• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.5
• /
• pp.597-603
• /
• 2018

This Study investigates the Structural Integrity of Boats for Divers, given increased demands for Underwater and Recreational use. We conducted research on a Small Catamaran with a Moon Pool in the center of the Hull, using the Finite Element Method to calculate allowable stress based on the ISO Rule. We computed the coefficients defined in ISO 12215-5 and TC118.1225-7, and determined the suitability of using the ISO Standard and Allowable Stress Design method (ASD) by applying Longitudinal Bending Moment, Torsional moment, and Bottom Slamming Load. We also applied the Ultimate Strength Design Method (LFRD) using Finite Element Analysis (FEA). As a Result of this Research, it was found that ships with a Moon Pool do have Structural Integrity according to their Design in accordance with ISO and KR Regulations.

• The Journal of the Korea Contents Association
• /
• v.10 no.9
• /
• pp.309-317
• /
• 2010

The stainless steel wire is extensively used for the orthodontic treatment. But, the stainless steel wire that has commonly superior corrosion resistance has caused hypersensitive reaction or allergy as side effects because of corrosion in the oral environment. For improving the problem of corrosion, we was evaluated the suitability of the duplex stainless steel(DSS) as orthodontic wire through this study. The DSS wire was evaluated the mechanical strength and bio-stability for suitability and bio-compatibility as orthodontic wire. In this work, the DSS and stainless steel(SS) as common use of medical grade were prepared for the tensile strength test. The DSS wire were treated by heat. and Temperature conditions of the heat treatment were $28^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$, $800^{\circ}C$, $900^{\circ}C$, respectively. And the DSS wires that treated by heat on the optimum temperature condition were conducted the bending moment test and calculated the S-Max value and the modulus of elasticity. For evaluating the bio stability, each materials were conducted in vitro test for measuring the cell survival rate. The most interesting results was that the tensile strength test of SS wire($8.17\times10^4\;N/mm^2$) and DSS wire($8.05\times10^4\;N/mm^2$) that treated at $500^{\circ}C$ by heat were similar in mechanical strength. In the bio-stability study, the DSS has no cytotoxicity (p=0.05) Thus, we could make a conclusion that the duplex stainless steel wire has vastly superior corrosion resistance was suitable as orthodontic wire.

• Science of Emotion and Sensibility
• /
• v.24 no.4
• /
• pp.129-138
• /
• 2021

This study aimed to determine the effects of the shape and attachment position of stretchable textile sensors coated with carbon nanotube on their performance when used to measure children's joint movements. Moreover, the child-safe requirements for fabric motion sensors are established. The child participants were advised to wear integrated clothing equipped with the sensors of various shapes (rectangular and boat-shaped) and attachment positions (at the knee and elbow joints or 4 cm below the joints). The voltage change induced by the elongation and contraction of the fabric sensors was determined for arm and leg flexion-extension motions at 60 deg/s (three measurements of 10 repeats each for 60°and 90°angles, for a total of 60 repetitions). Their dependability was determined by comparing the fabric motion sensors to the associated acceleration sensors. The experimental results indicate that the rectangular-shaped sensor affixed 4 cm below the joint is the most effective fabric motion sensor for measuring children's arm and leg motions. In this study, we designed a textile sensor capable of tracking children's joint motion and analyzed the sensor shape and attachment position on motion sensing clothing. We demonstrated that flexible fabric sensors integrated into garments may be used to detect the joint motions of the human body.

• Korean Journal of Optics and Photonics
• /
• v.33 no.5
• /
• pp.218-229
• /
• 2022

We have investigated reliable inspection methods for finding the defects generated during the manufacturing process of lightweight, large-aperture satellite telescope mirrors using silicon carbide, and we have measured the basic physical properties of the mirrors. We applied the advanced ceramic material (ACM) method, a combined method using liquid-silicon penetration sintering and chemical vapor deposition for the carbon molded body, to manufacture four SiC mirrors of different sizes and shapes. We have provided the defect standards for the reflectors systematically by classifying the defects according to the size and shape of the mirrors, and have suggested effective nondestructive methods for mirror surface inspection and internal defect detection. In addition, we have analyzed the measurements of 14 physical parameters (including density, modulus of elasticity, specific heat, and heat-transfer coefficient) that are required to design the mirrors and to predict the mechanical and thermal stability of the final products. In particular, we have studied the detailed measurement methods and results for the elastic modulus, thermal expansion coefficient, and flexural strength to improve the reliability of mechanical property tests.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.28 no.1
• /
• pp.54-66
• /
• 2001

