This presentation summarises the results of a study on the effects of a transversal open crack on the normal bending modes of vibration of a solid beam. The study considers the cases of a beam in flexural vibration on simple supports, but the study can be generalised to more general boundary conditions, and to case of the beam in longitudinal vibration. The theoretical part of this study focuses on the effects of the crack depth on the resonance frequencies of the beam where the region near the crack with a lower stiffness is modelled as spring (longitudinal or torsional in the respective cases of axial or bending vibrations). The problem is solved relatively easily through considering the coupling of the two beam parts separated by the crack, and suitably modelling the crack as a spring. The numerical results show a tendency of the eigenresonances to diminish in value with crack severity, for both cases of axial and flexural vibrations. A simple experimental set-up is then mounted with a wooden bar as a test specimen, and the experimental results support the theoretical prediction to a crack depth of about half the transversal dimension of the beam. For deeper cracks coupling problems between the beam components appear making it thus difficult to determine properly the resonance frequencies of the flawed beam. A non theoretically supported study of the damping properties of the beam reveal also an alteration, namely an increase, of the loss factor of the beam as a function of the crack depth.
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