DAMAGE EVALUATION IN BEAM STRUCTURES USING VIBRATION DATA

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