Michele Pasquali

Advanced System Identification of Plates Using a Higher-Order-Spectral Approach: Theory and Experiment

A nonlinear system identification technique exploiting the dynamic response features of fully nonlinear physics-based plate models extracted by Higher-Order Spectral (HOS) analysis tools is developed. The changes induced by an imperfection in the dynamics through the structural nonlinearities are used as key detection mechanism. The differences in dynamic response of a baseline and a modified/imperfect structure are enhanced by the local nonlinearities induced by the structural modification which thus represent the specific objective of identification. The validation of the procedure and the developed algorithms is carried out through extensive experimental testing employing various plates, including isotropic and composite lay-ups, and excitation sources, including White Gaussian Noise and a train of impulses.Copyright

A nonlinear formulation of piezoelectric plates

A nonlinear piezoelectric plate model capable of accurately expressing the direct and converse piezoelectric effects is presented. The developed semi-intrinsic theory is meant to encompass large strains, displacements, and rotations that can occur in the plate as a consequence of a complete coupling between the mechanical and the electrical fields. Based on the assumption that a linear dependence of the electric potential on the plate thickness is not adequate to represent the potential electric energy, a specific structure to the field of admissible displacement is taken into account. A nonlinear regression technique is successively developed to detect the nonlinear dependence of the obtained solutions on the through-the-thickness coordinate. Particular warping functions characterized by the use of an ad hoc polynomial expansion adopted to express their dependence on the plate thickness direction are here considered to describe the shear and the extensional deformability of the plate transverse fibers. Linear constitutive relations for a transversely isotropic continuum are considered. The governing equations of motions for the model are finally obtained.

A nonlinear piezoelectric shell model: Theoretical and numerical considerations

A nonlinear piezoelectric shell model capable of accurately expressing the direct and the converse piezoelectric effect is discussed here with the support of numerical simulations. The theory under investigation is meant to be able to encompass a complete coupling between the mechanical and the electrical fields in the frame of geometrically exact shell formulations. To this aim, warping functions characterized by an ad hoc polynomial expansion in the shell through-the-thickness coordinate are considered to describe the shear and the extensional deformability of transverse fibers. The governing equations of motion are numerically implemented for the cases of a rectangular semi-cylinder and for a multilayered 90° rectangular cylinder. Numerical results show the effects of key geometric parameters and of the nature of the loading on the system response, evidencing that significant misrepresentations of the system behavior are possible if lower-order kinematics are taken into account.

Detection of Nonlinearities in Plates Via Higher-Order-Spectra: Numerical and Experimental Studies

Higher-order spectral (HOS) analysis tools are employed to extract the nonlinear dynamic response features of elastic and laminated plates by using both physics-based mechanical plate models and experimental data. Bispectral and trispectral densities are computed to highlight the presence and relative importance of quadratic and cubic nonlinearities. The former are associated with the presence of asymmetry either in the excitation or in the mechanical response of predeflected plates while the latter are due to midplane stretching effects. Besides the detection of these structural nonlinearities in perfect (baseline) fully clamped plates, the changes of such nonlinearities induced by the presence of small inertial imperfections (i.e., lumped masses) are identified and exploited to localize the imperfections. The numerical and experimental investigations are carried out both on isotropic and laminated composite plates subject to Gaussian white noise excitation. The effectiveness of the HOS-based procedure for detection of the nonlinearities is fully demonstrated for both types of plates.

Nonlinear System Identification of Composite Plates with Higher-Order Spectra: Numerical Analyses and Experimental Tests

A nonlinear system identification procedure based on a Higher-Order-Spectral (HOS) approach is developed. The fundamental element of the presented technique resorts to the HOS capabilities of detecting the changes induced in the system nonlinear dynamic behavior by the presence of a localized structural modification. Numerical tools for the estimation of the Higher-Order Spectra extracted from the time histories of a fully nonlinear physics-based plate model are implemented. An extensive experimental testing campaign is conducted on carbon/epoxy thin composite plates, in order to validate the presented identification procedure.