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    Effect of carbon filler-modified epoxy adhesive on failure behavior of bonded single-lap joint: an experimental study combined with digital image correlation method
    (Springer Heidelberg, 2022) Oz, Ozkan; Ozturk, Fatih Huzeyfe
    In this study, the effect of carbon filler-modified epoxy adhesive on the failure behavior of the single-lap joint (SLJ) was investigated through the experimental testing and digital image correlation (DIC) method. Carbon black (CB) and carbon fiber powder (CFP) were used as fillers to modify the adhesive. Carbon fillers were added individually into epoxy adhesive at the ratios of 0.5, 1, and 2.5 wt%. Pure and modified adhesive joints were tested under tensile load to determine the failure behavior of the joints. Moreover, DIC method was utilized to display the adhesive von Mises strain at the end of the bondline. Finally, SEM images were used to evaluate the fracture surfaces of the SLJs. As a result of the tensile tests, it was found that the CB- and CFP-modified epoxy adhesive increased the failure load and breaking displacement of SLJs. Among all the joints investigated in this study, SLJ bonded with adhesive containing 1 wt% CFP reached the highest failure load while the SLJ bonded with adhesive containing 2.5 wt% CB exhibited the highest toughness. DIC results and SEM observations revealed that the increase in the failure load and toughness of SLJs were associated with the increase in the ductility of the epoxy adhesive.
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    Effect of fiber content and plasticizer on mechanical and joint properties of carbon fiber powder reinforced PLA manufactured by 3D printing process
    (Taylor & Francis Ltd, 2023) Oz, Ozkan; Ozturk, Fatih Huzeyfe; Gulec, Can
    This study investigates the mechanical and joint properties of the carbon fiber powder (CFP) reinforced polylactic acid (PLA) manufactured by 3D printing process. Composite filaments with various contents of CFP (5 wt.%, 10 wt.% and 15 wt.%) were prepared using a single screw extruder. Adherends and tensile test specimens were printed by an open-source 3D printer. Polyethylene oxide (PEO) was used as a plasticizer to improve the ductility of the PLA and PLA/CFP composite. Experimental results revealed that the CFP considerably improved the mechanical properties and the joint strengths of the composite specimens. Incorporating PEO into the blends enhanced ductility for both tensile and joint specimens but reduced strength. The SEM images showed that the fiber/matrix adhesion is weak. However, the parallel orientation of the fibers to the load direction together with their uniform distribution in the matrix increased the mechanical properties of the composites. SEM observations also showed that the addition of PEO caused porous matrix structure which is responsible for the increase in ductility of the PLA and its composites. Global yielding (G.Y) criterion was used to predict the joint failure loads and a comparison was made between experimental and predicted failure loads. The comparisons showed that the G.Y criterion over-predicted the failure loads. The minimum and maximum difference between experimental and predicted failure loads were 12.96% and 28.10%, respectively. At last, recommendations for further studies were also presented.
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    An investigation on failure behaviour of bonded polylactic acid adherends produced by 3D printing process: experimental and numerical approach
    (Springer Heidelberg, 2023) Oz, Ozkan; Ozturk, Fatih Huzeyfe
    This study investigated the failure behaviour of adhesive bonded single lap joints (SLJs) of Poly (lactic acid) (PLA) adherends fabricated by 3D printing. Adherend printing angle (0 & DEG;, 45 & DEG; and 90 & DEG;) adherend thickness (2, 4 and 6 mm), and overlap length (12.7 and 25.4 mm) were chosen as joint design parameters. In addition to the experimental study, a 3D nonlinear finite element (NL-FE) analysis was performed to determine the variation of stress components in adhesive layer and the numerical failure load of SLJs. The material properties of adherends with different printing angles were defined using Hill yield criterion (HYC). The present study could be considered a novel one given that it presents an anisotropic yield criterion to evaluate the failure of adhesive bonded joints with printed adherends. An analytical expression was also derived to calculate the tensile stiffness of joints. Results obtained from the experimental tests and analytical expression indicated that increasing the adherend thickness, the overlap length, and the printing angle increased the strength and the tensile stiffness of joints, respectively. It was found that the combined effect of printing angle and adherend thickness on joint strength is more prominent for SLJs with overlap length of 25.4 mm. The highest printing angle of 90 & DEG; gave an 85.26% improvement in the failure load when the adherend thickness was increased from 2 to 6 mm for this group of SLJs. The accuracy of NL-FE model based on the HYC was evaluated by comparing the numerical failure loads and failure types with those from the corresponding experiments. NL-FE analyses proved that the HYC could capture the effect of joint design parameters on the strength of the SLJs.
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    MECHANICAL PROPERTIES OF GRAPHENE-NANOPARTICLE AND CARBON-NANOTUBE-REINFORCED PE-MATRIX NANOCOMPOSITES
    (Inst Za Kovinske Materiale I In Tehnologie, 2019) Erden, Mehmet Akif; Akgul, Yasin; Kayabas, Ozge; Ahlatci, Hayrettin; Cetinkaya, Kerim; Ozturk, Fatih Huzeyfe
    In this study, graphene-nanoplatelet (GNP) and carbon-nanotube (CNT) reinforced nanocomposites were produced with pressure molding. 1 w/% of GNPs and 1 w/% of CNTs were separately added to a polyethylene (PE) matrix and 0.5 w/% of both reinforcements was also jointly added to the PE matrix. In this manner. the effects of GNPs and CNTs on the mechanical properties of PE were compared and the synergistic effect was investigated. In order to examine the mechanical properties, a tensile test, a hardness test and a wear test were applied to the produced samples. Also, fracture surfaces and wear surfaces were investigated with a scanning electron microscope (SEM). It was observed that the graphene was distributed homogeneously in the polyethylene matrix. Thus, the GNP-containing samples showed better mechanical properties than the CNT-containing samples.
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    Optimization of adherend thickness and overlap length on failure load of bonded 3D printed PETG parts using response surface method
    (Emerald Group Publishing Ltd, 2024) Ozturk, Fatih Huzeyfe
    PurposeAdhesive bonding is critical to the effectiveness and structural integrity of 3D printed components. The purpose of this study is to investigate the effect of joint configuration on failure loads to improve the design and performance of single lap joints (SLJs) in 3D printed parts.Design/methodology/approachIn this study, adherends were fabricated using material extrusion 3D printing technology with polyethylene terephthalate glycol (PETG). A toughened methacrylate adhesive was chosen to bond the SLJs after adherend printing. In this study, response surface methodology (RSM) was used to examine the effect of the independent variables of failure load, manufacturing time and mass on the dependent variable of joint configuration; adherend thickness (3.2, 4.0, 4.8, 5.6, 6.4, and 7.2 mm) and overlap lengths (12.7, 25.4, 38.1, and 50.8 mm) of 3D printed PETG SLJs.FindingsThe strength of the joints improved significantly with the increase in overlap length and adherend thickness, although the relationship was not linear. The maximum failure load occurred with a thickness of 7.2 mm and an overlap of 50.8 mm, whilst the minimum failure load was determined with a thickness of 3.2 mm and an overlap of 12.7 mm. The RSM findings show that the optimum failure load was achieved with an adherend thickness of 3.6 mm and an overlap length of 37.9 mm for SLJ.Originality/valueThis study provides insight into the optimum failure load for 3D printed SLJs, reducing SLJ production time and mass, producing lightweight structures due to the nature of 3D printing, and increasing the use of these parts in load-bearing applications.