WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 13Citation - Scopus: 16Influence of Recycled Carbon Fiber Addition on the Microstructure and Creep Response of Extruded Az91 Magnesium Alloy(KeAi Communications Co., 2023) Kandemir, Sinan; Bohlen, Jan; Dieringa, HajoIn this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep. © 2023Article Citation - WoS: 29Citation - Scopus: 31Effect of Heat Input on Haz Softening in Fiber Laser Welding of 22mnb5 Steel(Elsevier, 2023) Tuncel, Oğuz; Aydın, Hakan; Davut, KemalThis study investigates the effects of heat input on the heat-affected zone (HAZ) softening in fiber laser welding of quenched 1.1 mm thick 22MnB5 steel. Laser power (1500-2500 W) and welding speed (40-120 mm/s) parameters are considered as the input process variables. Depending on the input parameters, the applied heat input varied between 12.5 and 62.5 J/mm. The results indicate that a minimum heat input of 50 J/mm is required for full weld penetration. Microhardness findings revealed that the drop in hardness in the HAZ region relative to the base material (BM) reached 39% due to grain coarsening caused by an increase in heat input under the welding conditions. Grain coarsening (prior austenite grains) is also detected in SEM analysis. In addition, grain coarsening at high heat input was also determined quantitatively in EBSD analyses. The proportion of 8.91 mu m grain size in the sample with high heat input is 4.2%, while it is 1.2% in the sample with low heat input. When the heat input increased from 12.5 to 62.5 J/mm, the width of the softened zone with the lowest hardnesses in the HAZ grew from 0.2 mm to 2.2 mm.Article Citation - WoS: 5Citation - Scopus: 6Effect of Coiling Temperature on the Structure and Properties of Thermo-Mechanically Rolled S700mc Steel(Technical Faculty in Bor, 2022) Di Nunzio, P. E.; Cesile, M. C.; Oktay, S.; Davut, Kemal; Şeşen, M. K.The boron-free S700MC steel is usually produced by exploiting the properties of a ferrite-bainite mixed microstructure formed by coiling the strips at a temperature of about 450 degrees C, i.e.below the bainite starting temperature. With the aim of further enhancing the mechanical properties of 6 to 10 mm thick strips, industrial tests were carried out at a coiling temperature of 600 degrees C to promote the formation of a structure of ferrite and carbides, which is also acceptable for this type of steel. Unexpectedly, a microstructure composed of ferrite and martensite was obtained. Compared to the ferritic-bainitic grade, the new structure is characterized by a slight decrease of the yield point but by an increase of the ultimate tensile strength by no less than 80 MPa, with a transition from a quasi-discontinuous to a clearly continuous yielding behaviour. Accordingly, the ratio of yield strength to tensile strength decreases from 0.90 to 0.75 and the impact energy decreases by 35 J and 60 J for the two gauge levels, respectively. The mechanical behaviour of the strips coiled at high temperature is explained as a direct consequence of the dual phase structure with a hard phase interspersed in a soft ferrite matrix. The presence of martensite is explained by the so-called incomplete bainite reaction. The partial transformation into ferrite after coiling and the long time required for the coil to cool down stabilize the untransformed austenite due to the carbon enrichment making bainite formation at lower temperatures impossible.Article Citation - WoS: 3Citation - Scopus: 4Microfluidic-Assisted Preparation of Nano and Microscale Chitosan Based 3d Composite Materials: Comparison With Conventional Methods(Wiley, 2022) Kimna, Ceren; Değer, Sibel; Tamburacı, Sedef; Tıhmınlıoğlu, FundaAlthough nanofillers contribute to improved physical characteristics and biological functionalities of polymer-based biomaterials, their dispersion in polymer matrices is still a challenging issue in terms of obtaining consistency for the inherent properties. To tackle this problem, homogenization techniques are applied to disperse the nanofillers in such polymers, however, these methods can cause undesired changes especially in the rheological properties and the physical structure of the biopolymer matrices. Recently, as a novel homogenization technique, microfluidization has been used to homogenize polymer nanocomposites to minimize these limitations. In this study, two different nanocomposite structures as chitosan/montmorillonite (CS/MMT) and chitosan/polyhedral oligomeric silsesquioxane nanocages (CS/POSS) were homogenized with microfluidization and investigated in terms of physical alterations. Furthermore, the effect of microfluidizer technique on material characteristics was compared with conventional homogenization techniques, i.e., ultrasonic bath and sonication in terms of