Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 11Citation - Scopus: 12Finite Element Analysis of Low-Speed Oblique Impact Behavior of Adhesively Bonded Composite Single-Lap Joints(Springer, 2023-04-14) Atahan, M. Gokhan; Apalak, M. KemalThe development of a realistic numerical model that predicts the impact behavior of adhesively bonded composite joints is important for many industrial sectors such as automotive, aerospace, and marine. In this study, it was aimed to develop a numerical model that can predict the low-velocity oblique impact behavior of composite single-lap joints close to the experimental results. The validation of the proposed numerical model was carried out with the results of the previously experimentally tested joints. In explicit finite element analysis, the orthotropic material model and Hashin's damage criterion were used in the numerical model of composite adherends. The adhesive region was divided into three different regions. The cohesive zone model (CZM) was used to determine the damage initiation and propagation in the upper and lower interface regions of adhesive. The middle region of the adhesive between the two cohesive interfaces was modeled with an elastic-plastic material model to reflect the plastic material behavior of the adhesive in the analysis. The effects of impact angle, fiber orientation, and overlap length on adhesive damage initiation and propagation were investigated in detail. There is a good agreement between the numerical and experimental results, considering the contact force-time variations and composite and adhesive damage. The impact angle and fiber angle had a significant effect on the impact behavior of the composite joints and the adhesive damage initiation and propagation. The increase in impact angle and fiber angle caused a decrease in the maximum contact force value. Adhesive damage propagation patterns varied according to the composite fiber orientation. In addition, since the shear toughness of the adhesive is higher than its tensile toughness, the amount of adhesive damage and damage propagation rate decreased as the impact angle increased.Conference Object Evaluation of the Performance of Geotextiles Using Finite Element Analysis in the Settlement Results: A Case Study in Kayseri, Turkey(Korean Geosynthetics Society, 2018) Yalçın, Hakan; Akin, Muge K.; Çabalar, Ali FiratGeotextiles are successfully designated for the reinforcement of soils to solve certain settlement as well as bearing capacity problems in difficult ground conditions. Furthermore, geotextiles are used for the stability of man-made slopes. In this study, the performance of geotextiles for soil improvement is evaluated by considering various geotextile types that have different axial stiffness values. The stiffness values are compared using a finite element method (FEM) based software PLAXIS 2D. As case study, Kayseri Organized Industrial Site in Turkey was chosen for the comparison of these geotextiles for a specific soil profile during analyses. Besides, the FEM based approach is also considered for the settlement, axial force and the effective stress changes during the application of geotextiles. The selected geotextiles are also correlated using scanning electron microscope (SEM) analyses. The results indicated that the axial stiffness (EA) can be considered with the effect on the possible soil settlement and axial force values. The settlement values reduced with increase in stiffness of reinforcement. © 2021 Elsevier B.V., All rights reserved.Article Citation - WoS: 3Citation - Scopus: 5Elliptical Quantum Rings With Variable Heights and Under Spin-Orbit Interactions(MDPI, 2023-09-11) Mora-Ramos, Miguel E.; Vinasco, Juan A.; Radu, A.; Restrepo, Ricardo L.; Morales, Alvaro L.; Sahin, Mehmet; Duque, Carlos A.We investigate the electronic properties of a semiconductor quantum ring with an elliptical shape and non-uniform height, allowing for distributed quantum-dot-like bulges along its perimeter. The adiabatic approximation and the finite element method are combined to calculate the allowed electron states in the structure under the effective mass approximation, considering the contributions from Rashba and Dresselahaus spin-orbit interactions and the Zeeman effect in the presence of an applied magnetic field. We discuss the features of the calculated spectra for two different ring geometries: a symmetric one with four dot-like bulges, and an asymmetric one with three hilled protuberances. The information about those states allows us to