• Journal of Industrial Technology
• /
• v.23 no.A
• /
• pp.149-156
• /
• 2003

The development and maintenance of a sound bond are essential requirements of concrete repair and replacement. The bond property of a overlay to its substrate concrete during the lifetime is one of the most important performance requirements which should be quantified. A standard or a verified bond strength measurement method is required at field for screening, selecting materials and quality control for overlay or repair materials, but no test method has been adopted as a standard. In this study, a concrete pull off bond strength measurement method for field application is proposed and evaluated. This study compares the splitting tensile test, slant shear test, nipple pipe direct tensile test, flexural adhesion test, briquette tensile test, jumbo nail pull-out test and core pull-off test with their test procedures. From these comparison and investigation, core pull-off test is selected as a main topic of this study because of it's suitability for in situ testing, simplicities in field application and clearness at interface boundary condition. Thus, the proposed core pull off test is evaluated to be the most appropriate method for field application in a simple manner. The fracture surface and fracture mode could be easily determined by visual observation of failure surface of the field specimen. The core pull off test was found to be sensitive to surface condition and latex contents at latex modified concrete.

• Journal of the Korean Ceramic Society
• /
• v.43 no.12 s.295
• /
• pp.768-774
• /
• 2006

The microstructure of Ni-YSZ cermets was controlled with fine and coarse starting powders (NiO and YSZ) to obtain a optimum strong and conductive tubular anode support for SOFCs. Three types of cermets with different microstructures, i.e., coarse Ni-fine YSZ, fine Ni-coarse YSZ, and fine Ni-fine YSZ, were fabricated to investigate their electrical and mechanical properties. The cermets from fine NiO powder showed high electrical conductivity due to the enhanced percolation of Ni particles. The cermet by foe Ni and coarse YSZ showed excellent electrical conductivity (>1000 S/cm) despite its high porosity $(\sim40%)$ but it showed poor mechanical strength due to the lack of percolation by YSZ particles and due to large pores. Thus fine NiO and YSZ powders were used to make strong and conductive Ni-YSZ support tube by extrusion. The microstructure of the anode tube was modified by the amount of polymeric additives and carbon black, a pore former. Ni-YSZ tube (porosity $\sim34%$) with the finer microstructure showed better performance both in electrical conductivity (>1000 S/cm) and fracture strength $(\sim140\;MPa)$. Either flat or circular NiO-YSZ tubes with the length from 20 to 40cm were successfully fabricated with the optimized composition of materials and polymeric additives.

• Journal of the Society of Cosmetic Scientists of Korea
• /
• v.39 no.3
• /
• pp.225-231
• /
• 2013

Oil in water nanoemulsion of astaxanthin was prepared by high pressure homogenization. The emulsifying conditions including emulsifier type, concentration and astaxanthin concentration were optimized. Stability of nanoemulsion was measured using zetasizer, freeze-fracture scanning electron microscope (FF-SEM), particle analyzer and colorimeter. The mean diameter of the dispersed particles containing astaxanthin ranged from 160 to 190 nm. Size distribution was unimodal and extended from 40 to 200 nm. The nanoemulsion prepared by glyceryl citrate/lactate/linoleate/oleate had smaller particle size and narrow size distribution. Stable incorporation of astaxanthin in nanoemulsion was performed and checked using high performance liquid chromatography (HPLC), freeze-fracture scanning electron microscope (FF-SEM). Physical stability of nanoemulsion was not significantly changed during storage at both light and thermal condition for a month with zeta potential value of -41 mV meaning stable colloid.

• Magazine of the Korea Concrete Institute
• /
• v.8 no.5
• /
• pp.171-178
• /
• 1996

This study evaluated mechanical characteristics and performance of recycled concrete as a pavement material for use in low volume road. The recycled concrete was prepared by replacing a half of coarse aggregate with recycled coarse aggregate. Natural sand from a source was used as fine aggregate together with admixtures, such as plasticizer and fly ash (0.8% and 5% by wt. of total binder, respectively). From experimental evaluation. it was found that flexural strength. compressive strength, elastic modulus and fracture toughness of recycled concrete at 28 days were approximately $45kg/cm^2$, $250kg/cm^2$, $230,000kg/cm^2$ 및 $0.863 MPa{\cdot}m^{1/2}$. respectively. Long term strength and fracture toughness were improved significantly at the age of 6 months. In conclusion. mechanical properties of the recycled concrete were acceptable for use as concrete pavement materials in low-volume roads in rural and urban areas.

