@phdthesis{,
    author = {Mittermeier, Christoph},
    title = {Beitrag zur kontinuumsmechanischen Modellierung des Glasübergangs und der daraus resultierenden physikalischen Alterung},
    editor = {},
    booktitle = {},
    series = {},
    journal = {},
    address = {},
    publisher = {},
    edition = {},
    year = {2017},
    isbn = {},
    volume = {},
    number =  {},
    pages = {},
    url = {},
    doi = {},
    keywords = {Materialmodellierung, Polymere, Glasübergang, physikalische Alterung},
    abstract = {Glassy polymers, a subspecies of the synthetics, are widely used in industrial applications. In the design process of products made from this material in addition to regarding its chemical properties it is particularly important to consider the material’s viscoelastic behaviour. This behaviour leads to an instantaneous and a delayed answer in thermomechanical and caloric changes of state. In this work, an elaborate overview over the existing experiments and modelling approaches regarding this behaviour is given. The overview shows that an initial value problem is not able to reproduce the real characteristics of the material completely. This is caused by the physical ageing respectively the delayed degeneration of the structural non-equilibrium state which arises during isobaric cooling through the glass transition. Existing experiments indicate that the glas transition itself represents the instantaneous behaviour and physical ageing the corresponding delayed behaviour. This interpretation correlates with the general state equations which are formally derived in this work based on rational thermodynamics. In the derivation, also the volumetric-isochoric split of the stress power is considered. Thus, the state equations include isochoric, volumetric and caloric inner variables which can describe the non-linear viscoelastic relations of the glass transition. This leads to the assumption that the glass transition can also be excited by isochoric, isothermic and adiabtic changes of state. Existing experiments which are discussed in the overview prove this assumption. The well known theory of the free volume which leads to the non-linear relation between the structural state and the viscosity is also revisited in the overview. Based on this relation, the glass transition and the subsequent physical ageing can be explained. This explanation also shows that the theory of the free volume is equivalent to the theory of the fictive temperature. The overview is followed by the report about the experimental results which are produced by dilatoric, caloric and mechanical experiments on an exemplary polyurethan. The evaluation of these results considers the thermomechanical and caloric interaction of the state variables and the influence of the free volume on the isochoric viscosity. Afterwards a suitable approach for the energy-density is discussed as the base for the derivation of the particular state equations. After the adjustment of these equations on experimental data the equations are validated by further experiments. In conclusion, an overview about the explored relations is given which motivates the outlook to prospective research objectives.},
    note = {},
    
    school = {Universität der Bundeswehr München},
    
}