solution, nano – (e.g., hydrodynamic size, drug encapsulation) and macroscopic material characteristics (e.g., porosity, mechanical properties, swelling and thermal degradation). It was found that the microfluidizer homogenization improves the physical characteristics in both nano and macroscale materials: Nanospheres obtained from CS/MMT composites showed enhanced stability, uniform size distribution (<100 nm, PDI: [removed]50%) whereas 3D porous CS/POSS scaffolds showed improved structural uniformity (i.e., homogeneous and interconnected microstructure) and enhanced thermal and mechanical properties. The obtained results indicate that the microfluidizer homogenization ensures a successful nanofiller dispersion in polymer matrices, thereby improving the biomaterial characteristics impressively compared to the sonication methods.Article Citation - WoS: 39Citation - Scopus: 41Effect of Post Fabrication Aging Treatment on the Microstructure, Crystallographic Texture and Elevated Temperature Mechanical Properties of In718 Alloy Fabricated by Selective Laser Melting(Elsevier, 2022) Özer, Seren; Bilgin, Güney Mert; Davut, Kemal; Esen, Ziya; Dericioğlu, Arcan.FThe effect of building direction and post fabrication aging treatment on the microstructure, crystallographic texture and high temperature mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) method was investigated. After aging, arc-shaped structures seen in as-fabricated samples disappeared and converted into a mixture of columnar and equiaxed grains. Nano-sized γ″ and/or γ′ precipitates were formed upon aging; however, MC type carbides and Laves phase encountered in as-fabricated samples were not dissolved completely after aging. Moreover, aging did not alter the texture ((001)//building direction (BD)) of as-fabricated samples. Mechanical properties of the alloys under tension were influenced by the build direction, aging time and test temperature. As-fabricated samples produced in vertical direction exhibited higher room temperature strengths with lower ductility due to orientation of overlapped prior melt pools. Room temperature tensile test results revealed that peak aging caused a significant improvement in ultimate tensile strength (UTS), from 1066.5 MPa and 998.4 MPa to 1408.5 MPa and 1330.4 MPa whereas elongation values decreased from 27.5% and 32.2% to 19.6% and 23.7% in vertically and horizontally built samples, respectively. Peak-aged samples (aged at 700 °C for 8 h) tested at 600 °C displayed serrated regions in their stress-strain curves due to dynamic strain aging (DSA). Although strength values of the samples displayed an expected decrease by temperature, ductility of the samples reduced to minimum at temperatures around 700–800 °C, which was attributed to intermediate temperature embrittlement.Article Citation - WoS: 41Citation - Scopus: 45High Temperature Tensile, Compression and Creep Behavior of Recycled Short Carbon Fibre Reinforced Az91 Magnesium Alloy Fabricated by a High Shearing Dispersion Technique(National Engineering Research Center for Magnesium Alloys of China, Chongqing University, 2021) Kandemir, Sinan; Gavras, Sarkis; Dieringa, HajoThe present study seeks the feasibility of using short carbon fibres recycled from polymer matrix composites as alternative to virgin carbon fibres in the reinforcement of magnesium alloys. The microstructures, high temperature mechanical and creep properties of AZ91 alloy and its composites with various recycled carbon fibre contents (2.5 and 5 wt.%) and lengths (100 and 500 ?m) were investigated in the temperature range of 25–200 °C. The microstructural characterization showed that the high shear dispersion technique provided the cast composites with finer grains and relatively homogenous distribution of fibres. The materials tested displayed different behaviour depending on the type of loading. In general, while enhancements in the mechanical properties of composites is attributed to the load bearing and grain refinement effects of fibres, the fluctuations in the properties were discussed on the basis of porosity formation, relatively high reinforcement content leading to fibre clustering and interlayer found between the matrix and reinforcement compared to those of AZ91 alloy. The compressive creep tests revealed similar or higher minimum creep rates in the recycled carbon fibre reinforced AZ91 in comparison to the unreinforced AZ91. © 2021Article Citation - WoS: 3Citation - Scopus: 3Investigations of Flame Retardant Properties of Zinc Borate Accompanying With Huntite and Hydromagnesite in Polymer Composites(Polish Mineral Engineering Society, 2020) Atay, Hüsnügül Yılmaz; İçin, Öykü; Kuru, BuketFires have been a danger to human beings for the centuries. As people lost their lives and property in fires, they tried to fight