| This dissertation is part of an overall research whose primary objective is focused on the development of life prediction methodologies for use in certification methods of different flywheel designs. To this end, a comprehensive analytical model for analyzing rotating disks is presented in the first part. This model is capable of performing an elastic stress analysis for single/multiple, annular/solid, anisotropic/isotropic disk systems, subjected to pressure surface tractions, body forces (in the form of temperature-changes and rotation fields) and interfacial misfits. Results of an extensive parametric study are presented to clearly define the key design variables and their associated influence. In general, the important parameters were identified as misfit, mean radius, thickness, material property and/or load gradation, and speed; all of which must be simultaneously optimized to achieve the "best" and most reliable design.; The influence of material time-dependency and anisotropy in the form of potential failure is investigated in the second part. In this regard two main issues are addressed: adequate handling of material anisotropy with time dependency (viscoelasticity/viscoplasticity) in the material model and characterizing the long-term cyclic behavior of isotropic/anisotropic material including material complex ratchetting behavior. Utilizing a finite element program linked with a user defined material model, two flywheel designs are investigated: A simple (filament wound) type design and the more complex Multi Directional Composite (MDC) design. In particular, the focus is on the following aspects: (i) geometric constraints, (ii) material constraints, (iii) loading type, and (iv) the fundamental character of the time-dependent response, i.e., reversible or irreversible. The bulk of the results presented were obtained using a composite (PMC IM7/8552 135 0C) material system. This and others materials were characterized prior their application in the analysis.; As a main and general conclusion, both the preload (single or multidisk) and the MDC rotor designs will be significantly influenced by time-dependent material behavior, provided the application temperature is sufficient for the given material. This influence varies, depending on the geometric and material conditions. Furthermore, the comparison between the reversible (viscoelastic) and irreversible (viscoelastoplastic) material representation shows that the former is incapable of capturing the accumulation of inelastic strain due to cyclic loading "material ratchetting". |
