• The Journal of Engineering Geology
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• v.25 no.4
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• pp.587-598
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• 2015

We examined various existing threshold methods for the determination of the first arrival time of acoustic emission (AE), and developed a new variable threshold method that could determine the first arrival time of AE more accurately and more quickly than existing methods. The new method, a modification of an existing threshold method, does not fix the threshold, but applies variable thresholds for the AE signals according to noise analysis. Two- and three-dimensional models were established to test the effectiveness of the new method. It could determine source locations of AE in a two-dimensional model 38.3% more accurately than the pre-existing threshold methods. Its accuracy improvement over the existing methods in a three-dimensional model was about 15.2%. A practical test involved measuring the source locations of AE during three-point bending tests of granite cores. The new method placed the sources closer to the fracture plane than did the pre-existing methods, indicating its superior (and quicker) ability to determine the source locations of AE.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.551-565
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• 2017

A spray-applied waterproofing membrane which consists of polymers has a relatively higher constructability and adhesion than the conventional sheet-type waterproofing materials. Additionally, the spray-applied waterproofing membrane generally shows a waterproofing ability as a composite structure with shotcrete or concrete lining. Because its purpose is waterproofing at the structure, structural effects were not well reported than waterproofing abilities. In this study, structural effects of the membrane-attached concrete lining were evaluated using 3-point bending test by the numerical method. From the analysis, a load-displacement behavior of the concrete lining and fracturing energy after yielding were compared with various conditions. Consequently, concrete lining with spray-applied waterproofing membrane shows higher flexural strength and fracturing energy than the single-layer concrete lining.

• Resources Recycling
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• v.19 no.5
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• pp.31-43
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• 2010

To fabricate porous SiC candle filter for filtration facility of the IGCC system, the candle type filter preforms were fabricated by ramming and vacuum extrusion process. A commercially available ${\alpha}$-SiC powders with various particle size were used as starting raw materials, and $44\;{\mu}m$ mullite, $CaCO_3$ powder were used as non-clay based inorganic sintering additive. The candle typed preforms by ramming process and vacuum extrusion were sintered at $1400^{\circ}C$ for 2h in air atmosphere. The effect of forming method and particle size of filter matrix on porosity, density, strength (flexural and compressive strength) and microstructure of the sintered porous SiC candle tilters were investigated. The sintered porous SiC filters which were fabricated by ramming process have more higher density and strength than extruded filter in same particle size of the matrix, and its maximum density and 3-point bending strength were $2.00\;g/cm^3$ and 45 MPa, respectively. Also, corrosion test of the sintered candle filter specimens by different forming method was performed at $600^{\circ}C$ for 2400h using IGCC syngas atmosphere for estimation of long-term reliability of the candle filter matrix.

• Journal of Bio-Environment Control
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• v.26 no.3
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• pp.215-220
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• 2017

This study was conducted to improve the insufficiency of fruit vegetable grafting system developed by National Institute of Agricultural Sciences, Rural Development Administration. When the rotary blade cut the stem of scions and rootstocks, the grafting failure at curved cutting surfaces happened. The cutting depth of a tomato seedling by a rotated cutter was calculated 0.11 mm even when the cutting arm length and the maximum stem diameter were 50 mm and 5 mm, respectively. Mathematical analysis and high-speed photography showed that there was no problem by cutting in straight the stem of scions and rootstocks. The compression test of seedling stems to design the optimal shape of gripper showed that stems were not completely restored when they were compressed above 0.8 mm and 0.6 mm in case of rootstocks and scion, respectively. This study found that the bending angle of stem of tomato seedlings at the grafting period was 10 degree on average. The optimal gripper finger was the edge finger type which could be precisely set center point by adjusting the distance between fingers. In addition, it was found that most of seedling could be grasped without damage when the finger-to-finger distances is set to 2.5 mm for scion and 3.0 mm for rootstocks and finger are coated by 1 mm-thick flexible material.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.301-310
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• 2006

