Shear band formation in plastic bonded explosive (PBX)

Dey, Thomas N.; Johnson, J. N.

doi:10.1063/1.55648

Cited by 6 publications

(4 citation statements)

References 4 publications

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“…Samples taken to large strains showed evidence of strain localization in the form of shear band formation. This observation is important for understanding not only the mechanical behaviour but also the impact sensitivity of the material, since shear bands are recognized to play a role in explosive initiation (Winter and Field 1974, Frey 1981, Swallowe and Field 1981, Field et al 1982, Krishna Mohan et al 1989, Ho 1992, Dey and Johnson 1998.…”

Section: Evidence Of Shear Band Formation During Failurementioning

confidence: 99%

Temperature–time response of a polymer bonded explosive in compression (EDC37)

Williamson¹,

Siviour²,

Proud³

et al. 2008

J. Phys. D: Appl. Phys.

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The compressive strength of the energetic composition EDC37 has been measured at a temperature of 293 ± 2 K over a range of strain rates from 10−8 to 103 s−1, and at a strain rate of 10−3 s−1 over a range of temperatures from 208 to 333 K. The results show that failure stress is a monotonic function of applied strain rate or temperature, which is dominated by the relaxation properties of the polymeric binder; this is confirmed by dynamic mechanical thermal analysis performed on both EDC37 and its binder. Similarities between the compressive strain rate/temperature data sets can be understood by temperature–time superposition; data collected at a strain rate of 10−3 s−1 over a temperature range 208 to 333 K were mapped onto a plot of strain rate dependent strength at 293 K, using an empirically determined sensitivity of −13.1 ± 0.3 K per decade of strain rate. Sample size was noted to have a modest effect on the stress–strain behaviour; small length to diameter ratios gave results consistent with an increased degree of confinement. Samples taken to large strains exhibited strain localization in the form of shear bands.

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Section: Evidence Of Shear Band Formation During Failurementioning

confidence: 99%

Temperature–time response of a polymer bonded explosive in compression (EDC37)

Williamson¹,

Siviour²,

Proud³

et al. 2008

J. Phys. D: Appl. Phys.

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“…The sample has failed by shear localization. The relevant mesoscale mechanism of shear localization at low levels of strain is considered in [10], examples of shear localization due to micro-fracture mechanisms leading to reaction in granular materials can be found in [11]. It is uncertain why some samples fail by shearing at low strain while others are densified leading to an increased strength.…”

Section: Resultsmentioning

confidence: 99%

High Strain and Strain-Rate Behaviour of Ptfe∕aluminuim∕tungsten Mixtures

Addiss¹,

Cai²,

Walley³

et al. 2008

AIP Conference Proceedings

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Conventional drop-weight techniques were modified to accommodate low-amplitude force transducer signals from low-strength, cold isostatically pressed 'heavy' composites of polytetrafluoroethylene, aluminum and tungsten. The failure strength, strain and the post-critical behavior of failed samples were measured for samples of different porosity and tungsten grain size. Unusual phenomenon of significantly higher strength (55 MPa) of porous composites (density 5.9 g/cm 3 ) with small W particles (<1 μm) in comparison with strength (32 MPa) of dense composites (7.1 g/cm 3 ) with larger W particles (44 μm) at the same volume content of components was observed. This is attributed to force chains created by a network of small W particles. Interrupted tests at different levels of strain revealed the mechanisms of fracture under dynamic compression.

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“…With such a raw signal, integral (19) would inherit much numerical noise, which would prevent us from determining a discriminating threshold value for the ignition criterion.…”

Section: Threshold Valuementioning

confidence: 99%

“…Then, the criterion is used to compute whether the local heating, due to these quantities, is sufficient for the material to ignite. This criterion can take into account ignition through localization at adiabatic shear bands, like in [19], since frictional heating between grains is compatible with shear banding. In fact, the Browning & Scammon criterion can take into account the high level of plastic shear strain inside these bands, whose size is comparable with the coarse grain size.…”

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confidence: 99%

Ignition of a confined high explosive under low velocity impact

Gruau

Picart

Belmas

et al. 2009

International Journal of Impact Engineering

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In the framework of low velocity impact studies, dedicated to safety analyses of plastic bonded explosives (PBX), we propose a new numerical tool, designed for restituting the ignition of a HMX (high melting point explosive) based composition. Major results are the use of a concrete-like constitutive law for the PBX and an efficient implementation of an ignition criterion. We also put forward two variants of classical Steven tests, which enable us to visualize either a dot ignition or an unusual ring-shaped ignition. It is shown that the calculation tool is able to restitute accurately both results. © 2008 Elsevier Science. All rights reserved Keywords: PBX safety, Steven test, ignition criterion ---* Corresponding author. Tel.: +33-2-47-34-41-73 ; e-mail: cyril.gruau@cea.fr, didier.picart@cea.fr IntroductionHigh explosive parts confined in pyrotechnic devices can unintentionally ignite, when submitted to impacts, even at low velocities. Ignition can then evolve to more violent and undesired events, such as deflagration or detonation. Prediction of such transitions being hardly tractable, we are focusing our attention on the ignition stage, which is the very first event that must be correctly restituted, in the framework of safety analyses.The considered high explosive is composed of a poly-dispersed distribution of HMX grains, with a mean diameter of 200 µm, which are mixed with a few percentage of a polymeric binder. An isostatic compaction process is used to reduce the composition porosity at few percentages. Its mechanical response is similar to the behavior exhibited by PBX-9501, another explosive composition.The low velocity impacts of interest may occur during transport, storage, assembling or disassembling of devices, leading to a great number of accident scenarios. Thus, safety analyses of pyrotechnic structures involve many parameters, like target configuration (shape, materials and boundary conditions) and mechanical loadings (characteristics of the projectile and its movement law), which prevents us from dealing only with experimental techniques. The aim of this paper is to describe a numerical tool designed for the ignition, applied to this kind of accidental configurations.In order to validate such a numerical tool, an experimental database is needed. The so-called "Steven test", introduced by Chidester and co-workers [1] was modified to simplify the boundary conditions and to limit strain localization [2]. This test is devoted to the determination of a safety threshold (in terms of impact velocity), under which no violent reaction is observed. Figure 1 shows three pictures taken during one of these tests.International Journal of Impact Engineering 2 Fig. 1. High speed recording of an impact test (the PBX sample is confined inside the steel target): picture before impact, during impact and at the beginning of reaction (the configuration of the target is given on Figure 15, target 3, projectile velocity = 77 m/s).Deflagrations and detonations induced by low velocity impacts are not the resul...

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Shear band formation in plastic bonded explosive (PBX)

Cited by 6 publications

References 4 publications

Temperature–time response of a polymer bonded explosive in compression (EDC37)

Temperature–time response of a polymer bonded explosive in compression (EDC37)

High Strain and Strain-Rate Behaviour of Ptfe∕aluminuim∕tungsten Mixtures

Ignition of a confined high explosive under low velocity impact

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