Nonlinear Ultrasonic Crack Detection Based on 3D-Printed Phononic Crystal Filters.

Nonlinear ultrasonic testing is capable of sensitively detecting second harmonic waves generated by micro-cracks in materials. However, the inherent second harmonics of experimental system generated by ultrasonic equipment hazardously interfere with the detection signal and compromise the damage recognition. Here, by introducing 3D-printed acrylic phononic crystal (PC), we aim to improve the damage sensitivity of nonlinear ultrasound by filtering out undesirable nonlinear harmonics. Two sensing devices related to periodic corrugation and lattice structure are proposed to generate stopband frequencies to suppress harmonics generated by ultrasonic instrumentation. These intriguing features can also be utilized to reliably detect the cracks on the damaged aluminum plate. These findings pave the avenue for the potential development and application of nonlinear ultrasonic detection systems in the precise nondestructive testing (NDT) field.