An in-depth understanding of dynamic ductile fracture is one of the most important steps to improve the survivability of critical structures such as the lost Twin Towers. In the present thesis, the macroscopic fracture modes and the fracture mechanisms of ductile structural components under high velocity impact are investigated numerically and theoretically. Attention is focused on the formation and propagation of through-thickness cracks, which is difficult to experimentally track down using currently available instruments. Studied are three typical and challenging types of impact problems: (i) rigid mass-to beam impact, (ii) the Taylor test, and (iii) dynamic compression tests on an axisymmetric hat specimen. Using an existing finite element code (ABAQUS/Explicit) implemented with the newly developed Bao-Wierzbicki's (BW) fracture criterion, a number of distinct failure modes including fragmentation, shear plugging, tensile tearing in rigid mass-to-beam impact, confined fracture, petalling, and shear cracking in the Taylor test, are successfully recreated for the first time in the open literature. All of the present predictions are in qualitative agreement with experimental observations.