Fraunhofer Institute for Microstructure of Materials and Systems IMWSInline thermography for quality monitoring of thermoplastic UD tapes is to be established in the "UDiMi" project. The Fraunhofer Institute for Microstructure of Materials and Systems IMWS in Halle (Saale) is linking sensor, process, and microstructure data for this purpose. This will enable the production of resilient, lightweight, and recyclable semi-finished products as well as digital material maps. This supports faster process adjustments, improved quality control, and the introduction of digital twins.
Fiber-reinforced plastics enable a construction method in which the material is adapted to the load situation. Unidirectionally reinforced tapes (UD tapes) are particularly suitable for this purpose. They exhibit high mechanical strength and stiffness, especially in the fiber direction. Depending on the load situation in the component, individual layers of UD tape are stacked and oriented in the component. This results in load-bearing and highly resilient structures with reduced component weight. UD tapes, in which the reinforcing fibers are embedded in a matrix of thermoplastics, also offer considerable advantages for large-scale production and recyclability.
These semi-finished products have therefore become established in many areas where a combination of lightweight construction, resource efficiency, and recyclable material systems is sought. A prerequisite for the industrial use of UD tapes is high-quality manufacturing using efficient processes. This requires a reliable monitoring of relevant quality characteristics during the manufacture of UD tapes.
Currently, however, only external properties (e.g., thickness and weight per unit area of the tapes) are usually recorded in the process with low data resolution. There are also insufficient solutions for the particularly critical issue of impregnation quality. If the reinforcing fibers in the matrix are not sufficiently saturated, the mechanical performance of the semi-finished products decreases significantly. Until now, however, this has only been checked after the tape has been manufactured – if it then turns out that the impregnation quality is insufficient, the corresponding semi-finished products are rejected.
Inline sensor system to analyze UD tapes thermographically
In the project "Digitization of microstructure-based material information of thermoplastic UD tapes using inline sensor technology (UDiMi)," Fraunhofer IMWS therefore aims to develop improved solutions within two years. To this end, an inline sensor system is to be set up that analyzes UD tapes thermographically. The corresponding data will be compared with the resulting semi-finished product quality, which is determined by mechanical tests. The process data of the plant and the microstructure of the UD tapes will also be included.
"We link the data from the inline sensor technology with the associated machine data and the basic correlation with the microstructure of the semi-finished products manufactured. This allows a deeper understanding of the interrelationships and thus completely new possibilities for quality control in the ongoing process. In addition, faster and more resource-efficient process adaptation and process development becomes possible," says Marianne John, who heads the project at Fraunhofer IMWS.
The feasibility of such inline sensor technology for thermographic detection of internal structural features has already been successfully demonstrated at Fraunhofer IMWS in preliminary work, for example, the detection of defects in thermoplastic UD tapes. So far, however, this approach has only provided insights in individual cases. The "UDiMi" project aims to further develop this into a scientifically validated testing methodology, in particular for interpreting inline-detected material characteristics and for clarifying the relationship between the detected structural characteristics, the process parameters, and the mechanical behavior of the UD tapes. This will provide reliable information on characteristics such as fiber content (volumetric and gravimetric), fiber distribution, fiber orientation, and fiber-matrix bonding. At the same time, it will enable the targeted optimization of critical process parameters during the actual manufacturing trials – machine-specific adjustments during the ongoing process can further improve tape quality.
Automated, non-destructive characterization
The results of the non-destructive material characterization, which is to be largely automated, will be verified by means of real experiments under actual process conditions on a laboratory melt impregnation plant. UD tapes in various formulations and with different fiber contents will be used for this purpose. The aim is to create digital material cards with validated characteristic values that enable the use of different material systems as well as semi-finished tapes with customized properties. In addition, existing standards are to be reviewed and adapted with regard to their applicability to UD tapes.
"With this new method of quality assessment, we want to support material-friendly and customized material development in the field of thermoplastic composites. If we succeed in establishing powerful inline characterization methods, this will be an important contribution to the development of digital twins for industrially relevant processes in the field of plastics processing. This can also support the further market penetration of UD tapes," says John.
(October 9, 2025)