The paper presents a unified computer assisted automatic damage identification technique based on a damage
index, associated with changes in the vibrational and wave propagation characteristics in damaged structures.
An improved ultrasonic and vibration test setup consisting of distributed, high fidelity, intelligent, surface
mounted sensor arrays is used to examine the change in the dynamical properties of realistic composite
structural components with the appearance of damage. The sensors are assumed to provide both the low
frequency global response (i.e., modal frequencies, mode shapes) of the structure to external loads and the
(local) high frequency signals due to wave propagation effects in either passive or active mode of the
ultrasonic array. Using the initial measurements performed on an undamaged structure as baseline, the
damage indices are evaluated from the comparison of the frequency response of the monitored structure with
an unknown damage. The technique is applied to identify impact damage in a woven stiffened composite
plate that presents practical difficulties in transmitting waves across it due to scattering and other energy
dissipation effects present in the material and the geometry of the structure. Moreover, a sensitivity analysis
has been carried out in order to estimate a threshold value of the index below which no reliable information
about the state of health of the structure can be achieved. The feasibility of developing a practical Intelligent
Structural Health Monitoring (ISHM) System, based on the concept of "a structure requesting service when
needed," is discussed.