Critical Plane Fatigue Damage Analysis of a High Speed Microgenerator Shaft

Fatigue life estimation is one of the most important design considerations in mechanical parts which are subjected to alternating loads. When loads act along several axes, multiaxial fatigue approach should be used to obtain more accurate results than uniaxial fatigue method. In this paper stress analysis of the steel shaft of a high speed microgenerator rotor with 47750 rpm and 100kW is carried out using analytical stress formulation. Mean and alternative components of stresses have been distinguished. Because alternating stresses act on shaft, fatigue may occur and regarding to existence of alternating torsional and bending stresses in the same time, multiaxial fatigue analysis is essential. Also the range of alternating stresses is small compared to fatigue endurance limit. So the multiaxial fatigue criteria based on stress have been chosen. Then multiaxial fatigue damage and critical plane orientations of Findley and McDiarmid criteria have been identified using an analytical formulation in a MATLAB code. Finally, fatigue life of each critical point of shaft has been calculated using maximum damage in respective critical plane. In this way, effect of frequency difference between torsional and bending stresses has been considered.