• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.1A
• /
• pp.31-37
• /
• 2012

The phase distribution in concrete materials strongly affects its material properties. It is important to identify the spatial distribution of void in concrete because the void in concrete materials affects mechanical behavior and permeability significantly. Therefore, a proper method to describe the void distribution of a material is needed. In this research, CT(computed tomography) is used to examine and to quantify the void distribution of porous concrete specimens. 3D concrete digital specimens are created by subsequent stacking of 2D cross-sectional images from CT. Then, probability distribution functions such as two-point correlation, lineal-path and two-point cluster functions are used for void distribution characterization. It is confirmed that probability distribution functions obtained from CT images are effective in characterizing void distributions including the anisotropy and percolation.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.37 no.6
• /
• pp.1025-1032
• /
• 2017

In this paper, the level of service (LOS) is defined for high-speed railway links and rolling stocks. Based on this LOS, how to manage high-speed railway facility is also suggested. The LOS is divided into 6 levels from A to F. The measurement of effectiveness (MOE) for railway links is derived from the relationship between a total delay time and a railway link utilization ratio. Another MOE, volume over capacity (V/C), is also proposed. On the other hand, the LOS for high-speed railway rolling stocks is based on the density of people in a rolling stock. Above all, LOS D is defined to the total number of seats. Then, LOS A is 50% of the LOS D, LOS B is 70% of the LOS D, LOS C is 90% of the LOS D and LOS D~F is defined as the maximum seats and standing people at the level of each. Finally, a method to manage high-speed railway links and rolling stocks is proposed in order to keep the level of service at the target by the government.

• Korean Journal of Computational Design and Engineering
• /
• v.21 no.4
• /
• pp.389-396
• /
• 2016

The necessity for environment-friendly material development has emerged in the recent automotive field due to stricter regulations on fuel economy and environmental concerns. Accordingly, the automotive industry is paying attention to carbon fiber reinforced plastic (CFRP) material with high strength and stiffness properties while the lightweight. In this study, we determine a shape of lower control arm (LCA) for maximizing the strength and stiffness by optimizing the thickness of each layer when the stacking angle is fixed due to the CFRP manufacturing problems. Composite materials are laminated in the order of $0^{\circ}$, $90^{\circ}$, $45^{\circ}$, and $-45^{\circ}$ with a symmetrical structure. For the approximate optimal design, we apply a sequential two-point diagonal quadratic approximate optimization (STDQAO) and use a process integrated design optimization (PIDO) code for this purpose. Based on the physical properties calculated within a predetermined range of laminate thickness, we perform the FEM analysis and verify whether it satisfies the load and stiffness conditions or not. These processes are repeated for successive improved objective function. Optimized CFRP LCA has the equivalent stiffness and strength with light weight structure when compared to conventional aluminum design.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.11
• /
• pp.683-687
• /
• 2017

We investigated the structure of an ultra-thin insulating board with low thermal conductivity along z-axis, which was based on the idea of void layers created during the glass infiltration process for the zero-shrinkage low-temperature co-fired ceramic (LTCC) technology. An alumina and four glass powders were chosen and prepared as green sheets by the tape casting method. After comparison of the four glass powders, bismuth glass was selected for the experiment. Since there is no notable reactivity between alumina and bismuth glass, alumina was selected as the supporting additive in glass layers. With 2.5 vol% of alumina powder, glass green sheets were prepared and stacked alternately with alumina green sheet to form the 'alumina/glass (including alumina additive)/alumina' structure. The stacked green sheets were sintered into an insulating substrate. Scanning electron microscopy revealed that the additive alumina formed supporting bridges in void layers. The depth and number of the stacking layers were varied to examine the insulating property. The lowest thermal conductivity obtained was 0.23 W/mK with a $500-{\mu}m-thick$ substrate.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.8
• /
• pp.665-672
• /
• 2013

One of the major causes of stiffness and strength degradations in laminated composite structures is the delamination between composite layers. In most engineering applications, laminated composite structures have certain curvatures. If the curved composite structure is subjected to bending that tends to flatten the composite structures, through the thickness stresses can be generated in the thickness direction of the composites. Under normal operation open mode delamination could occur at the sites of peak interlaminar stress. This paper describes a technique to determine radial direction stress of a laminated composite structure using a curved beam. Stacking sequence effects of interlaminar stress were studied. The radial location and intensity of the open mode delamination stress were calculated and compared with the results obtained from the analytical solution and finite element method.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.40 no.3
• /
• pp.337-343
• /
• 2020

The third phase of NASA's 3D-Printed Habitat Challenge (part of a NASA's Centennial Challenges Program competition) required entrants to build a one-third-scale space exploration habitat (10 ㎡) using 3D-printing technology. This study addresses a proposed habitat (diameter: 3 m, height: 2 m) in accordance with the competition rules. The study focus is to find the most appropriate binder when KOHLS-1 was mixed for extruding and stacking as 3D printing feedstock using pellets, and to build a prototype structure as required by the competition. Unlike previous studies, this study was based around the binders and construction method, not around axis transfer velocity, flow rate, and heater temperature.

