Prof D Eakins, University of Oxford, UK

Freezing the supersonic: Revealing the mesoscale of dynamically compressed matter through fast, synchrotron X-ray imaging
When Feb 05, 2018 02:00 PM to
Feb 15, 2018 03:00 PM
Where LR8
Contact Name
Contact Phone 01865-283446
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Impact is a fundamental and ubiquitous process which subjects materials to rapid combinations of high pressure, temperature and deformation. These extreme conditions often drive behaviour not seen at ambient pressure in the form of novel deformation pathways (e.g. jetting, vorticity), failure modes (shear localization, spall), or nucleation of non-equilibrium phases. Enhancing the performance of materials in demanding environments relies upon better understanding of the link between these unique behaviours and the underlying mesoscale. This however has been experimentally inaccessible until recently, due to the short timescale (<100 ns) and subsurface nature of the processes of interest. Recent years have seen a rapid advance in capabilities for dynamic, sub-surface X-ray probing, with researchers at the Advanced Photon Source and LCLS exploiting the brightness and coherence of 3rd and 4th generation light sources to interrogate with high resolution the vast richness of mesoscale deformation. These emergent capabilities have the potential to bridge the gap between bulk time-resolved diagnostics and mesoscale modelling, providing exquisite resolution of the hierarchical origins of dynamic material behaviour. One area of particular promise lies in the study of porous/granular materials, whose dynamic compaction response plays an integral role in a range of terrestrial applications such as novel materials synthesis, blast mitigation and protection, and mining, to space and astrophysical phenomena including satellite shielding, impact cratering and early solar system formation.

 

In this talk, I discuss recent efforts to exploit new capabilities for dynamic X-ray imaging at the European Synchrotron Radiation Facility, to interrogate the high-rate/shock response of granular materials under impulsive loading. Using a small-scale single-stage gas gun, a wide range of heterogeneous systems have been subjected to impact velocities from a few m/s to 800 m/s, with sequences of X-ray phase contrast images, consisting of up to 512 images separated by 176 ns, recorded using a multi-camera indirect detection system. By revealing mesoscopic features of shock compression for the first time, this new technique allows in situ visualisation of the distribution of shock states during shock compression, wave profile evolution, and the damping of spatial perturbations due to the effective powder viscosity/strength, providing unparalleled validation of component EOS and strength, and highlighting the importance of high-resolution sub-surface imaging in the study of highly heterogeneous materials. Further utility of this technique for a broad range of mechanical behaviours including dynamic tensile failure, and cavity collapse for novel fusion engineering, will also be showcased. Finally, new measurement opportunities presented by the future EBS upgrade will be discussed.