• Journal of the Korean Ceramic Society
• /
• v.40 no.9
• /
• pp.891-896
• /
• 2003

Novel fabrication technique was developed for high strength Reaction-Bonded SiC (RBSC) hot gas filter for use in IGCC (Integrated Gasification Combined Cycle) system. The room and high temperature fracture strengths for Si-melt infiltrated reaction-bonded SiC were 50-123, and 60-66 MPa, respectively. The average pore size was 60-70 $\mu\textrm{m}$ and the porosity was about 34 vol％. RBSC infiltrated with molten silicon showed improved fracture strength at high temperature, as compared to that of clay-bonded SiC, due to SiC/Si phase present within SiC phase. The thickness for SiC/Si phase was increased with increasing powder particle size of SiC from 10 to 34 $\mu\textrm{m}$. Pressure drop with dust particles showed similar response as compared to that for Schumacher type 20 filter. The filter fabricated in the present study showed good performance in that the filtered powder size was reduced drastically to below 1 $\mu\textrm{m}$ within 4 min.

• Restorative Dentistry and Endodontics
• /
• v.36 no.1
• /
• pp.1-11
• /
• 2011

Introduction: The aim of this paper is to discuss the mechanical and geometric features of Nickel-titanium (NiTi) rotary files and its clinical effects. NiTi rotary files have been introduced to the markets with their own geometries and claims that they have better ability for the root canal shaping than their competitors. The contents of this paper include the (possible) interrelationship between the geometries of NiTi file (eg. tip, taper, helical angle, etc) and clinical performance of the files as follows; - Fracture modes of NiTi rotary files - Non-cutting guiding tip and glide path - Taper and clinical effects - Cross-sectional area and clinical effects - Heat treatments and surface characteristics - Screw-in effect and preservation of root dentin integrity - Designs for reducing screw-in effect Conclusions: Based on the reviewed contents, clinicians may have an advice to use various brands of NiTi rotary instruments regarding their advantages which would fit for clinical situation.

• Journal of Ocean Engineering and Technology
• /
• v.33 no.5
• /
• pp.394-399
• /
• 2019

Plywood is a laminated wood material where alternating layers are perpendicular to each other. It is used in a liquefied natural gas (LNG) carrier for an insulation system because it has excellent durability, a light weight, and high stiffness. An LNG cargo containment system (LNG CCS) is subjected to loads from gravity, sloshing impact, hydrostatic pressure, and thermal expansion. Shear forces are applied to an LNG CCS locally by these loads. For these reasons, the materials in an LNG CCS must have good mechanical performance. This study evaluated the shear behavior of plywood. This evaluation was conducted from room temperature ($25^{\circ}C$) to cryogenic temperature ($-163^{\circ}C$), which is the actual operating environment of an LNG storage tank. Based on the plywood used in an LNG storage tank, a shear test was conducted on specimens with thicknesses of 9 mm and 12 mm. Analyses were performed on how the temperature and thickness of the plywood affected the shear strength. Regardless of the thickness, the strength increased as the temperature decreased. The 9 mm thick plywood had greater strength than the 12 mm thick specimen, and this tendency became clearer as the temperature decreased.

