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

Abstract

Head-to-head comparisons are made between calculations and experimental data on shock-driven pore collapse in the transparent material, poly(methyl methacrylate) (PMMA). Simulations are performed using SCIMITAR3D, an Eulerian sharp-interface multi-material code, while plate impact experiments are visualized using ultra-high speed x-ray imaging. The experiments and simulations are conducted over a wide range of loading conditions; from low strength loading regimes where adiabatic shear banding predominates all the way up to the regime where hydrodynamic pore collapse is expected. PMMA is modeled using an isotropic rate-dependent plasticity model for the deviatoric stress response and a Tillotson equation of state for the pressure. Calculations are primarily done in 2D, to save computational effort, but a limited number of 3D calculations are also performed to assess the differences entailed by the dimensionality. The 2D calculations are in fairly good agreement with the experimental results, for the evolution of pore shape. 3D calculations, while quite computationally intense, indeed produce better agreement with experimental data. The computations also agree well with the experiments in delineating the loading strength at which a transition from the strength-dominated to hydrodynamics-dominated pore collapse occurs. This work provides confidence in the ability of Eulerian, sharp interface computational techniques to correctly represent and understand the mechanics of shock-loaded porous condensed phase materials over a range of loading conditions.

Influence of Void Configurations on Hot Spot Temperature in PBXs under Impact Loading

“…The simulation results were in good agreement with the experimental results. Additionally, experiments and simulations were performed to analyze the shock-induced pore collapse behaviors of 3-, 4-, and 6-mm-diameter pores in poly(methyl methacrylate) at four different shock strengths [12,13]. For all four shock strengths, the predicted results based on the simulations were in close agreement with the experimental results.…”

Novel method to control explosive shock sensitivity: A mesoscale study to understand the effect of thermally expandable microsphere (TEM) inclusions in high explosives (HE) microstructure

“…The Mie-Gruneisen equation of state form was used for PMMA with reference cold curves following the Tillotson fit for PMMA. 37 A detailed description of the PMMA material model and its implementation in the current framework is provided in a recent work. 37 While the use of a fuel oil equation of state (EOS) itself was an approximation, the limited range of data required further approximation for a suitable EOS for these simulations, and we extrapolated the Hugoniot data from Robbins et al 38 to lower density.…”

“…37 A detailed description of the PMMA material model and its implementation in the current framework is provided in a recent work. 37 While the use of a fuel oil equation of state (EOS) itself was an approximation, the limited range of data required further approximation for a suitable EOS for these simulations, and we extrapolated the Hugoniot data from Robbins et al 38 to lower density. An exponential fit between the pressure and the compression ratio η ¼ V/V 0 was obtained, where V is the specific volume and V 0 is the reference specific volume.…”

Head‐To‐Head Comparison of Molecular and Continuum Simulations of Shock‐Induced Collapse of an Elongated Pore in an Energetic Molecular Crystal

“…Pore collapse has been studied by various researchers, providing characterization and quantification of the effects of shock intensity and pore shape for circular/ spherical [5,19,20], elliptical [21][22][23], and arbitrary-shape pores [22,[24][25][26]. Continuum models have typically employed isotropic constitutive descriptions, such as elasticperfectly plastic [19,22,26] or rate-dependent Johnson-Cook (JC) J2 plasticity [27][28][29], that are calibrated empirically [30,31] for limited intervals of loading conditions. Calculations with such semi-empirical, isotropic material models have yielded valuable insights and quantitative information on hotspot evolution, elucidating hydrodynamic (jetting) and, for JC-J2 treatments, shear-banding contributions to energy localization.…”

“…(Henceforth, we use 2D pore‐shape descriptors for convenience where the meaning is unambiguous.) Shear‐banding phenomena have been studied in the context of collapse of radially symmetric pores using both MD [20, 28, 39, 42, 43] and continuum models [27–29, 39, 42, 43]. The presence of shear bands during shock‐induced collapse of elongated pores has also been observed in MD calculations [23]; however, the emanation of shear bands from, and their interaction with, elongated (crack‐like) pores has not yet been examined using continuum models.…”