Experimental and numerical study of damaged cantilever

The introduction of a crack in a steel structure will cause a local change in the stiffness and damping capacity. The change in stiffness will lead to a change of some of the natural frequencies of the structure and a discont inuity in the associated mode shapes. This paper contains a presentation of the results from experimental and numerical tests with hollow section cant ilevers containing fatigue cracks. Two different finite-element (FE) models have been used to estimate the modal parameters numerically. The first FE model consists of beam elements. The second FE model consists of traditiona l rectangular shell elements and one rectangular shell element with a trans verse, internal, open crack. The analytical results from the numerical mode ls are compared with data obtained from experimental tests. The numerical m odels give good agreements with the experimental data. The beam model takes into account only the first mode of the crack evaluation. In the shell mod el all three modes of the crack growth are taken into account. Nevertheless , the results obtained for both models are satisfactory because the beam is subjected to bending. It can be concluded that it is sufficient to use cra ck models for calculating natural frequencies in bending, taking into accou nt the first mode of the crack extension only.