This paper presents the durability analysis of a machine shaft subjected to bending with torsion, based upon the stress analysis at a notch which joins segments of different cross-sections (circular and square respectively) of the shaft. During the specific operating conditions of the equipment which’s part the shaft is, this notch has proven to be critical, causing premature failure. The durability analysis is carried out based on the real loading conditions, allowing the stress state evaluation at the base of the notch for different radii, using ABAQUS 6.9-3 finite element analysis program. The experimental studies carried out on the shaft’s material, 41Cr4 steel, resulted in the determination of material properties and of torsion fatigue curves in case of two different heat treatments. The cycles composing the equivalent stress spectrum are counted using the rainflow algorithm. The number of loading blocks to failure (number of load spectrum repetitions), considering the real operating conditions, is obtained using Miner’s rule, based on the rotating bending fatigue curve, corrected corresponding to the shaft’s specific characteristics. The proposed calculation method, based on the variation in time of the stress tensor during operating conditions, leads to the determination of the optimal notch radius for which the shaft’s durability falls between prescribed limits.
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