• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.9-16
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• 2009

The object of this study is to develop new examination technique for detecting debond in adhesive interface of different kinds of materials. Ultrasonic signal was modeled by theoretically analyzing ultrasonic propagation phenomenon of the adhesive interface and debonding interface. The test method using the phase reversal of the debonding interface applied to the FRP/Rubber test block. Aluminum/Rubber test block with the flat bottom hole was manufactured to evaluate quantitatively the minimum detection ability of defects. The pulse echo reflection method and the phase reversal method were mutually compared and it was estimated that the phase reversal method could detect the debond on the basis of the theoretically predicted ultrasonic signal and ultrasonic test data.

• Structural Engineering and Mechanics
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• v.14 no.5
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• pp.565-574
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• 2002

This paper presents a method for predicting premature separation of carbon fiber reinforced plastic (CFRP) plates from strengthened steel beams. The fracture criterion based on material-induced singularity is formulated in terms of a singular intensity factor. Static test on double strap joints was selected to provide the critical stress intensity factor in the criterion because good degree of accuracy and consistency of experimental data can be expected compared with the unsymmetrically loaded single lap joints. The debond/separation loads of steel beams with different CFRP lengths were measured and compared with those predicted from the criterion. Good agreement between the test results and the prediction was found.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.485-490
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• 2000

Because of occuring easily the crack, debond, lutting on asphalts pavement of bredge decks under traffic's heavy weigt load. We investigated the application of latex modified concrete to resurface and repaire bridge decks for preventing the above problems. Here, Using the ordinary portland cement and high early cement, We rested mix design, workability, compressive strength, adhesive power, drying shrinkage, carbonation, and economic estimation etc. We selected the condition of application to resurface and repaire bridge decks and detected high early cement is superior to ordinary portland cement in results of analyzing the application of the repairing bridge decks and economic estimations.

• Journal of Korean Association for Spatial Structures
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• v.4 no.3 s.13
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• pp.85-91
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• 2004

Rehabilitations of reinforced concrete(RC) structures using advanced fibre-reinfored plastic(FRP) composites has become very popular in last few years. Typical method of strengthening strategy using FRP composite is bonding the CFRP plate or sheet on the surface of existing concrete structures. Many researches, however, have shown that bonding FRP plate or sheet on the surface of concrete has tendancy to debond prematurely induced by stress concentrations at the end of the plate. In order for overcoming the premature failure, the filling-up method which places FRP-rod into the existing concrete sawing groove has been developed. Through filling-up test results, aims of this research is to investigate the efficiencies of the filling-up method and is to determine the availabilities of traditional flexural theories that has provided all over the world.

• Smart Structures and Systems
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• v.19 no.4
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• pp.371-382
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• 2017

Concrete filled steel tubes are extensively applied in engineering structures due to their resistance to high tensile and compressive load and convenience in construction. But one major flaw, their vulnerability to environmental attack, can severely reduce the strength and life of these structures. Degradation due to corrosion of steel confining the concrete is one of the major durability problems faced by civil engineers to maintain these structures. The problem accelerates as inner surface of steel tube is in contact with concrete which serves as electrolyte. If it remains unnoticed, it further accelerates and can be catastrophic. This paper discusses a non-destructive degradation monitoring technique for early detection corrosion in steel tubes in CFST members. Due to corrosion, damage in the form of debonding and pitting occurs in steel sections. Guided ultrasonic waves have been used as a feasible and attractive solution for the detection and monitoring of corrosion damages in CFST sections. Guided waves have been utilized to monitor the effect of notch and debond defects in concrete filled steel tubes simulating pitting and delamination of steel tubes from surrounding concrete caused by corrosion. Pulse transmission has been used to monitor the healthy and simulated damaged specimens. A methodology is developed and successfully applied for the monitoring of concrete filled steel tubular sections undergoing accelerated chloride corrosion. The ultrasonic signals efficiently narrate the state of steel tube undergoing corrosion.

• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.737-742
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• 1994

The fracture energy of glass fiber/carbon fiber/epoxy resin hybrid composite system was investigated in the aspect of fracture mechanism. Epoxy resin matrix was DGEBA-MDA-SN-HQ system. On the interface of glass fiber and matrix, post debone friction energy provided a major contribution to the fracture energy, and debonding energy and pull-out energy were of the similar value. In the case of fracture on the interface of carbon fiber and matrix, pull-out energy was the major contributor.

• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.53-58
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• 2017

In this paper, we propose a new method to debond between mixed finite elements for porous media in ABAQUS (2014). ABAQUS just provides debonding algorithm for the u-p model using cohesive elements in standard version. However, this approach has a drawback that it is hard to simulate complex debonding problems like element separation, rigid body motion, and contact between separated elements in standard version. ABAQUS-explicit can resolve these complex problems, but cohesive elements for the u-p model cannot be applied. We introduce a new algorithm for debonding for porous media instead of using cohesive elements. In this method, subroutines VUMAT to apply constitutive models and VDISP to separate elements in ABAQUS are used to simulate debonding problems. In addition, a simple 2-D example is demonstrated in the ABAQUS-explicit solver.

• Journal of Korean Association for Spatial Structures
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• v.5 no.4 s.18
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• pp.71-77
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• 2005

Bonded CFRP Plate method used murk in reinforcement method is very efficient for stress increment of reinforced members. But CFRP plate dosen't display enough its capacity and have the destruction characteristic of premature failure that reach failure by debond plate, because near-surface-bond using epoxy. Such destruction character of reinforced specimens take the influence at variables as steel reinforcement ratio, concrete strength, kind of reinforcement materials, reinforced length, property of epoxy used in binder and so on. In this study, performed experiment results are compared and considered on flexural performance of Near Surface Mounted Reinforcement used CFRP-Rod, as complement about structural behavior of RC beam reinforced flexural capacity in CFRP plate and premature failure of reinforcement material. Main variables of RC beam applied CFRP Plate external bond method are experimental variables as reinforcement length, reinforcement position (tension face and side face of beam) and existence of ironware in end parts. In case of CFRP-Rod, variable is reinforcement length.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.

• The korean journal of orthodontics
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• v.39 no.4
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• pp.234-247
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• 2009

Objective: The purpose of this study was to evaluate the shear bond strength of rebonded ceramic brackets according to each condition and find an appropriate method to rebond ceramic brackets with proper shear bond strength in clinical practice. Methods: The study consisted of 12 experimental groups, according to the types of brackets, debonding methods, and treatment methods of the bracket base. Shear bond strength was measured, and adhesive residues left on the tooth surface were assessed. The base of the bracket was examined under scanning electron microscopy. Results: The shear bond strength of the monocrystalline ceramic bracket group was significantly higher than thatof the polycrystalline bracket group with only sandblasting (p < 0.05). There was no significant difference in shear bond strength between groups that used rebonded brackets which were debonded with shear force and debonded with laser (p > 0.05). The shear bond strength of the sandblasted/silane group was significantly higher than that of the selectively grinded group with a low-speed round bur and the sandblasted only group (p < 0.001). The retentive structure was more presented in groups where laser was applied than in groups where shear force was applied to debond brackets prior to rebonding. The bracket bases which were treated before rebonding presented smoother surfaces than new brackets. Conclusions: Shear bond strength could be increased by applying a silane coupling agent after sandblasting before rebonding. Also, the bond strength of the selectively grinded group with a low-speed round bur and the sandblasted group showed acceptable bond strength for clinical orthodontic treatment.