The aim of this study was to investigate the fluoride release and some mechanical properties including 3-point bending strength, amount of abrasion, surface hardness, water sorption/solubility and cytotoxicity of the newly developed composite resins containing 8, 16, 24 wt% $SrF_2$ glass filler (VF8, VF16, VF24) and four commercially available composite resins, Heliomolar(HE), Verdonfil(VE), Z100(ZH) and Aelitefil(AE). To investigate cytotoxic effect, agar overlay assay was done. Amount of fluoride released into distilled water was measured over a 62-days period from VF8, VF16, VF24 and HE. Results were as follows: 1. Experimental composite resins showed similar mechanical properties to commercial composite resins, but 3-point bending strength and surface hardness of experimental composite resins were inferior to ZH. 2. Over a 62-day Period, the amount of fluoride released was ordered: VF24>VF16>VF8>HE. In experimental composite resins, the amount of fluoride released was 9-23 times greater than HE and seemed to be proportional to the content of $SrF_2$ glass filler. 3. Experimental composite resins and all control composite resins showed mild cytotoxicity. This study showed significantly greater fluoride release from newly developed composite resins than control(HE) and addition of $SrF_2$ glass filler did not decrease mechanical properties or increase cytotoxicity of composite resin. The results from this study imply that newly developed composite resin have adequate mechanical properites, mild cytotoxicity and some potential for secondary caries prevention.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.2
• /
• pp.191-198
• /
• 2009

Statement of problem: Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force. Purpose: The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic. Material and methods: Heat pressed ceramic(ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire(Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens(width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine(Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope(JSM-6360, JEOL, Japan) under platinum coating. Results: The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics(P<.001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire. Conclusion: The results of this study showed that wire inserted ceramics have a high strain characteristic. However, wire inserted ceramics was not enough to use at posterior area of mouth in relation to flexural modulus and flexural strength. Therefore, we need further studies.

• Restorative Dentistry and Endodontics
• /
• v.34 no.5
• /
• pp.424-429
• /
• 2009

This study aimed to assess the influence of different cross-sectional area on the cyclic fatigue fracture of Ni-Ti rotary files using a fatigue tester incorporating cyclical axial movement. Six brands of Ni-Ti rotary files (ISO 30 size with. 04 taper) of 10 each were tested: Alpha system (KOMET), HeroShaper (MicroMega), K3 (SybronEndo), Mtwo (VDW), NRT (Mani), and ProFile (Dentsply). A fatigue-tester (Denbotix) was designed to allow cyclic tension and compressive stress on the tip of the instrument. Each file was mounted on a torque controlled motor (Aseptico) using a 1:20 reduction contra-angle and was rotated at 300 rpm with a continuous, 6 mm axial oscillating motion inside an artificial steel canal. The canal had a $60^{\circ}$ angle and a 5 mm radius of curvature. Instrument fracture was visually detected and the time until fracture was recorded by a digital stop watch. The data were analyzed statistically. Fractographic analysis of all fractured surfaces was performed to determine the fracture modes using a scanning electron microscope. Cross-sectional area at 3 mm from the tip of 3 unused Ni-Ti instruments for each group was calculated using Image-Pro Plus (Imagej 1.34n, NIH). Results showed that NRT and ProFile had significantly longer time to fracture compared to the other groups (p < .05). The cross-sectional area was not significantly associated with fatigue resistance. Fractographycally, all fractured surfaces demonstrated a combination of ductile and brittle fracture. In conclusion, there was no significant relationship between fatigue resistance and the cross-sectional area of Ni-Ti instruments under experimental conditions.