Second harmonic generation of ultrasonic waves propagating in unbounded media and plate-like structure has been vigorously studied for tracking material nonlinearity, however, second harmonic guided wave propagation in tube-like structures is rarely studied. Considering that second harmonics can provide sensitive information for structural health condition, this paper aims to study the second harmonic generation of guided waves in metallic tube-like structures with weakly nonlinearity. Perturbation method and modal analysis approach are used to analyze the acoustic field of second harmonic solutions. The conditions for generating second harmonics with cumulative effect are provided in present investigation. Flexible polyvinylidene fluoride comb transducers are used to measure fundamental wave modes and second harmonic ones. The work experimentally verifies that the second harmonics of guided waves in pipe have a cumulative effect with propagation distance. The proposed procedure of this work can be applied to detect material nonlinearity due to damage mechanism in tube-like structure.
Functional second harmonic generation microscopy probes molecular dynamics with high temporal resolution
