Browsing by Author "Sahin, Ömer Sinan"

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Citation - WoS: 4
Citation - Scopus: 4
Dynamic Characterization and Damage Analysis for the Thermoplastic Fiber-Reinforced Epoxy Composites Exposed To Repeated Low Velocity Impact
(Sage Publications Ltd, 2023) Sözen, Betül; Coşkun, Taner; Sahin, Ömer Sinan
In the current study, contrary to conventional fiber-reinforced composites, polyamide fiber was used as reinforcement material, and the effects of thermoplastic fiber reinforcement on repeated low velocity impact (LVI) responses of composites were examined. In this regard, polyamide fiber-reinforced composites were fabricated using the vacuum-assisted hand lay-up method (VAHLM) and then exposed to repeated LVI loadings. Experimental tests were performed on the specimens for 100 impacts with a constant velocity of 3 m/s, which is equivalent to 25.2 J, and the impacts of repeated LVI loadings on the dynamic responses such as peak force, energy absorbing/rebounding, total impulse, bending stiffness and contact stiffness were examined. Moreover, the damage mechanisms resulting from the relative damage accumulation depending on the impact numbers were examined. According to the findings, the thermoplastic polyamide fibers absorbed more than 60% of the applied energy, and the absorbed energy increased with ascending impact number. Furthermore, the thermoplastic fiber-reinforced epoxy composites gained stiffness with increasing impact, which was linked to the thermoplastic chain structure. Despite quite a number of impact loadings, no serious damage mechanisms such as fiber breakage, perforation, or penetration were observed, and the specimens maintained their structural integrity. Due to the higher energy absorption of thermoplastics, the utilization of polyamide fibers in composites has been found to be well suited for applications subjected to repeated impacts.
Citation - WoS: 6
Citation - Scopus: 5
Effects of Low-Velocity Impact on Vibration Behaviors of Polyamide Fiber-Reinforced Composites
(Springer Heidelberg, 2022) Coskun, Taner; Yar, Adem; Demir, Okan; Sahin, Ömer Sinan
Fabric and resin materials, fiber orientations, volume fraction and knitting patterns are highly effective for the mechanical and dynamic properties of the composite materials. These materials can be subjected to impact loads at various energy levels depending on their application areas, and thus causes the material properties to change. Therefore, experimental studies have been carried out to determine the dynamic properties for the polyamide fiber-reinforced epoxy composites, which can be defined as a novel composite material variation, before and after low-velocity impact. In this context, the composite specimens were subjected to one and two repeated low-velocity impacts under 25.2 J constant energy. Apart from that experimental vibration tests were conducted under free-free boundary conditions to determine how dynamic properties such as natural frequency, flexural modulus, and specific damping capacity will change with the consequent distortion in the structural integrity. For the current study, at least three samples were subjected to the experimental tests to verify obtained results, and standard deviations revealed that results were reliable and repeatable. As a consequence of the current study, it has been concluded that the composite specimens have high matrix volume fractions due to the knitting architecture of the polyamide fabrics. Moreover, since the polyamide fabrics have spacious mesh weave, an improvement for the damping properties has been achieved due to the increased fiber-resin interface. It has been observed that polyamide composite specimens exhibited approximately 11.5% specific damping capacity, and had relatively higher damping properties compared to the conventional materials. It was also revealed that the degradation in the specific damping capacities was observed by virtue of the low-velocity impact but it was not significantly effective on the dynamic properties due to the limited damage area. Additionally, it was found that polyamide fiber-reinforced composites can be used as the optimum material for the application areas in which high damping and impact resistance are required.
Citation - WoS: 7
Citation - Scopus: 9
Experimental and Numerical Investigation of the Structural, Thermal and Acoustic Performance of Reinforced Concrete Slabs With Balls for a Cleaner Environment
(Springer Int Publ Ag, 2023) Arslan, Musa Hakan; Özkilic, Yasin Onuralp; Arslan, H. Derya; Sahin, Ömer Sinan
This study conducted a comprehensive experimental and numerical assessment to investigate the effect of plastic circular balls placed in the middle of a section of a reinforced concrete slab on strength, ductility, thermal, and acoustic performance. The ball diameter/slab thickness (D/H), grades of concrete, and longitudinal tensile reinforcement ratio (rho) in the slab were selected as the main variables. The variation in thermal and acoustic performance depending upon the ball's diameter was investigated as well. The results showed that the slab's load-carrying capacity, ductility, and energy dissipation capacity did not differ if the D/H ratio did not exceed 0.4; however, significant decreases in these values were observed when the D/H ratio exceeded 0.4. Moreover, the increase in the concrete and reinforcement's strength had a negative effect on the slab with a D/H ratio of 0.8. The experimental results revealed that balled slabs are 3.15 times superior with respect to thermal conductivity and provide 1.38 times more insulation to absorb sound compared to non-balled slabs. In the numerical study of the slabs' thermal performance, the mean surface temperature and heat flux on the slab where the heat transfer takes place decreased as the ball diameter increased. As seen in acoustic models, the level at which the slabs absorbed sound varied depending upon both the diameter of the balls and the sound frequency.
Citation - WoS: 1
Citation - Scopus: 1
Influences of Various Thermoplastic Veil Interleaves Upon Carbon Fiber-Reinforced Composites Subjected To Low-Velocity Impact
(SAGE Publications Ltd, 2025) Coşkun, Taner; Tarih, Ömer Sinan; Yar, Adem; Gündoğdu, Ömer; Sahin, Ömer Sinan
Throughout their service life, composite materials may be subjected to impact loads, which can result in some damage mechanisms that cause degradation in mechanical and dynamic responses. Especially matrix-induced cracks and delamination can have significant effects on the final properties, and cause serious problems if the necessary precautions are not taken. In the current study, Carbon Fiber-Reinforced Polymer (CFRP) composites interleaved with Fine Glass (FG), Polyetherimide (PEI), Polyetheretherketone (PEEK), Polyimide (PI) and Poly-Phenylene Sulphide (PPS) thermoplastic veils were fabricated, and exposed to LVI tests under 25.2 J constant impact energy to determine how veils affect the dynamic properties. The selected veils are commercially available materials and are used for various purposes. In this regard, it was aimed to examine the usability of these commercially available veils as interlayers and to examine the impacts of the veils used as interlayers on the LVI characteristic of CFRP composites. According to the present study, it was found that veil interleaves significantly affect the composite stiffness, and accordingly, relevant LVI responses such as total impulse, bending stiffness, interaction times etc. For instance, approximately 21.2% reduction in the peak displacement and 73.23% increment in the bending stiffness were observed due to FG veil interleaves. On the other hand, when the effects of veil types were examined, the maximum and minimum variations in the LVI responses were observed for the FG and PEI interleaves, respectively, and FG veils were found to be the most effective veil types for the CFRP composites. It was also revealed that veil interleaves strengthen the interlaminar region between plies and delamination resistance, and thereby improved the Delamination Threshold Loads for all configurations. © The Author(s) 2024.