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Fragment and bullet impact pose a serious threat for many weapon systems because of their potential to induce violent reactions in the energetic materials (explosives and propellants) contained within them. In some scenarios detonations have been observed under conditions insufficient to cause SDT or DDT. These events have been labelled XDT (X for unknown, Detonation Transition). It has generally been assumed that XDT arises as the result of some combination of damage to the energetic material and re‐shock or re‐compression of this damaged material. In this paper we review the results of our previous experimental studies aimed at understanding the conditions under which XDT may occur as the result of fragment impact. In addition, we describe some new experiments with improved instrumentation to help elucidate the key processes. Based on the experimental evidence and some simple modelling we then propose a phenomenological model for the XDT process.

There is a clear difference in cook‐off vulnerability between highly‐loaded pressed compositions such as LX‐14 (pressed 95.5% HMX/4.5% binder), which yield violent responses, and cast compositions with low loadings, such as CPX 301 (85% RDX/15% HTPB), which yield relatively mild responses. These two classes of composition differ primarily in the quantity of binder, and in the manufacturing method used in production. An experimental study was conducted in an attempt to determine the filling proportion beyond which violent responses are observed. Here we describe a series of small‐scale cook‐off experiments which studied pressed compositions of 88%, 91%, 95% and 96% HMX, mixed with cured, cross‐linked HTPB. The experiments used a novel glass‐windowed test vehicle, instrumented internally with thermocouples. A trend of increasing event violence with increasing proportion of HMX was found, although in none of the experiments was mass reaction recorded. The results from these experiments are discussed.

In this paper we report new experimental results on the detonation characteristics of nitromethane containing high volume percentages of essentially inert additives. In particular, we have studied the detonation of packed beds of small spherical glass and aluminium particles saturated with pure nitromethane. These mixes are found to have reduced detonation velocities and critical diameters compared to the liquid explosive alone. We conclude with a general discussion of the propagation mechanism in such materials.

Initiation thresholds generated by oblique impacts of rods and spheres are examined, and their relationship to normal impacts of cones are explored. Experimental data from rod impacts show two distinct response regions for bare or lightly covered charges, the division between them depending on the point at which a steady-state oblique shock can no longer be sustained. This steady-state region is eliminated by thicker barriers, but the variation of threshold with impact angle is virtually the same as for the non-steady regime in bare HE. Both rod datasets show a dependency on impact angle rather than a function of its cosine. Cones follow the rod relationship, but spheres are unique amongst these projectile geometries in showing a dependency on the cosine of the angle.

Ultra high-speed digital photography has been used to record the onset and build-up of reaction in nitromethane charges that have been impacted by steel fragments. The nitromethane charges were housed in PMMA cylinders and back-lit using conventional flash bulbs. Flat plates of aluminum were glued to one end of the cylinder and PMMA plates to the other. The completed charge was positioned to allow normal impact of the projectiles through the aluminum barrier plate. The events were filmed using an Imacon 468, ultra high-speed digital image system, capable of framing at up to 100 million pictures per second. Using this system it was possible to record detailed photographic information concerning the onset and growth of reaction due to shock initiation of the nitromethane charges. The results obtained to date are consistent with the established concepts for initiation of homogeneous and heterogeneous materials.

In this paper we describe the development of a coupled molecular dynamics and quantum chemistry approach to the study of shock-induced chemical reactions. The method has been applied to study the interaction between small numbers of energetic molecules undergoing collisions at velocities typical of detonations. Preliminary results for nitromethane and nitric oxide are presented, and discussed in the context of mechanisms operating at, or just behind, detonation fronts. The paper concludes by describing our plans to extend the approach to consider larger systems.

This paper describes the methodology behind the development of a new explosive burn model based on Arrhenius kinetics for both homogeneous and heterogeneous explosives types. The model has been developed over the last four to five years and is incorporated into the DYNA2D hydrocode as a new equation of state. The basic homogeneous model has been extended to consider heterogeneous materials by specifying a size and number density of hotspots. The hotspots are gas filled bubbles which are assumed to collapse adiabatically. Using the model it has been possible to match threshold values for shock initiation of a secondary explosive subjected to fragment impact.

In this paper, we report results of projectile impact experiments into both pure, and amine-sensitised nitromethane. A variety of projectile geometries were used to impact charges covered by aluminium barriers of varying thickness. From these experiments, threshold conditions for detonation were determined. These results have been interpreted in terms of both a classical thermal explosion model, and by use of a 2D hydrocode incorporating an Arrhenius burn routine. The values of the Arrhenius parameters used to fit the results are discussed in the light of possible decomposition schemes for nitromethane.

In this paper we report the results of 3D molecular dynamics simulations of shock and thermally induced chemical reactions in a model energetic material. A heteronuclear diatomic lattice interacting via an Abell-Tersoff potential has been used as the model system. The energies and time-scales required to induce reaction by these stimuli are analysed, and the implications for reaction processes in detonation discussed.

In this paper we report the results of molecular dynamics simulations of shock initiation in an energetic material. An Abell‐Tersoff potential has been used to represent a lattice of diatomic molecules capable of undergoing an exothermic reaction. This model system has been employed to investigate the critical conditions for, initiation of a chemically sustained shock wave. The effect of shock pulses of differing amplitude and duration have been studied, and some variations in the potential parameters have been considered to examine the influence of potential barriers on the initiation thresholds. Finally the results of these simulations are compared with the classical picture of initiation in homogeneous explosives.