Under the action of alternating load, even if the stress amplitude is far less than the yield strength of the material, serious stress concentration will occur at the casting defect. The direct result of the stress concentration is that the material at the casting defects appears a slip band, which then forms a micro notch.

The formation of micro notches further increases the stress concentration caused by casting defects. To a certain extent, micro notches directly develop into notches with crack initiation, causing local plastic deformation of materials at a small stress level, forming crack sources, and then further expanding under cyclic load.

The stress concentration caused by casting defects has been studied. Gao YX et al. Carried out a finite element analysis of the stress concentration around the two-dimensional hole of cast aluminum alloy A356-T6. It is generally believed that the degree of stress concentration around casting defects is closely related to the shape and location of casting defects.