The Influence of Eccentricity on the Crack Breathing in a Rotating Shaft

Abstract

Machine failures very often occure as a result of the presence and propagation of fatigue cracks caused by the loads and actions that they are subjected to. Those failures sometimes are catastrophic and produce personal injuries or economic problems. The shafts, that perform in bending and torsion, present additional disalignments and, or the unbalances that alter the normal function of the components. When a cracked shaft rotates, the crack opens and closes in what is called the breathing mechanism in which the crack passes from an open state to a close state with a transition between both situations producing a partial opening or closing of the crack. In this paper we present a finite element study of the influence of the eccentricity in a rotating cracked shaft. The model chosen for this study is the classical Jeffcott rotor. To simulate the rotation of the shaft, different angular positions have been considered. The influence of the mass eccentricity in the opening of the crack has been studied considering different angles of ecentricity measured from the position of the crack. In this paper we present the comparison of the partially opening or closing of the crack considering different angles of rotation and different positions of the eccentricity. The work shows the influence of the unbalance of rotating shafts in the crack breathing mechanism and will enable the prediction of the influence of this behaviour on the values of the stress intensity factor and in the propagation of cracks.