Analysis of Rotor Robustness of Ultra-high Speed Switched Reluctance Machines over 1 Million rpm Using Cohesive Zone Model

Ultra-high speed electric machines are gaining in popularity in more and more applications. Besides permanent magnet (PM) machines, switched reluctance machines (SRMs) are another good choice because of its intrinsic simple rotor geometry. A novel rotor design of an ultra-high speed SRM was proposed for special applications over 1 million rpm in [1]. However, due to the unique design element of using clamping arms rather than regular rotor sleeves for the purpose of reducing the equivalent air gap length, small gaps will appear between the rotor stack and the shaft because of the high centrifugal force, which may cause failures in ultra-high speed situations. In this paper, a model of fracture mechanics, namely the cohesive zone model (CZM), is introduced for use in analyzing the high speed mechanical robustness of the improved rotor design, where high strength adhesives are used to increase the bonding as well as to reduce the high localized stress. Then, a detailed finite element model is built in ANSYS to simulate the debonding process of the clamping arms on the shaft. A parametric study is conducted to analyze the shaft mechanical robustness for different rotor length under different adhesive strength. The results show that the maximum output torque can be increased by 15% and the highest strength on the shaft is reduced by 60% with the improved design. The model introduced in this paper will also provide a good reference for estimating the mechanical stress of high speed electric machines when adhesives are applied.