• Journal of the Korean institute of surface engineering
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• v.45 no.3
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• pp.130-135
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• 2012

Hydrogen charging was electrochemically conducted at high strength DP steels and TRIP steel with varying charging time. The penetration depths and the mechanical properties with charging conditions were investigated through the distribution of micro-hardness and the microstructural observation of the subsurface zone. The micro-Vickers hardness was measured to evaluate the hydrogen embrittlement of subsurface zone in addition to the microscope investigation. It was shown that the hydrogen amounts decreased in DP steels and TRIP steel with increasing hydrogen charging time. As shown by micro-Vickers hardness test and small punch test results, micro-Vickers hardness and SP energy for DP steels and TRIP steel decreased with increasing hydrogen charging time, for constant value of charging current density. SEM investigation results for the hydrogen contained samples showed that the major fracture behavior was brittle fracture which results in dimples on fractured surface and the size of dimples were decreased with increasing hydrogen charging time. These results indicate that hydrogen embrittlement is the major cause for the fracture of high strength steels and also micro-Vickers hardness test and small punch test is a valuable test method for hydrogen embrittlement of high strength sheet steels.

• Restorative Dentistry and Endodontics
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• v.44 no.2
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• pp.19.1-19.9
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• 2019

Objectives: The purpose of this study was to evaluate the cyclic fatigue, bending resistance, and surface roughness of EdgeEvolve (EdgeEndo) and ProTaper Gold (Dentsply Tulsa Dental Specialties) nickel-titanium (NiTi) rotary files. Materials and Methods: The instruments (n = 15/each) were tested for cyclic fatigue in single- ($60^{\circ}$ curvature, 5-mm radius) and double-curved (coronal curvature $60^{\circ}$, 5-mm radius, and apical curvature of $30^{\circ}$ and 2-mm radius) artificial canals. The number of cycles to fracture was calculated. The bending resistance of both files were tested using a universal testing machine where the files were bent until reach $45^{\circ}$. Scanning electron microscopy and x-ray energy-dispersive spectrometric analysis were used for imaging the fractured segments, while the atomic force microscope was used to quantify the surface roughness average (Ra). Results: EdgeEvolve files exhibited higher cyclic fatigue resistance than ProTaper Gold files in single- and double-curved canals (p < 0.05) and both files were more resistant to cyclic fatigue in single-curved canals than double-curved canals (p < 0.05). EdgeEvolve files exhibited significantly more flexibility than did ProTaper Gold files (p < 0.05). Both files had approximately similar Ni and Ti contents (p > 0.05). EdgeEvolve files showed significantly lower Ra values than ProTaper Gold files (p < 0.05). Conclusions: Within the limitation of this study, EdgeEvolve files exhibited significantly higher cyclic fatigue resistance than ProTaper Gold files in both single- and double-curved canals.

• Journal of Technologic Dentistry
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• v.41 no.2
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• pp.71-80
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• 2019

Purpose: In this study, to evaluate the effect of oxide changes on the shear bond strength according to the composition of Ni-Cr alloys for porcelain fused matal crown, T-4 alloys, Zeroy alloys and Zeroy-X alloys were selected. Methods: 20 specimens were fabricated using selected Ni-Cr alloys and porcelain powders. A Ni-Cr alloy having a diameter of 5 mm and a height of 25 mm was produced and the metal surface was polished. Porcelain powder was fired on the polished metal surface to a diameter of 5 mm and a height of 3 mm. The experiment group consisted of three groups, T-4(TNA), Zeroy(ZNA) and Zeroy-X(ZXA). The fabricated specimens were mounted on a jig of a universal testing machine(UTM) and fracture strength was measured by applying a shear force at a UTM crosshead speed of 0.5 mm/min. The fracture strength was calculated as the bond strength between the porcelain and the alloy. The surface of the fractured alloy was analyzed by X-ray diffraction(XRD) and scanning electron microscopy(SEM), and the components of the oxide were measured by energy dispersive X-ray spectroscopy(EDX) line profile method. Results: In SEM, XRD and EDX analysis, yttrium tended to increase the mechanical and chemical bonding forces. The shear bond strength of ZXA group containing yttrium showed the highest value at 27.53 MPa. Conclusion: Based on the results of this study, it is considered that the yttrium-added Ni-Cr alloy is clinically acceptable in porcelain shear bond strength.

