Nanoindentasyon yöntemi ile grafin-epoksi nanompozitlerin mekanik özelliklerinin belirlenmesi

Developing technology let society use more sophisticated materials by which better performance is gained in many fields of application. Composite materials are some of those associated materials. While they provide with lighter devices, vehicles etc., they decreases the amount of energy to be consumed.Thanks to its strong C-C bonds, carbon-based materials are some of the mostly used reinforcement phases in composites. Especially when they are synthesized to nano sizes, better results are observed in the matrices where they are added.Graphene has the unrolled form of carbon nanotubes which has great mechanical properties. It usually exists in the form of agglomeration of plates rather than a single layer. When it is produced as single or several layers, it exhibits better performance and transfers its excellent properties to the matrix better than single walled carbon nanotubes do.The factors such as relatively high production costs, and use of nanomaterials and any other technological materials as coating besides as structural elements make tensile test a challenging method for material characterization. Nanoindentation test is a goodsolution for such constraints. Compared to a tensile test, very small and less numbers of specimens are enough for a nanoindentation test.Although much progress has been made, more steps are needed to be taken for the exact determination of stress-strain curves using nanoindentation tests, which is originally gained from tensile tests.In this study the determination of viscoplastic material properties of a graphene-epoxy nanocomposite, of which the production and the nanoindentation experiments was performed by the thesis coordinator Prof. Özgen Ü. ÇOLAK, and Ardavan ZANDIATASHBAR, using the tests and numerical models of nanoindentation were researched.This thesis consists of five chapters. After giving a literature abstract, purpose of the thesis, and hypothesis in the first chapter, a detailed literature review on the material, and the method were presented in the second and third chapters, respectively. In the fourth chapter, the method of determination of viscoplastic parameters using nanoindentation was introduced. Finally, the results were discussed in the last chapter.In the second chapter, brief information about the structure, properties and various synthesis methods of graphene, epoxy and graphene/epoxy nanocomposite were given. Advantageous and disadvantageous of graphene compared to other carbon based nano materials were explained.Third chapter covers the emergence of nanoindentation technique, and the theoretical base of nanoindentation to obtain young?s modulus. Beginning with Brinell, hardness measurement techniques and then theories developed to explain the indentation contact were indicated. The contributions done to the method of derivation of Young?s modulus were provided in accordance with the dates of the works. Applicability of the method for viscoplastic materials was stated.In chapter four, method of derivation of viscoplastic material properties of graphene-epoxy nanocomposite using nanoindentation tests and numerical simulations was examined and positive results were gained. While examining this method some determinations were done on the numerical modelling of nanoindentation.Results were briefly discussed in the chapter five.