Induction-based Thermographic Inspection of Composites

Rapid growth in the performance and capabilities of thermography, and the increased use of composite materials in the construction and repair of military and commercial aircraft, has strongly positioned it as a viable NDI technique. In Phase I, ThermalWave Imaging, Inc. and UD-CCM propose to develop an AC coupled, non-contact Non-Destructive Evaluation (NDE) technique that can evaluate 3-D state of carbon fiber composite structures using their inherent electrical resistance characteristics. Thetechnique relies on low-power induction heating to generate small levels of local 3-D volumetric heating and subsequent thermal image evaluation for defect and damage detection. The 3-D heat generation profile is a function of the inherent carbonfiber-based electrical resistance network in the composite and any changes in the network due to damage or defects will affect heat generation capability (pattern and temperature). In addition, the presence of damage or defects will cause localizedmagnetic flux concentrations (same concept as eddy current sensors) resulting in localized heating at the defect, making them easily detectable. The proposed technique has many advantages including the elimination of interconnects and embedded sensors,scanning of large surface areas rapidly, usability with current in-service structures and the use of industry standard induction and IR detection hardware. Successful development and implementation of the proposed induction heating based thermographysystem, for detecting and quantifying size and depth of damage in composite components, will fill a wide-spread void in current capability for both commercial and military aerospace industry segments. Conventional NDI techniques such as UT, and X-ray haveshown limited success for this particular need, not to mention long inspection times, high cost of operation, health and safety issues, and inadequate portability.Our Phase I proposal was formulated based on input from current and prospective customers in Government and private aerospace manufacturing, service, and R&D, including Air Force, Navy, NASA, commercial airline, and military NDE personnel. We found thatseveral major aerospace and power generation customers (Boeing, Airbus, GKN Westland, Lockheed-Martin, Siemens Westinghouse, GE) were still using conventional inspection techniques such as UT, and X-ray for detection of sub-surface defects with moderatesuccess, not to mention long inspection times, high cost of operation, health and safety issues, and inadequate portability. These customers indicated a high degree of interest in an NDI system that would incorporate the advanced features of the pulsedsystems that they were using on other applications.