• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.727-732
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• 2022

Applying the calculated cross-sectional reduction due to the corroded rebar investigated in the field to the numerical analysis model, the damage pattern and delamination of concrete in the field showed a tendency relatively similar to the numerical analysis results. It was analyzed that when the expansion pressure due to corrosion of the reinforcing bar is greater than the tensile stress of the concrete, cracks are generated and the concrete cover can be fracture. As a result of this study, the correlation between the corrosion rate of reinforcing bars and the crack occurrence of the concrete cover of the subway box structure was verified based on the numerical analysis and field test results. To prevent rebar corrosion, the corrosion rate can be reduced by applying rust prevention to the reinforcing bar and changing the material. In the case of exposed to a corrosive environment, the tensile strength of the concrete is improved by adjusting the concrete compressive strength to secure durability against the expansion pressure caused by the corroded rebar.

• Tribology and Lubricants
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• v.39 no.1
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• pp.8-12
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• 2023

This study presents a molecular simulation of adhesion control between carbon nanotube (CNT) and Ag thin film deposited on silicon substrate. Rough and flat Ag thin film models were prepared to investigate the effect of surface roughness on adhesion force. Heat treatment was applied to the models to modify the adhesion characteristics of the Ag/CNT interface based on thermal wetting. Simulation results showed that the heat treatment altered the Ag thin film morphology by thermal wetting, causing an increase in contact area of Ag/CNT interface and the adhesion force for both the flat and rough models changed. Despite the increase in contact area, the adhesion force of flat Ag/CNT interface decreased after the heat treatment because of plastic deformation of the Ag thin film. The result suggests that internal stress of the CNT induced by the substrate deformation contributes in reduction of adhesion. Contrarily, heat treatment to the rough model increases adhesion force because of the expanded contact area. The contact area is speculated to be more influential to the adhesion force rather than the internal stress of the CNT on the rough Ag thin film, because the CNT on the rough model contains internal stress regardless of the heat treatment. Therefore, as demonstrated by simulation results, the heat treatment can prevent delamination or wear of CNT coating on a rough metallic substrate by thermal wetting phenomena.

• Composites Research
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• v.22 no.4
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• pp.33-40
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• 2009

Fiber orientation effects on the impact surface fracture of the glass plates coated with the glass fiber/epoxy lamina layer were investigated using a small-diameter steel-ball impact experiment. Four kinds of materials were used: soda-lime glass plates, unidirectional glass fiber/epoxy layer(one ply, two plies)-coated, crossed glass tiber/epoxy layer (two plies)-coated glass plates. The maximum stress and absorbed fracture energy were measured on the back surface of glass plates during the impact. With increasing impact velocity, various surface cracks such as ring, cone, radial and lateral cracks appeared near the impacted site of glass plates. Cracks in the plate drastically diminished by glass fiber coating. The tiber orientation guided the directions of delamination and plastic deformation zones between the tiber layer and the glass plate. Impact surface-fracture indices expressed in terms of the maximum stress and absorbed energy could be used as an effective evaluation parameter of the surface resistance.

• Composites Research
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• v.21 no.2
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• pp.8-14
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• 2008

Decrease of strength in composite material is generally caused by water absorption. It makes fracture of material, and loss of money or human lives. The objective of this study is to investigate the causes of decrease in strength by water absorption. Mechanism of water absorption was supposed as three steps. This mechanism is consisted of absorption into resin, absorption between resin and surface treatment agent, and delamination between fiber and resin. Conditions of test were supplied differently; kinds of fiber and resin, immersion time etc. Both of reversible reaction and irreversible reaction occurred simultaneously. Most of decrease in strength was finished at 2.5% water absorption, and the strength was recovered. At 4% water absorption, most of decrease was caused by irreversible reaction, therefore, there was a tendency not to be recovered in strength.

• Composites Research
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• v.19 no.1
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• pp.1-8
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• 2006

Prediction of damage caused by low-velocity impact in laminated composite plate is an important problem faced by designers using composites. Not only the inplane stresses but also the interlaminar normal and shear stresses playa role in estimating the damage caused. But it is well known that the conventional approach based on the homogenization has the limit in description of damage. The work reported here is an effort in getting better predictions of dynamic behavior and damage in composite plate using DNS approach. In the DNS model, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. In the view of microscopic mechanics with DNS model, interlaminar stress behaviors in the inside of composite materials are investigated and compared with the results of the homogenized model which has been used in the conventional approach to impact analysis. Also the multiscale model based on DNS concept is developed in order to enhance the effectiveness of impact analysis, and we present the results of multiscale analysis considering micro and macro structures simultaneously.

