Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Art and Construction Related Qualities of 14th‒15th Century Monuments in a Rural Landscape on the Western Coast of Türkiye(KeAi Communications Co., 2024) Hamamcıoğlu Turan, Mine; Aktaş, Engin; Toköz, Özge DenizThis study aims to contribute to the understanding of the evolution of art and construction in the early settlements established by Turkish communities on the far west Asian coast by focusing on two developed examples in Urla Peninsula. Conventional surveying and evaluation techniques of architectural restoration and civil engineering were utilized. Key findings include the understanding of the hierarchy of rural settlements in the studied landscape: old Çesme the most developed village of peninsula in the 16th century. It was positioned along a valley in distance to coast, but in control of harbor that played significant role in commerce between Europe and Asia. Its mosque and tomb, dated to late 14th – early 15th centuries, used to crown it. Cylindrical minaret tower of mosque, domed tomb tower on a cubical base and squinch in the transition zone of mosque are evidences for Central Asian roots. Usage of local lime stone, re-usage of andesite blocks, framing of the stone blocks with bricks, and pendentive in tomb refer to Roman-Byzantine constructions. The study presents the development of Turkish art and construction on the far west Asian coast in the 14th‒15th centuries. Findings will be a guide for related conservation management in similar contexts. © 2024 The Author(s)Conference Object The Challenges and Advantages of Macro Modeling in Ansys Software for Seismic Vulnerability Assessment of Historic Masonry Structures(National Technical University of Athens, 2023) Demir, Hatice Ayşegül; Yücetürk, Kutay; Aktaş, Engin; Hamamcıoğlu Turan, MineThis study aims at creating an advancement guideline for a software which can be used for seismic vulnerability assessment of historic masonry structures by revealing the results of an experience related to the macro modeling of a historic masonry building. The case study structure is Bergama Bedesten (15th-16th centuries) located in Bergama, Izmir, Turkey. ANSYS software is used for the Finite Element Modeling of the structure. The seismicity at its location is determined and the structural response under lateral loads is obtained together with the dynamic characteristics. Mesh design, component creation according to the used material change in structural elements, contact surface identification, the arrangement of the stress scales, and result interpretation are realized. For these stages, the challenges are discussed with the solutions. The advantageous aspects of the software are explained. For the challenges, in mesh design, the ineffectiveness of cartesian method for some elements was detected and tetrahedrons method was chosen. In contact surface identification, the overlapping portions of structural components could not be detected by the software exactly, so the manual surface separation was realized. In the stress level interpretation, the lack of assignment for material limit strength values to the analysis scale was experienced and the addition of limit values was carried out. The scale also needs manual arrangement for the increase of interval numbers of stress values to emphasize vulnerable zones. This flexibility of scale to be arranged can be seen as an advantage, as well. The 3d section and axonometric view creation provide the presentation of stress changes at inner and outer surfaces of the structure which is another positive side. © 2023 COMPDYN Proceedings. All rights reservedArticle Citation - WoS: 9Citation - Scopus: 13Analysis of Adhesively Bonded Joints of Laser Surface Treated Composite Primary Components of Aircraft Structures(Elsevier, 2023) Martin, Seçkin; Nuhoğlu, Kaan; Aktaş, Engin; Tanoğlu, Metin; İplikçi, Hande; Barışık, Murat; Yeke, Melisa; Türkdoğan, Ceren; Esenoğlu, Gözde; Dehneliler, SerkanThe performance of the adhesively bonded aerospace structures highly depends on the adhesion strength between the adhesive and adherents, which is affected by, in particular, the condition of the bonding surface. Among the various surface treatment methods, as state of the art, laser surface treatment is a suitable option for the CFRP composite structures to enhance the adhesion performance, adjusting the roughness and surface free energy with relatively minimizing the damage to the fibers. The aim of this study is the validation and evaluation of the adhesive bonding behavior of the laser surface-treated CFRP composite structures, using the finite element technique to perform a conservative prediction of the failure load and damage growth. Such objectives were achieved by executing both experimental and numerical analyses of the