Abstract
Most catastrophic mechanical failures in propeller shafts occur by the surface cracks. These, are due to fatigue under cyclic bending combined with steady torsion: Mode I combined with steady Mode III. An analysis of the influence of steady torsion loading on a fatigue crack in shafts is presented for semi-elliptical surface cracks; this by way of the VNA Solution-Finite Element Alternating Method (VNA-FEAM) . Long cracks growth analysis has been done on cylindrical models in steel. Cyclic bending combined with steady torsion in order to simulate real conditions on power rotor shafts. The growth and shape of the evolution of semi-elliptical surface cracks, starting from the surface of a cylindrical model, has been analyzed under several loading conditions. The results show a significant reduction of the crack growth rate when a steady torsion Mode III is superimposed to cyclic Mode I. In this paper, the VNA-FEAM analysis also indicates that Stress Intensity Factor (SIF) values at the corner of the crack's surface, of the shaft model, are closely related with the steady torsion value and depend on the direction of the applied torque.
