Damage Detection in a Stiffened-Plate Using Modal Strain Energy Differences
An aluminum stiffened-plate panel resembling aircraft- fuselage construction was tested in the laboratory with a laser doppler velocimeter. The purpose of the test was to extract out-of-plane mode shape data before and after the infliction of damage to evaluate a global NDE damage localization technique. The NDE damage localization technique is based on modal strain energy differences between the undamaged and damaged states. The modal strain energies were computed from bending and twisting curvatures obtained using an iterative bi-variate curve-fit procedure on estimated curvatures obtained from finite differences of the mode shapes. Strain energy differences between pairs of matching modes of the undamaged and damaged structure locate the inflicted damage by indicating increases in the modal strain energy. The damage indications provided by several modes are normalized using a standard norm and fused using an average approach to create damage maps.