Glass Competence Center

Glass is a ubiquitous material in modern engineering applications, prized for its transparency, strength, and versatility. However, glass is inherently brittle, and its susceptibility to crack initiation and propagation poses significant challenges in structural and safety-critical contexts. Understanding how cracks propagate in indented glass specimens under subsequent loading is therefore critical for enhancing the safety and reliability of glass- based structures and products.

The outcomes of this thesis are expected to contribute to the knowledge base on glass fracture mechanics and safety assessment. Moreover, the findings may have practical implications for improving the design and perfor- mance of glass components in engineering applications, such as architectural glazing, automotive windshields, and electronic displays.

While the glass panes in conventional lattice shells are typically used only as infill elements, activating the full load-bearing potential of glass can contribute significantly to reducing the material and energy resources of substructures for glass facades.

A current research project is investigating the integration of local and linear connection structures in glass supporting structures, which should help to better exploit the structural potential of the glass panes used and thus reduce the steel consumption in substructures to a necessary minimum. This should ultimately enable the construction of transparent glass structures with a wide variety of shapes and applications.

Vacuum insulated glazing is a highly energy efficient glazing system. Yet, its setup (more precisely the array of support pillars necessary to withstand the high loads of atmospheric pressure (10 tonnes/m2)) evokes complex stress distributions and high stress gradients locally. This can result in the formation of so-called cone cracks which can develop into through-thickness cracks and can thus lead to catastrophic failure of these glazing units. In the design of VIGs it is typically assumed that the glass-pillar contact is not of concern if the separation of pillars is limited. Yet, investiga- tions of various VIGs show that cracks occur anyway and failure can originate at a pillar.

Vacuum insulating glasses (VIGs) are an innovative window technology with the potential to revolutionize energy-efficient buildings. Windows and transparent facade elements are the main sources of heat loss and CO2 emissions in buildings.VIGs consist of glass panes with a vacuum gap that minimizes thermal effects and improves the energy balance of building envelopes. Small spacers in the va- cuumed inter-pane space ensure stability over decades and significantly influence the behavior of VIGs. Investigation of this influence and the development of standards for the use of VIGs are crucial for the introduction of energy-optimized window and facade systems in Germany and Europe. VIGs could thus make a significant contribution to sustainability in construction.

In order to reduce the consumption of raw materials, the production of climate-damaging gases, and the generation of waste, the topic of the circular economy has been coming to the fore for some time. The circular economy is a holistic approach that aims to use raw materials and the resulting products efficiently and for as long as possible. It includes repairing, reusing and recycling.

The aim of a current research project is to predict complex crack propagation during the glass breakage process as well as the resulting fragment geometry and size. To this end, ISM+D is creating a database from experimental studies in which glasses with different thermal toughness levels are broken in a targeted manner. The wave propagation in the glass body resulting from the impact is recorded with special sensors. The fracture pattern is analyzed by means of digital image processing.

Possible topics for a thesis (Bachelor or Master):

- Numerical characterization of fracture morphologies in thermally toughened glasses.

- Stochastic modeling of fracture morphologies in thermally toughened glasses

To address the desire for transparent facades, glass 3D printing will be used to create novel joints for facade applications. Figure 1 shows the construction chamber of the glass 3D printer at the TU Darmstadt, which is to print molten glass onto a heated base plate made of glass.

To understand the process of glass 3D printing, the heating of the base plate using a hot plate and gas burner and the subsequent cooling will be studied. In order to know and reduce the risk of breakage during printing, temperatures and stresses during printing will be studied. For this purpose, a thermographic camera is available to measure the temperature of the glass surface, see Fig. 2b. Numerical simulations are possible to calculate stresses during heating. After cooling, residual stresses may remain in the glass, affecting the optical and mechanical quality of the component. The residual stresses can be studied after printing using stress optics, see Fig. 2a. Experiments on heating and cooling the base plate on the glass 3D printer can be carried out in a thesis.

Vehicle safety has the task of developing vehicles in such a way that accidents are avoided or the consequences of accidents are reduced as much as possible. In the field of pedestrian protection, so-called impactors are used to represent parts of the human body (head, hip and leg) and to assess the risk of injury in the event of a collision with the vehicle. The criteria and limits for assessing impactor load cases are defined and continuously developed by legislation (UN R 127) and consumer protection organizations (Euro NCAP). For example, the area of the windshield is newly included in the legal impact area and extended beyond the previous level for the Euro NCAP consumer protection test.

Further information, application requirements and documents to be submitted, etc. can be found here

Laminated glass consists of at least two sheets of glass joined by a polymer interlayer. In the event of glass breakage, a residual load-bearing behavior occurs in which tensile stresses caused by bending are removed via the polymer interlayer. Numerical mapping of the material behavior of the interlayer in the case of large deformations, as occurs in the case of failure of one or more glass sheets, is currently not possible. The material behavior in this case depends on temperature and loading duration as well as on the magnitude of the load, so that nonlinear viscoelastic material models are necessary.

The innovative and smart glass product eyrise®, based on liquid-crystal technology, can change its transparence and color within seconds. The edges of the glass panes are sealed with a stiff polymeric adhesive. The employed adhesive layers are thin and thereby shear resistant while simultaneously providing a high adhesion between the two adherends. Due to the geometry of the adhesive layer and the requirements of later numerical investigations, two experimental setups are to be dimensioned. By those means, the fracture toughness for both crack opening mode I and II are to be determined while the similar strength of adhesive and adherends have to be considered.