Session R2: DR Dynamic Response of Materials

Dynamic Experiments using IMPULSE at the Advanced Photon Source

The ability to examine the dynamic response of materials at extreme conditions requires diagnostics that can provide real-time, in situ$, $spatially resolved measurements at the appropriate length. Recent advances in synchrotron sources and diagnostics coupled to dynamic loading platforms are transforming the dynamic compression field to allow for such investigations. In the current work, recent experimental efforts on the IMPULSE (IMPact System for ULtrafast Synchrotron Experiments) capability at the Advanced Photon Source (Argonne, IL) will be highlighted to describe the development of the capability and its use to examine phenomena including jet-formation in metals, compaction, crack formation and propagation, and material strength and failure. These experimental results have relied in part on: 1) the development of a robust optically multiplexed intensified detector configuration to obtain the first shock movies and 2) gun system improvements to better synchronize the impact event with the 60-ps width X-ray bunch. The IMPULSE capability is expected to continue to reveal novel phenomena for materials subjected to high strain rate loading while developing the required knowledge base to ensure success for future facilities including the Dynamic Compression Sector at the Advanced Photon Source and LANL's MaRIE.   

X-ray Diffraction on Shocked Solids: Past Results and Future Prospects at the Dynamic Compression Sector

Real-time X-ray diffraction measurements in shocked solids represent an important development for understanding the response of shocked solids at the lattice and microscopic levels. Two examples of recent X-ray diffraction work on shock compressed single crystals will be reviewed. First, insight into shocked crystal microstructure was obtained through analysis of X-ray diffraction peak broadening caused by shock-induced microstructural heterogeneities. Second, macroscopic strength of single crystals shock compressed along an axis with 3-fold or higher rotational symmetry was determined from average longitudinal lattice strain (determined from X-ray diffraction) and macroscopic longitudinal stress (determined from continuum methods). The use of X-rays as a probe of the shocked state will be greatly enhanced by the Dynamic Compression Sector (DCS), currently under development at the Advanced Photon Source (APS). The DCS, a user facility, will be dedicated to understanding dynamically compressed condensed matter using X-ray scattering/diffraction and X-ray imaging measurements. X-ray measurement timescales will vary from about 100 ps to over a $\mu $s and multi-frame capabilities will allow time-dependent changes to be monitored. An overview of the planned X-ray beam characteristics at DCS will be used to show simulations of various material phenomena of interest in dynamic compression research. Simulation results will also be compared to single pulse X-ray diffraction measurements at the APS on ambient samples. Work supported by DOE/NNSA, and carried out in collaboration with Y. M. Gupta.   

Observation of ultrafast dynamic compression at the lattice-level; experimental capabilities and early science at the Linac Coherent Light Source

An in-depth understanding of the stress-strain behavior of materials during ultrafast dynamic compression requires experiments that offer in-situ observation of the lattice at the pertinent temporal and spatial scales. To date, the lattice response under extreme strain-rate conditions (\textgreater 10$^{8}$ s$^{-1})$ has been inferred predominantly from continuum-level measurements and multi-million atom molecular dynamics simulations. Several time-resolved x-ray diffraction experiments have captured important information on plasticity kinetics, while limited to nanosecond timescales due to the lack of high brilliance ultrafast x-ray sources. Here we present new experimental capabilities at the Linac Coherent Light Source (LCLS) combining ultrafast laser-shocks and serial femtosecond x-ray diffraction. The high spectral brightness ($\sim$ 10$^{12}$ photons per pulse, $\Delta $E/E$=$0.2{\%}) and subpicosecond temporal resolution (\textless 100 fs pulsewidth) of the LCLS x-ray free electron laser allow investigations that link simulations and experiments at the fundamental temporal and spatial scales for the first time, thus enabling validation of plasticity models at these extreme strain rates. We describe early pump-probe experiments at LCLS that offer insights to the transient lattice states and compare with predictions from large-scale molecular dynamics simulations. A movie of the lattice undergoing rapid shock-compression, composed by a series of single femtosecond x-ray snapshots, demonstrates the transient behavior while successfully decoupling the elastic and plastic response in a polycrystalline material. We discuss future directions that LCLS can offer to the materials science community, ultimately leading to a predictive understanding and control of the material response during ultrafast dynamic compression.   

In-situ probing of Low Density Porous Materials

The shock response of porous materials is of interest in High Energy Density Physics because the PdV heating from void closure allows off principle Hugoniot states for modeling many astrophysical processes. While continuum models exists of shockwave propagation in foams the relevant physical phenomena spans three different length scales: the micro-length scale defined by the pore size and length between solid structures in the foam (10 to 1000nm), the shock front thickness which determines material and energy flow (0.1 to 100nm), and the hydrodynamic length scale associated with the expanding spherical wave ($>$10 $\mu$m), all of which impact the shock response of the low density foam. With the advent of new HED experimental facilities for generating shockwaves at x-ray light sources this gives new tools for performing pump probe experiments to understand the microstructural response of low density materials. Currently, we have used x-ray radiograph to make Hugoniot EOS measurements the of shock compressed low density SiO2 and Carbon based foams. We will show recent result of measurements of experiments conducted on the Omega laser facility and discuss imaging shockwaves in low density foams on the soon to be commissioned DCS end station at APS and the MEC end station at LCLS. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.