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Öğe A Comparative Evaluation of Numerical and Analytical Solutions to the Biadhesive Single-Lap Joint(Hindawi Ltd, 2014) Ozer, Halil; Oz, OzkanThis paper attempts to address the detailed verification of Zhao's analytical solution including the moment effect with the two-and three-dimensional finite element results. Zhao compared the analytical results with only the 2D FEA results and used the constant bond-length ratio for the biadhesive bondline. In this study, overlap surfaces of the adherends and the adhesives were modelled using surface-to-surface contact elements. Both analytical and numerical analyses were performed using four different biadhesive bondline configurations. The 3D FEA results reveal the existence of complex stress state at the overlap ends. However, the general results show that analytical and numerical results were in a good agreement.Öğe 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 HuzeyfeIn 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.Öğe 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, CanThis 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.Öğe An experimental investigation on the failure loads of the mono and bi-adhesive joints(Taylor & Francis Ltd, 2017) Oz, Ozkan; Ozer, HalilBi-adhesive (or mixed-adhesive) joint is an alternative stress-reduction technique for adhesively bonded lap joints. In this work, an experimental study was performed to assess the effect of bi-adhesive bondline on the failure load of mono-adhesive and bi-adhesive single-lap joints. The first step in the experimental study related to mono-adhesive joint, the overlap length was checked using the Global yielding criteria. For the selected overlap length, failure loads of AV138, Araldite 2015 and DP-8005 mono-adhesive joints were determined. It was seen that the highest failure load occurred in the Araldite 2015 mono-adhesive joint. Secondly, the bi-adhesive joints were considered as two different adhesive combinations (AV138+2015, AV138+DP-8005). An interesting result was obtained that the considered bi-adhesive joints with two different adhesive combinations (AV138+2015, AV138+DP-8005) give joint strengths higher than the joint strengths of the adhesives used individually, even if ductile adhesive has a joint strength higher than that of the stiff adhesive. In the last step of this study, experimental investigation was then focused on the determination of optimum bond-length ratio for the bi-adhesive joint. Optimum bond-length ratio for bi-adhesive joint was then investigated using three ratios (0.3, 0.5, 0.7). It is concluded that the adhesive type and the bond-length ratio play an important role in the bi-adhesive bondline. Comparisons of the experimentally determined failure loads and shear strengths with available closed-form solutions were also carried out. Experimental failure loads were in good agreement with those obtained from the Volkersen method and Global yielding criteria.Öğe Investigation of the effects of central rectangular gap located in the adhesive layer on failure load and joint stiffness(Springer Heidelberg, 2022) Oz, Ozkan; Ozer, Halil; Elen, Nurhan CevikThe purpose of this study is experimentally and numerically to reveal the effects of rectangular gap located in the middle of the adhesive layer on the failure load of the single lap joint with various adhesives. The presence of a rectangular gap in the bondline center can be considered both as an adhesive defect and, when gap limits are set correctly, it can also be considered as an adhesive saving. What is intended to be done in this study is to reveal these limits correctly. The effects of the gap length, adhesive type on the von Mises equivalent stress distribution and failure load in the recessed joints were analyzed numerically. For this purpose, four different gap lengths and three different adhesives were considered. The tensile stiffness investigations for the recessed joints were performed. In addition, the effect of the gap length on the failure load of the recessed joints with various adhesives was investigated experimentally. As a result, in the design of recessed joint, although the effect of other parameters considered was also involved, it was seen that especially the adhesive property was clearly the main design parameter.Öğe 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 HuzeyfeThis 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.Öğe Joint Stress Optimization by the Hybrid Adhesive Lap Joint(Trans Tech Publications Ltd, 2012) Ozer, Halil; Oz, OzkanHybrid adhesive joint is an alternative stress reduction technique for the adhesively bonded joints. Hybrid adhesive means that it is used dual adhesives in the overlap region. Adhesive having high modulus of elasticity should be located in the middle of the bondline and the other adhesive having low modulus of elasticity at the ends. In this study, the effect of the hybrid adhesive bondline on the distributions of the peeling, shear and von Mises stress components at the single lap joint were investigated by using three-dimensional finite element model. The results show that the considered stress components can be optimized by using hybrid adhesive joint.