• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.47-52
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• 2024

The demand for FRPs that are corrosion-free and have an excellent tensile strength-to-weight ratio. However, there is a lack of research on the mechanical properties of FRP in the form of rebars, especially the changes in performance due to heating. Therefore, in this paper, 60 tensile and compression specimens of CFRP rebars with a diameter of 12 mm were fabricated and subjected to direct tensile and direct compression tests, and their performance was evaluated according to the heating temperature. It was found that as the heating temperature increases above 300 ℃, the performance decrease becomes larger due to the burning of epoxy. The compressive strength was found to be much lower than the tensile strength, but the modulus of elasticity was found to be the same in tension and compression.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.205-216
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• 2009

As a subsequent study, this paper presents a comparative evaluation of structural responses in asphalt pavements with stabilized foundations. The approach based on a finite element analysis which incorporates non-linear behaviors of pavement geomaterials is used to estimate each performance indicator under standard single axle loading condition. In addition, results from laboratory tests are used to provide physical and mechanical properties of stabilized geomaterials for analyzing various pavement structures. Changes in pavement responses with varying layer thickness and stabilizer contents were investigated. It is found that the effect of layer thickness and stabilizer content is a critical factor in structural response of stabilized pavements. Moreover, a design criterion is proposed for selecting minimum contents of stabilizer of coarse-grained geomaterials based on a result of unconfined compressive strength and proper layer thickness of foundations.

• Fire Science and Engineering
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• v.27 no.6
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• pp.21-25
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• 2013

Fire resistance steel, grading 490 MPa, had developed by using Thermo-mechanical control process (TMCP) and it has better performance at welding, seismic resistance than those of the ordinary structural steel, But the fire resistance performance is required to verify against the ordinary fire resistance, FR 490. Therefore this study was done to make database of mechanical properties at high temperature and to evaluate the structural stability at high temperature in terms of materials and structural member such as H-section from that of FR 490. The result of this study was that the structural stability of TMCP was lower than that of ordinary FR 490 at the range up about $700^{\circ}C$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.10
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• pp.1408-1412
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• 2013

High power pulse generating technology is to accumulate the energy for relatively long and then to create a strong force by emitting the energy very fast. High power pulse generating technology has recently been using in various fields like environments, industry, research, military and so on. Numerous studies about high power pulse generators have already been performed and commercialized in various conditions. However, in aspect of their size and weight, it is hard to carry the generators which currently have been developed. For these reasons, din nations like America or Russia, the researches have been performed for Ferroelectric Generators(FEG), which have relatively simple structure and are economical. To realize the ferroelectric generator, in this study, we selected the PZTs which have different physical properties respectively, and then shocked them using explosives. The PZT samples with volumes of $0.31{\sim}0.94cm^3$ were depolarized by shocked and produced the waveform that have peak voltages of 4.28 ~ 15kV. The lowest relative permittivity sample generated much higher peak voltage. And sudden voltage drops which seem to be caused by dielectric breakdown were observed in some experiments using low young's modulus samples. Also, increase in thickness led to increase in peak voltage, but the ratio of the voltage rise did not reach the ration of the thickness increase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.859-869
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• 2009

The sharp indenters such as Berkovich and conical indenters have a geometrical self-similarity in theory, but different materials have the same load-depth curve in case of single indentation. In this study, we analyze the load-depth curves of conical indenter with angles of indenter via finite element method. From FE analyses of dual-conical indentation test, we investigate the relationships between indentation parameters and load-deflection curves. With numerical regressions of obtained data, we finally propose indentation formulae for material properties evaluation. The proposed approach provides stress-strain curve and the values of elastic modulus, yield strength and strain-hardening exponent with an average error of less than 2%. It is also discussed that the method is valid for any elastically deforming indenters made of tungsten carbide and diamond for instance. The proposed indentation approach provides a substantial enhancement in accuracy compared with the prior methods.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.73-80
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• 1997

