Multi-crack damage identification and quantification using Lamb wave-based structural health monitoring

The simultaneous presence of multi-crack damage in a structural component is a crucial issue affecting system safety. To address the accurate and quantitative monitoring of multi-crack damage in an aeronautical structure, an innovative multi-crack damage localization, orientation and quantification algorithm using Lamb wave-based structural health monitoring is presented in this paper. An improved Hausdorff distance-based weighted average imaging methodology is introduced for precise multi-crack damage position identifications. To account for the critical role of crack orientation in damage quantification, a cross-orthogonality-based method is developed, enabling orientation detection at arbitrary positions and angles while simplifying the problem into a mathematical formulation. A wave scattering sources-based quantification algorithm incorporating the estimated position and orientation information is further proposed to estimate the multi-crack lengths. Additionally, a singular elliptic trajectories removal scheme is presented to suppress useless ambient noise and enhance the damage information discriminability. Experiments on the aircraft wing-box structure of a real airplane are implemented to substantiate the proposed techniques. Due to the outstanding properties, such as flexibility, electrically stabilized and applicability to complex structures, the sensor layer with built-in PZT sensor network surface-installed on the monitored structure is adopted to generate and receive Lamb wave signal. The results manifest that the proposed monitoring algorithm, without prior information or calibration required, is effective and straightforward for detecting multi-crack damage. This study can also provide a feasible technique for accurately locating and quantitatively identifying cracks in some concealed parts or inside the structure.