David A. Fredenburg

The influence of morphology on the low- and high-strain-rate compaction response of CeO2 powders

The low- and high-strain-rate compaction response of three distinct morphology CeO2 powders was measured experimentally. At low-strain-rates, the compression path was found to vary with initial particle morphology as a result of differences in initial packing structure and particle rearrangement at low stresses. However, similar compression responses were observed at higher stresses under low-strain-rate loading. Dynamic experiments were performed at impact velocities between 0.15 and 0.78 km/s, and resulted in compaction stresses of 0.51-4.59 GPa in the powders. In contrast to the behavior observed at low stresses and low-strain-rates, dynamic loading resulted in a similar compaction response for all morphology powders. The dynamic results were treated with a Hayes equation of state augmented with a P-α compaction model, and good agreement between experimental and theoretical results was achieved. From the observed similarities in compressibility for the three morphology powders at elevated stresses at b...

MESO‐SCALE SIMULATION OF THE SHOCK COMPRESSION RESPONSE OF EQUIAXED AND NEEDLE MORPHOLOGY AL 6061‐T6 POWDERS

With component sizes approaching the mesoscale, conventional size microstructures offer insufficient homogeneity in mechanical properties, forcing microstructures to be reduced to the nanoscale. This work examines the effect of a nanocrystalline surface layer on the dynamic consolidation response of two different morphology Al 6061‐T6 powders. Shock‐propagation through equiaxed and needle morphology Al 6061‐T6 powder beds initially at 73.5 and 75.0% theoretical density, respectively, is simulated at constant particle velocities ranging between 150 and 850 m/s. Shock velocity‐particle velocity relationships are determined for powders both with and without the presence of a 2 μm high strength surface layer, which is representative of a nanocrystalline surface layer. Significant deviations in dynamic response are observed with the presence of the surface layer, especially at lower particle velocities. The equation of state (EOS) for both the homogeneous particles and those with a high strength surface layer ...

Shock Consolidation of Nanocrystalline Aluminum for Bulk Component Formation.

Al 6061‐T6 powder particles with a partially nanocrystalline graded microstructure in three distinct morphologies are compacted at an impact velocity of 650 m/s. Recovered samples are characterized to determine degree of compaction, deformation characteristics, and mechanical properties. Compacts range from 96–98% of theoretical density, exhibiting relatively low elastic moduli. Nano‐indentation yields relatively consistent hardness values of ∼1.4 GPa, indicating hardness of starting powders is preserved after compaction. Micro‐indentation indicates varying degrees of compaction through specimen cross‐section, which is supported by EBSD and optical microscopy.

Systematics of Compaction for Porous Metal and Metal-Oxide Systems

The effects of particle morphology and initial density is examined with respect to the shock densification response of initially porous metal (Cu) and metal-oxide (CeO2) materials. Specifically, the ability of a continuum-level compaction model to capture the measured densification trends as a function of initial density and particle morphology are investigated. Particle morphology is observed to have little effect on the densification response of both Cu and CeO2, while initial density appears to have a stronger effect. In terms of continuum-level compaction strength, Cu and CeO2 exhibit dissimilar trends.

Shock and Release Response of Unreacted Epon 828: Shot 2s-905

This document summarizes the shock and release response of Epon 828 measured in the dynamic impact experiment 2s-905. Experimentally, a thin Kel-F impactor backed by a low impedance foam impacted an Epon 828 target with embedded electromagnetic gauges. Computationally, a one dimensional simulation of the impact event was performed, and tracer particles were located at the corresponding electromagnetic gauge locations. The experimental configuration was such that the Epon 828 target was initially shocked, and then allowed to release from the high-pressure state. Comparisons of the experimental gauge and computational tracer data were made to assess the performance of equation of state (EOS) 7603, a SESAME EOS for Epon 828, on and off the principal shock Hugoniot. Results indicate that while EOS 7603 can capture the Hugoniot response to better that 1%, while the sound speeds at pressure are under-predicted by 6 - 7%.

U) Design Considerations for Obtaining Deep Release in Reacted Epon 828

Our document summarizes results from one-dimensional calculations performed to investigate the release behavior of reacted Epon 828. Two design goals were set, (1) the product phase had to be achieved upon the initial shock loading, and (2) a deep release state could be achieved. Both transmission and front surface impact geometry were investigated. Moreover, the two design criteria were met with the front surface impact design employing a modi ed projectile.

(U) Analysis of shock-initiated PBX-9501 through porous CeO2

The attenuation properties of an impact initiated PBX-9501 explosive through several thicknesses of CeO2 powder is investigated. The CeO2 is at an initial porous density of 4.0 g/cm3 , roughly 55 % of theoretical maximum density. Measurements of the input (into the powder) and propagated (through the powder) wave profiles are measured using optical velocimetry. Results show a reduction of the average wave speed, CX, and peak steady-state material velocity, uP , with increasing powder thickness from 1.5 - 5.0 mm.