On estimating axial strains using FBG sensors in single fiber composites

Abstract

Several factors that impact the calculation of axial strain evolution using fiber Bragg grating (FBG) sensors during the manufacturing of tin/bismuth alloys, ice, and epoxies are investigated. Axial and radial strains in the embedded fiber are impacted by the elastic properties and relative volumes of the fiber and the matrix as well as by the aspect ratio of the fiber. Numerical and analytical composites evaluation approaches are used to determine the relationships between the strains in the fiber and those in the matrix. Radial strains in the fiber can have a significant impact on the Bragg wavelength shift and need consideration to accurately determine matrix strains, especially when the matrix has a high stiffness compared to the glass optical fiber containing the FBG sensors. For stiffer materials such as ice and tin/bismuth alloys investigated in this research, it is shown that the use of a simplified formula that ignores radial strains leads to significant errors.