Damage detection with spatially distributed 2D Continuous Wavelet Transform

When materials in a structure suffer damage, the mechanical response of the structure is modified, particularly in the vicinity of the damaged zones. Such local perturbations in the structural response generally are very small but they can be detected using wavelet transform techniques. To this end, a distributed two-dimensional (2D) Continuous Wavelet Transform (CWT) algorithm is developed which can use data from discrete sets of nodes and provide spatially continuous variation in the structural response parameters to monitor structural degradation. Combined with an embedded sensor network to provide nodal response signals, this algorithm has the potential for Structural Health Monitoring (SHM). The advantageous features of this algorithm are its reliance on local data, its ability to yield spatially continuous information, and its limited communication and computation requirements. The feasibility of the method is demonstrated using two illustrative examples: one is based on the crack-tip strain field of a plate subjected to bi-axial loads, and the other is based on the deflection field of a simply supported plate with defects subjected to static or impacting transverse loads (using a finite-element method (FEM) to obtain solutions). For each case, a set of discrete data is used to simulate the nodal sensor response, and then the 2D CWT is applied to detect the damage. The damage positions are accurately located and the damage severity is qualitatively assessed. In addition, a 3D data case (2D spatial signal with time history) is examined to demonstrate the feasibility of using a 3D CWT for SHM.