Structural health monitoring using transmittance functions

A technique for structural health monitoring that can detect damage away from a sensor location and during operation of a structure is presented. The technique, Transmittance Function Monitoring, uses vibration measurements to detect damage, but without measuring the excitation force or using a model of the structure. Accelerometers or piezoceramic patches are attached to the structure for sensing, and piezoceramic patches or inertial actuators are used for exciting the structure. The sensor-actuator system actively interrogates the structure using broadband excitation, and transmittance functions between consecutive sensors from the healthy structure are stored as historical data. Changes in the functions are then used to detect, locate and assess damage to the structure. Transmittance functions can be computed from different types of measured structural responses. Here, structural translations and curvatures are used to detect damage on a composite beam. The sensitivity of the two different methods is compared, and the optimal frequency range to detect damage is experimentally determined. In addition, the wavelengths of the structural mode shapes are computed to estimate the highest frequency at which the structural response can be measured by a given length piezoceramic sensor. (C) 1999 Academic Press.