• Proceedings of the KSR Conference
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• 2002.10a
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• pp.72-79
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• 2002

The effects of carbon black on the critical J-value and the surface fracture morpology of the carbon-black filled natural rubbers were investigated. Different kinds of carbon blacks resulted in different critical J-values, surface, and roughness. It was noticed that the critical J-value was almost the same regardless of the length of a pre-crack. In addition, different kinds of carbon blacks resulted in different fracture morphologies, and micro-scale and macro-scale roughnesses. The critical J-value could be linearly expressed by the micro-scale roughness and the macro-scale roughness and it seemed related to the size distribution of carbon black particles. And we also found that the macro-scale ms roughness was more sensitive than the micro-scale ms roughness to the critical J-value by the result of correlation coefficient, r$^2$.

• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.617-622
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• 1992

In order to study on the effect of SiC whisker in flexural strength characterization of macro defect-free (MDF) cement composites, which composed of high alumina cement and polyvinyl alcohol, microstructural characterization of the composite specimens fabricated by the addition of SiC whiskers was investigated. Microproes are created around the SiC whisker, MDF cement didn't react with the SiC whisker. However, flexural strength of the composites have been improved. Fracture morphology of the composites, presents mainly intergranular type fracture passing around the unhydrated particles and siC whiskers, and partially transgranular type fracture. The main strengthening mechanisms of the MDF cement composites reinforced with SiC whiskers are characterized by crack deflection, microcracking, and bridging of cracks.

• Nuclear Engineering and Technology
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• v.34 no.2
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• pp.132-141
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• 2002

The effects of microstructure on fretting wear were investigated in Inconel 690 tube. The microstructure observation indicated that the solution annealing temperature and time affected the grain size of the Inconel 690 tubes. The carbide morphology, along grain boundaries, was mainly affected by thermal treatment time and temperature. The wear test results showed that specimens with larger grain size and with coarse carbides along grain boundaries had better wear resistance. Cracks were found in specimens with carbides along the grain boundary, while few cracks were found in carbide free specimens. It seemed that the carbides on grain boundary assisted crack formation and propagation in carbide containing specimens. On the other hand, the micro-hardness of specimen did not have a major role in fretting wear. It could be inferred from the SEM images of worn surfaces that the main wear mechanism of carbide containing specimen was delamination, while that of carbide free specimen was abrasion.

• Progress in Superconductivity and Cryogenics
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• v.12 no.2
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• pp.5-8
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• 2010

In this study, the effect of bending strain on the transport property and critical current of lap and butt-jointed (non-laminated) BSCCO tapes has been investigated. The samples were joined using a mechanically controlled jointing procedure. To achieve a uniform thickness at the joint a single point loading contact has been devised. GFRP mandrels with different bending radii which support the sample during bending have been used. $I_c$ have been measured at 77 K and self field. In the case of easy bending test for jointed BSCCO tapes, sudden degradation of $I_c$ is caused by the local strain concentration due to non uniform deformation at the edge parts of the joint. In the case of hard bending test of jointed BSCCO tapes transverse macroscopic crack at specific subsection caused a large $I_c$ degradation. The transport property of jointed BSCCO tapes in each bending mode was discussed with the damage morphology occurred.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.2
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• pp.153-161
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• 2009

After several PWSCCs were found in Bugey(France), Ringhals(Sweden), Tihange(Belgium), Oconee, Arkansas, Crystal Fever, Davis-Basse, VC Summer(U.S.A.), Thuruga(Japan), USNRC and PNNL started the research on PWSCC, that is, PINC project. The aim of this project is to fabricate and obtain representative NDE mock-ups with flaws to simulate tight PWSCC cracks, to identify and quantitatively assess NDE methods for accurately detecting, sizing and characterizing tight cracks such as PWSCC, to document the range of locations and crack morphologies associated with PWSCC and observed responses and to incorporate findings from other ongoing PWSCC research programs, as appropriate. By participating in PINC project, Korean morphology technique about PWSCC and NDE technique have improved and become similar lever with other advanced country. Therefore, the evaluation technique of integrity for nickel alloy component has been improved by cooperation with university, research institute and industries.

