• 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.

• Journal of Korean society of Dental Hygiene
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• v.9 no.3
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• pp.248-261
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• 2009

Objective : This study was performed in order to figure out Oral Health Actual Condition in Elementary School Teachers in Deagu area. This study was conducted from March through May 2008. Method : A total of three hundred and ten Elementary School Teachers were surveyed. The collected data were analyzed by Oral Health Actual Condition and cognition, Diet habit or living and one's own intellect health state, Oral disease sign symptoms of percent and 2-test and One-way ANOVA test by using SPSS12.0 Program. Results : 1. The most of result Frequencies of tooth brushing per one day were 3 over 91.0% and Oral Examination, Oral Health Education need. 2. The result of oral disease sign and symptom were hypersensitivity due to cold food(39.0%), halitosis(21.6%), gingival bleeding tendency(21.3), clicking sound on TMJ(18.7%), hypersensitivity due to tooth burshing(17.1%), easy crown fracture and to be fine(10.0%), pain on TMJ or limitation of mouth opening(7.1%). 3. The most of result age a group oral hygiene assistance article age 20 for interdental tooth brushing(46.4%), age 50 over not used interdental tooth brushing 38.5%. 4. The result of sign and symptom and snack following was statistically significant(P<0.05), health of own cognition and Oral health of own cognition was statistically significant(P<0.001). Conclusion : The study of understanded the Subjective Elementary School Teachers Oral Health Actual Condition and Promotion of Oral Health follow up Oral examination and Oral Health Education have to system groping.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.28 no.3
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• pp.216-225
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• 2002

Hyaluronic acid (HA) is an almost essential component of extracellular matrices. Early in embryogenesis mesenchymal cells migrate, proliferate and differentiate, in part, because of the influence of HA. Since the features of embryogenesis are revisited during wound repair, including bone fracture repair, this study was initiated to evaluate whether HA has an effect on calcification and bone formation in an in vitro system of osteogenesis. Mouse calvaria Pre-osteoblast (MC3T3-E1) cells were cultured in ${\alpha}-MEM$ medium with microorganism-derivative hyaluronic acid that was produced by Strep. zooepidemicus which of molecular weight was 3 million units. The dosages were categorized in each 0.5, 1.0 and 2.0 mg/ml concentration experimental groups. After 2 and 4 days cultures in expeirmental and control groups, the tendency of cell proliferation, MTT assay, protein synthesis ability, collagen synthesis and alkaline phosphatase activity were analysed and bone nodule formation capacity were measured with Alizarin Red S stain after 29 days cultures. The cell proliferation was increased in time, especially the group of 0.5 and 1.0 mg/ml concentration of HA were showed prominent cell proliferation. After 2 and 4 days culture, experimental groups in general were greater cell activity in MTT assay. The protein synthesis was increased in all experimental groups compared to control group, especially most prominent in 1.0 mg/ml concentration group. The collagen synthesis capacity were increased in HA experimental groups, especially prominent in 1.0 mg/ml group and the activity of alkaline phosphatase were increased, especially also prominent in 1.0 mg/ml group, compared to control group. Above these, the activity of mouse carvarial pre-osteoblast cells was showed greater bone osteogenesis activity in all applied HA experimental group, especially group of 1.0 mg/ml concentration of HA.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.71-82
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• 2013

Eight small scale circular reinforced concrete columns (4.5 aspect ratio) were tested under cyclic lateral load with constant axial load. The selected test variables are longitudinal steel ratio (2.017%, 3.161%), transverse steel ratio, and axial load ratio (0, 0.07, 0.15). Volumetric ratio of spirals of all the columns is 0.335~0.894% in the plastic hinge region. It corresponds to 39.7~122.3% of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by seismic concept. The final objectives of this study are to provide quantitative reference data and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, steel fracture, etc. In this paper, describes mainly failure behavior, strength degradation behaviour, displacement ductility of circular reinforced concrete bridge columns with respect to test variables.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.157-171
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• 2019

The fracturing by liquid carbon dioxide ($LCO_2$) as a fracking fluid has been an alternative to mitigate the environmental issues often caused by the conventional hydraulic fracking since it facilitates the fluid permeation owing to its low viscosity. This study presents how $LCO_2$ injection influences the breakdown pressure, acoustic emission, and fracture morphology. Three fracturing fluids such as $LCO_2$, water, and oil are injected with different pressurization rate to the synthetic and porous mortar specimens. Also, the shale which has been a major target formation in conventional fracking practices is also tested to examine the failure characteristics. The results show that $LCO_2$ injection induces more tortuous and undulated fractures, and particularly the larger fractures are developed in cases of shale specimen. On the other hand, the relationship between the fracturing fluids and the breakdown pressure shows opposite tendency in the tests of mortar and shale specimens.

