Impact and Shear Ignition By Nonshock Mechanisms

Kennedy, James E.

doi:10.1007/978-3-540-87953-4_10

Cited by 6 publications

(3 citation statements)

References 14 publications

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“…In all cases, visible sites were observed along the outer edge of the material where the explosive powder was at its thinnest (vanishing thickness). Studies conducted by Kennedy 36 showed that when crushing an explosive the highest radial velocities occur at the outer edge of the material and suggested that high internal velocity gradients drove the visco-plastic heating that led to ignition.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Despite multiple tests and investigations, the mesoscale processes that allow an ignition to propagate into a violent outcome are still not fully understood. While it has generally been agreed since the 1940’s that ignition under drop hammer conditions requires the formation of localized ignition sites, − followed by visco-plastic shear heating, − there is lack of consensus concerning the adiabatic heating of gas bubbles entrained in the explosive, the role of melting during the event, the effect of the material particle size, , and the presence or absence of grit during testing. − Furthermore, when dealing with less sensitive materials, e.g., 2,4,6-trinitrotoluene (TNT), the determination of a “go” can be more difficult because substantial material remains after the test despite an audible “go” . As a result, the test is recommended for ranking explosives within one laboratory and is not generally utilized for the in-depth analysis of the ignition and propagation behavior of explosives.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Ignition Sites for the Explosives 3,3′-Diamino-4,4′-azoxyfurazan (DAAF) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazoctane (HMX) Using Crush Gun Impact Testing

et al. 2021

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The handling safety characteristics of energetic materials must be measured in order to ensure the safe transport and use of explosives. Drop-weight impact sensitivity measurements are one of the first standardized tests performed for energetics. They utilize a small amount of the explosive sample and a standard weight, which is dropped on the material from various heights to determine its sensitivity. While multiple laboratories have used the impact sensitivity test as an initial screening tool for explosive sensitivity for the past 60 years, variability exists due to the use of different instruments, different methods to determine the initiation, and the scatter commonly associated with less-sensitive explosives. For example, standard explosives such as 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX) initiate reliably and consistently on the drop-weight impact test, whereas insensitive explosives such as 3,3′-diamino-4,4′-azoxyfurazan (DAAF) exhibit variability in sound levels and the expended material. Herein we investigate the impact sensitivity of DAAF and HMX along with a more detailed investigation of ignition sites using a novel “crush gun” apparatus: a pneumatically powered drop-weight tower with advanced diagnostics, including high-speed visual and infrared cameras. Using this crush gun assembly, the ignition sites in HMX and DAAF were analyzed with respect to the effects of particle size and the presence of a source of grit. The formation of ignition sites was observed in both explosives; however, only HMX showed ignition sites that propagated to a deflagration at lower firing speeds. Finally, the presence of grit particles was shown to increase the occurrence of ignition sites in DAAF at lower firing speeds, though propagation to a full reaction was not observed on the time scale of the test. These results enable a better understanding of how ignition and propagation occurs during the impact testing of DAAF.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Analysis of Ignition Sites for the Explosives 3,3′-Diamino-4,4′-azoxyfurazan (DAAF) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazoctane (HMX) Using Crush Gun Impact Testing

et al. 2021

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“…The reduction has been attributed to thermal softening of the PTFE matrix that has presumably resulted in the generation of large number of critical ignition hotspots [ 25 ]. Mechanistically, the critical ignition hotspots are generated because of the formation of discrete adiabatic shear bands by virtue of the thermal softening of the PTFE [ 26 ].…”

Section: Reactive Structures Based On Fluoropolymer-based Bindersmentioning

confidence: 99%

Nanoenergetic Composites with Fluoropolymers: Transition from Powders to Structures

2022

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Over the years, nanoenergetic materials have attracted enormous research interest due to their overall better combustion characteristics compared to their micron-sized counterparts. Aluminum, boron, and their respective alloys are the most extensively studied nanoenergetic materials. The majority of the research work related to this topic is confined to the respective powders. However, for practical applications, the powders need to be consolidated into reactive structures. Processing the nanoenergetic materials with polymeric binders to prepare structured composites is a possible route for the conversion of powders to structures. Most of the binders, including the energetic ones, when mixed with nanoenergetic materials even in small quantities, adversely affects the ignitability and combustion performance of the corresponding composites. The passivating effect induced by the polymeric binder is considered unfavorable for ignitability. Fluoropolymers, with their ability to induce pre-ignition reactions with the nascent oxide shell around aluminum and boron, are recognized to sustain the ignitability of the composites. Initial research efforts have been focused on surface functionalizing approaches using fluoropolymers to activate them further for energy release, and to improve the safety and storage properties. With the combined advent of more advanced chemistry and manufacturing techniques, fluoropolymers are recently being investigated as binders to process nanoenergetic materials to reactive structures. This review focuses on the major research developments in this area that have significantly assisted in the transitioning of nanoenergetic powders to structures using fluoropolymers as binders.

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Viscous shear flow and heating of impact-extruded composite energetic materials

Yang

Dong

2023

International Journal of Mechanical Sciences

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Impact and Shear Ignition By Nonshock Mechanisms

Cited by 6 publications

References 14 publications

Analysis of Ignition Sites for the Explosives 3,3′-Diamino-4,4′-azoxyfurazan (DAAF) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazoctane (HMX) Using Crush Gun Impact Testing

Analysis of Ignition Sites for the Explosives 3,3′-Diamino-4,4′-azoxyfurazan (DAAF) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazoctane (HMX) Using Crush Gun Impact Testing

Nanoenergetic Composites with Fluoropolymers: Transition from Powders to Structures

Viscous shear flow and heating of impact-extruded composite energetic materials

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