Enhancing uniqueness properties in damage identification using sensitivity enhancing control

Precise identification of damage location and geometry through nondestructive testing (NDT) often entails the use of pattern recognition, signal processing or other postprocessing methods to enhance the signal to noise ratio in measured NDT signals. Mathematical inverse approaches, in which NDT signals are used to reconstruct discontinuity geometry, suffer from ill conditioning or lack of uniqueness of the measured variable to changes in geometry. In this paper, damage identification and uniqueness issues are reviewed for vibration analysis and eddy current testing. The inherent sensitivity of NDT to damage poses a limitation for using inverse or pattern recognition approaches for vibration based damage localization and eddy current based damage geometry reconstruction. Sensitivity enhancing control, a feedback control method for improving the sensitivity of NDT metrics to damage, improves numerical conditioning and uniqueness properties. The concept is demonstrated numerically and experimentally for both vibration analysis and eddy current testing.