Ultrasonic C-scan techniques for damage evaluation of Carbon Fiber Reinforced Polymers submitted to low energy impacts

Abstract

In this work, different approaches for damage evaluation in composite laminates using ultrasonic C-scan imaging were used: (1) amplitude and (2) time-of-flight (TOF) immersion pulse-echo and (3) air-coupled through-transmission. Five carbon/epoxy laminates with different stacking sequences and thicknesses were impacted. The immersion C-scan images were produced using different frequencies and were compared with the ones obtained by the air-coupled system. The images show that the different methodologies are all able to detect the defects and give reasonable information about their size. The TOF images provide better information about the defects, whenever the delaminations behavior over the sample thickness is of interest, for instance their location and evolution. Better image resolution with sharp defects contour were obtained for high frequencies, as expected. The main advantage of ultrasonic air-coupled system is the absence of water in the inspection procedure, which makes it simpler and less expensive. It is also important when the materials to inspect cannot be wetted for integrity or contamination reasons. As disadvantage, the air C-scan requires transmitted waves of higher power and a great amplification of the received signals in order to face the problem of acoustic losses associated with air.