• Journal of the Korean Society of Radiology
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• v.15 no.5
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• pp.697-704
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• 2021

It is hard to get Filaments which are materials of the 3D printing Fused Deposition Modeling(FDM) method as radiation shielding in Korea. and also related research is insufficient. This study aims to provide basic data for the development of radiation shields using 3D printing by evaluating the physical properties and radiation shielding capabilities of filaments containing metal particles. after selecting five metal filaments containing metal particle reinforcement materials, the radiation shielding rate was calculated according to the Korean Industrial Standard's protective equipment test method to evaluate physical properties such as tensile strength, density, X-ray Diffraction(XRD), and weight measurement using ASTM's evaluation method. In the tensile strength evaluation, PLA + SS was the highest, ABS + W was the lowest, and ABS + W is 3.13 g/cm³ which value was the highest among the composite filaments in the density evaluation. As a result of the XRD, it may be confirmed that the XRD peak pattern of the particles on the surface of the specimen coincides with the pattern of each particle reinforcing material powder metal, and thus it was confirmed that the printed specimen contained powder metal. The shielding effect for each 3D printed composite filament was found to have a high shielding rate in proportion to the effective atomic number and density in the order of ABS + W, ABS + Bi, PLA+SS, PLA + Cu, and PLA + Al. In this study, it was confirmed that the metal particle composite filament containing metal powder as a reinforcing material has radiation shielding ability, and the possibility of using a radiation shielding filament in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4A
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• pp.237-244
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• 2012

There is mounting recognition among concrete researchers that fiber reinforcement makes up for the inherent weakness in resisting tensile force of structural concrete. In practice of application of the fiber to concrete, however, several problems still remain to solve for assuring a uniform mix quality. The Kagome truss that is widely used in mechanical engineering field seems to be a good replacement for the steel fiber. This paper presents the test results of a pilot study for the concrete members reinforced by Kagome truss which is a periodic cellular metal of wire-woven. Three types of Kagome truss bulk were prefabricated and filled with normal concrete to make small-scaled test beams. The beams reinforced by a normal steel stirrups were also tested up to failure to compare the behavioral results. From the results obtained, it is appeared that comparing with beams reinforced by normal stirrups, the beams reinforced by Kagome truss showed better performance in load carrying capacity as well as ductility. Therefore, the Kagome truss is proved to be a good web shear reinforcing material.

• Journal of the Korean Geosynthetics Society
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• v.8 no.3
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• pp.9-16
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• 2009

In generally, ground surface strengthening such as using geotextile is needed to secure trafficability of construction equipment. Several calculation methods for bearing capacity for very soft ground improved by geotextile have been proposed already but they are not established yet. In this paper, elastoplastic finite element analysis is carried out to estimate bearing capacity improvement for very soft ground reinforced by geotextile. In conclusion, by reinforcing with geotextile the bearing capacity improvement of very soft ground is increased with the increase of the settlement after yielding. And it is enough that the length of geotextile is about 3~4 times of the loaded width for the effect to the bearing capacity improvement. Finally, the biggest tensile force of geotextile occurs at an edge of the uniform load.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.5 s.51
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• pp.73-83
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• 2006

The purpose of this study is to investigate the seismic behavior of reinforced concrete pier walls under cyclic out-of-plane loading and to develop improved seismic design criteria. The accuracy and objectivity of the assessment process can be enhanced by using a sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. A 4-node flat shell element with drilling rotational stiffness is used for spatial discretization. The layered approach is used to discretize the behavior of concrete and reinforcement through the thickness. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The method is verified a useful tool to assess the seismic performance of reinforced concrete pier walls subjected to cyclic out-of-plane load through comparing with reliable experimental results.

• Journal of Korean Association for Spatial Structures
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• v.20 no.2
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• pp.39-49
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• 2020

In this study, we will develop a hybrid cross-sectional shape of steel inserted type glued-laminated timber that can improve the strength of structural glued-laminated timber and maximize the ductility by using steel plate with excellent tensile and deformation ability. A total of three specimens were fabricated and the flexural performance test was carried out to evaluate the structural performance of the steel inserted type glued-laminated timber. In order to compare the effect of steel inserted glued-laminated timber, one structural glued-laminated timber test specimen composed of pure wood was manufactured. In addition, in order to evaluate the adhesion performance of the steel inserted, one each of a screw joint test specimen and a polyurethane joint test specimen was prepared. As a result, all the specimens showed the initial crack in the finger joint near the force point. This has been shown to be a cause of crack diffusion and strength degradation. The use of finger joints in the maximum moment section is considered to affect the strength and ductility of the glued-laminated timber beam. Polyurethane-adhesive steel inserted glued-laminated timber showed fully-composite behavior with little horizontal separation between the steel plate and glued-laminated timber until the maximum load was reached. This method has been shown to exhibit sufficient retention bending performance.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.301-301
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• 2003

