Surface and Edge Strength
The strength of the brittle material glass is decisive for the long-term performance of glass constructions. It depends essentially on the surface quality and the environmental conditions in the application. The aim of the research includes edge strength and its optimisation, surface strength and the high-temperature strength of glasses. For these investigations, destructive and non-destructive methods are used.
In facade and roof glazing systems, direct solar radiation can cause thermally induced glass edge breakage, which is not taken into account in the current standardization. The aim of the research is to investigate the physical relationship to thermally induced glass breakage. The research results are made accessible to practice through participation in standardization committees and industry associations.
Especially with tempered glass, inclusions in the bulk of the glass can not only affect the optical properties but also the safety of the manufactured building products. One type of inclusion that has such negative effects is nickel sulfide. Its crystal structure encounters a delayed phase transformation resulting in a volume increase. In thermally strengthened glass, this volume increase can cause spontaneous fracture of the entire glass pane. The relevant size range of such inclusions is between 50µm and 500µm, challenging the limits of contemporary detection systems.
A key parameter for the safety design of glass in structural engineering is its mechanical strength. This is determined by microscopic damage to the glass surface. The pre-stressing process introduces residual stresses in the form of compressive stresses at the surface and tensile stresses in the core of the glass. This can significantly increase the load-bearing capacity of the glass component.
Photoelasticity and Anisotropy
Mechanical stresses make glass a birefringent material that then has direction-dependent optical properties. When polarized light enters glass that is experiencing stresses from a thermal toughening process or from mechanical loads, optical iridescence can be observed. These black and white or colored patterns can be observed on glass facades and are referred to as anisotropy.