Erbayrak, Engin; Eker, Beril; Colak, Murat

This study primarily examines the strength of a single lap joint having a mixed adhesive overlap consisting of a single adhesive and its thermoplastic reinforced state under varying temperatures. In the single lap joint, Titanium-Boron reinforced A356 aluminum was employed as the metal adherend, while plain woven glass fiber-reinforced epoxy (GFRE) was employed as the composite adherend. In the application of the mixed adhesive overlap, the brittle adhesives were employed in the middle section of the lap joint, while the reinforcement of the thermoplastics was employed on the adhesives at both sides of the lap joint. The single lap joints were subjected to tensile tests at 1 mm/min loading rates under room temperature and 120 °C, which is the melting point of the copolyester. In the numerical analysis, the cohesive zone model was applied in order to define the adhesives; however, elastic isotropic and orthotropic material behaviors were employed for the metal and composite adherends, respectively. Eventually, it is determined that the strength of a mixed adhesive lap joint consisting of a single adhesive and its thermoplastic reinforced state is better than a lap joint made with the mono-adhesive alone. Although literature suggests that mixed adhesive overlaps can be formed using at least two different adhesives (one ductile and one brittle), this study demonstrated that a mixed adhesive zone can be created using a single adhesive and thermoplastic reinforcement.

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Ulay, Göksel; Akter, Mete; Çakıcıer, Nevzat; Ayata, Ümit

This study evaluated the effects of different weathering durations (168, 336, and 504 h) on surface hardness and adhesion strength of both heat-treated (1.5 h at 190 °C and 2 h at 212 °C) and untreated iroko (Chlorophora excelsa) wood surfaces after application of water-based varnish (WBV). Pendulum hardness (s) and pull-off adhesion (MPa) tests were performed after weathering. According to the results, in the untreated control group, hardness increased from 30 s to 45 s after 504 h of weathering, showing a 48% increase. In the samples treated at 190 °C, hardness increased from 25 s to 41 s after 504 h, showing a 61% increase. The highest increase was observed in the samples treated at 212 °C. Here, the hardness increased from 23 s to 44 s, representing a 91% increase after 504 h of weathering. The highest initial surface adhesion strength (5.30 MPa) was obtained in the unheated samples; however, this value decreased significantly after weathering. Although the initial adhesion strength was lower in the heat-treated samples, those treated at 212 °C for 2 h exhibited more stable weathering performance. The results show that the acceleration of weathering and the application of heat significantly affect the effectiveness of the varnish coating.

İncele

Erbayrak, Engin

The low-velocity impact behavior of single-lap joints was investigated in this study. In single-lap joints, woven carbon fiber reinforced epoxy (CFRE) and plain woven glass fiber reinforced epoxy (GFRE) laminates as well as a hybrid composite laminate (HCGFRE), which is formed by stacking carbon and glass composite laminates, are used as adherends. Araldite 2011 and Araldite 138 M/HV998 epoxy adhesives were used with different mechanical properties for joining similar and dissimilar composite adherends. Low-velocity impact tests were carried out with 40 J impact energy. Reaction force-time and impact energy-time graphs were obtained from the experimental study as impact response. In numerical analyses, the damage approach of composite adherend was modeled using composite stress-based failure model (Mat 59) and adhesives were modeled utilizing a mixed-mode cohesive zone model (Mat 138) that existed in LS-DYNA explicit finite element software. It was seen that the numerical results indicated a similar tendency with the experimental results due to the modeling of the adhesives using the proper cohesive zone model, the application of correct boundary conditions, and the selection of the correct contact type.

AtıfScopus9·WoS9·OpenAlex10

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