A real-space phase field model is employed to investigate the domain switching-induced shielding or anti-shielding of a magnetically impermeable crack in ferromagnetic materials with single and muki-domain states.Phase field simulations demonstrate that magnetization switching takes place from the crack tip due to the highly concentrated stress in a ferromagnetic thin plate with a stationary crack.Based on the stress and magnetic field obtained from phase field simulations,an I-integral method is established to calculate the crack-tip stress intensity factors (SIFs) in the ferromagnetic thin plate subjected to different values of mechanical load.The I-integral is not affected by the size of integral area and domain walls,which shows the applicability to the large-scale domain switching.The calculation results indicate that domain switching decreases the crack-tip stress intensity factors,resulting in domain-switching toughening in ferromagnetic materials.Furthermore,the domain switching in the multi-domain ferromagnetic plate induces a much larger decrease of stress intensity factor than in the single-domain one,which suggests that engineering magnetic domains leads to the design of tougher ferromagnetic materials.