Systematic multiparameter design methodology for an ultrasonic health monitoring system for full-scale composite aircraft primary structures

The successful utilization of guided wave-based structural health monitoring (SHM) for detailed quantitative diagnostic of damage in composite aircraft primary structures depends on the excitation frequency, geometry, and positioning of the piezoelectric transducers. This study proposes a novel methodology to consistently define those parameters, which is not tuned for a single damage size, does not resort to unrealistic usage of pure guided wave modes, and is applicable to a generic full-scale composite aircraft primary structure. The proposed criteria for designing the piezoelectric transducer network are based on sensor output, coupled electro-mechanical response of the transducer-structure assembly, energy transfer from the bonded piezoelectric transducer to the structure, wavefront coverage of the monitored area, and measurement equipment capabilities. The design methodology was successfully validated by testing the capabilities of the SHM system for the diagnostic of barely visible impact damage of different severities, applied in different locations on a full-scale thermoplastic composite aircraft stiffened panel.