Numerical study on effects of microstructure randomness on fatigue fracture of non-oriented electrical steel

Advances in battery technology and electrical drive systems has allowed for more versatility in mobile applications found in automotive, logistics and aerospace engineering. Rotor cores used for electrical motors are often made from thin sheet metals with a maximum thickness of 0.5 mm. During operation, this material is subjected to variable dynamic loading conditions. As a consequence, fatigue testing is required for a more complete material characterisation. However, experiments on thin metals are generally more challenging as they require finer testing equipment that can apply low loads with high precision. Therefore, a micro-fatigue machine can be implemented to identify the high cycle fatigue behaviour of thin electrical steel sheets. Further, the manufacturing process of electrical steels often results in non-oriented grain structures. In other words, the material properties can vary between adjacent grains at the surface, thereby influencing the fatigue crack initiation mechanism. To investigate this effect, a finite element analysis is performed that includes a randomly generated set of grains with different elastic material behaviour. Using a critical plane approach the impact on the fatigue life prediction is assessed.