In current study, Nanocomposites are reinforced with carbon nanofiber, carbon nanotube and SiC, etc. Since the nano reinforcements have the excellent mechanical, thermal and electrical properties compared with that of existing composites, it has lately attracted considerable attention in the various areas. Cu have been widely used as signal transmission materials for electrical electronic components owing to its high electrical conductivity. However, it's size have been limited to small ones due to its poor mechanical properties. Until now, strengthening of the copper alloy was obtained either by the solid solution and precipitation hardening by adding alloy elements or the work hardening by deformation process. Adding the alloy elements lead to reduction of electrical conductivity. In this aspect, if carbon nanofiber is used as reinforcement which have outstanding mechanical strength and electric conductivity, it is possible to develope Cu matrix nanocomposite having almost no loss of electric conductivity. It is expected to be innovative in electric conducting material market. The unidirectional alignment of carbon nanofiber is the most challenging task developing the cooer matrix composites of high strength and electric conductivity. In this study, the unidirectional alignment of carbon nanofibers which is used reinforced material are controlled by drawing process and align mechanism as well as optimized drawing process parameter are verified via numerical analysis. The materials used in this study were pure copper and the nanofibers of 150nm in diameter and of 10∼20$\mu\textrm{m}$ in length. The materials have been tested and the tensile strength was 75MPa with the elongation of 44% for the copper. it is assumed that carbon nanofiber behave like porous elasto-plastic materials. Compaction test was conducted to obtain constitutive properties of carbon nanofiber Optimal parameter for drawing process was obtained by analytical and numerical analysis considering the various drawing angles, reduction areas, friction coefficient, etc. The lower drawing angles and lower reduction areas provides the less rupture of co tube is noticed during the drawing process and the better alignment of carbon nanofiber is obtained.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.499-506
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• 2001

Eight direct tension tests were conducted to study the bond characteristics and crack behavior in high-strength concrete axial members. The main variable was the concrete strength up to 61-63 MPa. The specimens consisted of two different types of the short specimens modeled the part between transverse cracks and the long specimens having numerous transverse cracks. The results obtained show that the bond strength increases in proportion to compressive strength. Thereby, in high-strength concrete the length of stress-disturbed region is shortened and the space of adjacent transverse cracks become smaller. Although the concrete strength varies from 25 MPa to 61 MPa, the split cracking loads remain constant, while transverse cracking loads vary as variation of concrete tensile strength. Accordingly, the current code provisions for development length may need reconsideration in high-strength concrete members, and it is recommended that either thicker cover or transverse reinforcement should be additionally provided for high-strength concrete members.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.527-534
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• 2016

Beams strengthened in shear with Carbon Fiber Reinforced Polymer (CFRP) which had different transverse reinforcement ratio were tested to evaluate shear contribution in the CFRP and to analyze shear behavior of each test with Mohr's circle. Strain in the CFRP should be evaluated to estimate the shear contribution in the CFRP which is brittle material. Test results were compared each other based on the Mohr's circle which can correlate shear strain with both principal tensile strain and crack angle. With low transverse steel ratio, shear strengthening with CFRP not only increases the shear strength effectively but also minimizes the loss in shear contribution of concrete by limiting the development of crack. With high transverse steel ratio, the effect on shear strengthening with CFRP is not as much as the beam with low ratio. Therefore, the shear contribution in the CFRP should be evaluated based on the strain compatibility which can consider the interaction between steel and CFRP when determining the shear capacity of a strengthened member.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.89-94
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• 2014

The high Young's modulus and tensile strength of carbon nanotubes has attracted great attention from the research community given the potential for developing super-strong, super-stiff composites with carbon nanotube reinforcements. Over the decades, the strength and stiffness of carbon nanotube-reinforced polymer nanocomposites have been researched extensively. However, unfortunately, such strong composite materials have not been developed yet. It has been reported that the efficiency of load transfer in such systems is critically dependent on the quality of adhesion between the nanotubes and the polymer chains. In addition, the waviness and orientation of the nanotubes embedded in a matrix reduce the reinforcement effectiveness. In this study, we carried out performed micromechanics-based numerical modeling and analysis by varying the geometry of carbon nanotubes including their aspect ratio, orientation, and waviness. The results of this analysis allow for a better understanding of the load transfer capabilities of carbon nanotube-reinforced polymer composites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.2279-2286
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• 2015

Recently it has been actively studied that the use of hybrid GFRP-concrete structure with dual purpose of both a permanent forwork and main tensile reinforcement of GFRP plank. In applying general analysis and design technique to evaluate the performance of hybrid structures with cast-in-place high strength concrete and GFRP plank, it is essential that the characteristics of the bond slip model is identified. In this study a simplified bilinear bond slip model for hybrid structure with GFRP plank and cast-in-place high strength concrete is proposed. Maximum average bond stress of simple bond slip relationship that has been proposed in this study is 3.29MPa, initial slope is 35.66MPa/mm, the total slip is 0.23mm and interfacial fracture energy is 0.37kN/m.