The perforation process of steel plates at normal impact by cylindrical steel fragments together with the debris cloud expansion have been studied in the velocity range 2 -3 km/s. The fragments have a length-to-diameter ratio of 1.035 and a mass of 51g. Fragment and target materials are 9SMn28 and C45, respectively. Two plate thicknesses of 20 and 30 mm have been tested. These thicknesses are in the order of the penetration depth in the semi-infinite target. In addition the cratering in the semi-infinite target has been investigated. The crater dimensions on the target front side are comparable for both, the plate targets and the semi-infinite targets. The degree of fragmentation in the debris cloud increases with velocity and is smaller in case of the 30 mm target. The ratio of longitudinal to lateral dimensions of the debris clouds is independent of the target thickness, but dependent on the distance from the plate rear side. This ratio increases with distance and converges at larger distances versus nearly hemispherical expansion. A further goal of this paper is the application of a Lagrangian code to the numerical simulation of the impact process in the semi-infinite target. For this purpose the LS-DYNA2D code with a new erosion option has been used. Material input data are the static material properties as well as shock wave data determined from planar impact tests for the steels used here. LS-DYNA2D with its new erosion option can predict in a good agreement the particle velocity history of the planar impact tests and the crater shapes in the semi-infinite target.