• The Journal of Advanced Prosthodontics
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• v.15 no.1
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• pp.33-43
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• 2023

PURPOSE. This study investigated the physical and mechanical changes in the titanium base of three different hybrid abutment materials after cyclic loading by estimating the post-load reverse torque value (RTV), compressive side fulcrum wear pattern of titanium base, and surface roughness. MATERIALS AND METHODS. A total of 24 dental implants were divided into three groups (n = 8 each): Group Z, LD, and P used zirconia, lithium disilicate, and polyetheretherketone, respectively, for hybrid abutment fabrication. RTV was evaluated after cyclic loading with 50 N for 1.2 × 10⁶ chewing cycles. The compressive sides of the titanium bases were analyzed using a scanning electron microscope, and the roughness of the affected areas was measured using an optical profilometer after loading. Datasets were analyzed using Kruskal-Wallis test followed by Mann-Whitney tests with the Bonferroni correction (α = .05). RESULTS. Twenty-three samples passed the test; one LD sample fractured after 770,474 cycles. Post-load RTV varied significantly depending on the hybridabutment material (P = .020). Group P had a significantly higher median of post-load RTVs than group Z (16.5 and 14.3 Ncm, respectively). Groups LD and P showed minor signs of wear, and group Z showed a more pronounced wear pattern. While evaluating compressive side affected area roughness of titanium bases, lower medians were shown in group LD (Ra 0.16 and Rq 0.22 ㎛) and group P (Ra 0.16 and Rq 0.23 ㎛) than in group Z (Ra 0.26 and Rq 0.34 ㎛); significant differences were found only among the unaffected surface and group Z. CONCLUSION. The hybrid abutment material influences the post-load RTV. Group Z had a more pronounced wear pattern on the compressive side of titanium base; however, the surface roughness was not statistically different among the hybridabutment groups.

• Journal of the Korean Geotechnical Society
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• v.39 no.8
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• pp.17-28
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• 2023

Laboratory-scale hydraulic fracturing experiments were conducted on granite specimens at various viscosities and injection rates of the fracturing fluid. A series of cross-sectional computed tomography (CT) images of fractured specimens was obtained via a three-dimensional X-ray CT imaging method. Pixel-level fracture segmentation of the CT images was conducted using a convolutional neural network (CNN)-based Nested U-Net model structure. Compared with traditional image processing methods, the CNN-based model showed a better performance in the extraction of thin and complex fractures. These extracted fractures extracted were reconstructed in three dimensions and morphologically analyzed based on their fracture volume, aperture, tortuosity, and surface roughness. The fracture volume and aperture increased with the increase in viscosity of the fracturing fluid, while the tortuosity and roughness of the fracture surface decreased. The findings also confirmed the anisotropic tortuosity and roughness of the fracture surface. In this study, a CNN-based model was used to perform accurate fracture segmentation, and quantitative analysis of hydraulic stimulated fractures was conducted successfully.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.1
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• pp.84-95
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• 2001

Titanium is widely used in dentistry for its low density, high strength, fatigue resistance, corrosion resistance, and biocompatibility. But it has a tendency of surface damage under circumstance of friction and impact for its low hardness of the surface. Coating is one of methods fir increasing surface hardness. Its effect is to improve surface physical characteristics without change of titanium. Diamond-like carbon and titanium nitride are known for its high hardness of the surface. So that this study was aimed at the wear test and the cytotoxicity test of the commercially pure titanium and Ti-6Al-4V alloy which were deposited by diamond-like carbon film or titanium nitride film to acertain improvement of the surface hardness and the biocompatibility. A disk (25mm diameter, 2mm thickness) was made of commercially pure titanium and Ti-6Al-4V alloy and these substrates were deposited by diamond-like carbon film or titanium nitride film. Diamond-like carbon film was deposited by the method of radiofrequency plasma assisted chemical vapor deposition and titanium nitride film was deposited by the method of reactive arc ion plating. Then these substrates were tested about wear characteristics by the pin-on-disk type wear tester in which ruby ball was used as a wear causer under the load of 32N, The fracture cycles were measured by rotating the substrates until their films were fractured. The wear volume was measured after 150 cycles and 3,000 cycles using surface profiler. The cytotoxicity test was peformed by the method of the MTT assay. The results were as follows : 1. In the results of the wear volume test, commercially pure titanium and titanium alloy which were coated by diamond-like carbon film or titanium nitride aim had higher resistance against wear than the substrates which were not coated by any films (P<0.05). 2. In the results of the fracture cycle test and the wear volume test, diamond-like carbon film had higher resistance against wear than titanium nitride film (P<0.05). 3. In both coatings of diamond-like carbon aim and titanium nitride film, Ti-6Al-4V alloy had higher resistance against wear than commercially pure titanium (P<0.05) 4. In the results of the cytotoxicity test, diamond-like carbon film and titanium nitride film had little cytotoxicity as like commercially pure titanium or Ti-6Al-4V alloy (P>0.05).

