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Article Citation - WoS: 6Citation - Scopus: 6Excessive Damage Increase in Dual Phase Steels Under High Strain Rates and Temperatures(Sage Publications Ltd, 2021) Cobanoglu, Merve; Ertan, Rasim K.; Simsir, Caner; Efe, MertDamage formation in dual phase steels is a complex process and it may be sensitive to the deformation conditions and mechanisms. In this study, the damage parameter is measured and compared under quasi-static and industrial forming conditions (temperatures: 25 vs 200, 300 degrees C and strain rates: 10(-3)vs 10 s(-1)) for DP590 and DP800 steels. Resonance frequency and ultrasonic sound velocity techniques are utilized for the measurements to test the effectiveness and validity of each technique. At a given strain, the damage values can be up to 700% higher at industrial forming conditions, under which dynamic strain aging (DSA) controls the deformation behavior. DSA results in lower formability and is the likely mechanism responsible from the abnormal damage evolution. Measured damage parameters are also confirmed with the void fraction characterization by microscopy, which also provided details on the void shape and distribution with respect to the deformation conditions.Article Citation - WoS: 1Citation - Scopus: 1Flame Retarded Plasticized Poly(lactic Acid) Using Phosphorus-Based Additives(Sage Publications Ltd, 2024) Yesil, Sertan; Aytac, Ayse; Selim, FatmaIn this study, the synergistic effect of the flame-retardant additives on the properties of poly(lactic acid) (PLA) was investigated and at the same time, it was tried to increase the toughness of PLA by adding small amounts of phosphate-based additives to plasticized PLA as binary and ternary mixtures. Poly(ethylene glycol) (PEG) was used as a plasticizer. As flame retardant additives, ammonium polyphosphate (APP), tri-phenyl phosphate (TPP), and boron phosphate (BP) were used. Characterization of the composites was carried out by tensile test, impact test, differential scanning calorimetry (DSC), thermal gravimetric analyses (TGA), scanning electron microscopy (SEM), limiting oxygen index (LOI), and UL-94 horizontal burning tests. In addition, TGA-FTIR analyses were carried out to understand the thermal degradation mechanism of composites during combustion. According to the SEM micrographs of the burnt surfaces of the samples, a smooth and flat structure is observed in PLA/PEG/5TPP-5BP sample, while a porous structure and branching formations are observed in other composite samples. Among the composite samples, the best flame retardancy features were observed in the composite containing PLA/PEG/5APP-2.5TPP-2.5BP sample, and the highest impact strength and elongation at break values were obtained in the composite containing PLA/PEG/5APP-5TPP sample.Article Citation - WoS: 1Citation - Scopus: 2Change of Frontal Sinus in Age of According To the International Frontal Sinus Anatomy Classification(Sage Publications Ltd, 2023) Koksal, Ali; Demir, Berin Tugtag; Cankal, FatihBackground The radiological and surgical anatomy of the frontal sinus should be well-known in all age groups to successfully manage frontal sinus diseases and reduce the risk of complications in sinus surgery. Purpose To define frontal sinus and frontal cells according to the International Frontal Sinus Anatomy Classification (IFAC) criteria in pediatrics and adults. Material and Methods A total of 320 frontal recess regions of 160 individuals (80 pediatric, 80 adults) who underwent a computed tomography (CT) scan of the paranasal sinus (PNS) were included in the study. Agger nasi cells, supra agger cells, supra agger frontal cells, suprabullar cells, suprabullar frontal cells, supraorbital ethmoid cells, and frontal septal cells were evaluated in the CT analysis. Results The incidence rates of the investigated cells were determined to be 93.1%, 41.9%, 60.0%, 76.3%, 58.5%, 18.8%, and 0% in the pediatric group, respectively, and 86.3%, 35.0%, 44.4%, 54.4%, 46.9%, 19.4%, and 3.4% in the adult group, respectively. Considering the unilateral and bilateral incidence of the cells, agger nasi cells were highly observed bilaterally in both the pediatric group (89.87%) and the adult group (86.48%). Conclusion Our study results show that IFAC can be used as a guide to increase the chance of surgical treatment in the pediatric and adult groups and that the prevalence of frontal cells can be determined radiologically and contributes to the generation of estimations of the prevalence of frontal cells.Article Citation - WoS: 4Citation - Scopus: 4Multiloop State-Dependent Nonlinear Time-Varying Sliding Mode Control of Unmanned Small-Scale Helicopter(Sage Publications Ltd, 2020) Ozcan, Sinan; Salamci, Metin U.; Nalbantoglu, VolkanTime delays, parameter uncertainties, and disturbances are the fundamental problems that hinder the stability and reduce dramatically the tracking performance of dynamical systems. In this paper, a new state-dependent nonlinear time-varying sliding mode control autopilot structure is proposed to cope with these dynamical and environmental complexities for an unmanned helicopter. The presented technique is based on freezing the nonlinear system equations on each time step and designing a controller using the frozen system model at this time step. The proposed method offers an improved performance in the presence of major disturbances and parameter uncertainties by adapting itself to possible dynamical