Modelling shock initiation of HMX-based explosive

Wedge tests can provide data on the run distance of an impacted heterogeneous explosive but give no information on how the reaction is distributed behind the shock front. Data has recently become available from gas gun tests on EDC37 in which the reaction is monitored by embedded velocity gauges. The results show the relative contributions of fast reaction that takes place at the shock front and the much slower reaction that takes place typically a few millimeters behind the shock front. The slow reaction component is believed to be particularly important in the field of impact safety analysis. The embedded gauge experiments have been calculated using an ignition and growth model that has recently been incorporated into the AWE hydrocodes, Reaction rate parameters have been adjusted to provide a match to the gas gun results including shock behaviour in the unreacted explosive, the run distance plot and the velocity profiles. In future the model will be used to design more complex experiments and eventually to model accident scenarios.