Embedded fiber Bragg grating sensing for in situ monitoring of an adhesive shear modulus during glulam curing.

This study addresses the challenge of in situ monitoring of adhesive curing in glulam using an acousto-ultrasonic system with surface-bonded and embedded fiber Bragg grating (FBG) sensors and demodulated by edge filtering to enhance sensitivity. The measured time-of-flight shift extracted by FBG sensors increased with curing time, consistent with the shear modulus evolution from rheological tests, and a plateau indicated the transition to the glassy state. Finite element simulations validated this trend by modeling wave propagation under varying adhesive modulus, and the simulated time-of-flight shift agreed well with the experimental results. Both surface-bonded and embedded FBG configurations performed comparably in tracking the curing process, while the embedded sensors offered the additional advantage of enabling long-term service monitoring. The system thus offers a reliable solution for in situ shear modulus monitoring in glulam quality control.