DAMAGE EVALUATION IN BEAM STRUCTURES USING VIBRATION DATA

Abstract

ABSTRACT

The dynamic response of a straight beam is used to identify the occurrence of damage. Apparently there is an advantage in using natural frequencies changes as an indicator for damage occurrence, but some trade-offs exist. The first part of the paper is showing these trade-offs by studying a model of an intact straight rectangular cross-section beam built in ANSYS, and identifying its modal parameters. Then a transverse crack is assumed to exist across the beam length and the modal analysis is repeated. Three scenarios of crack sizes are analyzed. These have showed a change in natural frequencies together with new mode shapes arising. Moreover, there is a relation between crack location and the dynamic modal response of the beam, mainly mode shapes. Although the analysis based only on natural frequencies is easier to conduct and the occurrence of crack is clearly observed, the trade-off is that the location of the crack is not identified. In the second part of the paper another more effective crack detection methodology is presented. It is based on calculating the strain energy of each of the finite elements used in the model. This methodology is based on collecting vibrational data of the healthy structure, i.e., before any cracks exist, then the same data are collected when cracks have supposedly occurred. The two sets of data are used to calculate ratios of modal strain energies before and after crack occurrence. These ratios are then used to locate the cracked element. The methodology is implemented in a Matlab code, where a 2-D beam finite element formulations, with two DOF per node, are used. Various degrees of damage scenarios are assumed to investigate the validity of the methodology, by observing the change in modal strain energy. The obtained results show the effectiveness of the proposed methodology in detecting crack occurrence, its location, as well as providing information on its relative severity.