Detection and Evaluation of Impact Damage in Carbon/Carbon Composites Using Ultrasonic Infrared Thermography

This paper presents the application of an advanced thermal non-destructive testing method, known as piezoelectric transducer-based vibrothermography, for the real-time detection of hidden defects in a carbon/carbon (C/C) composite sample. The C/C sample, which contained twelve defects resulting from 5 J impact damage, was stimulated ultrasonically using four devices operating at frequencies of 22, 40, 60, and 100 kHz. The resultant surface temperature elevations associated with these defects were recorded and quantitatively analyzed using an infrared imager. Several critical issues that have not been adequately addressed in previous studies are examined in this work: 1) the efficiency of ultrasonic devices concerning the acoustic power absorbed by the test sample, including a novel methodology for measuring the ultrasonic energy absorbed; 2) the efficiency of ultrasonic devices in relation to stimulation frequency and total electric power; 3) the correlation between temperature signals in damaged areas and the power of ultrasonic excitation; 4) the quality of the contact between the transducer and the sample; 5) the distance between the stimulation point and a defect; and 6) the effectiveness of various image processing techniques in detecting low-power impact damage in C/C composites.