No abstract

Lamb wave-methods are reported to be very effective in detecting and localizing defects in thin plate structures. However, the accuracy of damage detection using Lamb waves is affected significantly by variations of environmental and operating conditions. In the present study, an improved methodology is presented to calculate the damage residue measure from current state responses that compensates the effect of operational and environmental changes. The proposed damage residue is obtained by comparing the current state responses of identical paths with the same propagation distance and direction. For damage localization in the structure, a modified delay-sum damage localization algorithm is introduced. The proposed damage residue measure is used along with the modified delay-sum algorithm to locate damage in a composite plate. The methodology is first presented through numerical simulations based on a finite element model and validated through experiments on a carbon fiber cross-ply configured composite plate. The insensitiveness of the proposed residue measure to temperature changes is demonstrated experimentally.

When a narrowband tone burst excitation signal is used to generate Lamb waves in the thin composite plates, a suitable frequency of the excitation signal is typically chosen to excite a solitary mode of Lamb wave in the structure. However, if and as the damage severity changes in the structure, it may be possible that the frequency of the excitation signal may influence the response metric. In the present work, the use of a chirp signal as an excitation signal for damage severity assessment is proposed. The use of a chirp signal as an excitation signal may prove suitable for damage severity assessment because the chirp response contains a large frequency bandwidth, and the cumulative effect of all the frequencies with the delamination is reflected in the damage index. The sensitivity of the chirp response to varying delamination sizes is investigated through numerical simulations and experiments. The damage index calculated using the chirp response showed a monotonic trend with an increase in damage severity, in contrast to a bidirectional trend of the damage index when conventional narrow excitation signals are used.