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    Discussion on the manuscript entitled Thermal residual stress in a functionally graded material system by K. S. Ravichandran, Materials Science and Engineering A, 201(1-2), pp. 269-276
    (Elsevier Science Sa, 2022) Baytak, Tugba; Topcu, Ismail; Bulut, Osman
    In the article entitled Thermal residual stress in a functionally graded material system, a strip element made of a combination of Al2O3 ceramic and Ni metal was considered as a functionally graded material to obtain the general expressions for thermal residual stresses. The results showed that the stress distribution changes continuously as the volume fraction of the ceramic varies according to a power function. However, an incorrect term for bending stiffness was used in this expression. In addition, the expression for the residual stress term, which is resulted from the uniform elongation of the strip fibers, should not be used to calculate the reactive bending moment. It must be obtained from the nonuniform distribution of thermal strain across the thickness. In this study, the derivation of the final expression for the thermal residual stress in a functionally graded strip element by the strain suppression method is discussed.
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    Examination of wear properties of Al/B4C composites reinforced with irregularly shaped B4C
    (Korean Assoc Crystal Growth, Inc, 2021) Topcu, Ismail
    In this study, Boroncarbide (B4C) powders were added as supplemental material to produce aluminum (Al) metal matrix composites (MMC) by mechanical alloying (MA) method. Three different B4C amount (5, 7,5, and 10 wt%) were used and three different temperatures (600, 620, and 640 degrees C) were applied for the sintering of the samples. Wear rate, hardness, and density of the produced composites were evaluated in order to investigate the effect of different B4C content and sintering temperatures. It was found that the increase in the B4C amount decreased the wear rate and density of the specimens while increasing the hardness. Moreover, the application of different temperatures had a positive effect on the density, hardness, and wear behavior of the specimens.
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    Investigation of wear behavior of Ti-6Al-4V/CNT composites reinforced with carbon nanotubes
    (Gazi Universitesi Muhendislik-Mimarlik mmfd@gazi.edu.tr, 2019) Topcu, Ismail; Güllüo?lu, Arif Nihat; Bilici, Mustafa Kemal; Özkan Gülsoy, HOzkan
    In this study, the effects of different production conditions and different sintering conditions on microstructure, density and wear resistance of Multi-wall carbon nanotubes (CNTs) powders reinforced with Titanium (Ti-6Al- 4V) powder by mechanical alloying were examined. The powders produced by mechanical alloying were compressed with a Cold Isostatic Press die under a pressure of 250 MPa in this molding machine to obtain cylindrical composite specimens. These raw specimens were extruded at 1275°C for 60 minutes in a high purity argon atmosphere and high vacuum (1.2 10-5 mbar). The erosive wear behavior of the Ti-6Al-4V / CNTs metal matrix composite was studied using a pin-on-disc wear tester. The abrasion behavior of a Ti-6Al-4V / CNTs alloy after various heat treatments has been studied on abrasive wear. Under appropriate conditions it has been shown that reinforced CNTs can reduce the wear rate by more than two orders of magnitude. Various investigations have been carried out detailing the reinforcement rates of this improved wear performance. The friction and wear data show a clear surplus value added to the composite Ti-6Al-4V wear modes. As a result, in the experimental studies made, it is seen that the wear resistance increase according to the v/v % CNTs ratio which is directly supplemented to the volume. However, this properties had been decrease with the %5 CNTs ratio. © 2019 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.
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    Mechanical properties of PLA and ABS parts produced with fused filament fabrication method
    (Korean Assoc Crystal Growth, Inc, 2021) Topcu, Ismail
    The use of special and specific parts that are easily produced by the additive manufacturing method is of great importance in the following process. The ease of the materials and the low cost of the open source printers increase the use of the Fused Filament Fabrication (FFF) method. Due to the differences in FFF technology, investigation of the effects of the parameters on the mechanical properties of materials is necessary to determine the usability of the functional parts. Tensile strength was determined as 46.8 MPa for polylactic acid (PLA) and 34 MPa for acrylonitrile butadiene styrene (ABS). Polylactic acid specimens have a better wear resistance than acrylonitrile butadiene styrene (12.9 g) samples with a weight loss of 5.1 g at 5000 m. According to the mechanical data Polylactic acid was found to be good properties than acrylonitrile butadiene styrene . In order to select most durable plastic for the unique application, the results of this study, which are given as graphs, diagrams and pictures, can help to the design engineers.
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    Sustainable biowaste conversion into microporous carbons for efficient energy storage solutions in sodium-ion batteries
    (Elsevier Sci Ltd, 2025) Yanilmaz, Meltem; Temel, Busra; Bayram, Edip; Tosun, Murat; Topcu, Ismail; Kim, Juran
    Sodium-ion batteries (SIBs) are prospective candidates for renewable energy storage technologies. However, SIB systems are still emerging, creating a demand for innovative, practical, and affordable active materials. Biomass-based hard carbons are promising anode materials for SIBs due to their easy accessibility, sustainability, and low cost.This study offers a novel, simple, and cost-effective method to produce microporous carbons from waste cotton using hydrothermal carbonization (HTC), KOH activation, and pyrolysis. Unlike previous studies on cotton-based carbons, the waste cotton-based microporous carbons were synthesized by the combination of HTC and KOH activation for the first time to be utilized as an anode in SIBs. Moreover, the influence of varying KOH concentrations on the structural and electrochemical properties of carbons was examined. The microporous carbon with a carbon/KOH ratio of 1/3, MC3, displayed a large surface area of 808 m2/g, abundant microporosity, and achieved a high reversible capacity of 330 mAh/g at 0.1 A/g, and good cyclability with a reversible capacity of 280 mAh/g at 1 A/g after 400 cycles. These results demonstrated that the microporous structure of MC3 provides fast and efficient ion transfer and an increased contact area between the electrode and electrolyte. In addition, the integration of hydrothermal carbonization and KOH activation improves electrochemical performance and offers substantial economic benefits, while incorporating wastewater treatment and KOH recovery strategies into the process can enhance scalability and environmental sustainability for industrial-scale production. Therefore, this research presents a cost-effective and scalable approach using a sustainable source to produce microporous carbon anode materials for SIBs, significantly benefiting the energy sector.