Improved Force Identification Techniques using Curvature Sensors: application to Damage Detection

Abstract

This study deals with the localization of damage in a beam, using methods which are insensitive to environmental variability. For this purpose, it considers the problem of adapting force identification techniques to the requirements of damage localization. Damage, when considered as a set of forces, creates a singularity in the structure, which can appear as a discontinuity in the spatial derivative of its transverse displacements. Damage or force localization methods attempt to locate and quantify such discontinuities. However, the damage effects are very small, when compared to those arising from forces, and can disappear due to the influence of low-level measurement noise. These considerations have led us to improve the conventional force identification techniques, in order to reduce their sensitivity to noise. The RIFF method ("Résolution Inversée Fenêtrée Filtrée"), which uses finite difference methods to compute highly noise sensitive spatial derivatives, is used to localize the forces. One major improvement proposed here is the use of curvature sensors (in the form of PVDF films), instead of displacements sensors, thereby avoiding the determination of two spatial derivatives and significantly increasing the noise robustness. Moreover, the derivatives are computed using the finite element method, rather than finite differences, which also improves the localization accuracy. When using these new sensors and calculus, the force identification techniques need to be rewritten, to enable damage to be localized, and new phenomena are detected. The aim of this study is to understand how force identification techniques can be used to locate damage, and to determine the improvements that could be made, in particular when using piezoelectric sensors as curvature sensors. Various numerical simulations of academic case studies illustrate the limitations and advantages of this approach.