• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1351-1360
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• 1993

The fatigue behavior of GFRP composites is affected by environmental parameters. Therefore, we have to study on effect of sea water on fatigue behavior of GFRP composites as to maintain the safety and confidence in design of ocean structure of GFRP. In this paper, we investigated the fatigue properties of chopped strand glass mat/polyester composite in synthetic sea water. (pH 8.2) In case of the glass fiber (CSM type) reinforced polyester composite materials, the fatigue crack in the both dry and wet specimens tested in air or synthetic sea water occurred at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The transition point occurred during the crack propagation shifted to high ${\Delta}K$ value as load increase but its point is not changed regardless of immersion or test environment under a constant load. The synthetic sea water degrades the bond strength between fiber and matrix, thereby the tendency of rapid deceleration and acceleration of the crack growth was appeared.

• Composites Research
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• v.16 no.3
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• pp.9-17
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• 2003

In order to simulate the crack connection between cords and the interply crack growth in the belt-layer of real tire, 2 ply rubber/cord laminate specimens with exposed edges were tested in 4~11mm displacement control. Measurement of the crack connection is evaluated when crack reaches the half of the length between 45$^{\circ}$ aligned cords, and the amount of the crack growth is measured by the steel probe method. 2 dimensional analytic modeling was performed to simulate the crack connection between cords at the exposed edges. Also, the theoretical life of the specimens was calculated from the crack connection life between cords(critical value) and from the critical value to the final failure by the use of Tearing energy(T); the strain energy release per unit area of one fracture surface of a crack. Then, theoretical life was compared with those of experiments. The life prediction up to the critical value has about 20% error compared to experimental life, and up to the final failure about 65% error. Therefore, total theoretical life has about 45% error compared to the experimental life, which is conceivable in the case of rubber.

• Journal of Digital Convergence
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• v.15 no.5
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• pp.305-315
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• 2017

This study examined the relationships sleep habits, daytime sleepiness, and problem behaviors. A cross-sectional survey design was used. Participants were 276 adolescents. Sleep habits, daytime sleepiness and problem behavior were measured by Adolescent Sleep Hygiene Scale (ASHS), Epworth Sleepiness Scale (ESS), and Korea-Youth Self Report (K-YSR), respectively. Data were collected from July to August, 2014 using self-reported questionnaires. Participants were middle school students, perceived their sleep time as enough and their sleep quality as good, have no problem behavior during sleep, and have no caffeinated drink for last a week were more likely to have higher score of sleep hygiene. Sleep habits score was associated negatively with daytime sleepiness and problem behaviors. Sleep impacts on physical growth, behavior, and emotional development of adolescent. Therefore, it is necessary to develop a sleep enhancement program for the good sleep habits of the adolescents, and to make efforts at home and school.

• Journal of Biomedical Engineering Research
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• v.39 no.1
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• pp.22-29
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• 2018

Intervertebral disc(IVD) mainly consists of Annulus fibrosus(AF) and Nucleus pulposus(NP), playing a role of distributing a mechanical load on vertebral body. IVD tissue engineering has been developed the methods to achieve anatomic morphology and restoration of biological function. The goal of present study is to identify the possibilities for creating a substitute of IVD the morphology and biological functions are the same as undamaged complete IVD. To fabricate the AF and NP combine biphasic IVD tissue, AF tissue scaffolds have been printed by 3D bio-printing system with natural biomaterials and NP tissues have been prepared by scaffold-free culture system. We evaluated whether the combined structure of 3D printed AF scaffold and scaffold-free NP tissue construct could support the architecture and cell functions as IVD tissue. 3D printed AF scaffolds were printed with 60 degree angle stripe patterned lamella structure(the inner-diameter is 5mm, outer-diameter is 10 mm and height is 3 mm). In the cytotoxicity test, the 3D printed AF scaffold showed good cell compatibility. The results of histological and immunohistochemical staining also showed the newly synthesized collagens and glycosaminoglycans, which are specific makers of AF tissue. And scaffold-free NP tissue actively synthesized glycosaminoglycans and type 2 collagen, which are the major components of NP tissue. When we combined two engineered tissues to realize the IVD, combined biphasic tissues showed a good integration between the two tissues. In conclusion, this study describes the fabrication of Engineered biphasic IVD tissue by using enable techniques of tissue engineering. This fabricated biphasic tissue would be used as a model system for the study of the native IVD tissue. In the future, it may have the potential to replace the damaged IVD in the future.

• Journal of the Korean Wood Science and Technology
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• v.18 no.4
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• pp.86-101
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• 1990

The primary objective of this research was to investigate the strength properties of Comply, a composite panel. fabricated with particle board as core material and veneer or plywood as face and back. 20types of comply composites were manufactured according to the four specific gravity levels(0.5, 0.6, 0.7 or 0.8) of particleboard core and three veneer or two plywood thicknesses for face and back. They were tested and compared with matching particleboard (control) on moisture content. specific gravity, bending properties(MOE, MOR SPL). nail resistance and internal bond strength. The obtained results were summarized as follows: The increasing effect of modulus of elasticity was shown by the increase of face and back veneer or plywood thickness. The modulus of rupture and stress at proportional limit of the comply composites bonded with 3mm thick veneers or 3mm thick plywood face and back were higher than 2mm thick veneer or 2mm thick plywood as face and back. Both of modulus of rupture and stress at proportional limit on bending of Comply were higher than those of control board. Also the modulus of elasticity of Comply showed much higher than that of control board. The nail resistance of Comply, composed of plywood as face and back was higher than that of veneer. The nail resistance of control board was higher than that of Comply at Sp.Gr 0.7 and 0.8 core boards. Internal bond of Comply, composed of 1mm and 2mm thick veneer as face and back was higher than that of 3mm thick veneer. The increasing effect of modulus of elasticity was shown by the increase of shelling ratio in Comply composed of veneer and plywood as face and back. The modulus of rupture was increased by the increment of shellmg ratio in Compiy, composed of plywood as face and back. The modulus of elasticity and modulus of. rupture of comply were higher than those of particleboard(control) in effect of shelling ratio. Therefore it was concluded that the mechanical property values of Comply were clearly greater than those of particleboard(control).