secondary bonded CFRP parts using a structural adhesive. In this regard, to complement physical experiments by means of numerical simulation, macro-scale 3D FEA of adhesively bonded Single Lap Joint and Skin-Spar Joint specimens has been developed employing the Cohesive Zone Model (CZM) technique in order to simulate bonding behavior in composite structures especially skin-spar relation in the aircraft wing-box.Article Citation - WoS: 15Citation - Scopus: 17Effects of Nanosecond Laser Ablation Parameters on Surface Modification of Carbon Fiber Reinforced Polymer Composites(SAGE Publications, 2023) Martin, Seçkin; İplikçi, Hande; Barışık, Murat; Türkdoğan, Ceren; Yeke, Melisa; Nuhoğlu, Kaan; Esenoğlu, Gözde; Tanoğlu, Metin; Aktaş, Engin; Dehneliler, Serkan; İriş, Mehmet ErdemRemoval of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/?45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition. © The Author(s) 2023.Article Citation - WoS: 8Citation - Scopus: 8Improving Adhesive Behavior of Fiber Reinforced Composites by Incorporating Electrospun Polyamide-6,6 Nanofibers in Joining Region(SAGE Publications, 2022) Esenoğlu, Gözde; Barışık, Murat; Tanoğlu, Metin; Yeke, Melisa; Türkdoğan, Ceren; İplikçi, Hande; Martin, Seçkin; Nuhoğlu, Kaan; Aktaş, Engin; Dehneliler, Serkan; İriş, Mehmet ErdemAdhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 +/- 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially.Article Citation - WoS: 4Citation - Scopus: 4Seismic Vulnerability Assessment of an Unanchored Circular Storage Tank Against Elephant's Foot Buckling(Springer, 2022) Bektaş, Nurullah; Aktaş, EnginPurpose Seismic vulnerability assessment of liquid containing storage tanks is the most vital relevance for industrial plants and society safety to endure damage during impending earthquakes. Because such systems also play an essential role in the public lifeline and also ensure continued use in emergencies. Furthermore, considering that the material contained in individual plants could be hazardous, requisite precautions have paramount importance against undesired leakage. The high internal pressure and axial forces exerted by the liquid in the steel tanks near the tank wall bottom produce elastic-plastic buckling, also known as Elephant's Foot Buckling (EFB). As far as the authors are aware, no study has been carried out that involves a critical assessment and comparison of IDA and truncated IDA-based EFB failure criterion. This study provides insight into incremental dynamic analysis (IDA) and truncated IDA-based seismic evaluation of cylindrical unanchored steel storage tanks by employing a developed pressure-based surrogate modeling approach. For this purpose, probability-based seismic assessment of a representative sample is considered based on IDA and truncated IDA approaches to identify the potential of the EFB failure and to explore potential enhancements in the sophisticated structural analysis model to prevent the hazardous effects of impending earthquakes. Methods Due to the significance of industrial plants for public safety and benefit, the structural response evaluation methods for different types of storage tanks have been widely reported. In the literature, the most comprehensive analytical assessment methodology is the IDA approach, in which nonlinear time-history analyses are considered in the finite element analysis model to assess the structural model's seismic performance. Results To generate fragility curves, both IDA approaches are employed, taking into consideration and ignoring uncertainty of material properties. The values of the two methods-based fragility curves approach each other as the magnitude of dispersion increases. Conclusion The two fragility curves give the probability of failures close to each other as the dispersion amount increases while considering the uncertainty of the material properties. In addition, fragility curves generated based on the truncated IDA have been found to give a higher probability of failure, up to 32.5 percent. When compared to the IDA-based fragility curves, the truncated IDA-based fragility curves were found to be on the conservative side.Article Citation - WoS: 7Citation - Scopus: 7A Comprehensive Study on Burst Pressure Performance of Aluminum Liner for Hydrogen Storage Vessels(ASME, 2021) Kangal, Serkan; Sayı, Abdülmecit Harun; Ayakdaş, Ozan; Kartav, Osman; Aydın, Levent; Artem, Hatice Seçil; Aktaş, Engin; Yücetürk, Kutay; Tanoğlu, Metin; Kandemir, Sinan; Beylergil, BertanThis paper presents a comparative study on the burst pressure performance of aluminum (Al) liner for type-III composite overwrapped pressure vessels (COPVs). In the analysis, the vessels were loaded with increasing internal pressure up to the burst pressure level. In the analytical part of the study, the burst pressure