Analysis of thermomechanical response of polycrystalline HMX under impact loading through mesoscale simulations

Abstract

We investigate the response of polycrystalline HMX 3,5,3,5, under impact loading through a 3-dimensional mesoscale model that explicitly accounts for anisotropic elasticity, crystalline plasticity, and heat conduction. This model is used to quantify the variability in temperature and stress fields due to random distributions of the orientations of crystalline grains in HMX under the loading scenarios considered. The simulations carried out concern the response of fully dense HMX polycrystalline ensembles under impact loading at imposed boundary velocities from 50 to 400 m/s. The polycrystalline ensemble studied consists of a geometrically arranged distribution of bi-modally sized and shaped grains. To quantify the effect of crystalline slip, two models with different numbers of available slip systems are used, reflecting differing characterizations of the slip systems of the HMX molecular crystal in the literature. The effects of microstructure and anisotropy on the distribution of heating and stress evolution are investigated. The results obtained indicate that crystalline response anisotropy at the microstructure level plays an important role in influencing both the overall response and the localization of stress and temperature. The overall longitudinal stress is up to 16% higher and the average temperature rise is only half in the material with fewer potential slip systems compared to those in the material with more available slip systems. Local stresses can be as high as twice the average stresses. The results show that crystalline anisotropy induces significant heterogeneities in both mechanical and thermal fields that previously have been neglected in the analyses of the behavior of HMX-based energetic materials. C 2014 Author(s)

Prediction of Probabilistic Detonation Threshold via Millimeter‐Scale Microstructure‐Explicit and Void‐Explicit Simulations

“…A variation of 30 % about the 100 % TMD was calibrated based on the work of Hardin et al. who found the coefficient of variation in the longitudinal stress field in the quasi‐steady region behind the stress wave front in polycrystalline HMX varies from 0.08 to 0.16 at piston velocities around 400 m/s. In this study, the grains are assumed to be perfectly bonded to one another.…”

“…Such variations lead to the heterogeneous behavior as seen in actual samples, thereby enabling a probabilistic analysis described later in this paper, while keeping the overall HMX density consistent at 100 % TMD. A variation of 30 % about the 100 % TMD was calibrated based on the work of Hardin et al [24] who found the coefficient of variation in the longitudinal stress field in the quasi-steady region behind the stress wave front in polycrystalline HMX varies from 0.08 to 0.16 at piston velocities around 400 m/s. In this study, the grains are assumed to be perfectly bonded to one another.…”

Plastic Dissipation and Hot‐Spot Formation in HMX‐Based PBXs Subjected to Low Velocity Impact

“…The interaction between grains is disturbed by the elastic and plastic anisotropy of the β-HMX crystals. For this reason, Hardin et al adapts the Barton and Zamiri single crystal models to a polycrystalline assembly subjected to low impact velocities of 50 to 400 m/s [20]. A heterogeneous temperature rise is observed, but initiation is not achieved at low strain rates.…”

“…This literature review shows that two mechanisms contribute to the appearance of hot spots: friction and plastic strain. Studies on PBX 9501 show that (1) plasticity alone, within a polycrystal, would not be effective in initiating chemical decomposition [20] and that (2) friction in cracks would allow thermal initiation of the material [15,24,25,28]. However, data obtained on X1 during low speed impacts show that the material first deforms by plastic yielding.…”

Dynamic Anisotropic Response of β‐HMX and α‐RDX Single Crystals Using Plate Impact Experiments at ∼1 GPa

“…Recently, many researchers examined the crystal plasticity model accounting for dislocation mobility at the subgrain scale to explain orientation-dependent behavior of energetic single crystals [20][21][22][23]. These physical-based mesoscale constitutive models contain several parameters [ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 which should be calibrated through complete and detailed experimental results to improve their predictive ability.…”