Notch Effect Under Cyclic Loading of Electrical Steel Strips

Electrical steel strips are iron–silicon steels which find their use in rotors of electric motors and improve their efficiency. The rotors are based on lamellae, which are sharply notched components. In this work, stress- and strain-controlled tests are carried out on electric strip NO30-15 and the influence of micro- and macro-notches is investigated. Two different edge conditions (polished and laser cut) and three different specimen geometries are considered. The results are compared with classical models for the consideration of roughness and notch effects. The material exhibits a load-dependent surface influence. The influence of the surface condition on the fatigue strength can be described according to Hück's model. Notched specimens have a higher support effect in the limit lifetime regime than in the fatigue strength. The dynamic support effect is constant in the limit lifetime regime, which is attributed to the dominant influence of the micro-notch of the laser edge. Approaches to describe the dynamic support effect are only used in the fatigue strength but underestimate it strongly, which can be attributed to the coarse microstructure of the material. The application of the local concept using a damage parameter shows a good consideration of the effects of mean stresses. However, the damage caused by local stresses and strains induced by geometric notches is overestimated compared to the test results.