Abstract: Three failure modes of penetration mechanisms, i.e., Taylor impact, petal-cap failure of Sunflower alike and plugging perforation, of Fragment Simulation Projectiles (FSP), were observed in the experiments of A3 steel blunt projectiles impacting 45 steel plates. Numerical simulations with LS-DYNA was conducted to analyze the various penetration mechanisms and the complicated material failures of projectile and target. Johnson-Cook models of strength and damage-cumulating failure were employed to describe the material behaviors of projectile and target, and adiabatic temperature-rise of local plastic deformation was included in the model. Different failure modes of projectiles and targets reappear in the numerical simulations in the different ranges of impact velocity, which agree well with the experimental observations. It further indicates that the failure mode of plugging perforation is the subsequent result of continuous perforation of projectile after petal-cap failure of Sunflower alike under higher velocity impact.