A Vibration and Wave Propagation Based Methodology for Near Real-Time Damage Monitoring of Composite Structures

This paper presents a novel approach to achieve near real-time damage monitoring whereby ultrasonic wave propagation and vibration data are analyzed to determine the location and degree of damage, requiring minimal operator intervention. An improved test setup, consisting of high fidelity sensor arrays, laser scanning vibrometer, data acquisition boards, signal conditioning and dedicated software has been implemented. The collected data are analyzed using a statistical damage index approach to determine the degree of damage to the structure as a function of time with a high confidence level. The statistical damage index approach is designed to overcome the complexity and variability of the signals in the presence of damage as well as the geometric complexity of the structure. It relies on the fact that the dynamical properties of a structure change with the initiation of new damage or growth of existing damage. Using measurements performed on an undamaged or partially damaged structure as baseline, the damage index is evaluated by comparing the changes in the frequency response of the monitored structure as a new damage occurs or an existing damage grows. The proposed algorithm does not require extensive rigorous signal processing, but it computes a single statistical damage parameter (statistic t) with a high confidence level (> 95%), which makes it very fast and automatic. The damage parameter vanishes if there is no change in the structure and its value increases with the severity and proximity of damage to the sensor locations. Thus if damage is initiated at a location within or near the sensor array, then its location and severity can be determined in real-time by the autonomous scheme. The method is applied to identify low velocity impact damage in stiffened composite panels for different arrangements of the source and the receivers.