• Journal of Conservation Science
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• v.16 s.16
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• pp.39-51
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• 2004

The standing Buddha named Taehwa 4 yew in the Jincheon were sculptured with rock cliff of the dark grey shale. Front of the Buddha statue shows $N40^{\circ}W$ strike with nearly vertical dip toward the back side. Rock blocks of the Buddha statue well developed with bedding and laminations whereas rock surface distributed into the various irregular discontinuities. Sculptured lines of the Buddha were uncertain because of degradation and exfoliations on the rock surface. The surface near the Buddha statue is highly contaminated with lichen and mosses, and accelerate physical and biological weathering owing to the roots of weed and bush along the fracture systems. For the conservational treatment, we treated with primary wet cleaning by air gun and secondary cleaning treatment using distilled water. Separated rock surface and fractured parts fasten and/or fill up the boundaries of the rock blocks using epoxy resin for conservation of rock properties. Some brittle surface was treatment with water repellent consolidant of ethyl silicates, and heterogeneous surface carried out color matching by acrylic pigments. Upper part of the Buddha statue dig out small ditch for rain water drainage, and near surface of the Buddha statue treat removal works for lichen, weeds and bush. The duration capacity of the Buddha constituting rocks are degraded by various weathering factors, therefore we suggest that this Buddha statue have need to do long term monitoring and synthetic conservation researches.

• Restorative Dentistry and Endodontics
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• v.35 no.6
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• pp.461-472
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• 2010

Objectives: This study evaluated microtensile bond strength (${\mu}TBS$) and short-rod fracture toughness to explain fractural behavior of repaired composite restorations according to different surface treatments. Materials and Methods: Thirty composite blocks for ${\mu}TBS$ test and sixty short-rod specimens for fracture toughness test were fabricated and were allocated to 3 groups according to the combination of surface treatment (none-treated, sand blasting, bur roughening). Each group was repaired immediately and 2 weeks later. Twenty-four hours later from repair, ${\mu}TBS$ and fracture toughness test were conducted. Mean values analyzed with two-way ANOVA / Tukey's B test ($\alpha$= 0.05) and correlation analysis was done between ${\mu}TBS$ and fracture toughness. FE-SEM was employed on fractured surface to examine the crack propagation. Results: The fresh composite resin showed higher ${\mu}TBS$ than the aged composite resin (p < 0.001). Mechanically treated groups showed higher bond strength than non-mechanically treated groups except none-treated fresh group in ${\mu}TBS$ (p < 0.05). The fracture toughness value of mechanically treated surface was higher than that of non-mechanically treated surface (p < 0.05). There was no correlation between fracture toughness and microtensile bond strength values. Specimens having high KIC showed toughening mechanism including crack deviation, microcracks and crack bridging in FE-SEM. Conclusions: Surface treatment by mechanical interlock is more important for effective composite repair, and the fracture toughness test could be used as an appropriate tool to examine the fractural behavior of the repaired composite with microtensile bond strength.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.370-375
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• 2004

Fatigue tests were carried out to find the fatigue characteristics in the super-long life range by using a cantilever type rotational bending fatigue test machine. Three kinds of specimen in bearing steels with the quenched and tempered in air (A and B, B: shot peened after heal treatment) and under vacuum conditions(C:non-shot peened)were tested in this study. S-N curves obtained from fatigue tests of C specimen tend to come dawn again in the super-long life range due to fish-eye type cracking, while most of A and B specimens fractured by surface defects such as scratches and slip lines. This duplex S-N behavior for the high strength steels have to be reviewed by the change of fracture modes.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.435-438
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• 1991

This work is aimed to clarify the effect of only crosslinking of polyethylene on the water tree propagation and thus the crosslinking of LDPE was made by use of $Co^{60}$ $\gamma$-ray irradiation at room temperature. For this purpose, before water tree testing under same test conditions, injection molded samples were made of LDPE using CNRS laboratory model and also some of them were irradiated under different dose rate for crosslinking. Afterwards, the aged specimens were put into microscopic investigation as a mean to compare their different morphological aspects by use of SEM for the fractured surface. The SEM observation points out that the untreed region in the irradiated PE shows the densed structure whereas that in the LDPE is not closely packed. Also in the water treed region of LDPE, the density and the dimension of voids are higher than those in irradiated PE. Based on our results, it seems that the difference in the PE structure could sufficiently contribute to cause the different water tree propagation of these materials.