Nonlinear acoustics with low-profile piezoceramic excitation for crack detection in metallic structures

Structural damage detection is one of the major maintenance activities in a wide range of industries. A variety of different methods have been developed for detection of fatigue cracks in metallic structures over the last few decades. This includes techniques based on stress/acoustic waves propagating in monitored structures. Classical ultrasonic techniques used in nondestructive testing and evaluation are based on linear amplitude and/or phase variations of reflected, transmitted or scattered waves. In recent years a range of different techniques utilizing nonlinear phenomena in vibration and acoustic signals have been developed. It appears that these techniques are more sensitive to damage alterations than other techniques used for damage detection based on linear behaviour. The paper explores the use of low-profile piezoceramic actuators with low-frequency excitation in nonlinear acoustics. The method is used to detect a fatigue crack in an aluminium plate. The results are compared with modal/vibration excitation performed with an electromagnetic shaker. The study shows that piezoelectric excitation with surface-bonded low-profile piezoceramic transducers is suitable for crack detection based on nonlinear acoustics.