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There is currently a requirement in many industries to inspect carbon fiber reinforced plastic (CFRP) components, such as those used in aircraft and for wind turbine blades to identify issues leading to potential failures. To detect surface cracks, pulsed eddy current (PEC) thermography is proposed as a powerful inspection technique, allowing the operator to observe the heating developed from the eddy current distribution in a structure using infrared imaging, detecting defects over a relatively wide area within a short time (of the order of milliseconds). In this paper, a PEC thermography inspection system for CFRP materials is studied and optimized. Using the system, the directional electrical conductivity of the CFRP material is observed through the surface heating pattern. Then, the normalized temperature rise and decay are investigated through the inspection of notches with varied depths and widths. The position invariance of the coil with respect to the notch along the fiber direction is also studied in the experiments. The work shows that PEC thermography can be used for defect detection and characterization through analysis of the surface heating pattern and the transient temperature change.
Date of Publication: Dec. 2011