Structural health monitoring of an adhesive disbond through electromechanical impedance spectroscopy

The aerospace industry continues to increase the use of adhesives for structural bonding due to the increased joint efficiency (reduced weight), even distribution of the load path and decrease in stress concentrations. However, the limited techniques for verifying the strength of adhesive bonds has reduced its use on primary structures and requires an intensive inspection schedule. This paper discusses a potential structural health monitoring (SHM) technique for the detection of disbonds through the in situ inspection of adhesive joints. This is achieved through the use of piezoelectric wafer active sensors (PWAS), thin unobtrusive sensors which are permanently bonded to the aircraft structure. The detection method utilized in this study is the electromechanical impedance spectroscopy, a local vibration method. This method detects disbonds from the change in the mechanical impedance of the structure surrounding the disbond. This paper will discuss how predictive modeling can provide valuable insight into the inspection method, and provide better results than purely empirical methods will provide. A method for identifying the appropriate frequency range and sensor locations is presented, and the method was verified experimentally using a large aluminum test article, and included both pristine and disbond coupons.