Eigenstructure assignment technique for damage detection in rotating structures

The detection and the identification of damage in a helicopter rotor blade are considered. An eigenstructure assignment technique is developed using measured modal test data and a finite element model of the blade to detect and to characterize the extent of damage in the system. Previous eigenstructure assignment techniques have not attempted to consider the centrifugal and gyroscopic fortes found in rotating systems. Additional elemental stiffness matrix terms are generated for the inboard elements due to the centrifugal force caused by the mass of the outboard elements. This force creates an enhanced sensitivity of the eigenstructure to mass changes, thereby leading to an improved damage detection capability The feasibility of the methodology is demonstrated analytically on a finite element model of the TH-55A main rotor blade in a vacuum.