Air-Coupled Ultrasonic Nondestructive Evaluation of Carbon/Carbon Composite Aircraft Disk Brakes

Air-coupled ultrasonic inspection has a great potential for non-contact and nondestructive inspection of various materials. The couplant contamination-free testing offers a great advantage to industry dealing with composite materials and especially CC composites. The air-coupled ultrasonic through transmission testing was performed on several commercial CC aircraft brake discs and CC materials to determine the minimum defect size, resolution and the signal penetration depth. The through transmission testing utilized the 120 and 225 KHz point focus transducers. The thickness of the tested discs was from 18 mm to 36.33 mm. The small specimens with the thickness of 30 mm contained flat bottom drilled blind holes and side drilled holes of various depths. The drilled hole diameters were from 1.588 mm to 12.7 mm. The test results proved the presence of a large delamination on one of the commercial discs. The signal leakage greatly affects the reliability of measured data around the edges of the tested specimens. The influence of the fiber orientation needs to be more investigated.

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