• Journal of the Korean Wood Science and Technology
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• v.45 no.5
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• pp.535-543
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• 2017

For column-beam gussets of wooden structures, slit-processed members inserted with a steel plate are used in general. In this study, a rigid portal frame bonded with a joint was fabricated and a semi-rigid portal frame was fabricated by making a wooden gusset, a replacement for steel plate, of which a half was integrated into the column member and the other half was joined with the beam member by drift-pins. The lateral strength performance of the wooden portal frame was compared with that of the steel plate-inserted joint portal frame. The lateral strength performance was evaluated through a perfect elasto-plasticity model analysis, sectional stiffness change rate, and short-term permissible shear strength. As a result of the experiment, the maximum strength of the rigid portal frame was lower than that of the steel plate-inserted joint portal frame. The yield strength and ultimate strength were calculated as 0.58 and 0.48, respectively, but the measurements of initial stiffness and cumulative ductility improved by 1.35 and 1.1, respectively. As a result of the perfect elasto-plasticity model analysis of the semi-rigid portal frame, the maximum strength was lower than that of the rigid portal frame, but the toughness after failure was excellent. Thus, the ultimate strength was higher by 1.05~1.07. The steel plate-inserted portal frame showed rapid decrease in stiffness with the progress of repeated tests, but the stiffness of the portal frames with a wooden joint decreased slowly.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.361-370
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• 2017

Through the use of finite element analysis and acoustic emission techniques we have evaluated the interfacial failure of a carbon fiber reinforced polymer (CFRP) repair patch on a notched aluminum substrate. The repair of cracks is a very common and widely used practice in the aeronautics field to extend the life of cracked sheet metal panels. The process consists of adhesively bonding a patch that encompasses the notched site to provide additional strength, thereby increasing life and avoiding costly replacements. The mechanical strength of the bonded joint relies mainly on the bonding of the adhesive to the plate and patch stiffness. Stress concentrations at crack tips promote disbonding of the composite patch from the substrate, consequently reducing the bonded area, which makes this a critical aspect of repair effectiveness. In this paper we examine patch disbonding by calculating the influence of notch tip stress on disbond area and verify computational results with acoustic emission (AE) measurements obtained from specimens subjected to uniaxial tension. The FE results showed that disbonding first occurs between the patch and the substrate close to free edge of the patch followed by failure around the tip of the notch, both highest stress regions. Experimental results revealed that cement adhesion at the aluminum interface was the limiting factor in patch performance. The patch did not appear to strengthen the aluminum substrate when measured by stress-strain due to early stage disbonding. Analysis of the AE signals provided insight to the disbond locations and progression at the metal-adhesive interface. Crack growth from the notch in the aluminum was not observed until the stress reached a critical level, an instant before final fracture, which was unaffected by the patch due to early stage disbonding. The FE model was further utilized to study the effects of patch fiber orientation and increased adhesive strength. The model revealed that the effectiveness of patch repairs is strongly dependent upon the combined interactions of adhesive bond strength and fiber orientation.

• Composites Research
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• v.16 no.5
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• pp.45-53
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• 2003

The experimental and numerical investigations on the failure characteristics of the secondary bonded composite single-lap joints were performed. The initiations and growths of cracks were observed using CCD camera and acoustic emission sensor during the tension tests of the joint specimens. The structural behaviors of the specimens were predicted by the geometric nonlinear two-dimensional finite element analysis. The three types of observed initial cracks were included in each finite element models and the strain energy release rates of each specimen models were calculated by VCCT(Virtual Crack Closure Technique) technique. The tension tests showed that the initial cracks occurred in the 60∼90% of final failure loads and the major failure modes of the specimens were adhesive failure and the delamination between the 1st and 2nd ply of laminate. The specimens with the thicker bondline had earlier crack initiation loads but higher crack propagation resistance and eventually better loading capability. The delaminations were mostly observed in the thicker bondline specimens. The mode I values of calculated strain energy release rates were higher than the mode II values in the all specimen models considering the three types of initial cracks. The mode I and total strain energy release rates were calculated as higher values in the order of initial crack in the edge interface, comer interface and delamination between the plies of laminate.

• Composites Research
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• v.28 no.4
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• pp.191-196
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• 2015

In this study, the static analysis and experiment were carried out on DCB specimens manufactured with aluminum foam in order to investigate the fracture toughness at the adhesive joint of the structure bonded with adhesive. In case of static analysis, all specimen models were shown to have the maximum reaction force when the forced displacement proceeded as much as 5 mm. The maximum reaction forces became 0.25 kN, 0.28 kN and 0.5 kN respectively in cases of specimen thicknesses of 35 mm, 45 mm and 55 mm. Two specimens in case of static experiment were selected to verify these analysis results. The maximum reaction forces were shown when the forced displacement proceeded as much as 5 to 6 mm. The maximum reaction forces became 0.22 kN and 0.3 kN respectively in cases of specimen thicknesses of 35 mm and 45 mm. By comparing the derived results, it could be shown that there was not much difference between the data of analyses and experiments. Therefore, It is inferred that the study data can be secured with only analysis by no extra experimental procedure. It is thought that the mechanical properties at the structure bonded of DCB with the type of mode III can be analyzed systematically.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.248-250
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• 2017

