Stamping processes induce plastic strain and changes in the thickness, shape and mechanical behaviour of sheet metal parts. Simulated crash tests on vehicles should theoretically take these changes into account in order to be as realistic as possible, but this is not actually feasible because the calculations required would be too time-consuming. Crash-modelling calculations, therefore, have to be based on simplifying hypotheses about the geometry and the mechanical behaviour of body parts. This study deals with the influences of such hypothesis on the impact behaviour of a 1-mm-thick steel dome bulged plastically at different thick strain levels ranging from −37% to −6% and impacted by an instrumented projectile with 13 m/s initial speed. Experimental results are compared to several impact finite element simulations based on different simplifying hypotheses about the geometry of the bulge and the strain hardening of the sheet metal and performed with the LS-DYNA finite element code.