In-situ strain measurements in the plastic deformation regime inside casted parts using fibre-optical strain sensors: A contribution to the production of intelligent parts

Fibre Bragg Gratings (FBGs) were employed as internal strain sensors within tensile specimens that were machined out of a casted aluminium alloy. Embedded FBGs have the potential to directly measure strains within a casted part for a better understanding of load cases for the part design process. In addition, if the FBGs remain in the part, strains can be measured under real-life conditions and return valuable evidence for health monitoring. The proof of application is provided by the presented tests by comparison of external and internal strain measurements. The step-wise calibration test gives evidence for a linear transition between external straining and internal response by the FBGs and thus a constant conversion factor was obtained. The application in a common tensile test proves a precise strain measurement by the FBGs and their durability until a short time before the specimens failed. These findings form the basis for an application of FBGs within real structural parts and thus the production of intelligent parts in future work. As a conclusion, internal strain measurements using FBGs have the potential to provide additional strain data compared to common methods and hence to improve the design process as well as to monitor casted parts under operating conditions.