• Steel and Composite Structures
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• v.37 no.5
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• pp.551-569
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• 2020

Vibration of vertically aligned-monolayered-nonuniform nanorods consist of functionally graded materials with elastic supports has not been investigated yet. To fill this gap, the problem is examined using the elasticity theories of Eringen and Gurtin-Murdoch. The geometrical and mechanical properties of the surface layer and the bulk are allowed to vary arbitrarily across the length. The nonlocal-surface energy-based governing equations are established using differential-type and integro-type formulations, and solved by employing the Galerkin method by exploiting admissible modes approach and element-free Galerkin (EFG). Through various comparison studies, the effectiveness of the EFG in capturing both nonlocal-differential/integro-based frequencies is proved. A constructive parametric study is also conducted, and the roles of nanorods' diameter, length, stiffness of both inter-rod's elastic layer and elastic supports, power-law index of both constituent materials and geometry, nonlocal and surface effects on the dominant frequencies are revealed.

• Journal of Korean Association for Spatial Structures
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• v.15 no.1
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• pp.57-64
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• 2015

This paper shows the test results of continuous reinforced concrete beams with external post-tensioning rods. Six three-span beams were prepared and tested to fail. Three beams were designed to have flexure-dominating behavior and the others to have shear-critical behavior. In each group, one beam without external post-tensioning rods was designated as a control beam and two beams had the external post-tensioning rods of 18 mm or 22 mm diameter. External post-tensioning rods were installed within an interior span of 6000 mm. They show V-shaped configuration because two anchorages were located at the top of interior supports and a saddle pin at mid-span was installed at the bottom of the beam. Test results show that the load and shear capacities of strengthened beams were increased when compared with the control beam. Additionally, the measured shear strength was compared with the strength predicted by ACI 318-11 code equations. The detailed ACI 318-11 equation predicted the measured shear strength and failure location of the continuous beam reasonably well.

• Journal of Korea Foundry Society
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• v.26 no.4
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• pp.180-183
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• 2006

The effects of adding Ni on microstructure and mechanical properties of Nodular Indefinite Chilled Iron (NICI) were studied. Thermal fatigue, hardness, tensile properties, wear resistance, are very important factors for NICI used for hot working roll and wire rod mill. The results show that addition 4% nickel has changed pearlite to bainite. Bainite matrix is superior to pearlite matrix on wear resistance, hardness and strength and will increase performance lifetime of NICI conventional roll material. Based in the bainitic microstructure, hardness and tensile property increase up to 48 HRc and $72\;kg/mm^2$, respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.946-956
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• 2008

Acoustic emission(AE) is low-energy seismic event associated with a sudden inelastic deformation such as the sudden movement of existing fractures, the generation of new fractures or the propagation of fractures. These events rapidly increase before major failure and happen within a given rock volume and radiate detectable seismic waves. Rock slopes are usually large in scale and there are many discontinuities in rock mass. AE waves are strongly attenuated when they propagate through joints. Thus we should resolve the attenuation problem to monitor large volume. In this study, we developed waveguide which is composed of two different materials, cement mortar and stainless steel rod. And several laboratory tests on developed waveguide are performed to obtain generalized AE parameters to predict the failure stage in rock slope. Comparing field data with experimental data in laboratory tests, failure stage of rock slope can be evaluated. To verify and optimize the developed monitoring method, we are now carrying out the field application at a rock slope.

• Journal of Korea Society of Industrial Information Systems
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• v.13 no.1
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• pp.22-29
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• 2008

This paper describes the developed results of vision system for the recognition of material management characters, which was included in the billet image. The material management characters, which was marked at the surface of billet, should be recognized before billet moves to the next process. Our vision system for the character recognition includes that CCD camera system which acquire billet image, optical transmission system which transmit captured image to the long distance, input and output system for the interface with existing system and software for the character recognition. We have installed our vision system at the wire rod line of steel & iron plant and tested. Also, we have performed inspection of durability, reliability and recognition rate. Through the testing, we have confirmed that our system have high recognition rate, 98.6%.

