Structural monitoring and displacement field estimation based on distributed fiber bragg grating sensors

Displacement field estimation by distributed strain sensors is a structure-inherent method, which has many applications, e. g. in structural monitoring or in adaptive structures. For displacement field estimation and for monitoring applications in structures, fiber Bragg grating (FBG) sensor systems are a valuable asset due to their versatility, high strain-resolution, high frequency range and high number of sensors that can be interrogated. Furthermore, FBG sensors are capable of being integrated into composite structures and can be used to measure temperatures as well as thermal strains. This work presents and expands several model-based and experimental methods of displacement field estimation with a special focus on the use of distributed FBGs in combined thermal and mechanical loads. By developing an integrated finite-element based modeling approach of the structure and the FBG system characteristics, the accuracy of displacement estimation is predicted for combined thermal and mechanical loads. This method is applicable to the geometry of any given structure, and demonstrated here on a telescope mirror. The modeling method and the sensor characteristics are verified experimentally. Various experimental investigations on FBG sensor systems for structural monitoring are performed: integration of FBG sensors in composite materials, thermal strain measurements using FBGs, noise characterization, cryogenic temperature measurements and high-frequency vibration measurements. The methods developed in this work can be applied to the following fields: wind turbine blades and aircraft wing structures as well as high-precision components in satellites under varying thermal loads such as optical benches, reflectors, antennas or optical mirrors.