Investigation of the mesoscopic scale response of low-density pressings of granular sugar under impact

Abstract

The mesoscopic scale response of low-density pressings of granular sugar (sucrose) to shock loading has been examined in gas-gun impact experiments using both VISAR and a line-imaging, optically recording velocity interferometer system in combination with large-volume-element, high-resolution, three-dimensional numerical simulations of these tests. Time-resolved and spatially resolved measurements of material motion in waves transmitted by these pressings have been made as a function of impact velocity, sample thickness, and sample particle size distribution. Observed wave profiles exhibit a precursor regime arising from elastic stress wave propagation and a dispersive compaction wave with superimposed localized particle velocity fluctuations of varying amplitude. Material motion associated with dynamic stress bridging leads compaction wave arrival by ∼2μs at the lowest impact velocity (0.25kms−1) employed in this study and <200ns at the higher values (0.7–0.8kms−1). Over the same range, the compaction wave becomes markedly less dispersive with wave ramp durations declining from ∼500to∼50ns. For impact velocities near 0.5kms−1 and samples varying in thickness from 2.27to8.03mm, a roughly steady wave behavior is obtained at the thinner end of the range; however, evidence of subtle wave evolution is apparent over this thickness range. Pressings of sieved sugar with different particle size distributions exhibit distinguishable differences in stress bridging and compaction wave behavior. These pressings somewhat limit stochastic behavior and provide favorable conditions for the development of quasiperiodic fluctuations in particle velocity, particularly in impacts generating incomplete compaction. The experimental results are consistent with the exceedingly complex wave field behavior evident in the numerical simulations and provide useful benchmark wave profiles (at the sample boundary) for validation of material models used in these calculations.

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

“…Another observation from Figure 9 is that the dispersion increases monotonically with imposed velocity in the Zamiri case but shows no simple trend in the Barton case. Specifically, the decrease in stress field variations at higher imposed velocities (above 100 m/s) in the Barton case is in agreement with the results by Trott et al 61 for a mock PBX under shock loading. In contrast, the increasing levels of stress fluctuations in the Zamiri case suggest that this material representation may be missing essential dissipation mechanisms represented by the additional slip systems in the Barton case or fracture planes which are not modeled here.…”

“…The results presented here indicate that the results based on the description of Barton et al more closely matches previously published data. 61 Therefore, the Barton model is likely a more realistic representation of the inelastic behavior of HMX crystals in the absence of fracture or other dissipative mechanisms. The calculations carried out also show that spatial variations of the critical resolved shear stresses (CRSS) of up to 15% in a material have minimal effect on the bulk or local material response for the polycrystalline specimens analyzed.…”

Anfo Response To Low-Stress Planar Impacts

“…Impact velocities range from 0.17-1.40 km/s. Figure 1 presents the experimental arrangement of the ORVIS system coupled to the gas gun, e.g., see [3,4]. In short, interference fringes from the ORVIS diagnostic is recorded on a streak camera where motion at the target is recorded as fringe displacement.…”

“…This work supports development of predictive tools aimed at the performance of non-ideal explosives [1,2,3]. In particular, ammonium nitrate plus fuel oil (ANFO) is one such non-ideal, heterogeneous explosive with two mean characteristic length scales, namely that of the in-prill porosity and the mean prill diameter [1,2].…”

On the development of an impact-loaded wedge test using ORVIS

“…Our ORVIS system was previously coupled to the gas gun for investigations of the shock response of low-density granular materials [2,3] and the image analysis relies on a "rolling push-pull" method [3,4]. With this method, the intensity modulation data along lines parallel to the time axis of the streak camera are determined at the fringe center along with 1/4, 1/2, and 3/4 the distance to the center of the neighboring fringe and treated as the data recorded by four PMT channels in a "push-pull" VISAR [5].…”