• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.5
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• pp.71-80
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• 2007

Because of the characteristics relating to high tensile ductility, High Performance Fiber Reinforced Cementitious Composites (HPFRCC) are studied to be adopted in repair and retrofit of buildings. A series of three shear wall specimens was tested under constant axial stress and reversed cyclic lateral loading in order to evaluate the seismic retrofit that had been proposed for the shear wall with the opening. The retrofit involved the use of newly developed ECC and MDF(Macro Defect Free), both of which are sprayed through the high pressure pump, over the entire face of the wall. The results indicate that two difference types of retrofitting strategy make the different effects of a rise in the strength and ductility of each specimen.

• Advances in aircraft and spacecraft science
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• v.5 no.3
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• pp.385-400
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• 2018

In this paper dynamic behavior (modal analysis and dynamic transient response) of a novel sandwich T-joint is numerically and experimentally investigated. An epoxy adhesive is selected for bonding purpose and making the step wise graded behavior of adhesive region. The effect of the step graded behavior of the adhesive zone on dynamic behavior of a sandwich T-joint is numerically studied. Finite element analysis (FEA) of the T-joints with carbon fiber reinforced polymer (CFRP) face-sheets is performed by ABAQUS 6.12-1 FEM code software. Modal analysis and dynamic half-sine transient response of the sandwich T-joint are presented in this paper. Two verification processes employed to verify the dynamic modeling of the manufactured sandwich panels and T-joint modeling. It has been shown that the step wise graded adhesive zone cases have changed the second natural frequency by about 5%. Also, it has been shown that the different arranges in the step wise graded adhesive zone significantly affect the maximum stresses due to transient dynamic loading by 1112% decrease in maximum peel stress and 691.9% decrease in maximum shear stress on the adhesive region.

• Steel and Composite Structures
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• v.33 no.1
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• pp.93-109
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• 2019

In the present study, vibration analysis of double bonded micro sandwich cylindrical shells with saturated porous core and carbon/boron nitride nanotubes (CNT/BNNT) reinforced composite face sheets under multi-physical loadings based on Cooper-Naghdi theory is investigated. The material properties of the micro structure are assumed to be temperature dependent, and each of the micro-tubes is placed on the Pasternak elastic foundations, and mechanical, moisture, thermal, electrical, and magnetic forces are effective on the structural behavior. The distributions of porous materials in three distributions such as non-linear non-symmetric, nonlinear-symmetric, and uniform are considered. The relationship including electro-magneto-hydro-thermo-mechanical loadings based on modified couple stress theory is obtained and moreover the governing equations of motion using the energy method and the Hamilton's principle are derived. Also, Navier's type solution is also used to solve the governing equations of motion. The effects of various parameters such as material length scale parameter, temperature change, various distributions of nanotube, volume fraction of nanotubes, porosity and Skempton coefficients, and geometric parameters on the natural frequency of double bonded micro sandwich cylindrical shells are investigated. Increasing the porosity and the Skempton coefficients of the core in micro sandwich cylindrical shell lead to increase the natural frequency of the structure. Cylindrical shells and porous materials in the industry of filters and separators, heat exchangers and coolers are widely used and are generally accepted today.

• Steel and Composite Structures
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• v.30 no.3
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• pp.217-230
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• 2019

One of the most important design criteria in underground structure is to design lightweight protective layers to resist significant blast loads. Sandwich blast resistant panels are commonly used to protect underground structures. The front face of the sandwich panel is designed to resist the blast load and the core is designed to mitigate the blast energy from reaching the back panel. The design is to allow the sandwich panel to be repaired efficiently. Hence, the underground structure can be used under repeated blast loads. In this study, a novel sandwich panel, named RC panel - Helical springs- RC panel (RHR) sandwich panel, which consists of normal strength reinforced concrete (RC) panels at the front and the back and steel compression helical springs in the middle, is proposed. In this study, a detailed 3D nonlinear numerical analysis is proposed using the nonlinear finite element software, AUTODYN. The accuracy of the blast load and RHR Sandwich panel modelling are validated using available experimental results. The results show that the proposed finite element model can be used efficiently and effectively to simulate the nonlinear dynamic behaviour of the newly proposed RHR sandwich panels under different ranges of free air blast loads. Detailed parameter study is then conducted using the validated finite element model. The results show that the newly proposed RHR sandwich panel can be used as a reliable and effective lightweight protective layer for underground structures.

