Narrow Results

Gd-doped ceria nano powder(~5 nm) was shock-loaded by a plate impact experiment using a single stage light gas gun. A computational model was used to simulate the shock state (pressure and density changes along time) of the sample in two dimensional Eulerian code. The predicted density of compacted sample from the simulation was about 90%. To reveal the effect of shock compaction on sintering behavior, the recovered sample was heat-treated and the microstructure was compared with that of a conventionally compacted and heat-treated sample.

Elastic stress wave theory is developed and the stress waves in the impacted plate are examined in the paper. Generalized linear elasticity is adopted where the couple stress and curvature tensor are both deviatoric tensors and they meet a linear constitutive relation. It is found that there exist volumetric, rotational, and deviatoric waves in the generalized elastic solids. However, for macro-scale elastic solids only two wave modes, namely a volumetric wave and a deviatoric wave should be taken into account. Wave motion in plate impact tests is studied that a volumetric wave and a deviatoric wave are proposed. A set of exact solutions is attained for elastic stress waves in an impact plate. Excitation of stress waves at impact surface and reflection at free surface are formulated. Propagation of stress waves in the plate is analyzed in the waveforms. The predicted stress history in a ceramic plate under impact is agreed very well with the experiment measurement.

The shock response of layered material systems is quite different from that of monolithic systems. Scattering inherent at the interfaces of heterogeneous materials is shown to play an important role in determining the structure of the wave profiles in layered systems. Experimental results of plate impact tests on periodic layered composites have shown an oscillatory response in the pulse duration phase of the stress wave profile. In this paper, multiple scattering at the heterogeneous interfaces is shown to explain this behavior very well. Combined with our earlier result that scattering can also be used to explain the sloping rise characteristics of the wave profile, it is concluded that scattering plays a very critical role in determining the entire structure of the shock profile. It is further shown that material heterogeneity, e.g., impedance mismatch, interface density, and thickness ratio affect the scattering processes and hence the structure of the stress wave profiles in a profound manner.