Mechanical measurements in filament-wound composite cylinders by optical fiber specklegram sensor

Filament wound (FW) composite structures are appealing alternatives to conventional materials due to their improved strength, reduced weight, and optical fiber integration capability. However, current (quasi) distributed sensing approaches rely on intricate and expensive interrogation systems. Therefore, this paper proposes a fiber specklegram sensor to detect radial stress/strain in an FW cylinder. The probe comprises a laser-illuminated multimode waveguide attached to the composite sample wall. The fiber outputs a characteristic speckle pattern that varies with the applied mechanical stimuli’ magnitude and location. Thus, we compute the correlation coefficient to quantify the specklegram changes in response to radial efforts, achieving force and strain sensitivities of ∼0.96 N^-1 and ∼0.04 (mε)^-1, respectively. Furthermore, choosing the reference speckle image discriminates force orientation and position along the cylinder’s extent through a single fiber/wavelength scheme. Such promising results motivate further development of a smart composite structure with integrated strain sensing ability.