Research on propagation of guided waves in thick beam and crack damage identification

In guided wave-based structural health monitoring technique, structure thickness and different damage forms impacting upon the propagation of guided wave plays a crucial role in the application of this technique to engineering practice. Propagation characteristics of guided waves in thick steel beam and the interaction between damages (cracks and notches) and guided waves are investigated. Mechanism of guided wave propagation in damaged structures is investigated by introducing cutting damages. Moreover, influence of the typical damage form in steel structures, fatigue crack, to guided wave propagation is further studied to verify the results obtained by using finite element analysis (FEA) method and notch simulation. Actual group velocities of guided waves in thick beam are calculated from experimental wave signals. The damage-reflected wave packages are therefore analyzed. Relations between the damage size and amplitude, phase and arrival time of guided waves are proposed for further applications in damage detection. Difference from the through-the-thickness damage in plate structure, crack/notch in thick beam can be symmetric and asymmetric. Effects of these two damage forms to guided wave propagation are inspected and summarized. Mechanism of guided wave mode conversion is analyzed and verified by using FEA method and experimental results.