Performance of Fiber-Optic Bragg Grating Sensors in CFRP Structures

摘要

In future aircraft, integrated sensors for monitoring structural performance and structural integrity will become increasingly important. For integration into carbon-fiber-reinforced composite structures, fiber-optic Bragg grating sensors represent a very promising approach. In order to characterize the behavior of integrated sensors for different mechanical load cases theoretical and experimental investigations were conducted. In the theoretical part of the work, an analytical approach was first used to determine the strain sensitivity of the Bragg sensor and the interface stresses at the coating. Using this model the effect of longitudinal and transverse tension has been studied for different stacking sequences of the composite material. We then compared the results of the analytical model with a finite element analysis. A good correlation between the analytical and the numerical approach was found. For the experimental investigations the CFRP was subjected to the load cases of transverse and longitudinal tension and longitudinal compression. For the strain sensitivity of the integrated Bragg sensors a good consistency of the theoretical and experimental work was found. As a result of the investigations, conclusions can be drawn as to the design of sensor coatings with regard to the minimization of transverse strain sensitivity effects and interface stresses. For commercially available coatings, high interface stresses were identified for strain levels relevant to practical applications (0.5 percent ). Furthermore, transverse strain sensitivity effects have to be taken into account for interpretation of the sensor signals. However, linear behavior of the integrated sensor can be observed.