Delamination detection at web/flange junction of I-section composite beam with fiber optical interferometer sensor

The identification of delamination location at the web/flange junction of I-beams is an important aspect of any structural inspection program. However, there are currently no published experimental results of it. This paper presents the results of an experimental investigation on the use of fiber optic based technique for early detection of delamination at the web/flange junction of a GFRP I-beam. A PZT transmitter was employed to create the stress waves in the beam element, and an optical fiber interferometric sensor with high sensitivity and long sensing arm was attached to the surface of the beam to serve as an ultrasonic receiver. From the laboratory validation, the proposed technique successfully captures the presence of delamination. Additional frequency component was observed at the delamination location and at the resonant frequency relating to the defect depth. The results also show a close correlation between the experiment and the theory.