Double casing warhead with sandwiched charge to produce multiple fragment groups for sequential hits: Concept and analysis of fragment velocity

•A novel fragment warhead with double casings sandwiched charge is proposed.•The different fragment velocities of each casing were measured by flash-radiography.•A formula was established to predict the fragment velocities of each casing.•The formula shows good agreement with the experimental and numerical results.•The fragment velocities of casing are affected by the size of the charge and casing.