• Composites Research
• /
• v.20 no.3
• /
• pp.17-24
• /
• 2007

In this study, the failure modes by ballistic impacts were studied both for a neat Kevlar woven fabric and a Kevlar liquid armor impregnated with shear thickening fluid (STF) containing silica particles. These two materials showed quite different failure modes macroscopically in ballistic impacts tests used by Cal.22 FSP and 9mm FMJ bullet. Yarn pull-out for the neat Kevlar woven fabric and yarn fracture occurred partially through all plies from 1st ply to last one for the STF-Kevlar are an important energy absorption mechanisms. The results observed by S.E.M showed commonly fiber damage which are torn skin in the longitudinal fiber direction, fiber split axially and fiber fracture for two materials. The reasons why STF-kevlar liquid armor material exhibits excellent ballistic performance are as follow: firstly the increased friction forces between yarn-yarn and fabric-fabric covered with silica particles and secondary the evolution of shear thickening phenomenmon resulting in suppression of yarn mobility.

• Advances in nano research
• /
• v.15 no.5
• /
• pp.467-484
• /
• 2023

Despite the significant features of fiber-reinforced cementitious composites (FRCCs), including better mechanical, fractural, and durability performance, their high content of cement has restricted their use in the construction industry. Although ground granulated blast furnace slag (GGBFS) is considered the main supplementary cementitious material, its slow pozzolanic reaction stands against its application. The addition of nano-sized mineral modifiers, including nano-silica (NS), is an alternative to address the drawbacks of using GGBFS. The main object of this empirical and numerical research is to examine the effect of NS on the strain-hardening behavior of cementitious composites; ten mixes were designed, and five levels of NS were considered. This study proposes a new method, using a four-point bending test to assess the use of nano-silica (NS) on the flexural behavior, first cracking strength, fracture energy, and micromechanical parameters including interfacial friction bond strength and maximum bridging stress. Digital image correlation (DIC) was used for monitoring the initiation and propagation of the cracks. In addition, to attain a deep comprehension of fiber/matrix interaction, scanning electron microscope (SEM) analysis was used. It was discovered that using nano-silica (NS) in cementitious materials results in an enhancement in the matrix toughness, which prevents multiple cracking and, therefore, strain-hardening. In addition, adding NS enhanced the interfacial transition zone between matrix and fiber, leading to a higher interfacial friction bond strength, which helps multiple cracking in the composite due to the hydrophobic nature of polypropylene (PP) fibers. The findings of this research provide insight into finding the optimum percent of NS in which both ductility and high tensile strength of the composites would be satisfied. As a concluding remark, a new criterion is proposed, showing that the optimum value of nano-silica is 2%. The findings and proposed method of this study can facilitate the design and utilization of green cementitious composites in structures.

• Journal of Trauma and Injury
• /
• v.37 no.2
• /
• pp.114-123
• /
• 2024

Purpose: Appropriate scoring systems can help classify and treat polytrauma patients. This study aimed to validate chest trauma scoring systems in polytrauma patients. Methods: Data from 1,038 polytrauma patients were analyzed. The primary outcomes were one or more complications: pneumonia, chest complications requiring surgery, and mortality. The Thoracic Trauma Severity Score (TTSS), Chest Trauma Score, Rib Fracture Score, and RibScore were compared using receiver operating characteristic (ROC) analysis in patients with or without head trauma. Results: In total, 1,038 patients were divided into two groups: those with complications (822 patients, 79.2%) and those with no complications (216 patients, 20.8%). Sex and body mass index did not significantly differ between the groups. However, age was higher in the complications group (64.1±17.5 years vs. 54.9±17.6 years, P<0.001). The proportion of head trauma patients was higher (58.3% vs. 24.6%, P<0.001) and the Glasgow Coma Scale score was worse (median [interquartile range], 12 [6.5-15] vs. 15 [14-15]; P<0.001) in the complications group. The number of rib fractures, the degree of rib fracture displacement, and the severity of pulmonary contusions were also higher in the complications group. In the area under the ROC curve analysis, the TTSS showed the highest predictive value for the entire group (0.731), head trauma group (0.715), and no head trauma group (0.730), while RibScore had the poorest performance (0.643, 0.622, and 0.622, respectively) Conclusions: Early injury severity detection and grading are crucial for patients with blunt chest trauma. The chest trauma scoring systems introduced to date, including the TTSS, are not acceptable for clinical use, especially in polytrauma patients with traumatic brain injury. Therefore, further revisions and analyses of chest trauma scoring systems are recommended.