The paper focuses on the further development of the model of the electromechanical impedance (EMI) of the
piezoceramics transducer (PZT) and its application for aircraft structural health monitoring (SHM). There was obtained
an expression of the electromechanical impedance common to any dimension of models (1D, 2D, 3D), and directly
independent from imposed constraints. Determination of the dynamic response of the system "host structure - PZT",
which is crucial for the practical application supposes the use of modal analysis. This allows to get a general tool to
determine EMI regardless of the specific features of a particular application. Earlier there was considered the technology
of separate determination of the dynamic response for the PZT and the structural element”. Here another version that
involves the joint modal analysis of the entire system "host structure - PZT" is presented. As a result, the dynamic
response is obtained in the form of modal decomposition of transducer mechanical strains. The use of models for the free
and constrained transducer, analysis of the impact of the adhesive layer to the EMI is demonstrated. In all cases there
was analyzed the influence of the dimension of the model (2D and 3D). The validity of the model is confirmed by
experimental studies. Correlation between the fatigue crack length in a thin-walled Al plate and EMI of embedded PZT
was simulated and compared with test result.
Some problems of the electromechanical impedance (EMI), especially its applications for structural health monitoring of aircraft bolt-joints and innovated approach of EMI prediction at loosening of bolt-joints are objectives of research. The full-scale test was performed using the Mi-8 helicopter tail beam. Effect of bolt-joint loosening was investigated by electromechanical impedance (EMI) method. It was shown that loosening of bolt-joint affects significant and stable
changes of EMI parameters. It was assumed that both as the weak shift of resonance frequencies or EMI magnitude and resistance change is caused mainly by damping variation. The developed 2D model of constrained PZT based on modal decomposition approach can be used for analysis of influence of the elastic properties and geometrical parameters to properties of constrained piezoelectric transducer. This model has some advantages and can also be useful for structural health monitoring of aircraft components with different possible damages including bolt-joint loosening.
Based on mode selective monitoring of the transport of guided ultrasonic waves with high temporal resolution
achieved by correlation techniques, a helicopter tail boom section, manufactured from aluminum, has been
monitored concerning structural health and load including monitoring under shaker driven conditions. The
characteristic sensitivities of the developed health and load monitoring schemes are presented together with
methods suitable for the compensation of the influence of temperature variations during monitoring.
Concerning the detection of loose joints, a novel monitoring scheme has been introduced capable to detect
fluctuations in joints including riveted joints and connections by high-locks. The currently operated system is
fully remote controlled and can be operated by internet. Concerning the rather compact size and power
consumption, the developed instrumentation is already suitable for in-flight respectively for on-ground hand
hold and battery powered operation. The observations, achievements, and results are presented, explained,
and discussed.
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