Multiple damage detection on aircraft composite structures using near-field MUSIC algorithm

• Near-field 2D-MUSIC algorithm based method is proposed for structural damage.
• Correlated 2D-MUSIC algorithm is present for locating multiple structural damages.
• The method is applied to aircraft composite oil tank showing its successful performance on complex composite structure.

Damages in composite structure can lead to significant reduction in local strengths. Therefore, it is important to localize these damages to give an early warning for maintenance of the aircraft. Since these damages may happen near the sensor array, the wave fronts are spherical and the far-field multiple signal classification (MUSIC) based methods with the plane wave hypothesis are no longer valid. Aimed at developing MUSIC algorithm to detect near-field damages, a new near-field 2D-MUSIC method using piezoelectric sensor array is presented first. Though ordinary MUSIC algorithms can be used to distinguish multiple sources, they request the signals from these sources are independent with each other. By using the active damage monitoring method, since all damage scattered signals are the damage reflection signals of the same active excitation one, they are all correlated. This gives rise to the difficulty to apply ordinary MUSIC methods to detect multiple damages in the structure using active monitoring approach. To distinguish multiple damages in the structure, a correlated near-field 2D-MUSIC method based on spatial smoothing algorithm is also proposed to solve the correlation problem of multiple damage detection. To verify the proposed methods, evaluation experiments are performed on a carbon fiber composite material plate and a real aircraft composite oil tank. The results prove the effectiveness of the presented methods to detect multiple damages on the complex composite structure.