Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Research Project Otomobil endüstrisi için mukavemeti yüksek seramik katkılı kapalı hücre alüminyum köpük metallerin geliştirilmesi(2009) Güden, Mustafa; Taşdemirci, Alper; Yüksel, Sinan; Toksoy, Ahmet Kaan; Gültürk, Elif; Karsu, Nurettin DenizFarklı seramik ve metal toz katkılarının Al toz tabletlerinde köpükleşme ve mekanik davranışlara etkileri incelenmiştir. Katkı malzemesi olarak sıvı Al ile ıslatılan Ti6Al4V ve diyatomdan elde edilen silika parçacıkları ve Al tarafından yarı ıslatılan SiC parçacıkları, SiC nano toz ve SiC viskır kullanılmıştır. Ti6Al4V parçacıklarının sıvı Al içerisinde küçük boyutlu TiAl3 intermetalik fazı oluşturması ile artan sıvı tablet viskozitesi köpüğün kararlılığını artırmakta; fakat, köpükleşmeyi azalmaktadır. Köpük kararlılığı ve köpükleşme uzaması kullanılan Ti6Al4V toz boyutu ve yüzdesi ile değişmektedir. Sıvı Al tarafında ıslatılan bir diğer toz olan diyatom SiO2 katkısında ise düşük yüzdelerde köpükleşme maksimum uzamaya kadar artmaktadır. Artan katkı yüzdelerinde ise viskozite artışı ile tabletlerin köpükleşmesi azalmaktadır. SiC katkılı tabletlerde köpükleşme, kullanılan tozların toplam yüzey alanı ile değişmektedir. Optimum parçacık toplam yüzey alanında (~100000 mm2), SiC içeren tabletlerin uzamaları katkısız tabletlere göre daha yüksektir. Küçük boyutlu tozlarda artan yüzey alanı düşük parçacık yüzdelerinin, büyük parçacık boyutlarında ise daha yüksek parçacık yüzdelerinin kullanılmasının gerekliliği gösterilmiştir. Mikroskobik çalışmalar SiC parçacıklarının çoğunlukla hücre duvar yüzeylerinde asılı, Ti6Al4V ve SiO2 parçacıklarının ise tamamen hücre duvar içlerinde yer aldığını göstermiştir. Çalışılan parçacık boyu ve yüzdelerinde SiC katkısı plato gerilmesi ve enerji emme miktarlarını sırası ile %35 ve %20 artırmaktadır. Simülasyon sonuçları kritik köpük yoğunluğunun altında ticari olarak kullanılan boş 6063 T6 Al ve çelik tüplerin köpük dolu tüplerden maliyet ve ağırlık açısından daha avantajlı olduğunu göstermiştir.Article Thermal and Acid Treatment of Diatom Frustules(International OCSCO World Press, 2011) Gültürk, Elif; Güden, MustafaPurpose: Diatoms, belonging to Bacilariophyta family, are single-celled microscopic (1-100 micron) plants living in aquatic environment. The diatom cell is protected inside a shell (frustule) constructed from amorphous nano-silica particles. It is proposed that the frustules and purified silica powders obtained from frustules can be used to reinforce composites. In this study, microstructural properties of two diatom frustules were determined and different methods were investigated for silica powder processing from diatom frustules. Design/methodology/approach: Natural (ND) and calcined (CD) diatom frustules were used in this study. The chemical and microscopic properties of the diatom frustules were determined using Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectrometry (FTIR) and energy dispersive X-Ray Florescence spectrometer (XRF). Two different processing routes were applied to process silica powder from diatom frustules. These included (i) leaching the frustules directly in HF, (ii) incorporating thermally treated frustules in to the liquid nitrogen. Findings: At increasing HF concentrations, the variety of shapes, nanopores and open voids were seen on the surface of frustules as silica particles were removed from the surface. SEM micrograph results showed that HF significantly etched inside the existing pore structure of the diatom frustules. HF concentration was found more effective in mass loss than the leaching time. Thermal treatment induced several cracks propagated between macro pores and nanopores of the frustules. Practical implications: Results show that thermal and acid treatments were not effective for obtaining silica powder from frustules. Ball milling can be used for silica powder processing from frustules in the further study. Originality/value: In this paper, the microstructural properties of ND and CD frustules were determined. The effect of thermal and acid treatment on frustules was investigated with SEM.Article Citation - WoS: 24Citation - Scopus: 26Diatom Frustule-Filled Epoxy: Experimental and Numerical Study of the Quasi-Static and High Strain Rate Compression Behavior(Elsevier Ltd., 2008) Taşdemirci, Alper; Yüksel, Sinan; Karsu, Deniz; Gültürk, Elif; Hall, Ian W.; Güden, MustafaIn this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress–time response and deformation sequence of the samples in high strain rate testing.Article Citation - WoS: 20Citation - Scopus: 21Calcined and Natural Frustules Filled Epoxy Matrices: the Effect of Volume Fraction on the Tensile and Compression Behavior(Elsevier Ltd., 2013) Gültürk, Elif; Güden, Mustafa; Taşdemirci, AlperThe effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0–12 vol.%) on the quasistatic tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix.