Here the archetypes of the elementary polyhedra of real polyhedron foam glasses described in the preceding chapter are used to find model foam glasses which are suited to the prediction of external fracture strengths. In order to enable this proposition, a relationship between randomly selected external surface loadings and the stress conditions within the cell structure which was derived using the finite element method was used as the basis. For this a failure criterion is needed. At the same time however, the elastic characteristic values of the foam glass are provided.

The fracture strengths and elasticity numbers were investigated experimentally on various polyhedron foam glass types (see section No. 1 of the introduction) as a function of the density  and the stereological parameter n*, in order to be able to compare them later with the characteristic values from model predictions. As was already determined in section No. 1.3.2 of chapter A of this dissertation, the cell structures of the foam glasses produced industrially or in the laboratory consist of an aggregation of very many base polyhedra arranged in manifold ways. The cell wall films of these foam glass samples, which were sometimes penetrated by expansion gas, usually consist of very irregularly shaped spherical foam glass. Here is must not be forgotten that the layout of these cell wall films as well as their cross-sectional shapes vary from film to film. From this it can be concluded that the computational effort for the prediction of the mechanical properties of the polyhedron foam glass based on a model which attempts to take into account the morphology which changes from place to place is certainly excessive.

It would also not lead to better results than a calculation based on a simplified model.

For these reasons we wish - as already mentioned - to use the archetypes discussed in section No. 1.4 of chapter A as the strarting point for the elementary polyhedra of real polyhedron foam glasses, which would be accessible for computer modelling within a reasonable time period.