Abstract: Crack is one of the main reasons for structure failure, and using ultrasonic Lamb wave can efficiently locate it in plate-like structures. Currently this technology can’t achieve specific characteristics of defects. Research on the interaction of Lamb waves with defects provides principle bases for high resolution inspection. Scattering parameter matrix(S-matrix) is employed to present the interaction of elastic wave with defects. FE and experiment research on Lamb wave oblique incident to crack is studied. Results illustrated that scattering field is non-uniform and show significant beam form phenomenon. With incident angle changing from 0° to 90°, the angle of the beam non-monotonic changes and energy of scattering wave rapidly decreases. When incident angle equal 0° and 90°, S-matrix is symmetric so that can be used to evaluate the expanding direction of crack. Using the characteristic of Lamb wave scattering in crack with oblique incident, more reasonable imaging algorithms and transducer distribution methods can be designed, which will provide an efficient way to inspect the crack with high resolution.

Key words: Crack, Lamb wave, Oblique incident, S0 mode, Scattering parameter matrix