varieties without a need of trimming the system on different operating conditions. Unlike the existing linear cascade autopilot structure, this study also proposes a nonlinear cascade state-dependent coefficient helicopter autopilot structure consisting of four separate nonlinear sub-systems. The proposed method is tested through the real time and PC-based simulations. To show the performance of the proposed robust method, it is also bench-marked against a linear sliding control control in PC-based simulations.Article Citation - WoS: 7Citation - Scopus: 7A New Strategy for Solving Store Separation Problems Using Openfoam(Sage Publications Ltd, 2022) Abuhanieh, Saleh; Akay, Hasan U.; Bicer, BarisThe ability of OpenFOAM to solve the problem of a store separating from an air vehicle (store separation problem) has been evaluated using a dynamic mesh (Overset/Chimera) technique for an industry-class (transonic and generic) benchmark test case. The major limitations of the standard libraries have been determined. To tackle these challenges, a new strategy has been proposed and implemented using only open-source libraries and tools. The strategy combines porting, modifying, and adapting an overset library from the OpenFOAM fork platform (foam-extend) to the standard OpenFOAM platform (ESI). Furthermore, in order to overcome the well-known weakness of the standard OpenFOAM compressible solvers, the newly adapted overset library was integrated with an open-source, density-based, and coupled solver (HiSA), which uses the OpenFOAM technology. Additionally, a force restrained model was developed to consider the externally applied forces on the store by the store ejectors. The accuracy of the developed strategy has been compared with wind tunnel tests and the solutions of two well-known commercial codes, showing good agreements with them. While the study has focused on simulations with inviscid Euler equations (typical of the test case considered here), the viscosity effect on the solution has also been studied with Navier-Stokes equations and compared with other results in the literature, showing minor differences. To the best of the authors' knowledge, this is the first work which studies and validates the store separation problem in transonic regime with OpenFOAM.Article Citation - WoS: 19Citation - Scopus: 19Interaction Between Assembled 3d Honeycomb Cells Produced From High Density Polyethylene and a Cohesionless Soil(Sage Publications Ltd, 2012) Gurbuz, Ayhan; Mertol, Halit CenanAssembled 3D high-density polyethylene honeycomb cells, providing confinement to arrest spreading of the soil in cells and creating relatively stiff bed that redistributes footing pressure over wider area, were used in the present study to enhance load-carrying capacity and to reduce settlement of base materials under a foundation. The effects of various test parameters including width, height, number of layers of the 3D honeycomb cells, vertical distance between layers of the cells and depth of stress zone of the foundation were studied. The test results indicated that considerable improvement in the load-carrying capacity (congruent to 3.0) and reduction in settlement of the foundation (congruent to 62%) were obtained with the implementation of the single layer of the 3D cells into cohesionless soils. The optimum effective distance between two layers of the 3D cells was 0.142 times the width of foundation, the ratio of effective width of 3D cells to the foundation was about 4.2 and the depth of influence stress zone of the foundation was about two times the width of the foundation.Article Citation - WoS: 36Citation - Scopus: 42Modeling and Analysis of Weighted-k-out-of-n< G System Consisting of Two Different Types of Components(Sage Publications Ltd, 2014) Eryilmaz, Serkan; Sarikaya, KadirThis article is concerned with the reliability analysis of a weighted-k-out-of-n: G system consisting of two types of components. The system is assumed to have n components which are classified into two groups with respect to their weight and reliability, and it is assumed to operate if the total weight of all working components exceeds a prespecified threshold k. The reliability properties of such a system are studied. The optimal values of the number of components in each group are also determined under a minimum required reliability by minimizing the total acquisition cost.Article Citation - WoS: 10Citation - Scopus: 11Consecutive k-out-of-n< Lines With a Change Point(Sage Publications Ltd, 2016) Eryilmaz, SerkanReliability analysis of consecutive k-out-of-n systems and their generalizations has attracted a great deal of attention in the literature. Such systems have been used to model telecommunication networks, oil pipeline systems, vacuum systems in accelerators, spacecraft relay stations, etc. In this paper, nonrecursive closed form equations are presented for the reliability functions and mean time to failure values of consecutive k-out-of-n systems consisting of two types of nonidentical components. The results are illustrated for reliability evaluation of oil pipeline system.Article Citation - WoS: 64Citation - Scopus: 74Production and Characterization of Poly (lactic Acid)-Based Biocomposites Filled With Basalt Fiber and Flax Fiber Hybrid(Sage Publications Ltd, 2020) Eselini, Najah; Tirkes, Seha; Akar, Alinda Oyku; Tayfun, UmitPoly (lactic acid) (PLA)-based biocomposites containing flax fiber (FF) and basalt fiber (BF) both separately and