Carbon fiber reinforced polymer (CRFP) materials are well suited to the rehabilitation of civil engineering structures due to their corrosion resistance, high strength to weight ratio and high stiffness to weight ratio. Their application in the field of the rehabilitation of concrete structures is increased due to the vast number of bridges and buildings in need of strengthening. However, RC members, strengthened with externally bonded CFRP plates, happened to collapse before reaching the expected design failure load. Therefore, it is necessary to develop the new strengthening method to overcome the problems of previous bonded strengthening method. This problems can be solved by prestressing the CFRP plate before bonding to the concrete. In this study, a total of 21 specimens of 3.3 m length were tested by the four point bending method after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with various prestress levels ranging from 0.4% to 0.8% of CFRP plate strain. All specimen with end anchorage failed by a plate fracture regardless of the prestress levels while the specimen without end anchorage failed by the separation of the plate from the beam due to premature debonding. The cracking loads was proportionally related to the prestress levels, but the maximum loads of specimens strengthened with prestressed CFRP plates were insignificantly affected by the prestress levels.

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.2
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• pp.197-207
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• 2011

The study aimed at examining how different reline resins affect flexural strength and flexural modulus of denture base. A total of 80 specimens ($64{\times}10{\times}3.3$ mm, according to ISO 1567:1999) of heat-polymerized resin, 40 specimens for (Lucitone199(Dentsply Int., NewYork, USA), SR Ivocap(Ivoclar AG, Schaan, Liechtenstein)) respectively, were polymerized according to the manufacturer's instructions and divided into eight groups(n = 10). Control group specimens remained intact. Specimens in the other groups were abraded on both sides to 2 mm thickness, and were relined in 1.3 mm thickness with 3 types of resins (Lucitone199(Dentsply), SR Ivocap(Ivoclar), and Rebase II(Tokuyama Co., Ltd, Tokyo, Japan)). All specimens were preserved in distilled water at $37^{\circ}C$ for 50 hours, and then were subjected to flexural strength testing in a universal testing machine using 3-point loading. A crosshead speed of 5 mm/min was used, and the distance between the supports was 50 mm. Data analyses included one-way analysis of variance(ANOVA) and the Tukey Honestly Significant Difference test (p=.05). Both heat-polymerized resin groups and auto-polymerized resin groups showed statistically low flexural strength and flexural modulus than control groups. Specimens relined with Lucitone 199 showed significantly higher flexural strength and flexural modulus than those relined with SR-Ivocap. Specimens relined with auto-polymerized resin showed significantly lower flexural strength and flexural modulus than those relined with heat-polymerized resin. Relining with heat-polymerized resins showed superior mechanical properties to relining with an auto-polymerized resin. Relining with the same heat-polymerized resin as the denture base does not affect mechanical properties of a denture. Lucitone199 using a compression-mould technique resulted in the highest flexural strength.

• The korean journal of orthodontics
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• v.37 no.6
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• pp.432-439
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• 2007

The purpose of this study was to evaluate the influence of intraoral temperature changes on the orthodontic force level of a superelastic nickel-titanium alloy wire. Methods: Nickel-titanium archwires of $0.016"{\times}0.022"$ thickness were tested with a three point bending test setup, and temperature changes were applied. The force level changes according to temperature changes were measured at a 1.5 mm deflection during the loading phase and a 1.5 mm deflection during the unloading phase from a deflection to 3.1mm. Ten cycles of thermal cycling from baseline $(37^{\circ}C)$ to cold $(20^{\circ}C)$ or hot $(50^{\circ}C)$temperature were applied. Results: Alter thermal cycling, the force level during the loading phase decreased and the force level during the unloading phase increased even after the temperature was changed to the initial $37^{\circ}C$. Conclusions: The results suggest that the orthodontic force level can not return to the initial force level after temperature changes. When applying superelastic nickel-titanium archwires, we must consider that a lighter force than the loading force and a heavier force than the unloading force will be applied after intraoral temperature changes caused by eating and drinking.

