizer are welded with alloy 600 weld material and therefore exposed to the primary water environment. PWSCC occurred in heater sleeve material and weld area of many foreign power plants. The current issue of domestic nuclear power plants are consequently concentrated to PWSCC of similar material. In order to improve the detection and the sizing of the PWSCC in the welding sleeve of the pressurizer, the automatic UT system and multi-directions probe sets have been developed. The experimental studies have been performed using the mock-up block containing artificial reflectors(ID connected EDM notch) and semi-artificial cracks made from thermal fatigue. The automatic UT System is applied in the detection and the length sizing of the ID/OD on the tube and the J-groove weld area of the artificial reflectors and results of the detection and the sizing are compared respectively. Also, the developed automatic UT system is successfully accomplished to inspect the heater sleeve and the J-groove weld area on the pressurizer for the detection of PWSCC.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.10
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• pp.704-710
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• 2014

Biomass is considered an alternative energy which can solve an greenhouse gas problem like $CO_2$ which is a major contributor to global warming. The biomass can be converted to various energy sources through thermochemical conversion. In this study, a continuous gasifier was engineered for a wood biomass gasification. The biomass was used a waste wood. The experiments of $CO_2$ gasification were achieved as the gasification temperature, moisture content and input $CO_2$ concentration. The results showed that the yield of producer gas increased with an increasing the gasification temperature. The amount of the light tar increased due to the decomposition of gravimetric tar by the thermal cracking, and the char was confirmed pore development through the SEM analysis. The CO concentration was increased with an increased input $CO_2$ concentration from Boudouard reaction. Through the parametric screening studies, the hydrogen and carbon monoxide concentration were 32.91% and 48.33% at the optimal conditions of this test rig.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.42-46
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• 2016

Hydrogen assisted cracking (HAC) is one of the most complicated problem in welding. Huge amount of studies have been done for decades. Based on them, various standards have been established to avoid HAC. But it is still a chronic problem in industrial field. It is well known that the main causes of the hydrogen crack are residual stress, crack susceptible micro structures and a certain critical level of hydrogen concentration. Even though the exact generating mechanism is unclear till today, it has been reported that the hydrogen level in the weld metal should be managed less than a certain amount to prevent it. Matsuda studied that the residual hydrogen level in the weld metal can be varied even if the initial hydrogen content is same. It is also insisted in this report that the residual hydrogen concentration is in stronger correlation with hydrogen crack than the initial hydrogen content. But, in practical point of view, the residual hydrogen is still hard to consider because measuring hydrogen level is time and cost consuming process. In this regard, numerical analysis is the only solution for considering the residual hydrogen content. Meanwhile, Takahashi showed the possibility of predicting the residual hydrogen by a rigorous FE analysis. But, few commercial software suitable for solving the weld metal hydrogen has been reported yet. In this study, two dimensional thermal - hydrogen coupled analysis was developed by using the commercial FE software MARC. Since the governing equation of the hydrogen diffusion is similar to the heat transfer, it is shown that the heat transfer FE analysis in association with hydrogen diffusion property can be used for hydrogen diffusion analysis. A series of simulation was performed to verify the accuracy of the model. For BOP (Bead-On-Plate) and the multi-pass butt welding simulations, remaining hydrogen contents in the weld metal is well matched with measurements which are referred from Kim and Masamitsu.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1057-1060
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• 2008

For high performance concrete, due to its low water cement ratio (water binder ratio) and addition of mineral admixtures, pretty high autogenous shrinkage and thermal deformation occur at very early age of casting (especially before hardening). This may lead to early age cracking of HPC structures, and then may influence the durability of HPC. This paper has monitored the early age properties of HPC successfully by embedded FBG strain sensor. The results showed that the deformation increased rapidly within the first day after HPC casting. And its value is up to $85{\mu}{\varepsilon}$, which is the 30% of two-month deformation ($280{\mu}{\varepsilon}$). Considering the durability and permeability of HPC, the first-day deformation is pretty high and can not be neglected. Also the superior capability of FBG sensors such as continuity, stability and multiplexed technique etc, has been demonstrated.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.2
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• pp.6-10
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• 2002

Al films (1000~4000${\AA}$)were deposited on glass and polymer(polyethersulfine) plastic substrates by DC-magnetron sputtering for plastic-based flat-panel displays. A stepped heating process was used both to improve the electrical characteristics and to diminish the thermal expansion of the polymer substrates. Following this procedure, we could succeed in sputtering Al films without any cracking or shrinkage of the polymer substrates. The treatment temperatures and deposited process of Al films were under 200$^{\circ}C$. Also, this low temperature fabrication process allows the application of plastic substrates. Scanning Electrom Microscopy, Atomic Force Microscopy, X-ray Dffractometry, and electrical measurements such as resistivity measurements were performed to investigate the properties of deposited the Al films and their reliability.