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4 Reactive Materials INTRODUCTION In this report, the term "reactive materials" (RMs) denotes a class of materials that generally combine two or more nonexplosive solids which, upon their ignition, react to release chemical energy in addition to the kinetic energy resulting when the high-speed projectile containing the reactive materials collides with the target.) When designed into munitions as part of the fragmentation component, reactive materials potentially have added benefit against soft targets, providing not only destruction similar to that achieved with inert fragments, but also energy release after penetration. The committee was briefed on aspects of this technology by investigators and program sponsors from ONR, the Naval Surface Warfare Center (NSWC)-Dahlgren, NSWC-IH, Eglin Air Force Base, ARDEC, Aerojet, and ATK Thiokol Propulsion. A reactive fragment initially delivers its energy to a very small area of a target, perforating or penetrating the intended target. However, the reactive fragment must hit a component of the target for the ignition of the reactive materials of the fragment and the initiation of subsequent reactions, either with itself or with parts of the target. Experimental firings against soft targets have shown enhanced blast damage, greatly increased observable external rupture damage, and potentially increased lethality when compared with conventional fragment performance. In most operational concepts presented to the committee, the performance of the RM fragment relies on initial penetration of the outer skin of the target, followed by impact of the RM fragment with interior solid components of the target to ignite the reactive material. There is also interest in and initial work underway to examine the application of reactive M.E. Grudza, D. Jann, C. Forsyth, W. Lacy, W. Hoye, and W.E. Schaeffer. 2001. Explosive Launch Studies for Reactive Material Fragments. Presented at the 4th Joint Classified Bombs/Warheads and Ballistics Symposium, Newport, R.l., June. 2 J.M. Goldwasser, ONR. 2001. Presentation to the committee. July 31. W. Hoye, NSWC-Dahigren. 2001. Presentation to the committee. October. 4 A.T. Nielsen. 2002. Presentation to the committee during its site visit to ATK Thiokol Propulsion. May. S. Struck. 2002. Presentation to the committee during its site visit to Eglin Air Force Base. May. - 5 20
REACTIVE MATERIALS 21 material warheads for hard target attack by replacing standard metal liners with reactive materials in shaped charges or explosively formed penetrators. However, this discussion focuses on the soft target application of reactive materials. Comparisons are made between reactive and inert fragments because of the near-term potential application of reactive fragments as direct replacements for inert fragments in existing fragmentation warheads. Th is com pa riven is shown i n Figu res 4-1 th rough 4 4.6 Figu re 4-1 i 11 ustrates the damage done by inert fragments to a guidance component of a missile. Figure 4-2 shows the greater damage caused when reactive fragments were employed against an identical guidance component. Similarly, Figure 4-3 exhibits the results of perforation damage from inert fragments on a missile body, and Figure 4-4 shows the effects of reactive fragments against the same target, illustrating the catastrophic destruction of the test object. FIGURE 4-1 Damage done by inert fragments to the guidance component of a missile. row ~ :~" ~ . I ~ \\_ 1 _ 1 FIGURE 4-2 Damage done by reactive fragments to a guidance component identical to that shown in Figure 4-1. FIGURE 4-3 Damage done to a missile body by a warhead's inert fragments. _ . ~ ~ ._ . it,, ~ ~ _ W. '~ ~:~ ~ _ . ~ . ~ -, y i,'' , < . ~ ., ,_ . . ~ ~ .,.+, . I; -` ~ , ~ · `~w^_L_ . ~ ~_.c_ ~~ . _ , . , ~ ~ . . . by, - . FIGURE 4-4 Damage done to the same target shown in Figure 4-3 by a warhead's reactive fragments. 6 Figures 4-1 through 4-4 come from W. Hoyels (ONR) August 25, 2001, presentation to the committee.
22 ADVANCED ENERGETIC MATERIALS Reactive materials can potentially damage targets by means of numerous mechanisms that may have cumulative effects: Perforation-increased internal temperature from the chemical reaction of the reactive material fragment, Explosion-induced shock/blast waves with enhanced impulse within the target, Overpressure, Carbon shorting of electronic components, and Reaction with and degradation of critical components. If the cumulative damage caused by the reactive fragments is great enough, the likelihood of immediately discernible kills is increased. Often, when a target is disabled by a conventional fragment, the exterior and structural damage may be limited, making it difficult to ascertain the result of an attack and prompting further attacks on what may be a neutralized target. A goal of reactive fragment development programs is to cause visually ascertainable damage resulting in improved damage assessment by standard means. Increased lethality is projected to arise from the use of reactive fragments because of a greater probability that sufficient damage will be done to a target with a smaller number of fragments and because there is a greater probability that a critical part of the target will be damaged by the secondary (chemical) reaction of the fragment within the target. The quantification of increased lethality is difficult owing to a number of uncertainties: Lack of confidence in the ignition of the reactive fragments; Questions regarding the energy transferred from a material of lower density than steel, Uncertainty about the overall probabilities of impacting the target, and Lack of knowledge about the physical integrity of the reactive fragments during launch. Energy release from reactive materials is potentially tunable, and other applications, such as reactive casings, shaped charge liners, and explosively formed penetrators, are envisioned. Moreover, a number of reactive systems are potentially useful. Those under consideration include thermites, intermetallics, metal-polymer mixtures, metastable intermolecular composites (MlCs), matrix materials, and hydrides. FINDINGS AND RECOMMENDATIONS Findings With regard to reactive materials, the committee found that . . · Reactive materials research and characterization are in an early state of exploration and development. Most experimental demonstrations of weapon effects from reactive materials have shown more extensive, externally visible target damage when compared with damage caused by inert fragments under similar conditions. Higher peak pressures and a detonation-like reaction were achieved in experiments with RM-4. The results in these cases were dramatic.7 I R.G. Ames, R.K. Garrett, and L. Brown. 2002. Detonation-like Energy Release from High-Speed Impacts of Polytetrafluoroethylene-Aluminum Projectiles. Presentation at 5th Joint Classified Bombs/ Warheads and Ballistics Symposium, Colorado Springs, June.
REACTIVE MATERIALS 23 Recommendations Research on reactive materials is very promising in terms of potential near-term payoff. The research may also have potentially longer-term, broader-based application. The committee recommends the following: Many trade-off studies should be conducted before reactive materials can move forward. The possibility of more advanced applications (such as liners and cases) should be explored. Appropriate analytical tools should be developed and used, along with critical experiments, to determine applicability. Other materials such as thermoplastics should be investigated in greater detail with lower processing temperatures to allow the use of other metals. Requirements regardingthe material properties of reactive materials should be correlated with results in realistic warhead tests including probability of kill. Greater emphasis should be given to materials engineering research and deployment methods to improve the lethality of reactive materials against both soft and hard targets.