Öğe On the von Mises elastic stress evaluations in the bi-adhesive single-lap joint: a numerical and analytical study(Taylor & Francis Ltd, 2014) Oz, Ozkan; Ozer, HalilBi-adhesive joints are an alternative stress-reduction technique for adhesively bonded joints. The joints have two types of adhesives in the overlap region. The stiff adhesive should be located in the middle and the flexible adhesive at the ends. This study is the extension of our previous paper to the von Mises stress evaluation and discusses the values and importance of the von Mises stresses in the bi-adhesive single-lap joint. Both analytical and numerical analyses were performed using three different bi-adhesive bondline configurations. The Zhao's closed form (analytic) solution used includes the bending moment effect. In the finite element models, overlap surfaces of the adherends and the adhesives were modeled using surface-to-surface contact elements. The contribution levels of the peel and shear stresses for producing a peak von Mises stress are also studied. It is concluded that the contribution level of the shear stress at where von Mises stress becomes peak is more than that of the peel stress. Joint strength analyses were performed based on the peak elastic von Mises stresses. It is seen that joint strength can be increased using bi-adhesive bondline. The analytical and numerical results show that the appropriate bond-length ratio must be used to obtain high joint strength.Öğe Recent Advances in Adhesively Bonded Lap Joints Having Bi-Adhesive and Modulus-Graded Bondlines: A Critical Review(Scrivener Publishing Llc, 2018) Oz, Ozkan; Ozer, HalilAdhesives have become a key research area because of their potential applications. Two important issues facing designers in designing the bonded joints are reducing the stress concentration and increasing the failure load. An important remedy is to use bi-adhesive and modulus-graded adhesive joints. Here, we provide a critical review of recent developments in the field of bi-adhesive and modulus-graded adhesive joints.Öğe Three dimensional finite element analysis of bi-adhesively bonded double lap joint(Elsevier Sci Ltd, 2012) Ozer, Halil; Oz, OzkanHybrid-adhesive joints are an alternative stress reduction technique for adhesively bonded joints. The joints have two types of adhesives in the overlap region. The stiff adhesive should be located in the middle and flexible adhesive at the ends. In this study, the effect of the hybrid-adhesive bondline on the shear and peeling stresses of a double lap joint were investigated using a three-dimensional finite element model. We developed a three dimensional model of the double lap joint based on solid and contact elements. Contact problem is considered to model the interface as two surfaces belonging to adherend and adhesive. Finite element analyses were performed for four different bond-length ratios (0.2,0.4,0.7 and 1.3). The results show that the stress components can be optimized using appropriate bond-length ratios. To validate the finite element analysis results, comparisons were made with available closed-form solutions. The numerical results were found in good agreement with the analytical solutions. (C) 2012 Elsevier Ltd. All rights reserved.Öğe The use of the exponential Drucker-Prager material model for defining the failure loads of the mono and bi-adhesive joints(Elsevier Sci Ltd, 2017) Ozer, Halil; Oz, OzkanIn this study, our previous experimental study was extended applying the exponential Drucker-Prager (EDP) yield criterion to define the numerical failure loads for mono and bi-adhesive single lap joints (SLJs) [Oz and Ozer, 2016]. Bi-adhesive (or hybrid adhesive) joint is an alternative stress-reduction technique for adhesively bonded lap joints. The joints have two adhesives with different moduli in the overlap region. Non-linear finite element analyses were carried out for mono and bi-adhesive joints implementing the EDP material model. Distributions of EDP maximum principal stress, equivalent stress and shear stress were obtained along the middle of the adhesive thickness. Numerical failure loads were compared with our previous experimental failure loads. In addition, hydrostatic stress and equivalent plastic strain distributions for these joints under the failure loading were obtained. The general results show that experimental and numerical, failure loads were in a good agreement. As a result, when bond-length ratios are selected properly and appropriate adhesives are used along the overlap length, the strength of bi-adhesive joints, compared to mono-adhesive joints, was found to increase considerably.
