Looking into the Crystal Ball: The Continued Need for Multiple Viewpoints in Damage Detection

We develop a methodology which is able to extract Ritz vectors from single and multiple shaker dynamic tests. It is shown that the identified 'experimental' Ritz vectors are identical to the analytically derived Ritz vectors when the dynamic test shaker locations and directions are used as the reference force locations in the analytical derivation. To verify the feasibility and accuracy of the extraction algorithm, dynamic response data and static test results from the Space Shuttle vertical stabilizer assembly experimental data base are utilized. Compared to static test data, accurate Ritz vectors were extracted using data from both accelerometer and laser scanning vibrometer based modal survey tests. A matrix update approach for damage detection using measured Ritz vectors is discussed. The approach represents an extension of Minimum Rank Perturbation Theory, which utilizes the fact that discrete damage is manifested in a structural finite element model typically as a low rank perturbation to the structural property matrices. The numerical and experimental studies again provide additional observations that Ritz vectors result in improved damage location and extent estimation than the corresponding modal parameters. (Author)