Karbon-alüminyum nanokompozitlerinin moleküler dinamik simülasyonu

Nanoscience and nanotechnology provide many research areas due to extraordinary properties of nanomaterials and nanocomposites. The most popular of these materials are mainly carbon based nanomaterials such as fullerene, nanotube and graphene as well as their composite structures formed with each other and other materials such as metals and polymers. Because of the fact that carbon nanomaterials have a high potential for new applications and a high possibility to improve current structures and systems, scientists investigate carbon structures to understand their properties and behaviors in a better way by both performing experiments and using computational methods and modelling. In this thesis, we investigate behaviors of two different nanostructures such as graphene coated aluminum and sandwich structure of aluminum, fullerene and graphene. To understand the characteristics of the structures, molecular dynamics simulations are performed under compressive and tensile loadings. Moreover, deformation behaviors of the nanostructures are observed by performing a common neighbor analysis. Firstly, we investigated the graphene coated aluminum nanostructure. The model of the nanostructure is created by a convergence of tensile analysis which is performed for different models with different dimensions and thicknesses. After determining the dimensions of the model, boundary conditions are applied as non-periodic simulation box and canonical ensembles at 0 K to accomplish static conditions. Tensile loading is simulated with a strain rate of 0.001 ps􀀀1 which is the value taken from literature. According to the result of the performed molecular dynamics simulation, elastic modulus and ultimate tensile stress of the structure and the pure aluminum is compared. Approximately 77.5% and 200% increase in elastic modulus and ultimate tensile stress is observed by graphene coating, respectively. Moreover, softening and hardening behaviors are observed for graphene coated aluminum nanostructure with higher failure strain value. Even though the tensile behavior is investigated, deformation characteristics are also examined for fully understanding of the nanostructure. Hexagonal close-packed atoms initiate the slip-slide mechanisms and undefined crystal structures move from graphene surface to the structure by the slip-slide mechanism. Because of that the density of atoms in undefined crystal structure is very high (i.e. 70% approximately), amorph behavior is observed. Thus, coated structure shows high resistance to the deformation and this resistance causes high tensile stress values under loading. Secondly, we investigated the aluminum-fullerene-graphene hybrid nanocomposite. In the model, fullerenes are merged in between two graphene sheets which are coated with an aluminum layer on both outer surfaces. For a detailed understanding of tensile and compressive behaviors, the effect of different fullerene types (i.e. C60, C80, C180, C240 and C320) are also observed. Periodic boundary conditions are applied to all dimensions of the structure. Welding of fullerenes to graphene layers is implemented to connection areas between fullerenes and graphene layers by a canonical ensemble at high temperatures. After welding, the ensemble is reduced to room temperature and applied to the entire structure. Tensile and compressive loadings are applied at different strain rates (i.e. 0.5, 0.3, 0.1, 0.05 and 0.005 ps􀀀1) to examine the effect of loading rate. From results for the compressive response, maximum and minimum stress values are 175 GPa and 85 GPa at 0.5 strain for the models C60 and C320, respectively. Due to the homogeneity of the structures, densification process shows differences and stress values differ from the model C60 to C320. The strain rate of the loading effects the characteristics of the structure. As a result of the change in the strain rate, hardening and softening regimes occur within densification process. While compression continues, body-centered cubic structure density increases under loading and to the end of the simulation these structures transform into the hexagonal close-packed structure. According to results for the tensile response, maximum and minimum stress values are 4.8 GPa and 2.5 GPa at 0.5 strain for the models C60 and C320, respectively. Similar to compressive response, tensional behavior shows differences and stress values differ from the model C60 to C320 because of homogeneity. The effect of the strain rate which causes hardening and softening regimes is observed. Deformation of the structure starts from the areas under and over the fullerenes where there is no graphene layer to hold the aluminum atoms. The undefined crystal structure is the dominant deformation structure during tensile loading.