Lamb Wave Based Total Focusing Method for Integral Grid-Stiffened Plate Damage Identification

The integral grid-stiffened plate is often used as the outer wall structure of spacecraft, which can reduce weight and increase strength. The Lamb wave is often used to detect damage of plate structure due to its advantages of strong penetration and minimum attenuation over long distances. When the Lamb wave crosses the stiffeners, the dispersion, reflection, transmission and mode conversion waves will be superimposed, resulting in difficulties in damage detection and structural health monitoring (SHM). This paper proposed an improved total focusing method (TFM) to locate damage in integral grid-stiffened plates based on distributed piezoelectric wafer active sensors (PWAS) array. Firstly, the appropriate working frequency was selected to generate the A0 mode Lamb wave depending on the structure and sensors, and the full matrix capture (FMC) method was introduced to collect data. Secondly, TFM was used to obtain the initial imaging results and the possible area of damage can be assessed and identified. Thirdly, the double window functions were proposed to extract the scattering signal related to the damage for the specific mode (A0). Lastly, the TFM was used again to obtain the final imaging results and the damage can be correctly identified. The proposed method has been verified by three-dimensional finite element (FE) simulation as well as experiments. The experimental results show that the damage in an aluminum alloy integral grid-stiffened plate can be located with the error of 13mm.