Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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  • Article
    Influence of Intra-Ply Discontinuities on the Mechanical Behavior of Continuous E-Glass Fiber Reinforced Composites
    (Sage Publications Ltd, 2024) Kilicoglu, Ahmet Suha; Tanoglu, Metin; Bilmez, Sinan Ali; Gunes, Mehmet Deniz; Erdogan, Hakan Salih
    This study examines how structural discontinuities created during production affect glass fiber-reinforced composite plates. Due to geometrical constraints, the composite microstructure's discontinuities can be categorized as inter-ply and intra-ply. Material testing was conducted at the coupon level as an initial step to ascertain material characteristics. Two full-scale models of intra-ply composite samples were manufactured by employing layers of glass fiber-reinforced prepregs. Discontinuities were generated in the samples using a computer numeric control cutter and then manually applied. The discontinuities' impact on the composite laminate's mechanical properties was assessed through full-scale pieces using three-point bending quasi-static tests. Servo-hydraulic actuators were used to conduct tests on the items. The experimental test results were compared with CAE analysis predictions by evaluating sectional fiber volume fraction. The characteristics of local discontinuities were analyzed using a microscope to enhance the findings of the CAE model. This comprehensive approach offers insights into the intricate connection between internal structural inconsistencies and the mechanical properties of continuous glass fiber-reinforced materials. It supports optimizing composite manufacturing processes and improves composite parts' structural reliability. Dislocation areas were found to result in the formation of resin-rich zones in this investigation. The exothermic curing process in the component's zones results in elevated temperatures, leading to a color change in the resin from clear to yellow. The yellow areas are easily recognizable and show decreased mechanical durability.
  • Article
    Fatigue-Resistant Design of Carbon/Epoxy Composites Based on a Failure Tensor Polynomial Model by Particle Swarm Optimization-Sequential Quadratic Programming Algorithm
    (Sage Publications Ltd, 2024) Deveci, Hamza Arda; Artem, Hatice Secil; Guenes, Mehmet Deniz; Tanoglu, Metin
    This article introduces a design procedure to find the optimum fiber orientations of carbon/epoxy composite laminates for fatigue life advancement. The approach incorporates a fatigue failure tensor polynomial model and employs a hybrid algorithm, combining particle swarm optimization and sequential quadratic programming. Firstly, material properties of quasi-static and fatigue of the carbon/epoxy composites, fabricated by the vacuum-assisted resin transfer molding method, were determined to be used in the model. Various design problems involving two optimization scenarios were then solved using the hybrid algorithm. The algorithm's performance was also evaluated by specific test problems, confirming its speed and robustness. The optimally fiber-oriented carbon/epoxy composite laminates having maximum fatigue lives were obtained for many critical in-plane cyclic loading cases. To validate the proposed design procedure, two optimum designs were experimentally verified under uniaxial loading conditions. The results indicated a good correlation between the estimated fatigue life of the optimally designed laminates and experimental data. This methodology offers a promising approach for the design of carbon/epoxy composite laminates with superior fatigue strength, particularly significant in specific industrial applications.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 9
    Politics of Waiting for Transformation in Protracted Urban Renewal Projects in Turkey
    (Sage Publications Ltd, 2023) Ay, Deniz; Penpecioglu, Mehmet
    This paper explores the politics of 'waiting' as a mode of governance in large-scale urban redevelopment projects. In designated renewal areas, residents/landowners are often subject to several episodes of waiting: waiting for the public authority for information on redevelopment visions; waiting for the plans and projects to become public; waiting for the court ruling if they appeal the plans; waiting for demolition upon plan approvals; and, finally, waiting for the constructions to be completed. Given the complexity of actors and institutions involved in the waiting, it becomes a conflictual political process. This prolonged waiting leads to an ongoing temporariness and precarious spaces of urban renewal. The course of waiting affects the reorganization of the city space now and in the future. We analyze two protracted urban renewal projects from Turkey, Fikirtepe in Istanbul and Karabaglar in Izmir, to explore how residents' decade-long waiting for urban change are shaped and how these diverse waiting experiences lead to different outcomes for the progression of the state-imposed urban renewal agendas. While Karabaglar residents have unified around active bottom-up resistance from the beginning to challenge the project-based plans the central government imposed, Fikirtepe residents pursued individual-level negotiations with developers to maximize private returns following the zoning incentives the public authority gave. Despite the socio-spatial similarities between these designated urban renewal project sites, variances in residents' collective waiting strategies have led to different urban politics around project-based urban change.
  • Article
    Citation - WoS: 9
    Citation - Scopus: 10
    Investigation of Hybridization Effect on Ballistic Performance of Multi-Layered Fiber Reinforced Composite Structures
    (Sage Publications Ltd, 2022) Üstün, Hikmet Sinan; Toksoy, Ahmet Kaan; Tanoğlu, Metin
    The aim of this study is enhancing the ballistic performance of multi-layered fiber reinforced composite structures by hybridization approach against fragment simulating projectile (FSP). For manufacturing of homogeneous and hybrid composite structures, 170 g/m2 twill weave aramid and 280 g/m2 plain weave E-Glass fibers were used with epoxy resin systems and two different thickness values for each composite panel were fabricated and tested to obtain a relationship between areal density and V50 parameters. Tensile, 3-point bending, and short beam strength tests of composite panels were performed, and ballistic performance of composite structures were measured by V50 test method with 1.1 g FSP threat. Ballistic performance of hybrid composite structures was compared with high-performance composite ballistic panel test results reported in literature. As a result, it was found that E-Glass fabric layers together with aramid fabrics increased the energy absorbing capability of hybrid composite panels and ballistic performance was enhanced to be similar or higher than ballistic fiber reinforced composites. Hence, hybridization was found to be an effective way to enhance ballistic performance of fiber reinforced composite structures.