• 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.

• Composites Research
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• v.13 no.4
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• pp.42-53
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• 2000

A study has been made to establish an optimum condition in the surface treatment and curing method that is important for the fabrication of Al 7075/CFRP laminates. PAA(Phosphoric Acid Anodizing) provided a good adhesive strength and FPL(Sulfuric / Sodium Dichromate Acid Etching) had a similar adhesive strength with PAA. On the other hand, the poor adhesive strength was shown on vapor degrease and CAA(Chromic Acid Anodizing). By using the atomic force microscope(AFM), it was found that the PAA oxide surface obviously had a greater degree of microroughness as compared to vapor degrease, CAA and FPL treated surfaces. These results support the concept of a mechanical interlocking of the adhesive with-in the oxide pores as the predominant adhesion mechanism. In curing methods, the adhesive strength of co-curing method was higher than that of secondary curing method. With respect to stability of specimen shape, the secondary curing method was better than co-curing method. DMA(Dynamic Mechanical Analysis) test revealed $T_g$ in curing times over 60 min is nearly same, so it is estimated they will have similar degree of curing and joint durability in using FM300M adhesive film.

• Composites Research
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• v.33 no.6
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• pp.360-364
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• 2020

Although research and development of existing steel-made Cowl Cross Member(CCM) was carried out with magnesium and plastic to make vehicles lighter, it is difficult to apply them to performance problems in the vehicle's mounting condition. Recently, the company is conducting research on the injection CCM of the composite insert as a lightweight component that is most suitable for mass-production of automotive parts. This is a manufacturing process that inserts composite injection bracket parts into aluminum bar, and the adhesion of the two parts is one of the important factors considering the vehicle's mounting conditions. In this study, the joint strength of Aluminum bar is one of the important factors as a study for the injection of aluminum bar into PA6-GF60 composite material. For the analysis of these research, the method of spraying adhesive to the aluminum bar and the case of knurling treatment have been analyzed and the bonding strength of the direction of rotation and lateral direction has been analyzed for each part between the aluminum bar of the cowl cross member and the shape of the injection component of composite materials.

• Composites Research
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• v.37 no.3
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• pp.238-245
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• 2024

In this study, as part of the development of a monitoring system for the efficient maintenance of steel pipes, an experimental study was conducted to evaluate the performance of steel pipes treated with modified polyethylene coating. In the case of the conventional mechanical pre-coating method, there was a deterioration in polyethylene adhesion during expansion testing, which led to the application of a chemical pre-treatment process using a calcium-mixed phosphate zinc film to resolve this issue. SEM and EDX analyses showed that the densest structure was observed at a Zn/Ca ratio of 1.0, and improved heat resistance compared to the conventional method was confirmed. Additionally, to prevent coating detachment during expansion, an evaluation of adhesion and elongation was conducted on steel pipes with modified polyethylene coating, incorporating materials such as elastomers based on maleic anhydride grafting, metal oxides, blocking agents, and slip agents. Experimental results showed that the specimen (S4) containing all modified materials exhibited more than a 25% performance improvement compared to the specimen (S2) containing only metal oxides. Lastly, the development and performance evaluation of wedge-shaped socketing and pressing wheels, which are part of the pipe fixing accessories, were conducted to prevent surface coating damage on the completed pipes.