Fatigue Behaviour of Thin Electrical Steel Sheets at Room Temperature

Electrical steel, also known as silicon steel, is a ferromagnetic material that is often used in electric vehicles (EVs) for stator and rotor applications. Since the design and manufacturing of rotors require the use of laminated thin electrical steel sheets, the fatigue characterization of these single sheets is of interest. In this study, a 0.27mm thick non-oriented electrical steel sheet was tested under cyclic loading in the load-controlled mode with the load ratio R = 0.1 at room temperature. The specimens were prepared using the Computer Numerical Control (CNC) machining method. The Smith-Watson-Topper mean stress correction was used to find the equivalent fully reversed stress-life (S-N) curve. The Basquin equation was used to describe the fatigue strength of the electrical steel and the fatigue parameters were extracted. Furthermore, a design curve with a reliability of 90% and a confidence level of 90% was generated using Owen’s Tolerance Limit method. The fracture mechanisms under cyclic loading were also studied using a scanning electron microscope. Crack initiation was determined to initiate from one edge and propagate to the other. Although the fracture mechanism was transgranular, the fracture surface displayed distinct regions of fatigue damage and cleavage fracture. The presence of aluminium nitrate precipitate particles contributing to crack initiation was confirmed using the energy dispersive x-ray spectroscopy technique.