• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.287-290
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• 2005

CFRP strips manufactured in factory are produced normally with smaller width and larger thickness than CFRP sheets. By this reason, bonding force between CFRP strips and concrete substrate is not sufficient to sustain tensile force in CFRP strips. Therefore premature debonding failure cannot be avoided when strengthening is done by simply bonding the CFRP strips. The flexural strength of RC beam strengthened with CFRP strips must be calculated based on the effective strain considering debonding failure. This paper presents test results of an experimental study conducted to evaluate the flexural strength on RC beams strengthened with CFRP strips. 7 specimens were tested with respect to bond length and amount of CFRP strips. From the test results, it was indicated that the strain of the CFRP strips achieved at debonding failure can be decreased less than 6,000$\mu$ depending on the amount of CFRP strips.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.264-271
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• 2005

This study investigates the behavior of fatigue crack propagating between holes or holes filled with another materials. When holes or the holes bonded with another materials exist near center crack symmetrically, crack propagation rate is influenced by the bonding force of brazing part and the elastic modulus ratio of another material to matrix. It is experimentally and analytically confirmed that the center crack stops when its tip reaches near the center line of the holes and a small crack is initiated from the boundaries of holes or the holes filled with another materials and it propagates to final fracture. The mechanical behaviors of center crack near another materials are also investigated.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.74-82
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• 2005

This study investigates the behavior of fatigue crack propagating between holes or holes filled with another materials. When holes or the holes bonded with another materials exist near center crack symmetrically, crack propagation rate is influenced by the bonding force of brazing part and the elastic modulus ratio of another material to matrix. It is experimentally and analytically confirmed that the center crack stops when its tip reaches near the center line of the holes and a small crack is initiated from the boundaries of holes or the holes filled with another materials and it propagates to final fracture. The mechanical behaviors of center crack near another materials are also investigated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.6
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• pp.479-485
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• 2002

We have investigated the effects of various wafers cleaning on glass/Si bonding using 4 inch Pyrex glass wafers and 4 inch silicon wafers. The various wafer cleaning methods were examined; SPM(sulfuric-peroxide mixture, $H_2SO_4:H_2O_2$ = 4 : 1, $120^{\circ}C$), RCA(company name, $NH_4OH:H_2O_2:H_2O$ = 1 : 1 : 5, $80^{\circ}C$), and combinations of those. The best room temperature bonding result was achieved when wafers were cleaned by SPM followed by RCA cleaning. The minimum increase in surface roughness measured by AFM(atomic force microscope) confirmed such results. During successive heat treatments, the bonding strength was improved with increased annealing temperatures up to $400^{\circ}C$, but debonding was observed at $450^{\circ}C$. The difference in thermal expansion coefficients between glass and Si wafer led debonding. When annealed at fixed temperatures(300 and $400^{\circ}C$), bonding strength was enhanced until 28 hours, but then decreased for further anneal. To find the cause of decrease in bonding strength in excessively long annealing time, the ion distribution at Si surface was investigated using SIMS(secondary ion mass spectrometry). tons such as sodium, which had been existed only in glass before annealing, were found at Si surface for long annealed samples. Decrease in bonding strength can be caused by the diffused sodium ions to pass the glass/si interface. Therefore, maximum bonding strength can be achieved when the cleaning procedure and the ion concentrations at interface are optimized in glass/Si wafer direct bonding.

• Tribology and Lubricants
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• v.16 no.6
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• pp.415-424
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• 2000

The use of magnetoresistive (MR) head requires much tighter control of particle contamination in a drive since loose particles on the disk surface will generate thermal asperities (TA). In this study, a spinoff test was performed to investigate the adhesion and removal capability of a particle to disk surface. Numerical simulation was also performed to investigate dominant factor of particle detachment and to support experimental results. It was shown that particles are detached from the disk surface by the moment derived from the centrifugal force and the drag force and that the centrifugal force and capillary force are the dominant force, which determines spin-off of a particle on the disk surface. Removal of particles smaller than several micrometers, which are the main source of TA generation, is extremely difficult since the adhesion forces exceed the centrifugal force. Lubricant types and manufacturing process also influence the particle removal. Lower bonding ratio and lower viscosity of the lubricant will help to increase the removal rate of the particles from the disk surface.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.625-630
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• 2009

