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Frequency reduction in elastic beams due to a stable crack: numerical results compared with measured test data

Andreaus U., Casini P., Vestroni F.

Engineering Transactions

2003

Vol. 51, iss.1

81-101

The presence of a crack could not only cause a local variation in the stiffness, but it could affect the mechanical behaviour of the entire structure to a considerable extent. The frequencies of natural vibrations, amplitudes of forced vibrations and areas of dynamic stability change due to the existence of such cracks. The vibration characteristics of cracked structures can be useful for non-destructive testing. In particular, the natural frequencies and mode shapes of cracked beams can provide insight into the extent of damage. The beam has been schematized as a 2-D continuous medium and discretized by means of quadrilateral finite elements. The lowest three natural frequencies (and the associated mode shapes) of the cracked cantilever beam, were obtained via both the modal and spectral analyses, and were compared with experimental data from literature in order to assess the reliability of different models of crack state, namely open crack and contact crack. Both the experimental and numerical results reveal the significant influence of the opening and closing conditions of the crack on the frequency reduction; namely this reduction decreases as more realistic contact phenomena are considered at crack interfaces.

A class of electro-mechanical systems: linear and nonlinear dynamics

Dell'Isola F., Vestroni F., Vidoli S.

Journal of Theoretical and Applied Mechanics

2002

Vol. 40 nr 1

47-71

The linear and nonlinear problems of dynamics of some electro-mechanical systems, characterized by a gyroscopic internal coupling, are analyzed. Since the technical importance of this system lies in the possibility of damping and controlling structural vibrations, the interest is focused on the energy exchanges between the mechanical and electric components. In order to maximize these energy transformations, the optimal values of the system parameters and their modifications in the nonlinear case are investigated.

Klasa układów elektromechanicznych: dynamika liniowa i nieliniowa. W pracy przedstawiono analizę liniowego i nieliniowego zagadnienia dynamiki układów elektromechanicznych, charakteryzujących się wewnętrznym sprzężeniem żyroskopowym. Ze względu na techniczną wartość problemu tłumienia i sterowania drganiami, główny nacisk położono na procesy wymiany energii między podzespołami mechanicznymi i elektrycznymi. W celu zmaksymalizowania przepływu i transformacji energii określono optymalne parametry układu i ich modyfikacje w przypadkku nieliniowym.