SEARCH RESULT

In the 21st century, most of the energy demand is covered from fossil fuels. However, fossil fuels cause high emissions of greenhouse gases and resources of the fossil fuels reduce day by day. Due to these disadvantages, researchers focused on to finding alternative and renewable energy sources. At this point, hydrogen has become an important energy source and many researchers have developed design and optimization procedure of composite hydrogen storage vessel in various fields uch as gas plants, power plants, aerospace, chemical and automotive industry. In the present study, the main purpose is to see effect of the different carbon/epoxy material type on optimum stacking sequences design of Type III pressure vessel. The first step is to gain the distribution of stress components based on Classical Lamination Theory (CLT). The second step is to determine the burst pressure of the Type III pressure vessel by using Tsai-Wu failure criteria and then to compare the result with analytical, experimental and numerical ones from literature. In the final part of the study, for different carbon/epoxy materials, the best possible combination of winding, stacking sequences and thicknesses of laminates satisfying minimum possible stress concentration have been obtained by Differential Evolution (DE) stochastic optimization method.

International Symposium on Light Alloys and Composite Materials
UHAKS

Ozan Ayakdaş Levent Aydın Melih Savran Nilay Küçükdoğan Savaş Öztürk

Lif takviyeli kompozitlerin hafiflik, sertlik, yüksek mukavemet gibi özelliklerinin yanı sıra istenen optimum mekanik özellikleri bünyesinde barındırabilmesi nedeniyle uzay, havacılık ve otomotiv gibi birçok modern mühendislik sektöründe kullanımı son yıllarda giderek artmaktadır. Kompozit malzemeler belirtilen bu alanlarda kullanımları sırasında basma, çekme ve burkulma gibi pek çok mekanik etkiye maruz kalmakta ve bu etkilere karşı dayanımlarının hesaplanması büyük önem arz etmektedir. Bu çalışmada, iki eksenli düzlem içi bası yükleri altında ve dört taraftan basit mesnetli 64 tabakalı Grafit/epoksi kompozitin burkulma karşıtı davranışının optimum tasarımı stokastik yöntemler (Differential Evolution, Simulated Annealing ve Nelder-Mead Algoritması) ile araştırılmıştır. Çalışma kapsamında simetrik ve balans olmak üzere iki farklı tabaka tipi çözümlenmiştir. Ayrıca, amaç fonksiyonunda kritik burkulma yük indeksi ve tasarım değişkenleri olarak fiber oryantasyonları kullanılmıştır. Çeşitli yükleme durumları ve plaka boyut oranları (a/b) için kritik burkulma yük indeksi maksimize edilmiştir. Bu tasarımları üreten optimizasyon kodu, Differential Evolution, Simulated Annealing ve sadece lokal optimumları bulabildiği düşünülen Nelder-Mead Algoritması kullanılarak «MATHEMATICA» ortamında geliştirilmiştir.

International Symposium on Light Alloys and Composite Materials
UHAKS

Aynur Ayvalık Levent Aydın Nilay Küçükdoğan Savaş Öztürk

Polymer composites with high thermal conductivity have been developed to use in various industries such as energy and electronic systems, and are being developed as lighter, more economical, chemically resistant and especially heat-dissipation polymer composites. In order to increase the thermal conductivity of polymer composites, metals, ceramics, semiconductors (carbon black, graphite, etc.) are used as additive materials. For this purpose, mixture rates of 30-40% for matrix and 40-70% for filler are used in composites produced [1]. Graphite is an ideal filler material that can be used in the production of thermally conductive polymer composites. Graphite is a unique layered nano-material with low cost, light weight, high thermal conductivity (110–130 W/mK at room temperature) which makes it the ideal additive material. The morphological structures of the additive materials directly affect the mechanical and physical properties of the composite. This information has also been noted in the study of Tu and Ye [2], where platelet-shaped fillers have advantages over other spherical or cylindrical morphologies. Many theoretical and empirical mathematical models are used to determine the influence of additive materials on the thermal properties of two phases composites [3]. In this study, thermal conductivity behaviors of graphite-polystyrene composites are shown by Effective Medium Theory (EMT) model. It has been observed that this model estimates fit well with experimental data.

International Symposium on Light Alloys and Composite Materials
UHAKS

Nilay Küçükdoğan Savaş Öztürk Levent Aydın

In recent years, laminated composites are fairly utilized in marine, automotive, aerospace, military and other engineering applications because of their high specific modulus (ratio between the young modulus and the density) and high specific strength (ratio between strength and density). In addition to these features, fiber reinforced composites have inherent tailorability such as fiber orientation and stacking sequence and provide great possibilities to designers against isotropic materials. Generally, fail occurs four ways in structure: overstressing (strength critical structure), over deflection (stiffness critical structure), resonant vibration, and buckling. In this regard, determination of the buckling load capacity of a laminated composite plate under in-plane compressive loads is crucial for the design of composite structures. The main aim of the study is to investigate the anti-buckling behavior of 64-layered graphite/epoxy laminated composite plates for various aspect ratios and load ratios.

International Symposium on Light Alloys and Composite Materials
UHAKS

Mehmet Akçair Melih Savran Levent Aydın Ozan Ayakdaş Savaş Öztürk Nilay Küçükdoğan

Research projects on the development of eco-friendly and lightweight engineering structures in the automotive industry have become obligatory due to End-of-Life Vehicles Directives and regulations on emission limits (Euro 5 & Euro 6). Traditional fiber reinforced composite materials consisting glass, carbon and /or combination of these have been usually preferred instead of traditional metallic materials (such as steel, aluminum, etc.) in the automotive industry. However, an ecological approach in the automotive industry has stated that natural fibers are of great importance as alternative reinforcing materials to glass fibers since being agricultural sustainable material and lighter. In addition to being eco- friendly and lightweight, natural fibers are lower cost than synthetic fibers. For the automotive industry, weight and cost reduction without sacrificing from mechanical properties is an always important issue. The cost of some natural fiber, glass and graphite fiber are shown in Figure 1

International Symposium on Light Alloys and Composite Materials
UHAKS

Melih Savran Levent Aydın Ozan Ayakdaş Savaş Öztürk Nilay Küçükdoğan