Crack Depth Analysis of a Rotating Shaft by Vibration Measurement

Abstract

The increasing development of measurement techniques for monitoring rotor plants requires improved possibilities for the interpretation of vibration response. Therefore, computer programs that have been used will have to be constantly updated. This especially concerns the modelling of a rotor for calculation purposes. This paper deals with a propagating crack that causes the slender uniform round shaft to vibrate about its main axis. Experiments using a stationary shaft are also performed. Beach marks are used to measure the crack depth and the actual shape of the cracked cross section. These results are compared with those obtained using the dc-potential method, applied to the same cracked cross-section. A finite element model for the cracked region of the rotor is then deduced from the experimental results. Three-dimensional 20-node elements are applied, so a single edge crack of the rotor can be described and varying forms of the cross section—as shown by the beach marks—can be modelled. The additional installation of nonlinear truss elements to the finite element structure permits the breathing of the cracked rotor to be calculated.