• Journal of the Korean Ceramic Society
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• v.45 no.10
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• pp.625-630
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• 2008

In the bone cement composed of dense granules of $\beta-Ca_3(PO_4){_2}(\beta-TCP)$ and $Ca(H_2PO_4){_2}H_2O$, the compressive strength, setting time and temperature rise were measured to observe the degradation of cement with respect to the stored days before setting. Decreases of compressive strength and temperature rise were observed, while setting time increased with respect to the stored days. The similar trends were repeated with the increase of temperature of storage. Such a change virtually meant the fading of the character of cement and it took place only when the two starting materials were mixed during storage. The degradation could be mitigated taking advantage of granular $\beta$-TCP instead of powdery one. The formation of $CaHPO_4$, which resulted from reaction with ambient humidity, was attributed to the degradation observed during storage. Dependence of the degradation behavior on mixing and temperature during storage was discussed in terms of the driving force for reaction of cement.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.12
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• pp.2995-3002
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• 2000

The remaining life estimation for the aged components in power plants as well as chemical plants are very important beacuse mechanical properties of the components are degraded with time of service exposure in high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components nondestructive techniques are needed to estimate the degradation. In this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at 630$\^{C}$. And the DC potential drop method and destructive methods such as tensile, K(sub)IC and hardness tests were used in order to evaluate the degradation of 1-Cr-1Mo-0.25V steels. The objective of this study is to investigate the possibility of the application of DCPD method to estimated the material degradation, and to analyse the relationship between the electrical relationship between the electrical resistivity and the degree material degradation.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.345-350
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• 2001

In order to perform elastic-plastic fracture mechanical analyses, fracture resistance curves for concerned materials are required. 1T-CT specimen was used to obtain fracture resistance curves. But the fracture resistance curve by the 1T-CT specimen was very conservative to evaluate the integrity of the structure. And fracture resistance curve was affected by the specimen geometry and crack plane orientation. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the 1T-CT specimen and to provide the additional safety margin. For these, the fracture tests using the real pipe specimen and standard 1T-CT specimen test were performed. 4-point bending jig was manufactured for pipe test and direct current potential drop method was used to measure the crack extension and length for pipe test. From the pipe and the 1T-CT specimen test results, it was observed that the J-integral of the 1T-CT specimen test at the crack initiation point was very small compare to that of the pipe specimen test.

• Carbon letters
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• v.7 no.1
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• pp.19-26
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• 2006

Three point bending tests of single edge notched beam (SENB) specimens were carried out to evaluate the fracture behavior of the fine-grain isotropic nuclear grade graphite, IG-11. To measure the crack initiation point and the subsequent crack growth, the direct current potential drop (DCPD) method and a traveling microscope were used. The effects of test variables like initial crack length, specimen thickness, notch type and loading rate on the measured fracture toughness, $K_Q$, were investigated. Based on the test results, the ranges of the test variables to measure the reliable fracture toughness value were proposed. During the crack growth, the rising R-curve behavior was observed in IG-11 graphite when the superficial crack length measured on the specimen surface was used. The increase of crack growth resistance was discussed in terms of crack bridging, crack meandering, crack branching, microcracking and crack deflection, which increase the surface energy and friction force.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.190-193
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• 2004

Two different diene monomers [dicyclopentadiene (DCPD) and 5-ethylidene-2-norbomene (ENB)] as self­healing agent for polymeric composites were microencapsuled by in-situ polymerization of urea and formaldehyde. The healing agents were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Exothermic reaction and glass transition temperature from DSC and storage modulus (G') and tan $\delta$ from DMA curves were analyzed for the samples cured for 5 min and 24 h in the presence of different amounts of catalyst. Micorcapsules were successfully formed for both diene monomers. Microcapsules containing the healing agent were manufactured and its thermal properties were characterized by thermo gravimetric analysis (TGA). Optical microscope (OM) and particle size analyzer (PSA) were employed to observe morphology and size distribution of microcapsules, respectively. Comparison of the two self-healing agents and their microcapsules with the two was made in this study.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.45.1-45.1
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• 2009

In this study, we investigated a calcium phosphate-calcium sulfate injectable bone substitute (IBS) with organic reinforcement of chitosan, citric acid and hydroxypropyl-methyl-cellulose (HPMC). The powder component of IBS consisted of tetra calcium phosphate (TTCP), dicalcium phosphate dihydrate (DCPD) and calcium sulfate dihydrate (CSD). The liquid component was a solution of citric acid and chitosan. The effect of HPMC in terms of setting time, compressive strength and apatite forming ability on this IBS was investigated. The mass content of HPMC in liquid phase was varied in array of 0%, 2%, 3% and 4%. The setting times obtained between 20 and 45 minutes. Compressive strength was achieved over 20 MPa after incubation at 370C and in 100% humidity for 28 days. Porosities were evaluated in relation with compressive strength. Elastic moduli of the 28 days after-incubation IBS were obtained around 4GPa

