In-situ strain measurement during solidification and cooling of aluminium alloys using regenerated fibre Bragg gratings

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A component-integrated sensor technology can enable the monitoring of aluminum casting components in production as well as in operation during their entire service life. The availability of sensor data acquired in situ during the casting process allows existing models describing the casting process to be further developed. These models will enable a better understanding of casting processes and their optimization by means of open loop control. In addition to that, deviations from set points during the casting process can be detected at an early stage using component-integrated sensor technology, and possible functional impairments of the component can be evaluated in the context of quality assurance, and suitable recommendations for the next casting can be given. For service monitoring, the cast-in strain sensors detect the stress history of the component during operation and may detect critical, hazardous stress conditions. This can be used to improve the operational safety, for example after misuse load cases. Similar to corresponding concepts employed in fiber composites, fiber optic sensor networks based on fiber Bragg gratings (FBGs) are considered here as a component-integrated sensor technology. The fiber-optic sensors are thereby cast-in together with the component during the casting process. The use of high-temperature stable and drift-reduced FBGs allows the investigation of the strain development during the solidification process at high temperatures. The basis for this is the experimental determination of the strain sensitivity and other sensor characteristics of FBGs at high temperatures. This topic is addressed for the first time in this research project. The sensor parameters determined at high temperatures are used to develop an FE sensor model. Employing this model, the undisturbed strain state of the aluminum and possibly residual stresses in the aluminum will be deduced from the sensor data. The FBG-based strain values determined during the casting process shall be verified with neutron diffractometric reference measurements in the neutron source Heinz Maier-Leibnitz. In addition, the application of the sensor method for the detection of residual stresses in a real composite casting component will be demonstrated in the proposed project.