The paper presents a damage characterization framework based on a simulation library and matching pursuit algorithm to estimate damage features in typical aerospace structures. The large damage database is generated by numeric simulation. The recent development of the University of Michigan’s Local Interaction Simulation Approach (UM/LISA) is an ideal tool for generating such a damage database in a very efficient manner. It includes capability for piezoelectric coupled field simulation, non-reflective boundary techniques, and contact penalty method for nonlinear guided wave simulation, and can execute on multiple-GPU platform for fast computation. The selected damage identification problem in the paper is modeled as contact interface and simulated in UM/LISA using the contact penalty method. The process first populates a library of possible damage signals using UM/LISA by varying damage parameters, such as crack length, depth and orientation. The matching pursuit decomposes the damage difference signals into atoms and the atom parameters are used as signal features. Then the algorithm evaluates a matching merit metric and its special distribution provides parametric regions of damage presence. A representative model of fatigue cracks on aluminum plate considering various crack scenarios is investigated to test the effectiveness of the algorithm. The relation between the crack features and signal features provides better understanding of the nonlinear interactions between the guided waves and fatigue cracks. The matching quality plots demonstrate that the framework can provide good estimation of the crack parameters.
A novel d36-type piezoelectric wafer fabricated from lead magnesium niobate-lead titanate (PMN-PT) is explored for the generation of in-plane horizontal shear waves in plate structures. The study focuses on the development of a linear phased array (PA) of PMN-PT wafers to improve the damage detection capabilities of a structural health monitoring (SHM) system. An attractive property of in-plane horizontal shear waves is that they are nondispersive yet sensitive to damage. This study characterizes the directionality of body waves (Lamb and horizontal shear) created by a single PMN-PT wafer bonded to the surface of a metallic plate structure. Second, a linear PA is designed from PMN-PT wafers to steer and focus Lamb and horizontal shear waves in a plate structure. Numerical studies are conducted to explore the capabilities of a PMN-PT-based PA to detect damage in aluminum plates. Numerical simulations are conducted using the Local Interaction Simulation Approach (LISA) implemented on a parallelized graphical processing unit (GPU) for high-speed execution. Numerical studies are further validated using experimental tests conducted with a linear PA. The study confirms the ability of an PMN-PT phased array to accurately detect and localize damage in aluminum plates.
Local interaction simulation approach (LISA) is a highly parallelizable numerical scheme for guided wave simulation in structural health monitoring (SHM). This paper addresses the issue of simulating wave propagation in unbounded domain through the implementation of non-reflective boundary (NRB) in LISA. In this study, two different categories of NRB, i.e., the non-reflective boundary condition (NRBC) and the absorbing boundary layer (ABL), have been investigated in the parallelized LISA scheme. For the implementation of NRBC, a set of general LISA equations considering the effect from boundary stress is obtained first. As a simple example, the Lysmer and Kuhlemeyer (L-K) model is applied here to demonstrate the easiness of NRBC implementation in LISA. As a representative of ABL implementation, the LISA scheme incorporating the absorbing layers with increasing damping (ALID) is also proposed, based on elasto-dynamic equations considering damping effect. Finally, an effective hybrid model combining L-K and ALID methods in LISA is developed, and guidelines for implementing the hybrid model is presented. Case studies on a three-dimensional plate model compares the performance of hybrid method to that of L-K and ALID acting independently. The simulation results demonstrate that best absorbing efficiency is achieved with the hybrid method.
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