Jin-biao Cai

An electromechanical impedance approach for quantitative damage detection in Timoshenko beams with piezoelectric patches

As a qualitative health monitoring method, the electromechanical impedance technique (EMI) has been widely studied. Due to the complexities of the damaged structures and the difficulties in high-frequency analysis, further information about the nature of damage cannot be obtained using EMI in its conventional non-model-based way. Thus, in this paper, a hybrid technology combining the EMI technique and reverberation matrix method (RMM) is proposed to quantitatively correlate damage in beam structures with high-frequency signatures for structural health monitoring. Timoshenko beam theory is employed to study the dynamics of beam-like structures bonded with multiple pairs of PZT patches. A piecewise, homogeneous beam model is introduced to approximate the nonhomogeneous beam in which inhomogeneity is introduced because damages of an originally uniform beam can be modeled by different cross-sectional properties. Here, only one-dimensional axial vibration of PZT wafers is considered. A shear lag model is adopted to simulate the interfacial bonding between PZT patches and the host beam. An analytical expression of impedance (or admittance) related to the response of the coupled model of the PZT patch-bonding layer–host beam system is derived and then investigated by comparing with other theories. Finally, covariance, a kind of non-parametric damage index, is also employed to identify the damage severity, propagation and location.

Application of EMI Technique for Crack Detection in Continuous Beams Adhesively Bonded with Multiple Piezoelectric Patches

Electro-mechanical impedance (EMI) is very effective for detecting the local incipient damages including small cracks in structures and has been validated by many experimental investigations. Meanwhile, some analytical models have been proposed to deal with dynamics of structures for health monitoring. However, there is little analytical work done to relate EMI signatures with crack parameters at ultrasonic frequencies. In this paper, a modified model combining EMI technique and reverberation matrix method (RMM) is proposed to quantitatively correlate crack parameters in continuous beams with high-frequency signatures for structural health monitoring. The model is based on Timoshenko beam theory with the crack treated as a massless rotational spring. The bonded PZT wafers are restricted to one-dimensional axial vibration. A shear lag model is adopted to simulate the interfacial bonding between PZT patches and the host beam. For the first time, an analytical expression of impedance (or admittance) involving information of cracks in this coupled smart structure system is derived. Comparison with existent numerical and experimental results is presented to validate the analysis. Based on this model, EMI signatures extracted from the PZT wafers can be used to identify cracks in a continuous beam.

Analytical modeling and static response of a curved beam with imperfectly bonded piezoelectric actuators

An analytical description of the static characterization of a curved beam with surface-bonded piezoelectric transducers is developed in this paper. The uniform curved beam is thin and actuated by distributed piezoelectric patches. The governing equations of these structures with small curvature are derived based on one-dimensional beam theory. The static analysis of the beam actuated by multiply distributed PZT patches is then given in detail based on a transfer matrix method. Furthermore, the actuation mechanism of the piezoelectric patches is also investigated, considering the effects of the interfacial shear stresses between the piezoelectric patches and the host elastic beam. Then, parametric studies on the static characteristics of the beam are performed to examine the effects of the parameters: applied electric field, the thickness and length of the PZT wafers and the thickness of bonding layers etc. Finally, an analytical expression reflecting the relation between the external load and electric voltage is established for the displacement control problem.

Model experiments of damaged structural identification based on electro-mechanical impedance technique

Based on the electro-mechanical impedance (EMI) technology for structural health monitoring, model experiments were carried out to study the damage identification in a steel beam which is widely used in structural engineering. A precise impedance analyzer HP4294A was used to extract and analyze the electricity admittance signals in different frequency domain from the original undamaged and damaged model steel beam. The damaged model is made by presetting artificial cracks with appointed location and depth in the steel beam, and the damaged severity is imitated with the different quantities of cracks. The experiment results showed that, the conductance signals shifted to the left with the propagation of damages in the beam. The conductance signals in different frequency domain respond differently to the same damaged model, and a suitable frequency domain signals can detect more effectively if damages occurred in the model. In order to characterize the damage severity of structure quantitatively, three different damage indexes were employed in analyzing. The result showed that the only index MAPD (mean absolute percentage deviation) could quantify the damage degree precisely and effectively. It is also noted that the location of the damages in the structures could be identified through reasonable distribution of piezoelectric-ceramic patches and by analyzing the peak offset of conductance signals. The experimental studies lay the foundation for damaged structural detection based on the EMI technology.

Recursive formulations for dynamic analysis of a smart cracked beam based on the method of reverberation-ray matrix

An accurate electro-mechanical impedance (EMI) model for analytical crack detection of a Timoshenko beam is established based on the improved reverberation-ray matrix method via the recursive formulations. The crack is treated as a massless rotational spring. A pair of PZT patches with free ends symmetrically bonded onto the beam is assumed in a state of pure one-dimensional axial motion under an out-of-phase harmonic electric force and hence a pure bending excitation of the beam is created. A Kelvin-type viscoelastic law is introduced into the EMI model to account for the bonding effect in order to improve the signature sensitivity to cracks. In order to develop the recursive formulations to reduce the size of the final equations in the method of reverberation-ray matrix (MRRM), new scattering relations are established by a matrix reduction technique. Then, an analytical expression of impedance containing crack parameters as well as other physical parameters is derived for crack detection of beams.

Delamination detection in laminated composite beams using electro-mechanical impedance signatures

This paper focuses on the delamination detection in composite beams using electro-mechanical impedance (EMI) signatures, which is directly related to the structures mechanical impedance. A model of a laminated beam including a delamination as well as installed PZT transducers is presented. Furthermore, the model has to take into account the dynamic behavior of the piezoelectric patches and simulate the presence of the imperfect bonding between the PZT patch and the host laminate based on a classic shear lag law. Then, an analytical expression of impedance involving information on the size and the position of a delamination in this coupled smart structure system is derived via the reverberation matrix method (RMM). Comparison with existent experimental and numerical results is presented to validate the present analysis. The numerical simulations allow us to study more closely the influence of some geometrical parameters such as sensor size and position. The analysis in this paper provides necessary theoretical basis for delamination detection in composite structures.