Integration of microstructural and embedded sensor designs for structural health monitoring of composite materials

Development of smart materials with inherent damage sensing and detection capabilities is of great interest to aerospace and other structural applications. Most of the existing smart materials are based on using embedded sensors to obtain information related to the health of the material. However, embedding sensors inside the material can lead to undesirable effects such as stress concentration and cause premature failure. Therefore, using the microstructural components of the materials for additional function of sensing of the structural health is the only other option. Such possibilities exist in select few materials only, which include particulate composites. The present study is focused on studying the feasibility of developing fiber and particle reinforced composites in smart materials. The sensing can be achieved by interrogating the optical modes (resonant frequencies) of a dielectric particle by coupling it to an optical fiber. The fiber carries light from a tunable diode laser. The optical modes are highly sensitive to the morphology of the particle. A minute change in the size, shape or refractive causes as shift of the resonant frequencies. The shift in the resonant frequencies can be interpreted quantitatively in terms of the morphology parameter that caused the change. Governing equations are developed for such sensor systems to derive quantitative relations between the stress applied on the particle and corresponding change in the resonant frequencies. These relations are validated with experimental results.