Ignition criterion for heterogeneous energetic materials based on hotspot size-temperature threshold

Abstract

A criterion for the ignition of granular explosives (GXs) and polymer-bonded explosives (PBXs) under shock and non-shock loading is developed. The formulation is based on integration of a quantification of the distributions of the sizes and locations of hotspots in loading events using a cohesive finite element method (CFEM) developed recently and the characterization by Tarver et al. [C. M. Tarver et al., "Critical conditions for impact-and shock-induced hot spots in solid explosives," J. Phys. Chem. 100, 5794-5799 (1996)] of the critical size-temperature threshold of hotspots required for chemical ignition of solid explosives. The criterion, along with the CFEM capability to quantify the thermal-mechanical behavior of GXs and PBXs, allows the critical impact velocity for ignition, time to ignition, and critical input energy at ignition to be determined as functions of material composition, microstructure, and loading conditions. The applicability of the relation between the critical input energy (E) and impact velocity of James [H. R. James, "An extension to the critical energy criterion used to predict shock initiation thresholds," Propellants, Explos., Pyrotech. 21, 8-13 (1996)] for shock loading is examined, leading to a modified interpretation, which is sensitive to microstructure and loading condition. As an application, numerical studies are undertaken to evaluate the ignition threshold of granular high melting point eXplosive, octahydro-1,3,5,7-tetranitro-1,2,3,5-tetrazocine (HMX) and HMX/Estane PBX under loading with impact velocities up to 350 ms À1 and strain rates up to 10 5 s À1. Results show that, for the GX, the time to criticality (t c) is strongly influenced by initial porosity, but is insensitive to grain size. Analyses also lead to a quantification of the differences between the responses of the GXs and PBXs in terms of critical impact velocity for ignition, time to ignition, and critical input energy at ignition. Since the framework permits explicit tracking of the influences of microstructure, loading, and mechanical constraints, the calculations also show the effects of stress wave reflection and confinement condition on the ignition behaviors of GXs and PBXs.

Microscopic characterization of defect structure in RDX crystals

“…The details obtained on the defects present in the examined RDX crystals can be used to further refine the modelling of energetic composite materials. Lately, significant steps forward have been achieved in describing the heterogeneity of energetic composite materials like PBXs, for example, by developing algorithms to create polydisperse packs of nonspherical shapes of granular explosives (Stafford & Jackson, 2010), by including the effect of metal particles on the deformationinduced heating of an explosive composite (Chakravarthy et al, 2013) and by modelling the hot-spot formation in granular and in PBXs (Handley, 2011;Barua et al, 2013). In the hot-spot modelling, mechanical loading of energetic composites cause frictional dissipation as a result of grain fracture or due to interparticle contacts, leading to local temperature increases that act as hot spots.…”

Tandem Molecular Dynamics and Continuum Studies of Shock‐Induced Pore Collapse in TATB

“…Wherever possible, fundamental information from experiment is also used. For energetic materials, this sequential approach is the one most commonly used for multiscale model development [5][6][7][8][9][10][11][12][13][14][15][16].…”

Hot spots in energetic materials generated by infrared and ultrasound, detected by thermal imaging microscopy

“…Electronic mail: dlott@illinois.edu crostructure, the method of energy input, and the hot spot sizes and lifetimes. 6,7 As a benchmark, it has been shown by calorimetry that RDX decomposes with a strong exotherm when heated to 530 K. 8 Almost all previous observations of hot spots in EM relied on visible emission techniques such as high-speed photography. 1,2,[9][10][11][12] Notable exceptions were two 1992 studies by Woody, 13,14 who used a fast IR detector array to obtain single time-gated images of shear bands created in salt crystals subjected to low-velocity impacts, and more recent works by Dickson and co-workers 15 and Perry and co-workers, 16 who studied impacted EM with a combination of visible and IR imaging.…”