This paper describes structural optimization of optical fiber-wound mandrel hydrophones with Finite Element Method (FEM). The hydrophone is supposed to have operation frequency range of up to 10 kHz and show omni-directional sensitivity pattern at 5 kHz. Studied parameters are mandrel geometry, molding thickness, and material properties of constitutional parts of the hydrophone. Theoretical calculation result shows that pressure sensitivity of the hydrophone increased as either mandrel length or molding thickness gets larger. Also higher pressure sensitivity requires a mandrel or molding material with relatively low Youngs modulus or Poissons ratio. Hydrophone bandwidth increases either as the mandrel length becomes shorter or as the mandrel becomes harder. The omni-directional characteristic is improved as the mandrel length becomes shorter, at 5 kHz. With the above results, we determine the structure of an optical fiber-wound mandrel hydrophone which has the pressure sensitivity of $30 {\times} 10_{-7}$ Rad./Pa, operation frequency range of up to 10 kHz, and shows omni-directional sensitivity pattern at 5 kHz.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.5
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• pp.61-71
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• 2007

Navier's and Finite element solutions based on the first-order shear deformation theory are presented for the analysis of through-thickness functionally graded plates and shells. The functionally graded materials are considered: a sigmoid function is utilized for the mechanical properties through the thickness of the isotropic structure which varies smoothly through the plate and shell thickness. The formulation of a nonlinear 9-node Element-based Lagrangian shell element is presented for the geometrically nonlinear analysis. Natural-coordinate-based strains are used in present shell element. Numerical results of the linear and nonlinear analysis are presented to show the effect of the different top/bottom elastic modulus, loading conditions, aspect ratios and side-to-thickness ratios on the mechanical behaviors. Besides, the result according to the variation of the power-law index of isotropic functionally graded structures is investigated.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.589-592
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• 2008

Recently, as importance of quality control of the structure has been recognized, non-destructive testing, determining quality of the structure without damage, has been widely applied. However, its application has been primarily focused on laboratory development because variety of parameters in field has been not fully experienced and understood. This study aims to evaluate the field applicability of the ultrasonic testing method for PC beams. Material properties of 18 cylinders, cured in the same field condition, were measured up to 60 days and compared to those of the ultrasonic measurements from 34 PC beams in field before tensioning. Test results indicate that uni-axial strength and elastic modulus of PC beams can be predicted within reasonable range using the ultrasonic technique. However, it is also noted that considerations on field condition is required to increase the reliability of estimation.

• Geotechnical Engineering
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• v.14 no.4
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• pp.5-16
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• 1998

The ground of Taegu area consists mainly of shales with elastic sedimentary rocks. These shales have a nonhomogeneous and anisotropic characteristics. So their physical and mechanical properties are very different due to the angles($\beta$ value) of bedding planes of sedimentary rock. In this study, the physical and mechanical characteristics of shales in Taegu area are studied by performing all kinds of rock test. According to results of test, apparent specific gravity of shale decreases as the $\beta$ value increases. On the contrary, porosity and absorption increase. Elastic wave velocity shorts the highest value at the $90^{\circ}$. And Young's modulus shows the maximum value at the $30^{\circ}$. The uniaxial strength, triaxial strength, cohesion and angle of friction show the minimum value at the $60^{\circ}$respectively.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.11
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• pp.1236-1244
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• 2012

A equivalent stiffness modeling has been performed for extracting the equivalent stiffness properties which are orthotropic elastic model from a large scale wind turbine rotor blade so that structure model can be constructed more simply for the three dimensional static aeroelastic analysis. In order to present the procedure of equivalent stiffness modeling, NREL 5MW class wind turbine rotor having the three stiffness information which are flapewise, edgewise and torsional stiffness was chosen. This method is based on applying unit moment at the tip of the blade as well as fixing all degree of freedom at the blade root and calculating the displacement from the load analysis to obtain the elastic modulus corresponding to equivalent stiffness referred to the NREL reports on blade divided into 5 sections respectively. In addition, one section was divided into 3 parts and the trend functions were used to make the equivalent stiffness model more correctly and quickly. Through the comparison of stiffness between the reference values and calculated values from equivalent stiffness model, the investigation of the accuracy on the stiffness values and the efficiency for constructing the model was conducted.