Modeling mesoscale energy localization in shocked HMX, Part II: training machine-learned surrogate models for void shape and void–void interaction effects

Abstract

Surrogate models for hotspot ignition and growth rates were presented in Part I, where the hotspots were formed by the collapse of single cylindrical voids. Such isolated cylindrical voids are idealizations of the void morphology in real meso-structures. This paper therefore investigates the effect of non-cylindrical void shapes and void-void interactions on hotspot ignition and growth. Surrogate models capturing these effects are constructed using a Bayesian Kriging approach. The training data for machine learning the surrogates are derived from reactive void collapse simulations spanning the parameter space of void aspect ratio (AR), void orientation ( ), and void fraction ( ). The resulting surrogate models portray strong dependence of the ignition and growth rates on void aspect ratio and orientation, particularly when they are oriented at acute angles with respect to the imposed shock. The surrogate models for void interaction effects show significant changes in hotspot ignition and growth rates as the void fraction increases. The paper elucidates the physics of hotspot evolution in void fields due to the creation and interaction of multiple hotspots. The results from this work will be useful not only for constructing meso-informed macro-scale models of HMX, but also for understanding the physics of void-void interactions and sensitivity due to void shape and orientation.

Mechanics of shock induced pore collapse in poly(methyl methacrylate) (PMMA): Comparison of simulations and experiments

“…On the other hand, for the 2.30 km/s shock, the centerline pore deformation is observed to be higher in 3D and in experiments than 2D. Overall, the 3D simulations are in closer agreement with experiments; however, 2D simulations are far less computationally expensive which allows for exploration of parameter spaces for pore collapse and for construction of surrogate models, as done in previous work [14,43,44].…”

“…An additional metric to quantify the dynamics of the pore collapse behavior as a function of the loading strength is the jet velocity and acceleration for the pore interface along the centerline, which are calculated using Eqs. (12)(13)(14)(15)(16)(17). As discussed in Section 2.4, the acceleration was only calculated for pressures ≥ 4.80…”

“…It is well known that pore collapse in HEs leads to intense hotspots that can grow into sustained reactive fronts that consume the surrounding solid material. In the case of a single pore [6][7][8][9][10][11][12][13] or a field of pores [11,12,14,15], the thermo-mechanics of pore collapse has now been well studied using simulations.…”

Modeling mesoscale energy localization in shocked HMX, part I: machine-learned surrogate models for the effects of loading and void sizes

“…The latter two functions on the right hand side of Eqns. (17) are obtained in Part II [7]. In this paper, two QoIs are extracted from the data derived from the meso-scale computations.…”

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

“…While doable , 3D continuum calculations are sufficiently expensive that production runs to characterize behavior across a range of loading regimes, pore sizes, and material morphologies will remain out of reach for the next few years. Furthermore, accurate simulations of fields of pores, anisotropic materials, description of rate‐dependent material response, damage, fracture, and other complex physics that are inherent in PBXs under shock loading have been explored by various researchers but are as yet restricted in terms of regime and model fidelity . Thus, accurate MD and continuum calculations of hotspot formation are still active areas of research.…”