In-situ and real-time measurement of single-lap-joint bonded area stress distribution based on FBG reflectance spectrum analyses and self-adaptive method

Abstract

Based on reflectance spectrum analyses of fiber Bragg grating (FBG) and self-adaptive method, one novel measurement method which can achieve in-situ and real-time bonded area stress distribution of single-lap-joint is proposed in this paper. Theory calculation model of this novel measurement method is established by using cohesive zone model and fiber transmission matrix theory. Duo to that inhomogeneous stress distribution of the bonded area broaden FBG reflectance spectrum, 3dB bandwidth besides center wavelength is also chosen as evaluation index in the self-adaptive method to reconstruct bonded area stress distribution. To verify the feasibility of this novel method, testing experiment is carried out on one single-lap-joint specimen. During the process of specimen preparation, two fiber Bragg gratings (TFBGs) are embedded at bonded area of the specimen to detect stress distribution at width direction and length direction. After experiment data analyses, stress gradient does not exist at width direction and relative errors of theory calculation and reconstruction stresses at length direction are all less than 5%. All these testing experiment results confirm that this novel method has certain practical value at real-time health monitoring of single-lap-joint.