• The Journal of Advanced Prosthodontics
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• v.10 no.2
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• pp.113-121
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• 2018

PURPOSE. The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes ($n-TiO_2$) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS. $TiO_2$ nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each $TiO_2$:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of $n-TiO_2$ addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS. SEM images of $n-TiO_2$ exhibited the presence of elongated tubular structures. The XRD pattern of synthesized $n-TiO_2$ represented the anatase crystal phase of $TiO_2$. Moderate to very strong significant positive correlations were observed between the concentration of $n-TiO_2$ and each of the 3 physicomechanical properties of PMMA (Pearson's P value ${\leq}.001$, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% $n-TiO_2$ were significantly higher than those of control ($P{\leq}.001$). Fracture toughness of samples reinforced with 5 wt% $n-TiO_2$ (but not those of 2.5% $n-TiO_2$) was higher than control (P=.002). CONCLUSION. Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.

• Journal of dental hygiene science
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• v.15 no.4
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• pp.407-412
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• 2015

This study investigated flexural properties of indirect Gum-shade composite resins for esthetic improvement. The material utilized in this study was Crea.lign, Twiny flow and Twiny paste (TP). Ten specimens were fabricated with a dimension of $25{\times}2{\times}2mm$ according to the ISO 4049. After fabrications, specimens were stored in the distilled water for 24 hours at the temperature of $37^{\circ}C$. Three-point bending test was performed in universal testing machine (Instron 3344; Instron, USA) at a crosshead speed of 1 mm/min until the failure occurred. TP exhibited a higher flexural strength (FS) and flexural modulus (FM) compared to the flowable materials. There were significant differences among the three materials in FS and FM. However, there was no significant difference in work of fracture (WOF) in all tested materials (p>0.05). In Weibull analysis, TP showed the greatest Weibull modulus which means a higher reliability of the materials. Also, Gum-shade composite resins revealed a strong correlation in all flexural properties. There was a positive correlation in FS-FM ($r^2=0.99$) and a negative correlation between FS-WOF and FM-WOF ($r^2>0.97$). Therefore, this confirmed that flexural property was important for mechanical behavior evaluation and useful information. To addition, this improved among mechanical properties correlation of materials as important factor.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.42 no.3
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• pp.144-150
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• 2016

Objectives: We compared the transbuccal and transoral approaches in the management of mandibular angle fractures. Materials and Methods: Sixty patients with mandibular angle fractures were randomly divided into two equal groups (A, transoral approach; group B, transbuccal approach) who received fracture reduction using a single 2.5 mm 4 holed miniplate with a bar using either of the two approaches. Intraoperatively, the surgical time and the ease of surgical assess for fixation were noted. Patients were followed at 1 week, 3 months, and 6 months postoperatively and evaluated clinically for post-surgical complications like scarring, infection, postoperative occlusal discrepancy, malunion, and non-union. Radiographically, the interpretation of fracture reduction was also performed by studying the fracture gap following reduction using orthopantomogram tracing. The data was tabulated and subjected to statistical analysis. A P -value less than 0.05 was considered significant. Results: No significant difference was seen between the two groups for variables like surgical time and ease of fixation. Radiographic interpretation of fracture reduction revealed statistical significance for group B from points B to D as compared to group A. No cases of malunion/non-union were noted. A single case of hypertrophic scar formation was noted in group B at 6 months postsurgery. Infection was noted in 2 patients in group B compared to 6 patients in group A. There was significantly more occlusal discrepancy in group A compared to group B at 1 week postoperatively, but no long standing discrepancy was noted in either group at the 6 months follow-up. Conclusion: The transbuccal approach was superior to the transoral approach with regard to radiographic reduction of the fracture gap, inconspicuous external scarring, and fewer postoperative complications. We preferred the transbuccal approach due to ease of use, minimal requirement for plate bending, and facilitation of plate placement in the neutral mid-point area of the mandible.