Fragmentation warheads are used in various circumstances to maintain a high probability of defeat against soft-targets. There are generally three different methods to design the fragmenting casing in order to obtain desired properties of the warhead; these are called natural fragmentation, pre-fragmentation and controlled fragmentation. In this work controlled fragmentation is studied by the use of numerical simulations based on the finite element method. The model is composed of an explosive with cylindrical geometry and an internally grooved casing, with V-shaped grooves. Various computational methods are applied and various cases are explored, a computational routine is presented to obtain controlled fragmentation and the results from a single case are analyzed in depth with the emphasis on states of stress and damage. In order to perform quantitative conclusions more work is required, both with numerical models and experiments.