SHM of Aerospace Bonded Structures with Improved Techniques Based on NEWS

This work aims at presenting techniques for the damage identification in single lap joints (SLJs). The two proposed experimental approaches, exploiting particular interactions of the structure with vibrational waves produced by piezoelectric sensors, allow to perform a Structural Health Monitoring (SHM) without a baseline. The first technique involves the excitation of the structure by means of stationary sinusoidal waves: the presence of a subharmonic in the frequency response spectrum at a receiver point indicates the presence of damage in the joint. In addition, through a simplified analytical model it is possible to relate the frequency of this subharmonic to the size of the damage. The second technique is based on the use of a tone burst: the exciting sensor sends this transient signal that travels through the bonded area and is subsequently read by the receiving sensor; the information received is the result of an interaction between the sent wave and the reflection of the boundaries, sensitive to possible damages. The attenuation of the burst, studied through the wave equations, gives indications on the size of the damage. Both experimental campaigns were carried out on aluminum SLJs bonded with acrylic adhesive, using piezoelectric sensors (one exciting and one receiving). Simplified analytical models were used to validate the experimental results. The good analytical-experimental correlation confirms the validity of the proposed approaches.