• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.28 no.5
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• pp.383-389
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• 2002

This is a retrospective study on emergency patients with active oral bleeding. The study was based on a series of 135 patients treated as emergency patients at Wonju Christian Hospital, from Jan. 1, 1997, to Dec. 31, 2001. The postoperative bleeding was the most frequent cause of active oral bleeding in emergency room and bleeding from trauma and medically compromised (bleeding disorders) patients were next in order of frequency. In the injury of maxillofacial vessels, peak incidence was occurred in the inferior alveolar vessel (42.9%), followed by the submucosal vessel of lip & cheek, the superior alveolar vessel, and sublingual vessels. The most common disease of bleeding disorders was vascular wall alteration (infection, etc), followed by liver disease, thrombocytopenic purpura, anti-coagulation drugs in order. In the characteristics of dental diseases on bleeding disorders, periodontal disease and alveolar osteitis (osteomyelitis) were more common. The hemostasis was most obtained by use of wound suture, simple pressure dressing, drainage for infection control and primary interdental wiring of fracture. In the complication group, the infrequent incidence was showed in vomiting, hypovolemic shock, syncope, recurred bleeding & aspiration pneumonia. In the uncontrolled oral bleeding, the injured vessels were suspected as skull base & ethmoidal vessels. In this study, authors found that the close cooperation between the dentistry (Oral and maxillofacial surgery) and the medicine (emergency & internal medicine) was the most important for early proper control of active oral bleeding. And then post-operative wound closure, drainage for infection control and previous systemic evaluation of bleeding disorders were critical for the prevention of postoperative bleeding in the local dental clinic.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.354-358
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• 2000

Tetragonal (t)-ZrO2/Al2O3 composites doped with Y2O3, Nb2O5, and Fe2O3 ((Y, Nb, Fe)-TZP/Al2O3) were prepared over the range containing Fe2O3 from 0.1 to 0.5 mol% with 0.1 mol% intervals to evaluate the effect of Fe2O3 addition on chromaticity, hydrothermal stability, and mechanical property of the composites. After autoclaving for 20 h at 18$0^{\circ}C$ under 3.5 MPa water vapor pressure, no tlongrightarrowm phase transformation was observed probably due to the preferential solid solubility of Fe2O3 in Al2O3, the presence of the rigid Al2O3 particles, and the inherent phase stability of (Y, Nb)-TZP. The optimized strength and the fracture toughness of the composite were 700 MPa and 8.5 MPa.m1/2, respectively, when 0.1 mol% Fe2O3 was added. The composites have shown a gradual color change from a slightly white ivory to a pale yellowish brown with increasing the Fe2O3 concentration.

• Nuclear Engineering and Technology
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• v.50 no.2
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• pp.218-222
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• 2018

An oxide-dispersion-strengthened (ODS) layer was formed on Zircaloy-4 tubes by a laser beam scanning process to increase mechanical strength. Laser beam was used to scan the yttrium oxide ($Y_2O_3$)-coated Zircaloy-4 tube to induce the penetration of $Y_2O_3$ particles into Zircaloy-4. Laser surface treatment resulted in the formation of an ODS layer as well as microstructural phase transformation at the surface of the tube. The mechanical strength of Zircaloy-4 increased with the formation of the ODS layer. The ring-tensile strength of Zircaloy-4 increased from 790 to 870 MPa at room temperature, from 500 to 575 MPa at $380^{\circ}C$, and from 385 to 470 MPa at $500^{\circ}C$. Strengthening became more effective as the test temperature increased. It was noted that brittle fracture occurred at room temperature, which was not observed at elevated temperatures. Resistance to dynamic high-temperature bursting improved. The burst temperature increased from 760 to $830^{\circ}C$ at a heating rate of $5^{\circ}C/s$ and internal pressure of 8.3 MPa. The burst opening was also smaller than those in fresh Zircaloy-4 tubes. This method is expected to enhance the safety of Zr fuel cladding tubes owing to the improvement of their mechanical properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.521-528
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• 2018

Military vehicles use run-flat wheels for emergency situations. Run-flat wheels can run required distance in a defined duration with the pressure loss tire. For the application of a run-flat system, wheels are designed in 2 pieces, including an inner rim and outer rim. These rims are assembled using clamping bolts. Clamping bolts determine the durability of military vehicle wheels because fracture of clamping bolts account for most wheel failures. For improving wheel durability, clamping bolt durability must be improved. In this study, wheel test conditions and bolt design were investigated. Existing test standards are not sufficient to conduct endurance tests. Supplementary conditions were investigated. Using these modified test conditions, the durability of wheels including clamping bolts was tested and verified. Results found the durability of wheels improved more than 168%. This study also proposes improvements in the design process of clamping bolts.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.4
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• pp.333-340
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• 2019

The effects of compaction methods on the sintering density, microstructures, and mechanical properties were investigated in ${\alpha}-alumina$ ceramics. ${\alpha}-Alumina$ powders were granulated with a 10% aqueous solution of polyvinyl alcohol (PVA). Uniaxially pressed (UAP) and cold isostatic-pressed (CIP) samples were prepared by pressing uniaxially at a pressure of 1 ton for 1 min, and isostatically at 200 MPa for 15 min, respectively. Subsequently, both types of samples were sintered at $1,200^{\circ}C$, $1,300^{\circ}C$, $1,400^{\circ}C$, $1,450^{\circ}C$, $1,500^{\circ}C$, $1,550^{\circ}C$, and $1,600^{\circ}C$ at a rate of $5^{\circ}C/min$ for 2 h. The CIP samples were better than the UAP samples for all properties measured, such as the sintering density, Vicker's hardness, and toughness. The CIP sample sintered at $1,400^{\circ}C$ showed the maximum Vicker's hardness and toughness; this may be attributed to the competing effects of a decrease in porosity and the growth of grains with increasing sintering temperature.

