Nonlinear ultrasonic imaging of imperfectly bonded interfaces.

A nonlinear ultrasonic imaging system is developed for detecting and imaging damages and defects with nm order gaps in industrial materials, which were undetectable by conventional ultrasonic imaging systems. A high power pulser generating large amplitude incident waves and high gain receiver with high-pass or band-pass filters extracting the second harmonic signals are combined with a conventional C-scan imaging system. The system is applied to visualize fiber/matrix debondings or matrix crackings in CFRP plates. It also visualizes anomalous substructures in amorphous diffusion-bonded interfaces, spot-welded nuggets, and projection-welded interfaces. This system would be also useful to detect semi-closed cracks whose opening is in nm order.