evaluate the linear optical absorption response associated with interlevel transitions between the ground and lowest excited states. This phenomenon takes place at resonant energies of only a few milielectronvolts. It is observed that spin-orbit interactions tend to quench this response under zero-field conditions in the case of symmetric confinement.Conference Object Citation - Scopus: 7Design of Capacitive Micromachined Ultrasonic Transducers (Cmuts) on a Flexible Substrate for Intravascular Ultrasonography (Ivus) Applications(Institute of Electrical and Electronics Engineers Inc., 2017-05) Hah, Dooyoung; Je, Changhan; Lee, Sung Q.Effects of substrate bending to the characteristics of capacitive miniaturized ultrasonic transducers (CMUTs) on a flexible substrate are studied through finite element analysis (FEA) for the design purpose. The target application of the devices is intravascular ultrasonography (IVUS) where transducers are brought to the proximity of the imaging targets so that high resolution images can be obtained without much concern of signal attenuation. In order to eliminate mechanical rotation used in the conventional IVUS, the transducer array can be manufactured on a flexible substrate and to wrap it around a cylindrical frame. It can be anticipated that the characteristics of the transducers will be altered by such bending of the substrate through geometrical dimension changes and stress induced. Pull-in voltages and resonant frequencies of CMUTs were studied via FEA for various bending radii and membrane thicknesses. It was found that both pull-in voltages and resonant frequencies become smaller for the transducers on a bent substrate compared to the ones on a flat substrate. It was also found that pull-in voltages decrease as the substrate bending radius is reduced. © 2017 Elsevier B.V., All rights reserved.Article Citation - Scopus: 2Deformation Behavior of Nanostructured Aluminum: Experiment and Computational Study(Elsevier Ltd, 2023-04) Deka, Surja; Mozafari, Farzin; Mallick, Ashis K.Nanocrystalline metals have been processed from powder predecessors in recent times in significant ways, and nowadays, materials are starting to be manufactured which are not only strong but also ductile. Nanocrystalline aluminum (Average grain size 51 nm) was synthesized through high-energy ball milling at the room temperature of microcrystalline powder. The particle size and crystallite sizes were obtained by Williamson Hall and found to be in good correlation with transmission spectroscopy (TEM) data. There was a significant increase in the mechanical properties of nanostructured aluminum in comparison to coarse-grained aluminum. Moreover, a phenomenological model of large-deformation, isotropic, rate-dependent plasticity is developed, which takes into account pressure dependency, plastic dilatation, and non-normal flow. The model has been incorporated into a finite element program. Compression and tension experiments were performed on nanocrystalline aluminum, and the constitutive parameters within the model were estimated from these experiments. The present study shows that the constitutive model successfully simulates the mechanical response of nanocrystalline aluminum with reasonable accuracy using our numerical finite-element capability. © 2023 Elsevier B.V., All rights reserved.Article Citation - WoS: 25Citation - Scopus: 26Comprehensive Analysis of Experimental and Numerical Results of Bond Strength and Mechanical Properties of Fly Ash Based GPC and OPC Concrete(Elsevier Sci Ltd, 2024-02) Aslanbay, Yuksel Gul; Aslanbay, Huseyin Hilmi; Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Atas, OguzhanNowadays, materials in the more environmentally friendly waste product class, which can be an alternative to standard Portland cement (OPC), are frequently used by researchers in concrete production. One of these, namely fly ash-based geopolymer concrete (GPC), should demonstrate its superiority over OPC in terms of chemical and mechanical properties to enhance its utilization. One of the mechanical properties of GPC is the bond strength between reinforcement and concrete. In this study, it was aimed to obtain bond strengths by performing tensile tests on GPC samples with varying sodium silicate/sodium hydroxide (SS/SH) and alkaline activator/fly ash (AA/FA) ratios. A pull-out experimental setup was prepared in accordance with RILEM Standard. Experimental results were compared with numerical results obtained from finite element models designed in ABAQUS software