Local defect resonance enhanced vibrothermography for fatigue crack detection in CF/PEEK composite plate

Carbon fibre-reinforced polyether ether ketone (CF/PEEK) composites are widely utilized in engineering applications due to their excellent mechanical properties. A rapid and effective non-destructive testing (NDT) technique is essential to ensure the structural integrity of CF/PEEK composites. However, conventional NDT methods still face considerable limitations in achieving high-sensitivity detection of internal fatigue cracks in composites. This research investigates the mechanism of crack local defect resonance (LDR) and extends it to the application of vibrothermography for fatigue crack detection and quantitative assessment. Initially, a vibration measurement combined with modal analysis was conducted to identify the LDR frequencies of fatigue crack in short carbon fibre-reinforced PEEK composite plates. When the specimens are excited at those modal frequencies, the crack is characterized by both out-of-plane and in-plane local resonances. A subsequent vibrothermography experiment with swept excitation further verifies the closely correlation between LDR and the thermal responses induced by the fatigue crack. Comparative experiments demonstrate that the temperature rise at the fatigue crack is higher when excited with the LDR frequency than when excited with the intrinsic frequency of the specimen and the transducer’s operating frequency. Additionally, the proposed method was combined with LDR modal analysis to achieve a quantitative assessment of crack length with a relative deviation of about 8.6%. The LDR-based vibrothermography for fatigue crack detection not only improves the detection sensitivity by enhancing the local heating effect in the defective region but also provides a new and efficient method for defect metrology.