Detection of small-flaw in carbon brake disc (C-C) using air-coupled ultrasonic C-scan technique

The purpose of this paper is to conduct the study on detection identification and assessment of internal defects for the C-C brake disc composite for aircrafts by applying non-contact air-coupled ultrasonic testing. The Non-contact Air-coupled Ultrasonic Testing (NAUT) used in this paper is the most advanced ultrasonic testing technique. It is a nondestructive testing that complements the energy loss occurred due to the acoustic impedance difference in the air with two transmitting/receiving non-contact ultrasonic probes and enables the non-contact ultrasonic testing through high-powered ultrasonic focusing by using high-frequency band ultrasonic Pulser- Receiver. In this paper, non-contact air-coupled ultrasonic detection experiment applied the Transmission Method and Reflection Method was conducted as follows; When detecting an internal defect of the carbon brake disc, we compared the C-scan results according to whether masking was applied to the side of the object to be detected, measured at the ultrasonic transmission frequencies of 340 kHz and 400 kHz respectively, to detect internal defects of the carbon brake disc through the measured C-scan images. In this way, we confirmed that there is a significant difference in the internal defect detection performance depending on the masking and the change in the ultrasonic transmission frequency value.