• Advances in nano research
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• v.7 no.2
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• pp.109-123
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• 2019

In this article, the free vibration analysis of annular sandwich plates with various functionally graded (FG) porous cores and carbon nanotubes reinforced composite (CNTRC) facesheets is investigated based on modified couple stress theory (MCST) and first order shear deformation theories (FSDT). The annular sandwich plate is composed of two face layers and a functionally graded porous core layer which contains different porosity distributions. Various approaches such as extended mixture rule (EMR), Eshelby-Mori-Tanaka (E-M-T), and Halpin-Tsai (H-T) are used to determine the effective material properties of microcomposite circular sandwich plate. The governing equations of motion are extracted by using Hamilton's principle and FSDT. A Ritz method has been utilized to calculate the natural frequency of an annular sandwich plate. The effects of material length scale parameters, boundary conditions, aspect and inner-outer radius ratios, FG porous distributions, pore compressibility and volume fractions of CNTs are considered. The results are obtained by Ritz solutions that can be served as benchmark data to validate their numerical and analytical methods in the future work and also in solid-state physics, materials science, and micro-electro-mechanical devices.

• Composites Research
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• v.21 no.6
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• pp.15-22
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• 2008

Reversed plane bending fatigue tests were conducted on SiC particle aluminum composite. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. The fatigue life of MMC is shorter than that of matrix because there exists interface debonding of SiC particles and matrix on the whole face of the notch part in the casting metal matrix composite(MMC). The coalescence of micro-cracks was observed in the tests conducted at high stress levels. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn-$K_{max}$ relationship.

• Steel and Composite Structures
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• v.50 no.1
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• pp.63-75
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• 2024

In this paper, the modified couple stress theory (MCST) and first order shear deformation theory (FSDT) are employed to investigate the free vibration and bending analyses of a three-layered micro-shell sandwiched by piezoelectric layers subjected to an applied voltage and reinforced graphene nanoplatelets (GPLs) under external and internal pressure. The micro-shell is resting on an elastic foundation modeled as Pasternak model. The mixture's rule and Halpin-Tsai model are utilized to compute the effective mechanical properties. By applying Hamilton's principle, the motion equations and associated boundary conditions are derived. Static/ dynamic results are obtained using Navier's method. The results are validated with the previously published works. The numerical results are presented to study and discuss the influences of various parameters on the natural frequencies and deflection of the micro-shell, such as applied voltage, thickness of the piezoelectric layer to radius, length to radius ratio, volume fraction and various distribution pattern of the GPLs, thickness-to-length scale parameter, and foundation coefficients for the both external and internal pressure. The main novelty of this work is simultaneous effect of graphene nanoplatelets as reinforcement and piezoelectric layers on the bending and vibration characteristics of the sandwich micro shell.

• Journal of Industrial Convergence
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• v.20 no.9
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• pp.59-70
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• 2022

Background: Diabetes education is an important factor in blood glucose control. Reinforced education is necessary for effective diabetes education. However, it is difficult to provide reinforced diabetes education within Korea's medical environment. Therefore, we want to analyze the effect of continuous diabetes education using mobile health care that can effectively provide repeated education without having to face the patient. Methods: This study is a multicenter, randomized, controlled, pre-post design study conducted to analyze the effect of a continuous diabetes education method. A total of 109 people were registered at five hospitals in south Korea, and they were randomly assigned to the app group (34 people) who received real-time coaching and repetitive training, the logbook group (37 people) who received face-to-face training after writing a blood glucose logbook, and the general group (38 people) who received a one-time diabetes education. The study was conducted for a total of 24 weeks. Twenty-one patients withdrew their consent and failed to perform an HbA1c. A final 88 patients were analyzed. The difference in HbA1c, Self-management behavior, and Quality of life before and after education was analyzed. Results: The study involved 51 (58%) male subjects, mean age was 55.8 years and mean duration of diabetes was 7.6 years. After 24 weeks of intervention, there was no significant difference in self-care behavior and quality of life between the three groups, but the HbA1c of the app group significantly decreased after education compared to the logbook group and the general group (F=4.62, p=.013). Conclusion: It can be seen through the app group that receiving real-time education is more effective in improving blood glucose management and continuous diabetes education is important.

