Damage detection using counter-mixing guided waves in a pipe

To address the challenge of low spatial resolution in detecting multiple damage zones in pipes and to achieve accurate localization and quantitative characterization of micro-damage, counter-directional guided wave mixing is proposed. The theoretical conditions for guided wave mixing are derived; the generation and propagation of combined harmonics are analyzed; and suitable guided wave modes are selected for 304 stainless steel pipes. Combined harmonic generation is verified through numerical simulations, and the influence of the damage coefficient, damage zone length, and number of fundamental wave cycles on the nonlinear parameter is investigated. Subsequently, spatial localization and resolution of multiple damage zones are studied. Results show that the selected guided wave modes can generate combined harmonics, and the nonlinear parameter increases linearly with the damage coefficient while exhibiting phased cumulative growth with increasing damage zone length. Spatial localization and resolution of multiple damage zones are achieved by tuning the number of fundamental wave periods. This method provides a new approach for detecting, localizing, and resolving multiple damage zones in pipes.