Non-Contact Ultrasound Systems for Detection of Fatigue and Corrosion Damage in Aircraft

The objectives of this research effort are to develop and apply non-contact laser, electromagnetic acoustic transducers (EMAT'S), and air-coupled ultrasonic technology to enhance means for ultrasonic detection of fatigue and corrosion damage in military aircraft structures. The methods under investigation include: (1) laser generation/EMAT detection, (2) laser generation/laser detection, (3) laser generation/air-coupled detection.

A completely new design laser generation system capable of generating discrete narrow band frequency ultrasound rather than the broad frequency band ultrasound generated by conventional laser pulses has been optimized and applied to EMAT detection of machined slots (simulation cracks) in an aluminum plate. A specially designed laser interferometer was also constructed which has a flat frequency response of 10 kHz to 10 MHz. This instrument provides absolute amplitude calibration throughout the entire test period. This system was used to examine an actual aluminum aircraft lap joint. Components were selected and an experimental air-coupled ultrasound system was constructed and tested