MODELLING AND OPTIMIZATION OF THE MECHANICAL PROPERTIES OF POLYMER NANOCOMPOSITES

The research activity here reported spans different areas of the nanocomposite material science, giving a contribution toward the advancement in its state of the art. The study of the effects of the filler distribution on the mechanical properties of nanomodified polymers is a major research topic which is carried out. Different computational and theoretical approaches have been developed, considering statistics, finite element analyses and micromechanics. Several nanomodified epoxy resins have been manufactured along with glass fibre reinforced laminates with nanomodified matrix. The effects of the nanomodification on the mechanical properties of these composites have been studied, in order to validate predictive models and supply technical data to material designers. The results obtained so far highlight the importance, in this class of materials, of the study of interactions at the nanoscale between the nanoreinforcement and the matrix. The thesis is articulated in an introduction, followed by two sections, dedicated to the experimental activity and the modelling one, and by an appendix. The introduction presents a brief overview on nanocomposites giving a primer to a reader devoid of prior experience with this class of materials. The experimental activity section is constituted by four chapters. The first one contains the results of mechanical tests performed on a nanoparticle reinforced epoxy, alongside an analysis on the processing parameters employed in the composite preparation. The enhancement in the nanocomposite fracture toughness is compared with a theoretical model, showing a satisfactory agreement. The second chapter reports the study of the effect of the testing temperature on the fracture toughness of the same material. The analysis highlights the fundamental importance of the processing parameters and of the testing temperature on the nanomodification effects. The third chapter considers a different aspect of the nanomodification: a nanoplatelet reinforced epoxy is used to prepare notched specimens and the strength analysis of the notched component is carried out. The fourth chapter reports the research activity performed on the study of the matrix nanomodification of glass fibre reinforced laminates. The effects on the matrix dominated mechanical properties and the feasibility in the production of a laminate with antibacterial bulk properties are analysed. The modelling section is constituted by three chapters. The first one contains a comparison between two approaches for the estimation of the elastic properties of a nanocomposite material, considering explicitly the presence of an interphase surrounding the nanoreinforcements. The first approach implements a two-step micromechanical model, while the second one is based on a finite element analysis. The second chapter reports the research activity carried out on the generation of representative volume elements of nanoparticle reinforced materials. A statistically based algorithm is implemented to minimize the volume element size while retaining its representativeness. The study of the interphase extent and of the overall elastic modulus, through finite element analyses, is reported. The third chapter extends these considerations to the generation of volume elements for nanoplatelet reinforced materials. The random sequential absorption approach is implemented and its hidden effects on the filler distribution highlighted. A new version of the algorithm is proposed to remove these unwanted behaviours. The appendix section is dedicated to the implementation activity of approaches which have not been completed yet. The results obtained on the use of molecular dynamics in the simulation of polymers and nanomodified polymers are reported. While a detailed procedure for the simulation of epoxy resins is listed, the approach for the study of nanoplatelet-epoxy interactions is still in progress.