Shock Wave Perturbation Decay in Granular Materials

Abstract

A technique in which the evolution of a perturbation in a shock wave front is monitored as it travels through a sample is applied to granular materials. Although the approach was originally conceived as a way to measure the viscosity of the sample, here it is utilized as a means to probe the deviatoric strength of the material. Initial results for a tungsten carbide powder are presented that demonstrate the approach is viable. Simulations of the experiments using continuum and mesoscale modeling approaches are used to better understand the experiments. The best agreement with the limited experimental data is obtained for the mesoscale model, which has previously been shown to give good agreement with planar impact results. The continuum simulations indicate that the decay of the perturbation is controlled by material strength but is insensitive to the compaction response. Other sensitivities are assessed using the two modeling approaches. The simulations indicate that the configuration used in the preliminary experiments suffers from certain artifacts and should be modified to remove them. The limitations of the current instrumentation are discussed, and possible approaches to improve it are suggested.

Interrogating heterogeneous compaction of analogue materials at the mesoscale through numerical modeling and experiments

“…The perturbation in the models appears to decay at a faster rate than the experiment becoming almost invisible by the final frame, whilst the radiograph still displays it clearly. This is consistent with previous studies that investigated shock wave perturbation decay in granular matter [11]. half is cropped to compare with radiographs and the white dashed line is the furthest location of the driver/powder interface in the models.…”

Probing the early stages of shock-induced chondritic meteorite formation at the mesoscale

“…In keeping with the estimation that some of the measured ( U wf , U dp ) states were released it was observed that shock velocity decreased as a function of time. These observations are promising for the validation of release models, and when combined with measurements of wavefront curvature suggest that mesoscale measurements of shock front dispersion and perturbation decay could be made to probe the effective viscosity of granular materials 9 . In Fig.…”

“…While these experiments have been used to provide information on the equilibrated shock state in various materials and have allowed for a calibration of continuum level models 8 , they inherently struggle to resolve the time-evolution of dynamic compaction at the sub-mm scale within the material. As a result these techniques are limited in their ability to discern exactly which mesoscopic processes govern material deformation at the macroscopic scale, and thus provide data which is not optimal for validating mesoscopic models 9 . Very recently, a number of in-situ , X-ray radiography experiments have been performed on shock-compressed materials at synchrotron light sources and X-ray free electron lasers.…”

Strength and Viscosity Effects on Perturbed Shock Front Stability in Metals

“…2. For materials with strength a factor of Yλ/A 0 is left so that an increase in wavelength or initial perturbation amplitude pushes a point up or down respectively [18]. This suggests sources of deviatoric stress could be validated through initial perturbation amplitude or wavelength changes (we were unable to show this due to a lack of larger kΔx values).…”