and were found to be compatible. When evaluated in terms of peak load and max bond stress values, GPC is superior to OPC. Compared to OPC an increase in the SS/SH ratio enhances mechanical properties such as compressive strength and bond load, whereas an increase in the AA/FA ratio with a value of 0.7 in the series has the opposite effect. In the finite element models, stress values are higher in samples with an AA/FA ratio of 0.5 compared to other ratios. An increase in the AA/FA ratio leads to a decrease in stress values. The analytical results are demonstrated that the proposed model can be utilized to assess the bond strength performance between traditional reinforced concrete and fly ash-based geopolymer concrete. Additionally, as a result of experimental studies, a formula that can be used to estimate bond strength based on GPC compressive strength and shows the superiority of GPC compared to studies in the literature has been proposed.Article Citation - WoS: 20Citation - Scopus: 21Application of the Collocation Method With B-Splines to the GEW Equation(Kent State University, 2017) Zeybek, Halil; Karakoc, S. Battal GaziIn this paper, the generalized equal width (GEW) wave equation is solved numerically by using a quintic B-spline collocation algorithm with two different linearization techniques. Also, a linear stability analysis of the numerical scheme based on the von Neumann method is investigated. The numerical algorithm is applied to three test problems consisting of a single solitary wave, the interaction of two solitary waves, and a Maxwellian initial condition. In order to determine the performance of the numerical method, we compute the error in the L-2- and L-infinity- norms and in the invariants I-1, I-2, and I-3 of the GEW equation. These calculations are compared with earlier studies. Afterwards, the motion of solitary waves according to different parameters is designed.Conference Object An Fem Study of Die Attach Packaging Effect on Nanomechanical Si Optical Filters(Institute of Electrical and Electronics Engineers Inc., 2017-05) Seok, Seonho; Hah, DooyoungThis paper presents a finite element analysis of die attach packaging stress effect on emerging nanomechanical silicon optical filters. The proposed silicon optical filter is composed of Si waveguides and a microring resonator having a few hundred nm in thickness and a few tens of μm in length. Photonic integrated circuit is typically implemented by attaching a new component to a common ceramic interposer with other components. Such an attachment process would be a cause of unwanted performance deviation of MEMS or NEMS devices due to the packaging stress. Therefore, an FEM model has been used to evaluate deflection and stress of NEMS waveguides and microring resonators which are main elements for the proposed optical filter. © 2017 Elsevier B.V., All rights reserved.Article Citation - Scopus: 32Numerical Solutions of the Kawahara Equation by the Septic B-Spline Collocation Method(International Academic Press, 2014) Karakoç, Seydi Battal Gazi; Zeybek, Halil; Ak, Turgut; Karakoç, Battal GaziIn this article, a numerical solution of the Kawahara equation is presented by septic B-spline collocation method. Applying the Von-Neumann stability analysis, the present method is shown to be unconditionally stable. The accuracy of the proposed method is checked by two test problems. L<inf>2</inf> and L<inf>∞</inf> error norms and conserved quantities are given at selected times. The obtained results are found in good agreement with the some recent results. © 2016 Elsevier B.V., All rights reserved.Article Citation - Scopus: 25A Cubic B-Spline Galerkin Approach for the Numerical Simulation of the GEW Equation(International Academic Press, 2016) Karakoç, Seydi Battal Gazi; Zeybek, Halil; Battal Gazi Karakoç, S.The generalized equal width (GEW) wave equation is solved numerically by using lumped Galerkin approach with cubic B-spline functions. The proposed numerical scheme is tested by applying two test problems including single solitary wave and interaction of two solitary waves. In order to determine the performance of the algorithm, the error norms L<inf>2</inf> and L<inf>∞</inf> and the invariants I<inf>1</inf>, I<inf>2</inf> and I<inf>3</inf> are calculated. For the linear stability analysis of the numerical algorithm, von Neumann approach is used. As a result, the obtained findings show that the presented numerical scheme is preferable to some recent numerical methods. © 2016 Elsevier B.V., All rights reserved.