• Journal of Powder Materials
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• v.26 no.3
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• pp.214-219
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• 2019

In this study, the microstructure and characterization of an overlay welding layer using Fe-based composite powders are reported. The effects of the number of passes and composition of powders on the microstructure and mechanical properties are investigated in detail. The welding wire and powders are deposited twice on a stainless-steel rod using a laser overlay welding process. The microstructure and structural characterization are performed by scanning electron microscopy and X-ray diffraction. The mechanical properties of the first and second overlay layers are analyzed through the micro-Vickers-hardness tester and abrasion wear tester. In the second overlay layer, the hardness and specific wear are approximately 840 Hv and $2.0{\times}10^{-5}mm^3/Nm$, respectively. It is suggested that the increase of the volume fractions of $(Cr,Fe)_7C_3$ and NbC phases in the second welding layer enhances the hardness and wear resistance.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.11
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• pp.19-26
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• 2018

This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.1035-1041
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• 2013

To evaluate the structural integrity and dynamic characteristic of the knuckle part of a KTX anti-roll bar, an experimental and a numerical approach were used in this study. In the experimental approach, the acceleration and strain data for the knuckle parts of the KTX and KTX-SANCHUN anti-roll bar were respectively measured to evaluate and compare its structural dynamic characteristics under the operating environments of the Honam line. In the numerical approach, the evaluation of its structural integrity was conducted using LS-DYNA 3D, and then, the reliability of the finite element model used was ensured by a comparative evaluation with the experiment. The numerical results showed that the stress and velocity field of the knuckle part composed of a layered structure of a thin steel plate and rubber were more moderate than those of the knuckle part made of only a thick steel block owing to the reduction of relative contact between the knuckle and the connecting rod. It was found that the knuckle part made of a thin steel plate and rubber was recommended as the best solution to improve its structural integrity resulting from the elastic behavior of the KTX anti-roll bar being enabled under a repeating external force.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.59-65
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• 2018

RC(Reinforced Concrete) structures are exposed to various exterior conditions, and the performances of both chloride resistance and freezing/thawing action are evaluated for those exposed to corrosive environment-sea shore. Recently developed FRP Hybrid Bars which is coated with glass fiber and epoxy with core steel has an engineering advantage of higher Elasticity than FRP rod. In this work, corrosion resistance, weight loss, and bond strength are evaluated for the FRP Hybrid Bar tested through freezing/thawing action for 300cycles. The double coated FRP Hybrid Bar shows the least weight loss without defection due to freezing/thawing action. Bond strength in FRP Hybrid Bar increases to 120% of normal steel through torturity effect with Si-coating. Bond strength in normal steel shows 0.86~0.89times in 3-day corrosion acceleration and 0.35~0.38times in 5-day corrosion acceleration, however, that in FRP Hybrid Bar shows little changes in bond strength before and after freezing/thawing action.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.44-49
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• 2013

Hydrogen penetration into a metal leads to damages and mechanical degradations and its content measurement is of importance. For a precise measurement, a sample preparation procedure must be optimized through a series of studies on sample washing and drying. In this study, two-step washing with organic solvents and thermal soaking in inert gas were tried with a rod-shaped, API X65 steel sample. The samples were machined from a steel plate and then washed in acetone and etyl-alcohol for 5 minute each and dried with compressed air. After then, the samples were thermally soaked in a home-made nitrogen gas chamber during 10 minute at different heat gun temperatures from 100 to $400^{\circ}C$ and corresponding temperature range in the soaking chamber was from 77 to $266^{\circ}C$ according to the temperature calibration. Hydrogen residue in the samples was measured with a hot extraction system after each soaking step; hydrogen residue of $0.70{\pm}0.12$ wppm after the thermal soaking at $77^{\circ}C$ decayed with increase of the soaking temperature. By adopting the heat transfer model, decay behavior of the hydrogen residue was fitted into an exponential decay function of the soaking temperature. Saturated value or lower bound of the hydrogen residue was 0.36 wppm and chamber temperature required to lower the hydrogen residue about 95% of the lower bound was $360^{\circ}C$. Furthermore, a thermal desorption spectroscopy was done for the fully soaked samples at $360^{\circ}C$. Weak hydrogen peak was observed for whole temperature range and it means that hydrogen-related contaminants of the sample surface are steadily removed by heating. In addition, a broad peak found around $400^{\circ}C$ means that parts of the hydrogen residue are irreversibly trapped in the steel microstructure.