Quasistatic component generation of group velocity mismatched guided waves in tubular structures for microdamage localization

Quasistatic component (QSC) of guided wave (GW) has relatively low attenuation due to low frequency and high sensitivity to microdamage. The group velocity matching between primary GW and its QSC or higher harmonics usually facilitates the measurement of nonlinear signals due to cumulative effect of amplitude, but it restricts the determination of microdamage location. While group velocity mismatch is general for most of the wave mode pairs in nonlinear GW testing, this study presents a novel method for identifying the location of early stage microdamage using QSC generation of ultrasonic GW propagation in tubular structures under group velocity mismatching condition. A three-dimensional finite element (FE) model is developed to provide insights into the generation and propagation characteristics of the QSC induced by both global material weak nonlinearity and simulated local microdamage in metallic pipes. The FE analysis verifies the L(0,1) mode of the QSC generated from propagations of different fundamental wave modes. The generation efficiency and cumulation feature of the QSC pulse are obtained and discussed. By exploiting the group velocity mismatching condition, a microdamage localization method is proposed based on the L(0,1)-QSC mode pair, which requires one-way excitation of only one primary wave. Experiments are conducted using early corrosion aluminum specimens to investigate the QSC pulse signals and verify the proposed method. The FE and experimental results demonstrate the fundamental properties of QSC generation by GWs in isotropic metallic hollow cylindrical structures. The feasibility of the proposed microdamage localization method is validated experimentally for promising industrial applications.