Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Stacking Sequences Optimization of Laminated Composites for Maximum Buckling Strength by Stochastic Search Methods(Izmir Institute of Technology, 2020) Adabaşı, Gökay; Artem, Hatice SeçilBased on materials developed and made available by humans, there are materials that will serve their purpose. Using lighter materials, especially in the field of aviation and space, significantly reduces the costs. However, lightness is not the only feature required in materials. In addition, the physical and mechanical properties of the materials must be at the desired level. Knowing the buckling load capacity of composite materials, which are widely used, is also very important in determining the material properties. Accordingly, an important focus of this thesis is to examine the behavior of different materials against the same loading; the other is to examine the increase in the critical buckling load factor although they have the same geometric structure. Critical buckling load factor is considered when performing the buckling analysis. The mechanical behavior of composite materials used by considering the factors of critical buckling load factor has been investigated and discussed. Different optimization methods have been used while making the optimum design of different composite materials with 48 and 64 layers in total. The verification of mechanical properties of materials was made with the help of coding. Subsequently, the referenced articles were verified to prove the accuracy of this code. Optimization was carried out by using material properties information from reference articles and verifying the code. As a result, considering the buckling strength of different layered composite materials, it has been found that the optimum designs depend on the load, load ratio, and plate aspect ratio.Master Thesis Optimum Design of Composite Hydrogen Pressure Vessels by Stochastic Search Methods(Izmir Institute of Technology, 2018) Sayı, Abdülmecit Harun; Artem, Hatice SeçilFiber-reinforced composite materials are extensively used in many engineering applications such as aircraft wings and frames, vehicle drive shafts, sport equipment, and pressure storage vessels. One of the reasons for the extensive use of laminated composite materials is their tailorable nature, which allows them to satisfy specific design objectives in an application. As an application, hydrogen-powered fuel cell vehicles require high amount of hydrogen to increase distance range. Hence, hydrogen is pressurized at elevated rates. Since, it is hard to satisfy safety and weight regulations for high pressure gas, composite storage vessels offering high strength with low weight are preferred. Optimization techniques are applied to the design of composite pressure vessels to maximize strength with comprising weight restrictions. In the thesis, first-ply failure optimizations of stacking sequence design of cylindrical composite pressure vessels with metal liner having 700-bar working pressure and safety factor of 2.0, have been performed using stochastic search algorithms which are Differential Evolution and Nelder Mead. Three separately categorized failure theories; Tsai-Wu, Maximum Stress and Hashin-Rotem criteria have been incorporated to failure analysis of the vessel designs. In addition, the effects of volume on the stacking sequence design have been investigated. Hence, four volumetrically separated pressure vessel designs have been considered. Change in volume has been provided by inner radius. Single objective optimization has been set to minimize failure criteria index which incorporates into classical lamination theory. Fiber orientation angles and number of plies are design variables. CPU time has been calculated to compare the workloads of algorithms. In conclusion, optimized pressure vessels have provided design targets and the difference in volume has caused variable fiber angle orientations, number of plies and CPU time.