Guided Waves Approach for Damage Diagnosis in GFRP Laminates

Abstract

In the area of non-destructive testing, ultrasonic wave propagation testing has proved to be very effective tool for damage detection & evaluation of the health of subject. Ultrasonic testing uses transmission of high frequency stress waves into a material to detect imperfections or to identify changes in material properties. The most commonly used ultrasonic testing techniques include pulse echo and pulse transmission technique, where stress waves are introduced into subject structure. Pulse echo is used to locate the exact position of damage and pulse transmission is used to evaluate the presence & magnitude of damage. Relative comparison of wave signatures in healthy and damaged composite laminates could lead to an indication related to the health of specimen being tested. Glass fibre-reinforced polymer (GFRP) laminated composites have been used as an alternative to other metals & alloys due to high strength-to-weight ratio, high stiffness-to-weight ratio, corrosion and fatigue resistance. These composites may be subjected to damages either due to manufacturing flaws like missing fibre, air-voids etc. or damages may develop under working condition. This report presents the use of ultrasonic NDT techniques to detect the damage in GFRP laminates, submerged in water, with seeded defects in the form of notches, missing fibre and delamination. Negative spike pulse is used as an input signal to sending transducer through Pulser/Receiver system and transmitted pulse is received at the other end by receiving transducer. Ultrasonic waves are introduced at suitable angles to excite the different modes in the subject specimen in both pulse echo and through transmission technique. The combination of pulse echo and pulse transmission voltage signals has been successfully used to detect the damage and localize the same by generating the tomograms of the specimen.