Nonlinear mixing-wave imaging of additively manufactured specimens with different porosity levels using a multimode...

Nonlinear ultrasonic techniques have attracted extensive attention for their superior capability in characterizing micro-defects which are hardly detectable by conventional linear ultrasonic approaches. However, the challenge in achieving effective imaging of local nonlinear responses has severely restricted the further engineering application. This paper theoretically establishes the inherent relationship between the deflection angle of difference-frequency reflected harmonics generated by in-plane nonlinear mixing of longitudinal and transverse waves and the mixing depth. It is demonstrated that, under specific theoretical constraints, the surface receiving position of the mixing wave remains constant regardless of the internal defect depth. This mechanism is verified by numerical simulations, based on which a novel multi-mode integrated ultrasonic transducer is developed. To verify the characterization performance of the proposed nonlinear mixing imaging method for porosity defects in additively manufactured components, four groups of additively manufactured specimens with different pore damage are prepared by precisely regulating the process parameters of laser additive manufacturing. On this basis, nonlinear parameter scanning and imaging of internal pore defects in the as-fabricated specimens are successfully realized using only a single integrated transducer. Theoretical analysis shows that, for fixed transducer parameters, the optimal receiving position only depends on the product of the frequency ratio and acoustic velocity ratio. This feature enables the proposed method to be extended to the inspection of arbitrary isotropic materials, providing a valuable reference for engineering applications of nonlinear ultrasonic techniques.