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.7
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• pp.1031-1038
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• 2001

In order to verify the analytical methods predicting failure behavior of cracked piping, full-scale pipe tests are crucial in nuclear power plant piping. For this reason, series of international test programs have been conducted. However, full-scale pipe tests require expensive testing equipment and long period of testing time. The objective of this paper is to develop a test system which can economically simulate the full-scale pipe test regarding the integrity evaluation. This system provides the failure behavior of cracked pipe by testing a wide-plate specimen. The system provides the failure behavior of cracked pipe by testing a wide-plate specimen. The system was developed for the integrity evaluation of nuclear piping based on the methodology of hardware-in-the-loop (HiL) simulation. Using this simulator, the piping integrity can be evaluated based on the elastic-plastic behavior of full-scale pipe, and the high cost full-scale pipe test may be replaced with this economical system.

• Korean Journal of Metals and Materials
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• v.47 no.7
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• pp.391-396
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• 2009

Tensile, low cycle fatigue, and fatigue crack growth rate tests were conducted at RT and $300^{\circ}C$ for type 304 stainless steel. Tensile was tested under displacement control and low cycle fatigue was tested under strain control. Fatigue crack growth rate test was conducted under load control and crack was measured by DCPD method. Yield strength and elongation decreased at $300^{\circ}C$. Dynamic strain aging was not detected at $300^{\circ}C$. Low cycle fatigue life increased but fatigue strength decreased at $300^{\circ}C$. Fatigue crack growth rate increased at $300^{\circ}C$. Dislocation structures were mixed with cell and planar and did not change with temperature. Grain size did not change but plastic strain increased at $300^{\circ}C$. Strain induced martensite after low cycle fatigue test increased at RT but decreased at $300^{\circ}C$. It was concluded that the increase of low cycle fatigue life at $300^{\circ}C$ was due to the decrease of strain induced martensite at which crack was initiated.

• Corrosion Science and Technology
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• v.18 no.1
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• pp.33-38
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• 2019

Alloy 600/182 with excellent mechanical/chemical properties have been utilized for nuclear power plants. Although both alloys are known to have superior corrosion resistance, stress corrosion cracking failure has been an issue in primary water environment of nuclear power plants. Therefore, primary water stress corrosion crack (PWSCC) growth rate tests were conducted to investigate crack growth properties of Alloy 600/182. To investigate PWSCC growth rate, test facilities including water chemistry loop, autoclave, and loading system were constructed. In PWSCC crack growth rate tests, half compact-tension specimens were manufactured. These specimens were then placed inside of the autoclave connected to the loop to provide primary water environment. Tested conditions were set at temperature of $360^{\circ}C$ and pressure of 20MPa. Real time crack growth rates of specimens inside the autoclave were measured by Direct Current potential drop (DCPD) method. To confirm inter-granular (IG) crack as a characteristic of PWSCC, fracture surfaces of tested specimens were observed by SEM. Finally, crack growth rate was derived in a specific stress intensity factor (K) range and similarity with overseas database was identified.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.655-659
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• 2019

Calcium phosphates such as HA (hydroxyapatite), β-TCP (tricalcium phosphate) and biphasic HA/β-TCP, were synthesized by wet chemical precipitation in aqueous solution combined with ball milling process. Nanosize powders of the calcium phosphates were synthesized using Ca(OH)2 and H3PO4. The effects of initial precursor Ca/P ratio (1.30, 1.50 and 1.67), ball milling process and post heat-treatment on the phase evolution behavior of the powders were investigated. The phase of resulting powder was controllable by adjusting the initial Ca/P ratio. HA was the only phase for as-prepared powders in both cases of Ca/P ratios of 1.50 and 1.67. The single HA phase without any noticeable second phase was obtained for the initial Ca/P ratio of 1.67 in the overall heat-treatment range. Pure β-TCP and biphasic calcium phosphate (HA/β-TCP) were synthesized from precursor solutions having Ca/P molar ratios of 1.30 and 1.50, respectively, after having been heat-treated above 700 ℃. The β-TCP phase has appeared on the pre-existing DCPD (dicalcium phosphate dihydrate) and/or HA phase. Dense ceramics having translucency were obtained at a considerably lower sintering temperature. The modified process offered a fast, convenient and economical route for the synthesis of calcium phosphates.