• Composites Research
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• v.20 no.6
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• pp.8-14
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• 2007

Debonding failure characteristics of the composite skin-stiffener specimens were experimentally investigated. The influences of bonding methods, types of stiffener shape and various secondary bonding parameters were evaluated. Present test results combined with the previous test results[1] showed that the failure displacement of the skin-stiffener specimens well evaluates the skin-stiffener debonding failure strength of the composite stiffened panels. The specimens with an open type stiffener had lower bending stiffness and larger failure displacement than those with a closed type stiffener. Secondary bonding and co-curing with adhesive had better failure strength than co-curing without adhesive film. Secondary bonded specimens failed by adhesive failure and co-cured specimens failed by delamination failure. As the bondline thickness was thinner, the skin-stiffener specimens had higher failure strength. The fillets had no influence on failure strength of the specimens. The influence of the surface roughness was shown according to types of stiffener shape.

• Journal of the Korean Wood Science and Technology
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• v.50 no.2
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• pp.134-147
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• 2022

The objective of this study is to determine the effect of fiber direction arrangement and layer composition of hybrid bamboo laminate boards on the physical and mechanical properties. The raw material used was tali bamboo (Gigantochloa apus (J.A. & J.H. Schultes) Kurs) rope in the form of flat sheets (zephyr) and falcata veneer (Paraserianthes falcataria (L) Nielsen). Zephyr bamboo was arranged in three layers using water-based isocyanate polymer (WBPI) with a glue spread rate of 300 g/m². There were variations in the substitution of the core layer with falcata veneers (hybrid) as much as two layers and using a glue spread rate of 170 g/m². The laminated bamboo board was cold-pressed at a pressure of 22.2 kgf/cm² for 1 h, and the physical and mechanical properties were evaluated. The results showed that the arrangement of the fiber direction significantly affected the dimensional stability, modulus of rupture, modulus of elasticity, shear strength, and screw withdrawal strength. However, the composition of the layers had no significant effect on the physical and mechanical properties. The bonding quality of bamboo laminate boards with WBPI was considered to be quite good, as shown by the absence of delamination in all test samples. The bamboo hybrid laminate board can be an alternative based on the physical and mechanical properties that can meet laminated board standards.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6A
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• pp.873-880
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• 2008

When checking the state of deterioration or damage structures, regular visual inspection has very important role. At this point, a visual inspection is performed mainly by sketch or photography with a camera of inspectors. If that happens, it takes a lot of effort and time to inspect appearance damages. The purpose of this study is to develop the automatic recognition system for a more efficient and effective inspection of appearance damages. In the process, the image processing technology and the data management & analysis system for damage recognition are mainly developed and applied. This automatic recognition system enables inspectors or clients to obtain correct data that can recognize a damage, such as, crack, water leakage, efflorescence, delamination (peeling), spalling, etc. In addition, this study takes aim at the effect of secure safety, functional maintenance and extension of design lifetime according to build up continuous and systematic data management system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.203-209
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• 2023

Cobalt sulfide nanocomposites were synthesized through a simple hydrothermal method as anode materials for sodium ion batteries (SIBs). In this work, a cobalt sulfide nanoparticle (CoS-NF) and a cobalt sulfide nanocomposite integrated with reduced graphene oxide (CoS@G-NC) were fabricated for electrochemical energy storage performance of battery. The as-prepared CoS@G-NC electrode exhibited reversible and stable cycle performance (62 % after 30 cycles at current density of 200 mA g^-1). The improved electrochemical property was attributed to the small grain growth and uniform distribution of cobalt sulfide during synthesis, which maximized the diffusion pathway for sodium ions and effectively suppressed the delamination and volume expansion of cobalt sulfide during the conversion reaction. The results provide promising anode materials for next-generation SIBs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.1
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• pp.19-32
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• 2024

An investigation into the detailed safety diagnosis report indicates that domestic highway bridges mainly suffer from defects, deterioration, and damage due to physical forces. In particular, deterioration is an inevitable damage that occurs due to various environmental and external factors over time. In particular, bridge deck is very vulnerable to cracks, which occur along with various types of damages such as rebar corrosion and surface delamination. Thus, this study evaluates a correlation between heterogeneous damage and deterioration environment and then identifies the main causes of such heterogeneous damage. After all, a bridge heterogeneous damage prediction model was developed using random forests to determine the top five factors contributing to the occurrence of the heterogeneous damage. The results of the study would serve as a basic data for estimating bridge maintenance and budget.