• Journal of Ocean Engineering and Technology
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• v.23 no.2
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• pp.69-73
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• 2009

The objective of this study was to obtain a better understanding of the delayed hydride cracking (DHC) of Zr-2.5Nb alloy. The DHC model has some defects: first, it cannot explain why the DHC velocity (DHCV) becomes constant regardless of an applied stress intensity factor, even though the stress gradient is affected by the applied stress intensity factor at the notch tip. Second, it cannot explain why the DHCV has a strong dependence on the method of approaching the test temperature by a cool-down or a heating-up, even under the same stress gradient, and third, it cannot predict any hydride size effect on the DHC velocity. The DHC tests were conducted on Zr-2.5Nb compact tension specimens with the test temperatures reached by a heating-up method and a cool-down method. Crack velocities were measured in hydrided specimens, which were cooled from solution-treatment temperatures at different rates by being furnace-cooled, water-quenched, and liquid nitrogen-quenched. The resulting hydride size, morphology, and distributions were examined by optical metallography. It was found that fast cooling rates, which produce very finely dispersed hydrides, result in higher crack growth rates. This different DHC behavior of the Zr-2.5Nb tube with the cooling rate after a homogenization treatment is due to the precipitation of the $\gamma$-hydrides only in the water-quenched Zr-2.5Nb tube. This experiment will provide supporting evidence that the terminal solid solubility of a dissolution (TSSD) of $\gamma$-hydrides is higher than that of $\delta$-hydrides.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.501-509
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• 2001

For the enhancement of ECT reliability on the primary water stress corrosion cracks of nuclear steam generator tubes, of which the occurrence is on the increase, it is important to comprehend the signal characteristics on crack morphology and to select an appropriate probe type. In this paper, the sizing accuracy and the detectability for the inner wall axial cracks of tubes were quantitatively evaluated using the following specimens: the electric discharge machined notches and the corrosion cracks which were developed on the operating steam generator tubes. The difference of eddy current signal characteristics between pancake and axial coil were also Investigated. The results obtained from this study provide a useful information for more precise evaluation on the inner wall axial tracks oi stram generator tubes.

• Analytical Science and Technology
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• v.6 no.2
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• pp.157-165
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• 1993

The potentiostatic etching dissolution method, which had been used for the quantification of precipitates in steel, was applied to investigate the origin of cracks occurred in 304 stainless steel during processing. The morphology of crack propagation was observed by SEM. EDS and EPMA were used for the analysis of chemical composition of large precipitates on the grain boundary. The crystal structure of these large precipitates was determined by X-ray diffraction and electron diffraction. In both a stainless steel plate and a wire, the crack propagated along the grain boundary. Large precipitates on the grain boundary were identified to be $M_2C$ and $M_{23}C_6$. Potentiostatic etching dissolution method was found to be appropriate to the sample preparation for the analysis of precipitates in stainless steel.

• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.393-399
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• 2018

Formation behavior of aluminum anodic oxide (AAO) films on Al6061 alloy was studied in view of thickness, morphology and defects in the anodic films in 20 vol.% sulfuric acid solution at a constant current density of $40mA/cm^2$, using voltage-time curve, observation of anodized specimen colors and surface and cross-sectional morphologies of anodic films with anodization time. With increasing anodizing time, voltage for film formation increased exponentially after about 12 min and its increasing rate decreased after 25 min, followed by a rapid decrease of the voltage after about 28 min. Surface color of anodized specimen became darker with increasing anodizing time up to about 20 min, while it appeared to be brighter with increasing anodizing time after 20 min. The darkened and brightened surfaces with anodizing time are attributed to an increase in thickness of porous anodic oxide film and a chemical damage of the films due to heat generated by increased resistance of the film, respectively. Cross-sectional observation of AAO films revealed the formation of defects of crack shape at the metal/oxide interface after 15 min which prevents the growth of AAO films. Width and length of the crack-like defect increased with anodizing time up to 25 min of anodizing, and finally the outer part of AAO films was partly dissolved or detached after 30 min of anodizing, resulting in non-uniform surface structures of the AAO films.

• Elastomers and Composites
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• v.43 no.1
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• pp.8-17
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• 2008

Styrene-butadiene rubber(SBR) has good abrasion resistance, miscibility, and anti-vibration property. however, it is easily damaged by ozone and swelled by hydrocarbon fluids because of unsaturation part in main chain, that causes loss of visco-elasticity and reduction of product's life cycle. Therefore, object of this study is to cope with this problem. SBR is blended with various proportion of ethylene-propylene-diene terpolymer(EPDM), which has excellent ozone and oxygen resistance, to improve physical properties and ozone resistance, and diverse analytical techniques are used to measure morphology, glass transition temperature$(T_g)$, ozone-resistance, degradation temperature, static spring constant, hardness for considering a suitability for anti-vibration industrial product. We found that the blend consisting of SBR 70% and EPDM 30% showed no crack after ozone test and good miscibility between SBR and EPDM from this study.