Papers by Author: Marco Gherlone

Abstract: Damage detection is a wide field of research and different approaches can be used to monitor structure integrity. Continuous monitoring of critical components is of vital importance to guarantee the safety of a structure. Variations in the dynamic response, in particular the curvature of mode shapes, are considered good indicators of the presence of possible defects. However noise, which often affects data, can lead to an erroneous calculation of the curvature, preventing the location of possible damage. The aim of this paper is to investigate the capability of the proper orthogonal decomposition (POD) to overcome noise, computing the curvature of proper orthogonal modes with a modified Laplacian operator. A numerical investigation on a cracked beam is compared to an analytical case present in literature. An extension of the mono-dimensional modified Laplacian scheme is introduced to study also plate-like structures. An experimental application on a vibrating composite plate will be presented in order to validate the numerical model.

Abstract: The present paper describes an experimental validation of a new structural damage detection method based on the Polynomial Annihilation Edge Detection (PAED) technique. It is well known that concentrated damage such as a crack, causes a discontinuity in the rotations and consequently in the first derivatives of the mode shapes. On this basis, the PAED, a numerical method for detecting discontinuities in smooth piecewise functions and their derivatives, can be applied to the problem of damage detection and localisation in beam-like structures for which only post-damage mode shapes are available. As described in this paper, in order to verify this approach experimentally (a numerical assessment having already been documented in previous papers), vibration tests on a cantilever steel beam with a saw-cut have been performed and the Operational Deflection Shapes (ODS) determined. As the approach requires a reasonably high spatial resolution of the ODS, a scanning laser vibrometer, capable of acquiring data rapidly at a very large number of observation points, was used.

Abstract: The aim of the work is to develop a procedure allowing the test engineer to determine the probability of finding a crack in a beam structure. The procedure is based on the use of wavelet analysis and the simulation is performed by taking advantage of spectral elements to represent accurately the dynamic behaviour of beam structures in the high frequency range. In this context, numerical analyses are performed with the final scope of simulating a real testing environment: measurement error is considered and spectral elements are used so as to avoid influencing the capacity of the procedure with regard to solving the inverse problem. In this article the relation between the excitation frequency and the probability of locating the fault is shown. In particular, it is demonstrated by simulation that the probability of correctly determining the fault location increases with the excitation frequency.

Abstract: The article deals with the application of a higher-order FEM approach to the analysis of the dynamic behaviour of undamaged and damaged multilayered composite plates. Some numerical examples show the accuracy of the developed plate mixed finite element, in terms of vibration frequencies and mode shapes, for different boundary conditions and with different damage geometries.

Abstract: The paper describes an on-going research effort aimed at detecting the presence of delamination damage in composite panels based upon their higher-frequency structural response. Two alternative damage indexes are examined that facilitate the identification of the location and extent of delaminations. The damage indexes do not require vibration measurements to be performed on the undamaged structure. Use is made of the bending and twisting curvatures corresponding to the higher-frequency mode shapes that are post-processed via two different smoothing techniques. The modal data are obtained via finite element models based on Mindlin theory and including delaminations. These are introduced using a sub-laminate strategy that permits multiple damages to be modelled through the thickness. Various delamination sizes and locations are examined with a random noise superposed on the data in order to ascertain the degree of sensitivity of the damage index to the noise in the experimental data.