Improvement of damage-assessment results using high-spatial density measurements

Abstract

Model-based damage assessment is based on measuring the distance between experimental and analytical results. In practice, measurements yield only partial mode shapes with respect to the total degrees of freedom present in the corresponding finite element model. Thus, before any damage detection method is implemented, the experimental mode shape has to be expanded to the same dimension of the numerical mode shape. Mode shapes expansion is a key point in the damage localisation process, since actual defects of the structure may be hidden by expansion errors. This paper introduces a new general procedure to the expansion/damage assessment process using an optimised choice for: the size of the expansion basis, the number of experimental degrees of freedom and the sensor placement. We introduce a new indicator to evaluate the problems inherent to the expansion/damage detection process using the minimisation of error on constitutive equations (MECE) technique. It provides insight of the inherent limitations of MECE and helps the decision making process on how many degrees of freedom should be measured and how many mode shapes should be used in the expansion basis. The procedure is illustrated using a finite element model of a plate-like structure, where the damage state is simulated as a reduction of the local stiffness.