• Journal of Powder Materials
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• v.26 no.2
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• pp.132-137
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• 2019

Tungsten carbide (WC) hard materials are used in various industries and possess a superior hardness compared to other hard materials. They have particularly high melting points, high strength, and abrasion resistance. Accordingly, tungsten carbide hard materials are used for wear-resistant tools, cutting tools, machining tools, and other tooling materials. In this study, the WC-5wt.%Co, Fe, Ni hard materials are densified using the horizontal ball milled WC-Co, WC-Fe, and WC-Ni powders by a spark plasma sintering process. The WC-5Co, WC-5Fe, and WC-5Ni hard materials are almost completely densified with a relative density of up to 99.6% after simultaneous application of a pressure of 60 MPa and an electric current for about 15 min without any significant change in the grain size. The average grain size of WC-5Co, WC-5Fe, and WC-5Ni that was produced through SPS was about 0.421, 0.779, and $0.429{\mu}m$, respectively. The hardness and fracture toughness of the dense WC-5Co, WC-5Fe, WC-5Ni hard materials were also investigated.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.33-39
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• 2018

In this study, important characteristics were identified for the Geosynthetic-soil interface using overburden pressure and saltwater and fresh water to evaluate silt shear behavior of the Geosynthetic-soil interface. In addition, waste landfill can secure spaces for waste disposal in the sea and this spaces can be used for additional facilities which will be necessary in the future. Analysis of behavior characteristics on interface of Geosynthetic-soil shows that, if analyzed using standard consolidometers, the consolidation stress of fresh water increased significantly more than saltwater. When analyzed using cyclic shear apparatus, saltwater and freshwater in both conditions, the displacement value increases as the wire gauges become closer to the lower module, and the shear fracture tends to occur radically under saltwater conditions than fresh water. Therefore, seawater, fresh water that act on the interface of geosynthetic-soil, and installation of facility using geosynthetic should be considered as important parameters that are essential for the dynamic design factor of the water controlling facility.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.6
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• pp.24-30
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• 2018

Dental implants are currently widely used as artificial teeth due to their good chewing performance and long life cycle. A dental implant consists of an abutment as the upper part and a fixture as the lower part. When chewing forces are repeatedly applied to a dental implant, gap at the interface surface between the abutment and the fixture is often occurred, and results in some deteriorations such as loosening of fastening screw, dental retraction and fixture fracture. To cope with such problems, a sealing-type abutment having a number of grooves along the conical-surface circumference was previously developed, and shows better sealing performance than the conventional one. This study carries out optimization of the groove shape by genetic algorithm(GA) as well as structural analysis in consideration of external chewing force and pretension between the abutment and the fixture. The overall optimization system consists of two subsystems; the one is the genetic algorithm with MATLAB, and the other is the structural analysis with ANSYS. Two subsystems transmit and receive the relevant data with each other throughout the optimization processes. The optimization result is then compared with that of the conventional one with respect to the contact pressure and the maximum stress. The result shows that the optimized model gives better sealing performance than the conventional sealing abutment.

• Korean Journal of Metals and Materials
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• v.50 no.11
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• pp.861-866
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• 2012

A dense nanostructured TiN-AlN composite was prepared from high-energy ball milled TiN-AlN mixture powders by pulsed current activated sintering (PCAS). A highly dense TiN-AlN bulk composite was obtained within 2 minutes at $1500^{\circ}C$ with the simultaneous application of 80 MPa pressure and pulsed current. The fine crystalline structure of the TiN-AlN mixture, which was obtained by high-energy milling, was effectively maintained during PCAS and resulted in the enhancement of the mechanical properties. The micro hardness and fracture toughness of TiN-AlN composite were $1780kg/mm^2$ and $5MPa.m^{1/2}$, respectively. The mechanical properties were higher than monolithic AlN or TiN.

• Korean Journal of Materials Research
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• v.32 no.1
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• pp.44-50
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• 2022

Transition metal carbides (TMCs) are used to process difficult-to-cut materials due to the trend of requiring superior wear and corrosion properties compared to those of cemented carbides used in the cutting industry. In this study, TMC (TiC, TaC, Mo₂C, and NbC)-based cermets were consolidated by spark plasma sintering at 1,300 ℃ (60 ℃min) with a pressure of 60 MPa with Co addition. The sintering behavior of TMCs depended exponentially on the function of the sintering exponent. The Mo₂C-6Co cermet was fully densified, with a relative density of 100.0 %. The Co-binder penetrated the hard phase (carbides) by dissolving and re-precipitating, which completely densified the material. The mechanical properties of the TMCs were determined according to their grain size and elastic modulus: TiC-6Co showed the highest hardness of 1,872.9 MPa, while NbC-6Co showed the highest fracture toughness of 10.6 MPa^*m^1/2. The strengthened grain boundaries due to high interfacial energy could cause a high elastic modules; therefore, TiC-6Co showed a value of 452 ± 12 GPa.