| This current research program illustrates through analytical and experimental modelling, the effect that a simulated crack has on the modal characteristics of a simple structure. ie., a cantilever plate, with 5 levels of damage.;The assessment involved creating a finite element model of the structure using an integrated software package, SDRC-I-DEAS to estimate the changes in various modal parameters, caused by a notch type crack. Additionally, a series of tests were carried out using response measurement equipment to experimentally determine the effect of the imposed defect. This was accomplished via measurement of dynamic response, using both accelerometers and strain gauges, and subsequent test data analysis using I-DEAS.;Results obtained from both phases of analysis showed that the crack could be detected, primarily through observation of reduction in natural frequency for a number of modes. The analytical model, in particular, provided a useful technique of crack location via observed inconsistencies in the plots derived from differences in both displacement and rotation mode shapes for cracked plates, with respect to a reference plate. The experimentation performed verified the analytical results, and provided additional insight into changes in damping, residue, and amplitude of dynamic response for frequency values at, and offset from those associated with the natural modes. This latter phenomena proved to be very sensitive and correlated well with observed changes in frequency. The measurement of strain response also proved to be a good indicator of crack existence with major increases in response magnitude, far exceeding the coresponding acceleration response. (Abstract shortened by UMI.)... |
