Same-direction coaxial ultrasonic body wave mixing nondestructive testing method based on third-order nonlinearity

The invention discloses a homodromous coaxial ultrasonic body wave mixing nondestructive testing method based on third-order nonlinearity, which comprises the following steps of: 1, selecting the frequency of an initial wave according to a resonance condition; 2, exciting initial transverse waves and longitudinal waves at the left end of the test piece to be tested, and controlling a mixed region of the two columns of waves by changing the excitation time interval of the two columns of initial waves so as to scan a specified region; and 3, the propagation direction of the newly generated mixed wave is opposite to that of the incident wave, the mixed wave is received at the left end of the test piece, signal processing is performed on the mixed wave, related parameters are extracted, and damage positioning is realized. Based on the three-order nonlinearity of a wave equation, the invention provides a novel homonymous coaxial ultrasonic frequency mixing detection method, and provides a novel resonance condition