Fraunhofer Institute for Microstructure of Materials and Systems IMWSIntrinsic stresses in glass can improve properties, but can also cause defects – and until now, they have been difficult to measure. The Fraunhofer Institute for Microstructure of Materials and Systems IMWS in Halle (Saale) is developing methods to detect such stresses down to the nanoscale and optimize them in a targeted manner. To this end, defined stress states are generated and analyzed using state-of-the-art electron microscopy as well as optical and micromechanical methods. The goal: more robust, durable, and resource-efficient glass products.
Glass has become an integral part of our everyday lives – whether in smartphones, tablets, or in vehicles as windshields. In addition to its many advantages, glass is characterized by its pronounced brittleness. It usually breaks suddenly without deforming beforehand. Small surface defects can grow into cracks that can destroy the glass component. However, it is not only external impacts such as falls or stone chips that can damage glass. Mechanical internal stresses within the material can also lead to defects. Such internal stresses either arise unintentionally during production and use, or they are deliberately introduced to improve properties such as thermal shock resistance or the load-bearing capacity of the glass at lower thicknesses.
Being able to detect and understand the distribution of such internal stresses down to the nanoscale would bring considerable advantages. For example, material and energy could be saved because glass could be manufactured in a more resource-efficient manner and with an improved service life. Glass could replace petroleum-based plastics in certain areas of application. Even more targeted optimization of material properties would also be possible. However, no suitable methods are currently available for such high-resolution analysis. These are to be developed in the "SpannGlas" project, which will run until December 2027.
To this end, the Fraunhofer team will first produce glasses of various compositions, into which specifically defined internal stresses will be introduced, for example by means of polishing, heat, ion or laser treatment. These stresses will then be measured optically and micromechanically. The next step will be to develop methods for detecting the generated internal stresses on a submicrometer scale using electron microscopy and comparing the results with those from the optical/micromechanical measurements. Parallel to this diagnostic workflow for local stress analysis, suitable methods for sample preparation must be found that do not further amplify the stresses that have been specifically generated beforehand. Novel synthesis approaches and the adaptation of laser and ion exchange processes are also among the project goals in order to ultimately develop mechanically more resistant glasses.
"With our many years of experience in the microstructure diagnostics of glasses and the micro- and nanostructure-based development of glasses and glass ceramics, as well as our excellent and recently expanded technical equipment, we have very good conditions for addressing these challenging issues. Developing approaches for the nanoscale-resolved determination of residual stresses in glass is a difficult task, but nevertheless one we are very keen to address. If the project goals are achieved, the results would be beneficial for forward-looking fields of application, such as the use of thin glass in microelectronics manufacturing.," says Dr. Katrin Thieme, who heads the project at Fraunhofer IMWS.
A key to this are new, powerful diagnostic technologies available to the team in Halle (Saale). These include 4D scanning transmission electron microscopy (4D-STEM), high-resolution low-loss electron energy loss spectroscopy (EELS), and high-loss extended energy loss fine structure (EXELFS) methods. This might make it possible to detect near-surface stresses caused by subsurface damage (SSD), which previously could not be detected in amorphous materials such as glass. It is also possible to clarify stress states induced by high-pressure synthesis, phase separation, crystallization, ion exchange, or laser swelling. Manufacturers can therefore reliably assess how grinding, polishing, and post-treatment processes affect the material in terms of minimal local stresses.
"We want to use the improved detectors in electron microscopy to detect local stress states, first qualitatively and then quantitatively. This will contribute significantly to deepening our understanding of nanoscale changes in glass. The knowledge gained can also support the development of new, more resistant glass compositions," says Thieme.
(October 14, 2025)