Fatigue Behavior of Stamped Electrical Steel Sheet at Room and Elevated Temperatures

Abstract

<div class="section abstract"><div class="htmlview paragraph">Electrical steels are silicon alloyed steels that possess great magnetic properties, making them the ideal material choice for the stator and rotor cores of electric motors. They are typically comprised of laminated stacks of thin electrical steel sheets. An electric motor can reach high temperatures under a heavy load, and it is important to understand the combined effect of temperature and load on the electrical steel’s performance to ensure the long life and safety of electric vehicles.</div><div class="htmlview paragraph">This study investigated the fatigue strength and failure behavior of a 0.27mm thick electrical steel sheet, where the samples were prepared by a stamping process. Stress-control fatigue tests were performed at both room temperature and 150°C. The S-N curve indicated a decrease in the fatigue strength of the samples at the elevated temperature compared to the room temperature by 15-25 MPa in the LCF and HCF regimes, respectively. Looking at the fracture surface, the room temperature samples at both the low- and high-cycle regimes showed some intergranular cleavage facets along with predominant transgranular facets in the crack initiation zone and transitioned to only transgranular cleavage facets in the crack propagation zone. In contrast, the high-temperature samples showed a smaller fatigue damage zone, and outside of this zone, the main failure mechanism was severe necking for both the low- and high-cycle samples. An important finding here was that the crack always initiated from the breakaway zone on the stamped edge of the samples. The higher temperature adversely affected the fatigue strength, as the higher temperature releases residual stresses and annihilates dislocation density induced during the sheet manufacturing and sample preparation, resulting in shorter fatigue life.</div></div>