Embedding of active devices in a printed circuit board has increasingly been adopted as a future electronic technology due to its promotion of high density, high speed and high performance. One responsible technology is to embedded active device into a dielectric substrate with a build-up process, for example a chipin-substrate (CiS) structure. In this study, desmear treatment was performed before Cu metallization on an FR-4 surface in order to improve interfacial adhesion between electroless-plated Cu and FR-4 substrate in Cu via structures in CiS systems. Surface analyses using atomic force microscopy and x-ray photoemission spectroscopy were systematically performed to understand the fundamental adhesion mechanism; results were correlated with peel strength measured by a 90o peel test. Interfacial bonding mechanism between electrolessplated Cu and FR-4 substrate seems to be dominated by a chemical bonding effect resulting from the selective activation of chemical bonding between carbon and oxygen through a rearrangement of C-C bonding rather than from a mechanical interlocking effect. In fact, desmear wet treatment could result in extensive degradation of FR-4 cohesive strength when compared to dry surface-treated Cu/FR-4 structures.

• Journal of Welding and Joining
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• v.30 no.3
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• pp.38-43
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• 2012

In this study, active metal brazing methods for $ZrO_2$ and Ti alloy were discussed. To get a successful metal-ceramic bonding, various factors (melting temperature, corrosion, sag resistance, thermal expansion coefficient etc. of base materilas and filler metal) should be considered. Moreover, in order to clarify bonding between the metal and ceramic, the mechanism of the interfacial structure of the joints should be identified. The driving force for the formation of metal and ceramic interfaces is the reduction of the free energy which occurs when their contact becomes complete. Interfacial bonding depends on the material combinations and the bonding processes. This study describes the bonding between ceramic and metal in an active metal brazing.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.225-228
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• 2006

To clarify the one body behavior of reinforcing bar and concrete, it is important to investigate bond characteristics between two materials. Bond strength is decided by applied force and interface area between reinforcing bar and concrete. And, the resultant force of chemical adhesive force, frictional force, and mechanical interaction are to be main factors. Property of concrete influences on chemical adhesive force and frictional force; bond strength is decreased by corrosion of reinforcing bar, as the result, durability is also decreased. In this study, to confirm bond characteristics with property of concrete, w/c ratio and blending of mineral admixture were selected as the main test parameters. The results obtained from this study will be used as the basic data for bond characteristics with corrosion.

• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.316-323
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• 2012

The aim of this study is to investigate the effect of post heat treatment on bonding properties of roll cladded Ti/MS/Ti materials. First grade Ti sheets and SPCC mild steel sheets were prepared and then Ti/MS/Ti clad materials were fabricated by a cold rolling and post heat treatment process. Microstructure and point analysis of the Ti/MS interfaces were performed using the SEM and EDX Analyser. Diffusion bonding was observed at the interfaces of Ti/MS. The thickness of the diffusion layer increased with post heat treatment temperature and the diffusion layer was verified as having $({\epsilon}+{\zeta})+({\zeta}+{\beta}-Ti)$ intermetallic compounds at $700^{\circ}C$ and an $({\zeta}+{\beta}-Ti)$ intermetallic compound at $800^{\circ}C$, respectively. The micro Knoop hardness of mild steel decreased with post heat treatment temperature; however, those of Ti decreased at a range of $500{\sim}600^{\circ}C$ and showed a uniform value until $800^{\circ}C$ and then increased rapidly up to $900^{\circ}C$. The micro Knoop hardness value of the diffusion layer increased up to $700^{\circ}C$ and then saturated with post heat treatment. A T-type peel test was used to estimate the bonding forces of Ti/Mild steel interfaces. The bonding forces decreased up to $800^{\circ}C$ and then increased slightly with post heat treatment. The optimized temperature ranges for post heat treatment were $500{\sim}600^{\circ}C$ to obtain the proper formability for an additional plastic deformation process.

• Membrane Journal
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• v.27 no.4
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• pp.358-366
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• 2017

The most important factor in the performances of polymer electrolyte membranes for fuel cells is how fast hydrogen ions can be transported along the water channel formed inside the electrolyte membrane. Since the morphology of the water channel and the diffusivity of the protons are very important factors for the proton transport behavior, various molecular dynamics simulation studies are being carried out to clarify this. The force-field is an important variable parameterizing the movement and interaction of each atom in molecular dynamics simulation. In this study, proton diffusivities of the 3D models of polymer electrolyte membranes were calculated in order to analyze the effects of various types of force-fields on the molecular simulation. It has been found that the charge value determining the non-bonding interaction plays a very important role in the formation of the water channel morphology, and the COMPASS force-field can calculate the accurate proton diffusion behavior. Accordingly, for molecular dynamics simulation of polymer electrolyte membranes, the proper selection of the force-field is very important due to its great effect on the proton diffusion as well as the final molecular structure.