Driven by globalization demand and aviation technology development, commercial airplanes become bigger and faster, such as Airbus 380 and Boeing’s 747-8. It has in turn significantly revealed the importance of quality and reliability of the aircraft braking system. Therefore, these products require testing after the production process to ensure safety and reliability. Nondestructive evaluation (NDE) methods are being used in aerospace industry to inspect flaws and damages for various materials and structures including composite materials. While several NDE methods are effective in inspection of thin Carbon-Epoxy composites, they are not very effective in detecting defects in thick Carbon/Carbon (C/C) composites such as C/C brakes and rotors. In order to develop our NDE capabilities to determine defects in C/C composite brakes by using the existing facilities, a comparative study was conducted of NDE methods for identifying subsurface defects in C/C composites. Three methods to detect defects in C/C were conducted. The first method used was transient infrared thermography. The second method used was air-coupled ultrasound. The third method used was thermal diffusivity mapping distribution. The results show the different advantages and disadvantages for each method. For infrared thermography method, it is a fast evaluation method with high thermal contrast. However, it is limited to detect surface defects 5mm in depth. Also, surface emissivity affected the ability of infrared thermography. For thermal diffusivity mapping distribution method, it is short evaluation time and can detect thick through thickness of material (20 mm). In addition, it measured thermal diffusivity and NDE inspected the sample in the same time. But, it needs precise timing control and two side inspection. For air-coupled ultrasound method, it can detect the location of defect (depth) and the precise size of defect. Moreover, it can detect thick through thickness of material (20 mm). However, it took a long evaluation time and lots of noise signal need to process. With the use of these methods, delamination defect could have been detected prior to final machining process of the C/C composite brakes. It will be saving the manufacturing company time and money.

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