The effects of the failure diameter of an explosive on its response to shaped charge jet attack

In order to shed some light on the response of explosives to the attack of small-diameter projectiles such as shaped charge jets, we conducted a computational study using the 2DE code and the Forest Fire explosive initiation model. Simulations of copper-jet attack against Composition B were made in order to determine modes of initiation and critical velocity for initiation as a function of jet diameter. We modeled the jet as a nonstretching cylindrical projectile with a flat tip. Its diameter was varied between 0.3 mm and 12.0 mm and its velocity was varied between 0.8 km/s. and 15.0 km/s. We observed two modes of initiation: (1) prompt, impact-mode initiation for both subsonic and supersonic penetration and (2) delayed, penetration-mode initiation only for supersonic penetration by small-diameter jets. The velocity threshold for large subsonic jets agrees with the Jacob-Roslund formula. For jets with diameters smaller than the failure diameter of the explosive they attack, higher velocities than predicted by Jacobs-Roslund are required for initiation. A critical threshold between impact- and penetration-mode initiation was determined over the entire supersonic range. A similar threshold between penetration-mode initiation and initiation failure has not yet been determined due to limitations of the code.