Simulation and low velocity impact testing on confined explosives

TNO Defence Security and Safety, performs in depth research in energetic material responses to several Insensitive Munitions (IM) stimuli like cook-off, bullet-fragment impact and shaped charge impact. The response of energetic materials to these stimuli depends strongly on the properties of these materials at onset and during an event. This is also true for the so-called low velocity impact, like impact on a spigot or the impact of debris on a munition item. Several years ago the low velocity impact research at TNO started with the development and research with the Ballistic Impact Chamber (BIC) and evaluating the corresponding theories. The Go-NoGo shear rate limit of PBXN-109 was compared with computational (Autodyn) values of several low (range from 50-200 m/s) velocity impact tests such as the UN friability test, Steven impact test, and explosive forming experiments performed at TNO. The results showed that the shear rate is one of the major parameters that determine whether or not an explosive substance is likely to react on impact, especially for the low velocity range. A few years ago TNO has built an impact test based on the well known Steven impact test capable of firing a 48 mm steel projectile with sabot in a 60 mm short barrelled gun. Instead of a flat piece, a confined cylindrically shaped piece of explosive is used making it a munition-like test. Several types of explosives and projectile forms have been tested. PBXes and more conventional explosives like a RDX/wax/graphite and pressed composition B, have been tested. Also a computer model of the impact test has been developed using the hydrocode Autodyn. Besides the shear and shear rate, the amount of “Effective Plastic Strain” and from there on the temperature increase, were calculated. The experimental set-up, the experimental as well as the simulation results and a comparison of those two are presented.