There are commercial and military applications in which a material needs to serve as a barrier that must subsequently be removed. In many cases it is desirable that once the barrier has served its function that it then be reduced to small pieces. For example, in pipelines and in downhole drilling applications, valves are needed to function as barriers that can sustain high pressures. Later the valves must be removed and essentially disappear or be rendered to such a small size that they do not interfere with the functioning of other equipment. Military applications include covers on missile silos or launch vehicles. Other applications might require that a component be used once as an actuator or for passive energy storage, and then be irreversibly removed, again so as not to interfere with the function or motion of other parts of the device. Brittle materials, especially those that are very strong, or are pre-stressed, are ideal candidates for these applications. Stressed glass can be produced in different sizes and shapes and the level of strength and pre-stress, both of which control the fragmentation, can be manipulated by varying the processing. Stressed glass can be engineered to fracture predictably at a specific stress level. Controlling the central tension allows the fragment size to be specified. The energy that is stored in the residual stress profile that results from ion exchange or thermal tempering processes can be harnessed to drive fragmentation of the component once it has been deliberately fractured. Energy can also be stored in the glass by mechanical loading. Energy from both of these sources can be released either to perform useful work or to initiate another reaction. Once the stressed glass has been used as a barrier or actuator it can never be ''used'' again because it fragments into many small unrecognizable pieces during the actuation. Under some circumstances it will interfere with the motion or functioning of other parts of a device. Our approach was to use stressed glass to develop capabilities for making components that can be used as barriers, as actuating devices that passively store energy, or as a mechanical weaklink that is destroyed by some critical shock or crush load. The objective of this project was to develop one or more prototype devices using stressed glass technology and demonstrate their potential for applications of interest. This work is intended to provide critical information and technologies for Sandia's NP&A and MT&A customers, and is relevant to commercial applications for these same materials. Most of the studies in this project were conducted using the Corning 0317 sodium aluminosilicate glass composition.
The effects of diameter on detonation velocity of packed granular beds of HNS (2,2',4,4',6,6'-hexanitrostilbene) and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, HNIW) will be discussed. Due to the novel nature of the diagnostic technique utilized here, a thorough discussion of the experimental method is provided. The dimension at which finite diameter effects occur was characterized by conducting simultaneous streak camera and framing camera measurements on miniature rate sticks similar in concept to traditional rate sticks. A significant difference between historical rate sticks and those discussed here comes in the form of how they were produced. A femtosecond laser was used to generate precision miniature rate sticks down to diameters of 187 μm. Finally, we will discuss the somewhat unexpected result of nano particulate generation of energetic materials due to the laser machining process.
A new approach to explosive sample preparation is described in which microelectronics-related processing techniques are utilized. Fused silica and alumina substrates were prepared utilizing laser machining. Films of PETN were deposited into channels within the substrates by physical vapor deposition. Four distinct explosive behaviors were observed with high-speed framing photography by driving the films with a donor explosive. Initiation at hot spots was directly observed, followed by either energy dissipation leading to failure, or growth to a detonation. Unsteady behavior in velocity and structure was observed as reactive waves failed due to decreasing channel width. Mesoscale simulations were performed to assist in experiment development and understanding. We have demonstrated the ability to pattern these films of explosives and preliminary mesoscale simulations of arrays of voids showed effects dependent on void size and that detonation would not develop with voids below a certain size. Future work involves experimentation on deposited films with regular patterned porosity to elucidate mesoscale explosive behavior.
Explosive initiation and energy release have been studied in two sample geometries designed to minimize stochastic behavior in shock-loading experiments. These sample concepts include a design with explosive material occupying the hole locations of a close-packed bed of inert spheres and a design that utilizes infiltration of a liquid explosive into a well-defined inert matrix. Wave profiles transmitted by these samples in gas-gun impact experiments have been characterized by both velocity interferometry diagnostics and three-dimensional numerical simulations. Highly organized wave structures associated with the characteristic length scales of the deterministic samples have been observed. Initiation and reaction growth in an inert matrix filled with sensitized nitromethane (a homogeneous explosive material) result in wave profiles similar to those observed with heterogeneous explosives. Comparison of experimental and numerical results indicates that energetic material studies in deterministic sample geometries can provide an important new tool for validation of models of energy release in numerical simulations of explosive initiation and performance.
The HMX {beta}-{delta} solid-solid phase transition, which occurs as HMX is heated near 170 C, is linked to increased reactivity and sensitivity to initiation. Thermally damaged energetic materials (EMs) containing HMX therefore may present a safety concern. Information about the phase transition is vital to predictive safety models for HMX and HMX-containing EMs. We report work on monitoring the phase transition with real-time Raman spectroscopy aimed towards obtaining a better understanding of physical properties of HMX through the phase transition. HMX samples were confined in a cell of minimal free volume in a displacement-controlled or load-controlled arrangement. The cell was heated and then cooled at controlled rates while real-time Raman spectroscopic measurements were performed. Raman spectroscopy provides a clear distinction between the phases of HMX because the vibrational transitions of the molecule change with conformational changes associated with the phase transition. Temperature of phase transition versus load data are presented for both the heating and cooling cycles in the load-controlled apparatus, and general trends are discussed. A weak dependence of the temperature of phase transition on load was discovered during the heating cycle, with higher loads causing the phase transition to occur at a higher temperature. This was especially true in the temperature of completion of phase transition data as opposed to the temperature of onset of phase transition data. A stronger dependence on load was observed in the cooling cycle, with higher loads causing the reverse phase transitions to occur at a higher cooling temperature. Also, higher loads tended to cause the phase transition to occur over a longer period of time in the heating cycle and over a shorter period of time in the cooling cycle. All three of the pure HMX phases ({alpha}, {beta} and {delta}) were detected on cooling of the heated samples, either in pure form or as a mixture.