together were prepared by melt blending method at the total constant ratio of 30 wt%. Mechanical properties, thermo-mechanical characteristics, thermal stability, flow behaviors, water uptake, and morphology of composites were investigated by tensile, hardness and impact tests, dynamic mechanical analysis (DMA), thermal gravimetric analysis, melt flow index (MFI) test, water absorption, and scanning electron microscopy, respectively. Mechanical test results show that tensile strength, elongation, elastic modulus, and impact strength are extended up to higher values with increase in BF content in hybrid composites. Conversely, the presence of FF displays a negative effect in which these values drop down drastically as the FF concentration increases. On the other hand, slightly higher hardness values are obtained by the addition of FF at higher loadings. DMA analysis reveals that BF inclusion leads glass transition temperature of PLA to one point higher, but hybrid and FF containing composites shift that temperature to lower values. Storage moduli of composites are enhanced with the increase in BF concentration and remarkable decreases are observed for FF-filled composites. Hybrid composites exhibit average MFI values between PLA/FF and PLA/BF composites.Article Citation - WoS: 6Citation - Scopus: 4Latent Dynamics of Movement Formation: the Kurdish Case in Turkey (1940s-1960s)(Sage Publications Ltd, 2015) Ozen, HayriyeThe attention of social movement studies has so far tended to focus on visible phases of movements, neglecting latent ones. This study argues that invisible mobilizations may be critical in preparing the groundwork of public mobilizations, particularly in authoritarian contexts. Using a process-oriented constructivist account of mobilization which incorporates insights from resistance studies, this article analyzes the Kurdish case in Turkey in the authoritarian 1940s and semi-authoritarian 1950s. Based on in-depth interviews, memoirs, newspaper reports, and official documents, it is demonstrated that a latent Kurdish dissent emerged in this period through the constitution of a sense of shared grievance and common identity both in hidden ways within the submerged networks of Kurdish students and professionals, and in public and visible, yet disguised, ways. Incubating the movement out of the gaze of the authorities within the authoritarian context, this latent dissent formed the groundwork of public acts of defiance and mobilization which emerged towards the end of the 1950s as the political changes encouraged Kurdish dissenters to publicly declare their opposition, and expanded in the more liberal context of the 1960s. Resume Les etudes des mouvements sociaux ont eu tendance jusqu'a present a privilegier les phases visibles de ces mouvements, negligeant les stades latents. Cette etude soutient que les mobilisations invisibles peuvent etre essentielles pour preparer le terrain des mobilisations publiques, en particulier dans un contexte autoritaire. En s'appuyant sur une interpretation constructiviste, axee sur le processus de mobilisation et reunissant des idees tirees des etudes des mouvements de resistance, cet article analyse le cas kurde dans la Turquie autoritaire des annees quarante et semi-autoritaire des annees cinquante. Fonde sur des entretiens approfondis, des biographies, des articles de journaux et des documents officiels, ce travail met en evidence l'apparition au cours de cette periode d'une dissidence kurde latente grace a la constitution d'un sentiment partage de mecontentement et d'identite commune au sein des reseaux secrets des etudiants et professionnels kurdes, de facon a la fois invisible et publique, mais dissimulee. Couvant a l'abri des regards des gouvernements autoritaires, cette dissidence latente a pose les bases des manifestations publiques de defiance et de mobilisation qui sont apparues a la fin des annees cinquante a l'occasion des changements politiques ayant encourage les dissidents kurdes a declarer publiquement leur opposition et favorise les mouvements sociaux dans le contexte plus liberal des annees soixante. Resumen La atencion de los estudios sobre movimientos sociales hasta ahora ha tendido a centrarse en las fases visibles de los movimientos, dejando de lado los latentes. Este estudio sostiene que las movilizaciones invisibles pueden ser centrales para la preparacion de las bases de movilizaciones publicas, en particular en contextos autoritarios. A partir de un relato constructivista orientado a los procesos de movilizacion que incorpora perspectivas de estudios de resistencia, este trabajo analiza el caso kurdo en Turquia en la decada autoritaria de 1940 y semi-autoritaria de 1950. Sobre la base de entrevistas en profundidad, memorias, informes de prensa y documentos oficiales, se demuestra que una disidencia kurda latente surgio en este periodo a traves de la constitucion de un sentimiento de agravio compartida y de identidad comun tanto en formas ocultas dentro de las redes sumergidas de estudiantes y profesionales kurdos, asi como de maneras publicos y visibles, aunque disfrazadas. Incubando el movimiento fuera de la mirada de las autoridades en el contexto autoritario, esta disidencia latente formo las bases del acto publico de rebeldia y movilizacion que surgio a finales de la decada de 1950 como los cambios politicos alentados disidentes kurdos para declarar publicamente su oposicion, y ampliado en el contexto mas liberal de la decada de 1960.