of the cylindrical part was predicted based on the modified von Mises, Tresca, and average shear stress criterion (ASSC). In the numerical analysis, a finite element (FE) model was established in order to predict the behavior of the vessel as a function of increasing internal pressure and determine the final burst. The Al pressure vessels made of Al-6061-T6 alloy with a capacity of 5 L were designed. The manufacturing of the metallic vessels was purchased from a metal forming company. The experimental study was conducted by pressurizing the Al vessels until the burst failure occurred. The radial and axial strain behaviors were monitored at various locations on the vessels during loading. The results obtained through analytical, numerical, and experimental work were compared. The average experimental burst pressure of the vessels was found to be 279 bar. The experimental strain data were compared with the results of the FE analysis. The results indicated that the FE analysis and ASSC-based elastoplastic analytical approaches yielded the best predictions which are within 2.2% of the experimental burst failure values. It was also found that the elastic analysis underestimated the burst failure results; however, it was effective for determining the critical regions over the vessel structure. The strain behavior of the vessels obtained through experimental investigations was well correlated with those predicted through FE analysis.Article Citation - WoS: 12Citation - Scopus: 15Probabilistic Investigation of Error Propagation in Frequency Domain Decomposition-Based Operational Modal Analysis(John Wiley and Sons Inc., 2021) Hızal, Çağlayan; Aktaş, EnginEach operational modal analysis (OMA) technique may produce significant errors during the identification procedure due to the applied methodology, environmental/operational conditions, and instrumentation. Consequently, those errors can adversely affect the quality of identified parameters. In this context, this study aims at providing a comprehensive discussion on the propagation of predictions errors in the frequency domain OMA. To mitigate the prediction errors those considered to be induced by modeling and measurement errors, an extended formulation is presented based on a recently developed Modified Frequency and Spatial Domain Decomposition technique. A comprehensive investigation is presented for the probabilistic modeling of output power spectral density (PSD), considering prediction errors. Numerical and real data applications are conducted to show the effectiveness of the proposed methodology.Article Citation - WoS: 2Citation - Scopus: 2Reliability of Corroded Steel Members Subjected To Elastic Lateral Torsional Buckling(Korean Society of Steel Construction, 2021) Uzun, Ertuğrul Türker; Aktaş, EnginStructural steel members are subjected to corrosion due to environmental condition. As a result, there is decreasing in the cross-section properties of the member. This causes different stability problems and reduction in the load carrying capacity of members. Then, the probability of failure, P-f increases due to corrosion. The need arises to determine expected level of safety for such members and systems. Besides, reliability of the steel structure is also effected by the structural stability problems that result decreasing in the resistance. Lateral torsional buckling is one of the most encountered problems in steel members and affected by the critical moment which is a function of lateral and torsional stiffness. Critical moment depends on the material properties, boundary conditions, unbraced length, load pattern, and the member's cross section. Under the corrosion, it is inevitable to observe changing in some of properties. In this study, a damage model to determine the reliability of a corroded I-shape steel member under linear moment gradient is developed considering corrosion exposure time. Uniform and varying thickness loss models are considered to show the corrosion effect. Influence of environmental condition on the load carrying capacity of the members is considered and their effects on member design is evaluated. As a result, it is concluded that load carrying capacity of steel members degrades and safety of them adversely effected. With presented formulas, it is ensured that the load carrying capacity and reliability indices of the steel members can be calculated practically under the examined situationsArticle Citation - WoS: 31Citation - Scopus: 32Development and Analysis of Composite Overwrapped Pressure Vessels for Hydrogen Storage(SAGE Publications, 2021) Kartav, Osman; Kangal, Serkan; Yücetürk, Kutay; Tanoğlu, Metin; Aktaş, Engin; Artem, Hatice SeçilIn this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of +/- 14 degrees to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance.