FBG-based optical extensometer for high-precision mechanical tests

This paper presents the theoretical basis for a fiber Bragg grating (FBG) based extensometer for high-precision mechanical tests. This is achieved by employing a compression mechanism with a highly stiff spring, that upon being extended transfers strain to the axis of a metal cylinder that has a bare SMF optical fiber inscribed with FBGs. The use of an etched fiber should improve sensitivity while neglecting the disadvantage of the brittleness that comes with it when embedding it into a housing metal cylinder. Upon this basis a theoretical model for strain transfer for the extensometer was developed and validated through a finite element method (FEM) analysis. This approach demonstrated the potential for achieving a sensitivity of up to 6.80 μm on the extensometer, offering a new and potentially more cost-effective solution compared to existing commercially available options.