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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. [ABSTRACT FROM AUTHOR]

Initial configuration, which can include particle size and shape, initial density, and void location, can affect the measured compaction responses of initially porousmaterials. In this work, both the low- and high-strain-rate compaction response of several different morphology CeO2 powders are investigated experimentally. Quasi-static compaction curves are found to exhibit distinct differences between the morphologies, where initial packing efficiencies and particle aspect ratios are found to dominate the low pressure response. At low-strain-rates, the largest particles with the highest aspect ratio are found to exhibit the stiffest response, while those that most resemble spherical particles offer the least resistance to initial densification. At high- strain-rates a transition in compliance is observed, where smaller equiaxed particles are found to exhibit greater resistances to densification. The role of particle morphology and its affect on the communication of particle-level stresses during quasi-static and dynamic densification are discussed, and emphasis is placed on the mechanisms that cause the morphology-based transition in compliance. [ABSTRACT FROM AUTHOR]

The compaction response of CeO2 powders with two distinct morphologies ranging in size from 300 nm to 10-14 μm are investigated through quasi-static and dynamic compaction experiments. In the quasi-static and low pressure dynamic regimes the high aspect ratio 10-14 μm particles exhibit a measurably stiffer response. However, as pressure increases in the dynamic regime a transition occurs suggesting shape effects dominate at low pressures while particle size becomes more important at higher pressures. Transmitted wave profiles are examined, and suggest non-equilibrium processes may occur following the initial compaction front. Furthermore, three formulations of the P-μ model are applied to the 300 nm compaction data, and a power law relation is found to yield the best fit to experimental data. [ABSTRACT FROM AUTHOR]

Predicting the dynamic crush-up response of heterogeneous powder mixtures is vital to the design of high-strain-rate experiments. A methodology has been developed which utilizes an experimentally obtained stress-density response in the low-strain-rate (quasi-static) regime to predict the dynamic densification response of powder mixtures. Specifically, the compaction behavior of an equivolumetric Ta + Fe2O3 mixture is investigated. Experimental data is analyzed within the scope of existing continuum level compaction models, where the present combination and manipulation thereof allows for an accurate prediction of the dynamic crush-up response of the Ta + Fe2O3 powder mixture. Discussion is also given regarding model extension to alternate systems. [ABSTRACT FROM AUTHOR]

The dynamic deformation and fragmentation response of 25% dense 9-cell linear cellular alloy (LCA) made of unaged 250 maraging steel, fabricated using a direct reduction and extrusion technique, is investigated. Explicit finite element simulations were implemented using AUTODYN finite element code. The maraging steel properties were defined using a Johnson-Cook strength model with previously validated parameters. Rod-on-anvil impact tests were performed using the 7.6mm helium gas gun and the transient deformation and fragmentation response was recorded with highspeed imaging. Analysis of observed deformation states of specimens and finite element simulations reveal that in the case of the 9-cell LCA, dissipation of stress and strain occurs along the interior cell wells resulting in significant and ubiquitous buckling prior to confined fragmentation. [ABSTRACT FROM AUTHOR]

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 are found to be best represented by a piecewise EOS. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]