• Applied Microscopy
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• v.16 no.2
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• pp.1-13
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• 1986

The purpose of this study was to investigate the morphology and intercellular junctions of the odontoblast of dental pulp in the rat incisor by means of the freeze fracture electron microscopy. Twenty male Sprague-Dawley rats weighing $150{\sim}200g$ were used. After being anesthetized by an intraperitoneal injection of 0.5 ml sodium pentobarbital per kg in body weight(60 mg/ml) the animals were perfused with 2.5% glutaraldehyde-2% paraformaldehyde fixative in 0.1 M cacodylate buffer, pH 7.2 through the ascending aorta for one hour. The incisors were carefully extracted from the jaws and demineralized by suspending them in 0.1 M EDTA in 3% glutaraldehyde (pH 7.2) for two weeks. After demineralization, the specimens were obtained from the portion divided into five equal parts. For freeze-fracture replication, demineralized tissues were infiltrated for several hours with 10%, 25% glycerol in 0.1M cacodylate buffer as a cryoprotectant and then frozen in liquid Freon 22 and stored in liquid nitrogen. Fracturing and replication were done in Balzers BAF 400D high-vacuum freeze-fracture apparatus at $-120^{\circ}C$ under routine $5X10^{-7}$ Torr vacuum. The tissue was immediately replicated with platinum unidirectionally at $45^{\circ}$ angle and reinforced with carbon at $90^{\circ}$ angle unidirectionally or by using a rotary stage. The replication process was monitored by a quartz-crystal device. The replicas were immersed in 100% methanol overnight. The tissue was then digested from the replica by clorox (laundry bleach), placed into 5% EDTA, and washed repeatedly with distilled water. The replicas were picked up on 0.3% formvar-coated 75 mesh grids and examined in the JEOL 100B electron microscope. The results were as follows; 1. Both in thin sections and freeze-fracture replicas, three types of intercellular junctions were recognizable in the plasma membrane of odontoblast: gap junction, tight junction and desmosome-like junction. 2. The nuclear pores were evenly distributed over the nuclear envelope. The pore complex formed a ring about 70 nm in diameter. 3. Gap junctions were found between odontoblasts as well as odontoblasts and neighbouring pulp cells (fibroblast, subodontoblastic cell process, nerve-like fibre). Gap junctions, which were round, ellipsoid and pear-shaped and 600 nm in diameter, were observed in the odontoblast. 4. Numerous round and ellipsoid gap junctions could be frequently seen on the plasma membranes in cell body and apical part of the odontoblasts. On the P face, the junctions were recognized as a cluster of closely packed particles, measuring about 9 nm in diameter, and on the E face, the junctions were recognized as a shallow grooves.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.689-696
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• 2003

Recently, Appendix A of ACI 318∼02 Code introduced the Strut-and-Tie Model(STM) procedure in shear design of deep flexural members. The STM procedure is widely used in the design of concrete regions where the distribution of longitudinal strains is significantly nonlinear, such as deep beams, beams with large openings, corbels, and dapped-end beams. Experimental study included five high-strength reinforced concrete deep beams with different detailing schemes for the horizontal and vertical reinforcement. The specimens were designed as simply supported beams subjected to concentrated loads on the top face and supported on the bottom face. At failure, all specimen exhibited primary diagonal crack running from the support region to the point load. Specimens which had mechanical anchorages(terminators) gives better representation of the load-carrying mechanism than the specimen had standard 90-degree anchorage at failure in deep flexural members. Based on the test results, shear design procedures contained in the ACI 318-99 Code, Appendix A of the ACI 318-02 Code, CSA A23.3-94 Code and CIRIA Guide-2 were evaluated. The Shear design of ACI 318-99 Code, Appendix A of the ACI 318-02 Code and CIRIA Guide-2 shown to be conservative predictions from 10% to 36% in the shear strength of the single-span deep beam which was tested. ACI 318-99 Code was the lowest standard deviation.