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22 June 2000 Damage detection using modal strain energy and laser vibrometer measurements
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Structural health monitoring for complex systems can contribute significantly to reduced life cycle costs. Many damage detection algorithms have been proposed in the literature for investigating the structural integrity of systems. Changes in modal strain energy have been used to detect the location and extent of damage in structures. In the previous studies, the stiffness matrix is analytically derived and assumed constant even after damage. This paper reports a study on the sensitivity of the modal strain energy method to the stiffness matrix and its accuracy in detecting the location and extent of damage. The modal strain energies for each element of the undamaged structure are computed for each mode using the original analytical matrix and measured modal data. Modal data from the damaged case is used to update the stiffness matrix by a simplified matrix update scheme. This updated matrix is used to correct the elemental matrices for the damaged system. Two case studies are presented in this work. The first is an experimental and analytical model of a cantilever beam and the second, a truss model of the European Space Agency. In the first case three identical aluminum cantilever beams are used. Damage is simulated on two of them by milling 1-inch long slots at two different locations on the beams. Modal data are obtained from experiment using Scanning Laser Vibrometer (SLV) and STAR software to extract the mode shape vectors from the experimental results. These are also compared with finite element simulations of the beams. The second case is an analytical example in which damage is simulated by reducing the area of one of the truss elements hypothetically by 50%. Results from these studies show a slight improved accuracy in determining the location of damage using an updated elemental stiffness matrix. For experimental results however, modal strain energy change method does not give an accurate location of the damages. There is need for further analysis of the application of modal strain energy techniques to damage identification. The results also demonstrate the potential of SLV as a structural health- monitoring tool.
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Andrew W. Otieno, Pengxiang Liu, Vittal S. Rao, and Leslie R. Koval "Damage detection using modal strain energy and laser vibrometer measurements", Proc. SPIE 3985, Smart Structures and Materials 2000: Smart Structures and Integrated Systems, (22 June 2000);

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