Life-Time-Assessment for Rotors for Electric Drives

The rotors of electric motors for vehicle drives are subject to time-varying loads in customer use due to mechanical, magnetic, electrical and thermal forces. To ensure the operational safety of the electric motor throughout the design life, a computational or experimental life-time assessment has to be performed. For this purpose, both the loading of the rotor as well as the resistance of the electric strip must be known. In this paper the loading situation of the rotor blades under service conditions is estimated with a simplified model which takes mechanical and magnetic forces into account. For the theoretical life-time-assessment the relevant material parameter under fatigue loading of the thin electrical steel must be known. While there are established and proven procedures both for proof of fatigue strength and for determining the required characteristic values for steel sheets for use in the bodywork and chassis area, there is still no corresponding procedure for the very thin electrical steel bands. The paper shows possibilities for the experimental determination of the fatigue strength characteristics. In addition, influencing factors on the fatigue behavior of electrical steel are shown.