• Steel and Composite Structures
• /
• v.26 no.4
• /
• pp.473-484
• /
• 2018

Free vibration of cross-ply laminated plates using a higher-order shear deformation theory is studied. The arbitrary number of layers is oriented in symmetric and anti-symmetric manners. The plate kinematics are based on higher-order shear deformation theory (HSDT) and the vibrational behaviour of multi-layered plates are analysed under simply supported boundary conditions. The differential equations are obtained in terms of displacement and rotational functions by substituting the stress-strain relations and strain-displacement relations in the governing equations and separable method is adopted for these functions to get a set of ordinary differential equations in term of single variable, which are coupled. These displacement and rotational functions are approximated using cubic and quantic splines which results in to the system of algebraic equations with unknown spline coefficients. Incurring the boundary conditions with the algebraic equations, a generalized eigen value problem is obtained. This eigen value problem is solved numerically to find the eigen frequency parameter and associated eigenvectors which are the spline coefficients.The material properties of Kevlar-49/epoxy, Graphite/Epoxy and E-glass epoxy are used to show the parametric effects of the plates aspect ratio, side-to-thickness ratio, stacking sequence, number of lamina and ply orientations on the frequency parameter of the plate. The current results are verified with those results obtained in the previous work and the new results are presented in tables and graphs.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.42 no.4
• /
• pp.203-210
• /
• 2019

Recently, a number of researchers have produced research and reports in order to forecast more exactly air quality such as particulate matter and odor. However, such research mainly focuses on the atmospheric diffusion models that have been used for the air quality prediction in environmental engineering area. Even though it has various merits, it has some limitation in that it uses very limited spatial attributes such as geographical attributes. Thus, we propose the new approach to forecast an air quality using a deep learning based ensemble model combining temporal and spatial predictor. The temporal predictor employs the RNN LSTM and the spatial predictor is based on the geographically weighted regression model. The ensemble model also uses the RNN LSTM that combines two models with stacking structure. The ensemble model is capable of inferring the air quality of the areas without air quality monitoring station, and even forecasting future air quality. We installed the IoT sensors measuring PM2.5, PM10, H2S, NH3, VOC at the 8 stations in Jeonju in order to gather air quality data. The numerical results showed that our new model has very exact prediction capability with comparison to the real measured data. It implies that the spatial attributes should be considered to more exact air quality prediction.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.47 no.11
• /
• pp.23-29
• /
• 2010

This paper presents a method for constructing a memory system using defective memory chips comprising faulty storage blocks. The three-dimensional memory system introduced here employs a die-stacked structure of faulty memory chips. Signals lines passing through the through-silicon-vias (TSVs) connect chips in the defect tolerant structure. Defective chips are classified into several groups each group comprising defective chips having faulty blocks at the same location. A defect tolerant memory system is constructed using chips from different groups. Defect-free storage blocks from spare chips replace faulty blocks using additional routing circuitry. The number of spare chips for defect tolerance is $s={\ulcorner}(k{\times}n)/(m-k){\urcorner}$ to make a system defect tolerant for (n+s) chips with k faulty blocks among m independently addressable blocks.

• Composites Research
• /
• v.17 no.4
• /
• pp.53-60
• /
• 2004

This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of CFRP laminate plates based on considerations of stress wave propagation theory. The absorbed energy of T300 orthotropic composites is higher than that of quasi-isotropic specimen over impact energy 6.8J, but in case of using T700 fiber, much difference does not show. Also, absorbed energy of T300 orthotropic composites, which are composed of the same stacking number and orientation became more than that of T700 fiber specimen; however there was no big difference in case of quasi-isotropic specimens. The delamination areas of the impacted specimen were measured with the ultrasonic C-scanner to find correlation between impact energy and delamination area. The fracture surfaces were observed by using the SEM (scanning electron microscope) through a low-velocity impact test in order to confirm the fracture mechanism.