Multi-scale shock-to-detonation simulation of pressed energetic material: A meso-informed ignition and growth model

Self Cite

All‐atom molecular dynamics (MD) and Eulerian continuum simulations, performed using the LAMMPS and SCIMITAR3D codes, respectively, were used to study thermo‐mechanical aspects of the shock‐induced collapse of an initially cylindrical 50 nm diameter pore in single crystals of 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB). Three impact speeds, 0.5 km s−1, 1.0 km s−1 and 2.0 km s−1, were used to generate the shocks. These impact conditions are expected to yield collapse mechanisms ranging from predominantly visco‐plastic to hydrodynamic. For the MD studies, three crystal orientations (relative to shock‐propagation direction) were examined that span the limiting cases with respect to the crystalline anisotropy in TATB. An isotropic constitutive model was used for the continuum simulations, thus crystal anisotropy is absent. The evolution of spatiotemporally resolved quantities during collapse is reported including local pressure, temperature, pore size and shape, and material flow. Multiple models for the melting curve and specific heat were studied. Within the isotropic elastic/perfectly plastic continuum framework and for the range of impact conditions studied, the specific heat and melting curve sub‐models are shown to have modest effects on the continuum hotspot predictions in the present inert calculation. Treating the MD predictions as ‘ground truth’, albeit with a classical rather than quantum‐like heat capacity, it is clear that – at a minimum – an extension of the constitutive model to account for crystal plasticity and anisotropic strength will be required for a high‐fidelity continuum description.

Section: Introductionmentioning

confidence: 99%

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

Zhao

Lee

Sewell

et al. 2020

Self Cite

“…They showed that the p À v closure model well captured the ZND behavior when compared to the p À T closure model. However, the model for our microscale (9) requires the use of switch-on functions that are functions of temperature. To avoid the (numerically costly) fully iterative approach, we adopt the explicit model as outlined in Stewart et al [31].…”

Section: Full Papermentioning

confidence: 99%

“…We first examine the baseline case of A HS ¼ 2x10 17 W/m 3 , p s ¼ 7:21GPa, d ¼ 20 mm, and N HS ¼ 300: Although it is well known that voids have a distribution [8], here we only consider a single size due to grid resolution; it is straightforward to incorporate a distribution of pore sizes into the model. The hot-spots are initially randomly located within the crystal boundaries so that the power deposition term (9) is only active in these regions. Figure 17a plots pressure contours at one instance of time and shows that a detonation wave has formed.…”

Section: Figure 14mentioning

confidence: 99%

Multiscale Approach to Shock to Detonation Transition in Energetic Materials

Jackson

Short

2019

In this work we present a multiscale approach for coupling the dynamics of void collapse at the microscale to simulations at the mesoscale. We solve the reactive Euler equations, with the energy equation augmented by a power deposition term. The reaction rate at the mesoscale is modelled using a pressure‐dependent power law. The deposition term is based on previous simulations of void collapse, modelled at the mesoscale as hot‐spots. The equation of state was previously calibrated for PBX 9501. The run‐to‐detonation distance is calculated as part of the numerical solution procedure. Results for 1‐D, 2‐D homogeneous, and 2‐D heterogeneous medium are presented, and show good agreement to experimental data.

“…Considering the different numerical modelling and simulation efforts for heterogeneous explosives, many of these can be divided into one of two approaches. One approach is aimed at studying explosives initiation (mesoscale) [12][13][14][15][16][17][18], while the other is aimed at studying propagation (continuum) [19][20][21]. A third approach, atomistic simulations, is acknowledged here as it pertains to the mesoscale, but it is not discussed in detail.…”

Section: Introductionmentioning

confidence: 99%

“…Current research [12][13][14][15][16][17][18][19][20][21][22] is progressing to close this knowledge gap from both sides. Finite element analysis (FEA) and Eulerian/Lagrangian hydrocodes, together with modern computing resources allow for an image to computation approach for mesoscale modelling [12]; in this approach, microstructure images are obtained both experimentally and synthetically [13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Modelling the Fluctuations of Reactive Shock Waves in Heterogeneous Solid Explosives as Stochastic Processes

Kittell

Yarrington

Lechman

et al. 2019

While current phenomenological burn models are useful for describing the average or bulk reactive flow behaviour of heterogeneous explosives, one fundamental weakness inherent to these models is the loss of detailed microstructural information at the scale of the calculation. In order to include the effects of the microstructure, and in particular the underlying material heterogeneities that influence the build‐up to detonation, a new paradigm is put forth for modelling sub‐grid, reaction‐induced fluctuations (i. e. “hot spots”) at the continuum level. This modelling approach assumes that the reaction rate is stochastic, rather than deterministic, and it uses Langevin‐type equations with a mathematical framework built upon Itô calculus and Lambourn's CIM model for shocked heterogeneous explosives. This approach follows directly from our previous letter, Ref. [1], and is inspired by the probability density function (pdf) methods used in turbulent reactive flows. Here, the stochastic burn model is derived, implemented, and exercised far beyond what has been shown in previous work. New hydrocode simulation results demonstrate the role of stochastic fluctuations during shock initiation; these fluctuations are approximated by collections of discrete particles, that evolve with drift (i. e. deterministic) and diffusion (i. e. stochastic) coefficients. Additionally, the particle values are propagated and averaged to calculate the heat release, yield strength, and material impedance in each computational cell. Hydrocode simulation results further show how the fluctuating hot spot energy may or may not be transmitted to the wave front, and result in a detonation wave‐like structure. The fundamental stochastic nature of this model permits simulations to have varying outcomes with the same initial conditions; this allows for go/no‐go estimation (e. g., marginal or failed detonations), which might possibly be calibrated using the statistical distributions from real materials. Mesoscale calculations of shocked heterogeneous explosives also show that these fluctuations are physically justified (i. e., Ref. [2]), and it is hypothesized that the pdf functions provide a link between the meso(grain) and continuum scales for practical engineering calculations. Thus, our approach is a paradigm shift for building efficient, reduced order continuum burn models, that represent the sub‐grid stochastic behaviour of shocked heterogeneous solid explosives.