The Mar-M-247 alloy is one of the most widely used materials for gas turbine components in aerospace filed and it shows excellent high temperature strength properties. Hot section parts, such as turbine nozzle and blade, are difficult to manufacture because of their complicated shape. So, the joining process usually applies to them. In this study, the high-temperature behavior of Mar-M-247 alloy at liquid diffusion bonding was investigated. Thus, we performed the diffusion bonding at $1,121^{\circ}C$ for 7 minutes, and observed changes in high temperature strength. As a result, the strength of the bonded specimens decreased by about 70% at $649^{\circ}C$, 60% at $825^{\circ}C$, and 45% at $1,000^{\circ}C$ compared to the base metal. As a result of observing the strength change with bonding time, the specimen bonded for 720 minutes showed a similar strength with the base metal at $649^{\circ}C$. Inferring this result, the joint is considered to be the one-body part.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.42-48
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• 2009

There are a number of factors affecting the continued airworthiness of composite structure. Unlike metal structure, damages made in manufacturing processes or maintenance repair procedures need to be considered. The different levels of degradation and damage, which may occur, must be considered for structural substantiation of static strength, stiffness, flutter, and damage tolerance. This can start with an evaluation of environmental effects for the particular composite material. Matrix-dominated composite properties, such as compressive strength, are most sensitive to moisture absorption and temperatures. Static strength substantiation includes the smaller damages that will not be detected in production or maintenance inspection while damage tolerance addresses larger damages that need to be repaired once discovered. In this paper, we intend to list the airworthiness regulations and advisory circular that are deemed closely related to the certification of composite airplanes.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.343-352
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• 2006

In the present paper, the nondestructive test method was suggest to establish the bonding status of a motor case assembly composed of a steel motor case, adiabatic rubber layer and an ablative composite tube with strain data, AE(acoustic emission) signals and UT(ultrasonic test) data. And, finite element analysis was conducted to verify quantitatively the bonding status of motor case assembly under inner pressure loading. The bonding status could be judged whether the bonding status is perfect or contact condition by the data correlation study with AE signals and strain data measured from air pressure test. And, to classify the bonding status of motor case and rubber layer among bonding layers, UT method was also applied. From this study, the bonding status could be classified and detected into fourth types for all bonding layers as follows: (1) initial un-bonding, (2) perfect do-bonding during an air pressure test, (3) partially de-bonding during an air pressure test, and (4) perfect bonding.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.1
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• pp.57-65
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• 2023

A vibration response-based detection system was used to investigate the adhesive areas of single-lap joints using a nonlinear transformation approach for deep learning. In industry or engineering fields, it is difficult to know the condition of an invisible part within a structure that cannot easily be disassembled and the conditions of adhesive areas of adhesively bonded structures. To address these issues, a detection method was devised that uses nonlinear transformation to determine the adhesive areas of various single-lap-jointed specimens from the vibration response of the reference specimen. In this study, a frequency response function with nonlinear transformation was employed to identify the vibration characteristics, and a virtual spectrogram was used for classification in convolutional neural network based deep learning. Moreover, a vibration experiment, an analytical solution, and a finite-element analysis were performed to verify the developed method with aluminum, carbon fiber composite, and ultra-high-molecular-weight polyethylene specimens.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.591-601
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• 2008

The purpose of this study was to investigate the performance of precast concrete segmental bridge columns with shear resistance connecting structure. The system can reduce work at a construction site and makes construction periods shorter. A model of precast concrete segmental bridge columns with shear resistance connecting structure was tested under a constant axial load and a cyclically reversed horizontal load. A computer program, RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures was used. An bonded or unbonded tendon element based on the finite element method, that can represent the interaction between tendon and concrete of prestressed concrete member, is used. A joint element is newly modified to predict the inelastic behaviors of segmental joints. The proposed numerical method gives a realistic prediction of performance throughout the loading cycles for several test specimens investigated.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.81-88
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• 2019

In this study, the effects of graphene oxide (GO) addition on electromigration (EM) lifetime of Sn-3.0Ag-0.5Cu Pb-free solder joint between a ball grid array (BGA) package and printed circuit board (PCB) were investigated. After as-bonded, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) was formed at the interface of package side finished with electroplated Ni/Au, while $Cu_6Sn_5$ IMC was formed at the interface of OSP-treated PCB side. Mean time to failure of solder joint without GO solder joint under $130^{\circ}C$ with a current density of $1.0{\times}10^3A/cm^2$ was 189.9 hrs and that with GO was 367.1 hrs. EM open failure was occurred at the interface of PCB side with smaller pad diameter than that of package side due to Cu consumption by electrons flow. Meanwhile, we observed that the added GO was distributed at the interface between $Cu_6Sn_5$ IMC and solder. Therefore, we assumed that EM reliability of solder joint with GO was superior to that of without GO by suppressing the Cu diffusion at current crowding regions.