• Korean Journal of Metals and Materials
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• v.47 no.3
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• pp.155-168
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• 2009

In this study, microstructural investigation was conducted on the separation phenomenon occurring during Charpy impact tests of API X80 linepipe steels. Particular emphasis was placed on the role of microstructural phases present in the API X80 steels such as acicular ferrite, bainite, and hard secondary phases. Detailed microstructural analysis of fractured impact specimens showed that highly elongated bainite worked as prior initiation sites for separations, and that the number and length of separations increased with increasing volume fraction of bainite. In the steels having high work hardenability, tearing-shaped separations were found because the hammer-impacted region was seriously hardened during the impact test, which led to the reduction in the impact toughness. As the test temperature decreased, the tendency of separations increased, but separations were not observed when the cleavage fracture prevailed at very low temperatures. Thus, the minimization of the formation of bainite and secondary phases in the steels would be beneficial for preventing or minimizing separations because separations deteriorated low-temperature impact toughness.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.4
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• pp.521-528
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• 2021

In this study, to repair damaged economizer fin tubes on ships, sealing treatment was performed after applying arc thermal spray coating technology using Inconel 625. A solid particle erosion (SPE) experiment was conducted according to ASTM G76-05 to evaluate the durability of the substrate, thermal spray coating (TSC), and thermal spray coating+sealing treatment (TSC+Sealing) specimens. The surface damage shape was observed using a scanning electron microscope and 3D laser microscope, and the durability was evaluated through the weight loss and surface roughness analysis. Consequently, the durability of the substrate was superior to that of TSC and TSC+Sealing, which was believed to be owing to numerous pore defects in the TSC layer. In addition, the mechanism of solid particle erosion damage was accompanied by plastic deformation and fatigue, which were the characteristics of ductile materials in the case of the substrate, and the tendency of brittle fracture in the case of TSC and TSC+Sealing was confirmed.

• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.727-732
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• 2022

Applying the calculated cross-sectional reduction due to the corroded rebar investigated in the field to the numerical analysis model, the damage pattern and delamination of concrete in the field showed a tendency relatively similar to the numerical analysis results. It was analyzed that when the expansion pressure due to corrosion of the reinforcing bar is greater than the tensile stress of the concrete, cracks are generated and the concrete cover can be fracture. As a result of this study, the correlation between the corrosion rate of reinforcing bars and the crack occurrence of the concrete cover of the subway box structure was verified based on the numerical analysis and field test results. To prevent rebar corrosion, the corrosion rate can be reduced by applying rust prevention to the reinforcing bar and changing the material. In the case of exposed to a corrosive environment, the tensile strength of the concrete is improved by adjusting the concrete compressive strength to secure durability against the expansion pressure caused by the corroded rebar.

• Composites Research
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• v.21 no.2
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• pp.8-14
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• 2008

Decrease of strength in composite material is generally caused by water absorption. It makes fracture of material, and loss of money or human lives. The objective of this study is to investigate the causes of decrease in strength by water absorption. Mechanism of water absorption was supposed as three steps. This mechanism is consisted of absorption into resin, absorption between resin and surface treatment agent, and delamination between fiber and resin. Conditions of test were supplied differently; kinds of fiber and resin, immersion time etc. Both of reversible reaction and irreversible reaction occurred simultaneously. Most of decrease in strength was finished at 2.5% water absorption, and the strength was recovered. At 4% water absorption, most of decrease was caused by irreversible reaction, therefore, there was a tendency not to be recovered in strength.

• Archives of Craniofacial Surgery
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• v.24 no.6
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• pp.273-277
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• 2023

Background: The clinical characteristics of pediatric nasal fractures can vary depending on the child's age, social activities, and environment. Therefore, this study aimed to analyze these characteristics in different age groups. Methods: We retrospectively reviewed of a series of patients aged under 12 years who received treatment between 2013 and 2021. The initial study design involved dividing the patients into four age groups, corresponding to different developmental ages, but there were no cases in infants aged 0 to 1 year. Therefore, the patients were divided into three groups: group I, between 2 and 5; group II, between 6 and 9; and group III, between 10 and 12 years of age. The following parameters were evaluated: sex, age, etiology, fracture type and severity, and the incidence of septal injuries. Results: In total, 98 patients were included in this study. In group III, the ratio of boys to girls was 3.88:1, exceeding the overall ratio of 1.97:1. The most common cause varied with age: slipping down in group I, bumping accidents in group II, and sports accidents in group III. Concomitant septal injuries were present in 4.17% of patients in group I, 5.71% of patients in group II, and 28.21% of patients in group III. Conclusion: Increasing age was accompanied by a greater tendency for male predominance and a higher prevalence of sports-related causes and septal injuries. Violence was infrequent but started to become a contributing factor during school age. These varying environmental factors across age groups can offer valuable insights into the epidemiology and clinical characteristics of pediatric nasal bone fractures.