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Advanced Non-destructive Technique for Debonding Inspection of Aircraft Composite Structures



A preliminary Structural Health Monitoring system for the detection and measurement of the debonding between the skin and the stringer flange, induced by low energy impacts in composite aircraft wing panels, is proposed. The whole system is conceived like an off-line system, aiming to be an alternative method to the current NDI/C-scan techniques, leading toward the reductions of costs and times. The system is composed of high frequency sensors/actuators piezoceramics (PZT), while the control algorithm is based on the elliptical triangulation method, in particular on the guided waves propagation inside the structure. This method is based on the measurement of the perturbations induced by discontinuities present within the structure, like the debonding. Such discontinuities, if crossed by a wave, affect the signal in both amplitude and path. Numerical results on small-scale stiffened panels made of carbon fiber reinforced plastic material are proposed in the work. Preliminary experimental results are presented and the complete verification and validation of the approach at laboratory level is in progress. Besides, the work is propaedeutic to bonded composite parts in general: parts situated in positions difficult to access or in remote locations with substantial time-consuming inspection operations and bonded patches are often used as economical repair strategy in place of component replacement, with significant cost-savings. In addition, due to the uncertainty of long-term adhesive performance and the inability to continuously assess the repair condition, this technique could overcome the current design practices for bonded parts that are inherently highly conservative; in fact, additional “special factors” to the design limit loads are applied to the structural parts and even more in absence of the repair.


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