• Journal of the Korean Society for Heat Treatment
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• v.27 no.4
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• pp.169-174
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• 2014

The effect of varying amounts of graphite and $TiB_2$ on the electrical conductivity of composite bipolar plates was systematically studied. In this study, Titanium diboride ($TiB_2$) which has a high electrical conductivity, was selected as a filler and a additive material instead of conventional graphite. For proper distribution of the filler and matrix materials, ball milling using alumina balls was conducted for 1h, and then the hot press method was applied for the preparation of composite samples. The results showed a rapid increase in the electrical conductivity of composite bipolar plates at the critical filler content. However, $TiB_2$ and graphite composite bipolar plates showed similar increases in the electrical conductivity even though $TiB_2$ has a higher electrical conductivity than graphite. In addition, it was also found that a small addition of $TiB_2$ to graphite filler could be very effective for increasing the electrical conductivity and flexural strength of the composite bipolar plate.

• Journal of Physiology & Pathology in Korean Medicine
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• v.31 no.4
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• pp.238-245
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• 2017

This retrospective observational study was aimed to evaluate that Daoyin Exercise therapy improves the symptoms related to lumbar disc herniation. We analyzed the medical records of 7 patients, who satisfied with inclusion and exclusion criteria. The subjects of the study were the patients who were prescribed Daoyin Exercise Therapy and Korean medical treatments for lumbar intervertebral disc herniation at Dunsan Korean Medicine Hospital of Daejeon University from July 25th, 2016 to March 31th, 2017. The effects of Daoyin Exercise Therapy was evaluated by comparing before and after taking Daoyin Exercise Therapy through 0-10 Numeric Rating Scale(NRS), Roland & Morris Disability Questionnaire(RMDQ), Trunk Extension Flexion(TEF) Program, EuroQol five Demension Questionnaire(EQ-5D, EQVAS) of the symptoms including lower back pain. The Daoyin Exercise Therapy combined with Korean medicine treatment reduced NRS($3.357{\pm}3.038$) and RMDQ($9.50{\pm}6.364$), and improved Muscle endurance($44.429{\pm}45.136$), EQ-5D($0.09{\pm}0.12$) and EQVAS($6.571{\pm}19.260$) of the 7 patients without side effects. These results implied that Daoyin Exercise Therapy might helps to improve symptoms of patients with lumbar disc herniation by reducing the symptoms of lower back pain and improving muscle endurance, quality of life, strength enhancement and core muscles.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1205-1210
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• 2011

Spinal instability known to be related to low back pain. However, the quantitative definition of spinal instability has not been established because there is a lack of consensus regarding clinical and radiological studies. In addition, the major factors affecting such instability have not been elucidated, although disc degeneration, disc injury, ligament injury, and isthmic defects are considered to result in such problems. In this study, individual and combined influences on spinal instability with a three-dimensional finite element model of a one-level lumbar spinal motion segment were investigated, under the assumption that the rotation and translation in the sagittal plane under flexion and extension represented the instability indices. The results could be helpful in understanding the causes and mechanisms of spinal instability in the lumbar spine.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.12
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• pp.1356-1363
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• 2009

The aim of this research is to construct eigenfrequency optimization codes for plates with Arbitrary Rank Microstructures. From among noise factors, resonance sound is main reason for floor's solid noise. But, Resonance-elusion design codes are not fixed so far. Besides, The prediction of composite material's capability and an resonance elusion by controlling natural frequency of plate depend on designer's experiences. In this paper, First, using computer program with arbitrary rank microstructure, variation on composite material properties is studied, and then natural frequency control is performed by plate topology optimization method. The results of this study are as followed. 1) Programs that calculate material properties along it's microstructure composition and control natural frequency on composite material plate are coded by Homogenization and Topology Optimization method. and it is examined by example problem. 2) Equivalent material properties, calculated by program, are examined for natural frequency. In this paper, Suggested programs are coded using $Matlab^{TM}$, Feapmax and Feap Library with Homogenization and Topology Optimization method. and Adequacy of them is reviewed by performing the maximization or minimization of natural frequency for plates with isotropic or anisotropic materials. Since the programs has been designed for widely use. If the mechanism between composite material and other structural member is identified, extension application may be possible in field of structure maintenance, reinforcement etc. through application of composite material.

• Journal of Digital Convergence
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• v.16 no.1
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• pp.351-356
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• 2018

The aim of this study is to propose guidelines for bus-stop information design that is more congested with the advent of U-Shelter, via case studies and focus group interviews. First, the literature research explored the concept of information design and correlation of information design and route map. Second, raising problems and consider improvement plans through case study in korea, overseas. Finally, current information design was evaluated and user's requests were derived through focus group interview. The current information design had problems with lack of priority, information overlaying, and hard recognition. Priority shall be selected by bus route, direction of bus, arrival time, interval, and operating time, and information overlay can be reduced into one. Also visualize the connection and direction between the lines using schematic and two-dimensional lines and shapes for recognition. Through this study, it will be used as a reference material to help improve and develop the bus-stop information design.