High temperature and low density metallic materials are being considered for thermal protection systems (TPS) for future aerospace applications. In this paper, a method for damage detection, location, and quantification using one actuator with distributed vibration sensors is presented for estimating virtual forces introduced by damage in a model aluminum honeycomb (H/C) TPS panel. A simplified analytical transverse vibration model of a homogeneous flat plate is considered to verify the method, which is then applied to the model aluminum H/C sandwich panel to demonstrate the method experimentally. First, a fully populated frequency response function matrix from the healthy panel is measured using an equal number of actuators and sensors. Virtual forces due to damage are then estimated by filtering data from the damaged panel using the healthy baseline response matrix. Second, a modal dynamic model for the sandwich panel is extracted using a single degree-of-freedom modal parameter estimation algorithm (Global Least Squares). The estimated modal frequencies and residues are used to build a dynamic observer to synthesize frequency response measurements unavailable with only one actuator. Modal impact testing is used to acquire frequency response functions, which serve as inputs to the frequency and residue parameter estimation process. It is shown that the virtual force method, with or without a modal observer, can detect damage due to density changes.
A Single Step Modal Parameter Estimation Algorithm: Computing Residues from Numerator Matrix Coefficients of Rational Fractions