the fire and their efforts in this area continued increasingly. Unfortunately, it is still not possible to completely reset the risk of starting the fire. But it seems likely to extinguish immediately after the fire has started, and this is very important to save people's lives. Scientists have been working in this field in recent years; they are concentrated on producing fire-resistant materials using different materials. This can be provided by different ways; either fire-resistant material can be produced new, or the fire resistivity can be provided by incorporating the additive material into a flammable material. In our previous studies, we used huntite and hydromagnesite minerals to give fire resistance property to polymer materials, very successful results were obtained. In this study, huntite and hydromagnesite minerals were used for accompanying with zinc borate in polypropylene composites in order to increase the flame retardant property of a polymeric materials. Different content of minerals were blended with polypropylene, and composites were produced by twin-screw extruder for observing synergistic effect. Scanning electron microscopy (SEM) analyses were conducted to determine the structural and morphological properties of the composites. Thermal properties were determined according to thermogravimetric analysis (TGA). Tensile and three point bending tests were carried out to obtain mechanical properties. Flame retardant performance was evaluated according to UL 94 vertically flammability test. It was concluded that very good synergistic effects were obtained that zinc borate was significantly influential with huntite/hydromagnesite in the flammability characteristics of composites because higher char formation is observed with zinc borate addtion. Moreover, the zinc borate reduced the smoke generated during combustion.Article Citation - WoS: 16Citation - Scopus: 24Developing Polymer Composite-Based Leaf Spring Systems for Automotive Industry(Walter de Gruyter GmbH, 2018) Öztoprak, Nahit; Güneş, Mehmet Deniz; Tanoğlu, Metin; Aktaş, Engin; Eğilmez, Oğuz Özgür; Şenocak, Çiler; Kulaç, GedizComposite-based mono-leaf spring systems were designed and manufactured to replace existing mono-leaf metal leaf spring in a light commercial vehicle. In this study, experimentally obtained mechanical properties of different fiber-reinforced polymer materials are presented first, followed by the description of the finite element analytical model created in Abaqus 6.12-1 (Dassault Systemes Simulia Corp., RI, US) using the obtained properties. The results from the finite element analysis are presented next and compared with actual size experimental tests conducted on manufactured prototypes. The results demonstrated that the reinforcement type and orientation dramatically influenced the spring rate. The prototypes showed significant weight reduction of about 80% with improved mechanical properties. The hybrid composite systems can be utilized for composite-based leaf springs with considerable mechanical performance.Article Citation - WoS: 9Citation - Scopus: 9Synthesis and Characterization of Novel High Temperature Structural Adhesives Based on Nadic End Capped Mda-Btda Copolyimide(IOP Publishing Ltd., 2018) Acar, Oktay; Varış, Serhat; Işık, Tuğba; Tirkeş, Seha; Demir, Mustafa MuammerA series of novel copolyimide structural adhesives were synthesized using 4,4′-diaminodiphenylmethane (MDA), 3,4′-oxydianiline (ODA) and 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride (BTDA) as co-monomers, and nadic anhydride as an end cap reagent. The adhesives with different MDA and ODA contents were examined in terms of their structure, thermal stability, mechanical properties, and adhesive performance. They have glass transition temperatures (T g) about 400 °C, with thermal stability up to 500 °C. The effect of diamine monomer compositions on adhesion performance and processability of the copolyimides were studied. The copolyimides exhibited adhesion strength up to 16.3 MPa at room temperature. Nadic end capped MDA-BTDA-ODA copolyimide resins gained adjustable and controllable processability with the addition of ether bridged aromatic segments. The copolyimide adhesive with equimolar composition of MDA:ODA is distinguished form the both commercial PMR-15 and LARC RP-46 polyimides in terms of its better processability and mechanical performance.Article Citation - WoS: 14Citation - Scopus: 16Microstructure and Mechanical Properties of A357/Sic Nanocomposites Fabricated by Ultrasonic Cavitation-Based Dispersion of Ball-Milled Nanoparticles(SAGE Publications Inc., 2017) Kandemir, SinanIn this work, A357/0.5 wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30 nm) and aluminium powders (<75 μm) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface.