- December 2021
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International Standard Serial Number (ISSN)
Rotating beams are simplifications of more complex mechanical components, which are characteristics of strategic areas, such as energy and transportation industries. Wind turbine blades, helicopter blades, open rotors, are examples of this kind of mechanical elements that can be modelled as rotating beams. Due to manufacturing defects or to the work conditions together with the agressive enviroments in which they operate, cracks can
appear and propagate affecting seriously their structural integrity. Different methods have been used to determine the presence of cracks in beams in general, and in rotating beam in particular. The most common are those regarding the characteristics of the dynamic behaviour: the natural frequencies. In this work, a methodology to accurately calculating the flapwise bending vibration natural frequencies of a rotating cracked beam is presented.
First of all, a 3D dynamic numerical model has been developed and the accelerations resulting from it have been used to approach a frequency domain analysis. The model takes into account the breathing crack behaviour and the contacts that are produced between the crack faces. The validation of the model has been made comparing the dynamic results with that obtained from the literature. On the other hand, It is relevant that the presence of a crack reduces the stiffness of the beam (with the consequent reduction of the natural frequency) while centrifugal forces tend to increase the stiffness (increasing the natural frequencies). This study has also been carried out in this work. An analysis of the natural frequencies vibration, for a wide velocity range, has been carried out, in order to separate the influence of the rotation and crack presence. The validated 3D FEM model together with the frequency spectrum analysis, will help, in the near future, to establish virtual experimental tests of large energy and transportation equipments and to obtain virtual results to feed procedures to detect and identify defects in these strategic devices.
- crack; breathing crack mechanism; cracked rotating beam; natural frequencies