Abstract: A new engineering model is developed for analysis of ballistic impact of moderately thick metallic plates struck by non-deformable projectiles with conical and ogival noses. The model considers two interconnected perforation stages. In the initial stage, it is characterized by ductile hole enlargement and radial plastic flow of the plate materials. The second stage is characterized by bulging and petalling occuring on the rear face of plates. Formulas for energy dissipated in the plate during ductile hole enlargement are derived from cylindrical cavity expansion theory. Wierzbicki formula for petalling of thin plates is used to evaluate the energy dissipated by bulging and petalling in the second stage. The penetration depth X₁ at the end of the first stage is determined by minimizing the total energy dissipated in the plate during the two stages. Analytical formulas for critical impact energy and ballistic limits are obtained. Comparison is made with previously published ballistic test data and the results of cylindrical cavity expansion approximation and single-stage ductile hole enlargement models.