Within the scope of the project, investigations were focused on UD-wound polymer composites, as they are used e.g. with the manufacturing of pressure vessels. Apart from starting to develop an ontology for the pressure vessel structure, a materials sub-ontology was created, mainly concentrating on materials common in the fiber winding technology. Others were only mentioned for a later completion. Generally, a subdivision of the materials into the two main groups metals and non-metals and the latter group again into the two groups ceramics and polymers was chosen in line with classical materials science.
Whenever a materials group contained materials, dominant in composite technology, they were subdivided more precisely, e.g. the groups glasses and polymers. Especially the latter group turned out to be of high complexity and thus was examined more detailed as described in the next chapter.
Any material can be characterized by use of its properties, always related to defined conditions. One distinguishes
[1/K]; thermal conductivity 
[W/(m²·K)]),
[MPa]; elastic modulus E [MPa])
properties which are either qualitative or quantitative. Qualitative properties are expressed with boolean (True or False) or by help of a range of discrete values [vdVM91]. Furthermore, certain properties are characteristic for a materials group, some are valid for all groups. A tensile strength for instance is defined for any kind of material, a decomposition temperature in contrast is only senseful for polymers. As a material is given an extension in one dominant direction (e.g. fibrous materials), its properties often become anisotropical, which results in various properties in different directions. Therefore fibers are always characterized by orthotropical properties, in and perpendicular to fiber direction.
The resulting ontology for materials is sketched in figures 5 and 6. This partition reveals that the two materials groups metals and non--metals
Figure 5: The materials ontology: metals
Figure 6: The materials ontology: non-metals
represent disjunctive groups substances which, according to their principle macromolecular organization, have different values for the properties. Therefore, the classification along the values of the properties mentioned above together with some principle behavior (e.g. isotropic vs. orthotropic) leads to this hierarchy. The leaves of the hierarchy (drawn as ellipses) represent actual materials that have a fixed chemical composition and fixed properties.
For the purpose of representing the ontology in Ontolingua
[Gru92] we adopted and enhanced
an ontology for engineering mathematics
[GO94] that
is already predefined and represented in Ontolingua. Additionally, we
introduced a new relation IN--INTERVAL that is used to define
intervals of physical quantities such that the intervals of more
specific materials groups are enclosed in the intervals of the more
general ones. We took into account the four properties (thermal
expansion, thermal conductivity, tensile strength, and elastic
modulus) as mentioned above. Also we defined two additional ontologies
for MECHANICAL QUANTITIES and THERMAL QUANTITIES. Those
extensions can be found in appendix A. The
representation of the materials ontology itself is shown in appendix
B.