Purpose – The purpose of this paper is to present the problems of the electromechanical impedance (EMI), especially its applications for structural health monitoring of aircraft bolt-joints and innovative approach of EMI prediction at loosening of bolt-joints. Design/methodology/approach – This experimental study includes the results of a full-scale test of the Mi-8 helicopter tail beam, particularly, its bolt-joints of a beam with other parts of the structure. One of the connecting frames of the tail beam was equipped with piezoelectric transducers (PZT) glued on the surface of the frame near the bolts. The bolts' loosening was investigated by using the EMI technology. Findings – It was demonstrated that loosening of the bolt-joint produces a significant and statistically stable change of the EMI metric. Presumably, both the small shift of resonance frequencies and the EMI magnitude and resistance change are caused mainly by damping variation at the bolt-joint loosening. In this analytical study, the 2D model of a constrained PZT is proposed. In contrast with the existing model, the modal decomposition analysis is used as a universal mean to express the dynamic properties and dynamic responses of both the transducer and the host structure. This approach, together with the finite element modal analysis, allows simulation of any complex system “PZT-host structure”. The model can be easily transformed also to the 3D one. The bolt-joint of the Mi-8 helicopter with the EMI measurement system was simulated by using the developed 2D model. The simulation results satisfactorily correspond to the test. Practical implications – The results of this research can be used for implementation in the structural health monitoring of bolt-joints and other aerospace structural components. Originality/value – The new experimental results on aircraft real bolt-joints were obtained. Especially significant is the original 2D model of the electromechanical impedance, based on the modal decomposition method, which can significantly improve the accuracy and the realistic description of the dynamic interaction between PZT and structure, as well as the dynamic response to the appearance of structural damage.

No abstract

The theoretical model of quasi-static crack growth in the elastic-plastic material under load variation in a wide range. Small-scale yielding is principal assumption and main restriction of proposed theory. The model of crack growth provides for continues and interrelated both the crack propagation and plastic deformation development. The nonlinear first-order differential equation describes the quasi-static process of crack growth. In dimensionless form this equation invariant in respect to geometrical configuration and material. The critical size of the plastic zone is proposed as the characteristics of material resistance which is directly connected with the fracture toughness, but more convenient in practical applications of invariant equation. The demonstration of solution is performed for the double cantilever beam that widely used as the standard (DCB) sample for measurement of the mode-I interlaminar fracture toughness. he short analysis of some properties of solution of the invariant equation and its application is done.

Earlier the effect of fatigue crack opening/closing (FCOC) to ultrasound guided wave propagation was investigated. The purpose of this article is to evaluate this effect to the electromechanical impedance (EMI) of the system "piezoelectric transducer / host structure. Experimental study performed using the flat samples of aluminum alloy. One of them had the 4 mm central hole. Other sample after fatigue testing had central fatigue crack of 40 mm length (including a 4 mm central hole for the initiation of a fatigue crack. Each sample was loaded by tensile axial static load from zero to 12 kN and the EMI measurement after eacn 2 kN incrementat of load. The EMI was measured in the frequency range of 20-40 kHz. It is established that the FCOC effect to magnitude and reactance of EMI mainly associated with variation of the capacitance of PZT under mechanical load. But the effect to the PZT resistance is more complex and more significant. The result of the study is the base of some procedure of fatigue crack detecting by the EMI method without baseline use. The developed model of EMI of ’host structure – PZT’ that is based on the modal decomposition of dynamic response of this system allows to solve main problems of the SHM system designing and optimizing of its parameters.

The basic purpose of given article is consideration of the problems connected with application of a method of concentrated weights in the tasks of mechanical systems dynamics at non-classic internal and external constraints. The method of the concentrated weights is convenient means of the analysis of dynamic properties of elastic mechanical systems. It has relative simplicity of definition of the parameters of equivalent discrete system, the clearness of computing algorithms and provides comprehensible accuracy of definition of the lowest natural frequencies. Doubtless advantage of a method is convenience of modeling of non-classic constraints of fastening and internal constraints between elements of complex systems. Such problems arise at the decision of practice tasks of the analysis of dynamics of real systems. The method is used for the analysis of vibra-tions of a beam with variable parameters at presence of elastic supporting of the beam and the attached additional concentrated weight. A result of dynamic analysis has a good correlation with the fatigue damages observed at fatigue test of a beam.