Investigation of real delamination detection in composite structure using air-coupled ultrasonic testing

Air-coupled ultrasonic testing (ACUT) is a non-destructive testing method that has been used to investigate composite defects. In this research, a new technique of creating a delamination defect is presented to produce a thin air gap for measuring realistic ultrasonic responses. Composite samples have been made of fiberglass and epoxy resin with six delamination defects in different sizes. A proper setup test has been established for the through-transmission ultrasonic inspection of the composite samples. For fault detection, statistical parameters are derived from ultrasonic response signals. Following dimensionality reduction, a support vector machine (SVM) classifier has been used to improve delamination detection accuracy. Also, the numerical simulation of ultrasonic testing on the composite specimen with delamination defects has been performed to obtain the test parameters. Although the ultrasonic responses have been significantly weakened by the delamination defects (air gaps) yet applying signal processing techniques following by an SVM classifier has proven to improve delamination detection in the composite.