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The dynamic tensile spall failure of additively manufactured (AM) two-layered bimetallic GRCop-84—Inconel® 625 alloys, with planar and slanted interfaces, is investigated using uniaxial-strain plate-impact gas-gun experiments. Multiple photon Doppler velocimetry (PDV) is used to monitor the back (free) surface velocity profiles and to determine the influence of the interface geometry on the spall failure. Micrographs of cross sections of recovered impacted samples reveal failure along the interface as well as in-material regions. Spall strengths determined from pull-back signals captured with the use of the multiple PDV probes illustrate different location-specific values for the same sample, corresponding to failure occurring in Inconel® 625, or GRCop-84, or along their interface, depending on the geometry of the interface. The results obtained from the experiments employing multiple PDV probes correlated with microstructural observations of cross sections of recovered impacted samples, provide a useful method for determining the complex spall failure response of two-layered bimetallic alloys, including the differentiation of the response of the respective alloy materials relative to that of the interface, in the same experiment. [ABSTRACT FROM AUTHOR]

When a system comprised of cells, carbon black nanoparticles, and delivery molecules is irradiated with a laser beam, the nanoparticles can absorb and dissipate the laser-delivered energy, producing thermal and acoustic output and fluid mechanical forces. These can then interact with the nearby cell membrane, forming membrane pores that exogenous molecules can diffuse through and access the cytosol. This process, "nanoparticle-mediated photoporation," can cause bio-effects like intracellular delivery of molecules and, at more extreme conditions, loss of cell viability. Through this work, we found that carbon black and carbon nanotubes generated greater bio-effects compared to graphite, diamond, or non-carbon materials, probably due to their more efficient laser energy absorption. Examining the dependence of bio-effects on energy absorption parameters like total energy absorbed, energy absorbed per nanoparticle, and energy absorbed per nanoparticle mass produced poor correlations. However, the correlation of bio-effects was much better with energy transduction parameters more closely related to the energy form transferred to cells like peak temperature, size, and number of vapor bubbles generated by the nanoparticles heated by the laser. A power-law relationship involving these three parameters indicated that peak nanoparticle temperature was the strongest determinant of bio-effects followed by bubble number and radius. This study provides a better understanding of the roles of energy absorption and transduction parameters on bio-effects during nanoparticle-mediated photoporation and facilitates the design of photoporation parameters that achieve desired bio-effects. [ABSTRACT FROM AUTHOR]

The performance of energetic materials subjected to dynamic loading significantly depends on their micro- and meso-scale structural morphology. The geometric versatility offered by additive manufacturing opens new pathways to tailor the performance of these materials. Additively manufactured energetic materials (AMEMs) have a wide range of structural characteristics with a hierarchy of length scales and process-inherent heterogeneities, which are hitherto difficult to precisely control. It is important to understand how these features affect AMEMs' response under dynamic/shock loading. Therefore, temporally and spatially resolved measurements of both macroscopic behavior and micro- and meso-level processes influencing macroscopic behavior are required. In this paper, we analyze the shock compression response of an AMEM simulant loaded under several impact conditions and orientations. X-ray phase contrast imaging (PCI) is used to track features across the observed shock front and determine the linear shock velocity vs particle velocity equation of state, as well as to quantify the interior deformation fields via digital image correlation (DIC) analyses. Photon Doppler velocimetry is simultaneously used to measure the particle velocities of the specimens, which are consistent with those obtained from x-ray PCI. The DIC analyses provide an assessment of the average strain fields inside the material, showing that the average axial strain depends on the loading intensity and reaches as high as 0.23 for impact velocities up to 1.5 km/s. The overall results demonstrate the utility of x-ray PCI for probing "in-material" equation of state and interior strains associated with dynamic shock compression behavior of the AMEM simulant. [ABSTRACT FROM AUTHOR]

Laser shock compression studies on Ce3Al metallic glass performed using a 3 J Nd:YAG laser indicate shock-induced crystallization, evidenced by the presence of a two-wave/stepped particle velocity profile and structural changes observed via X-ray Diffraction (XRD) analysis of recovered material. A direct shock-compression setup was designed with 25 μm thick Ni driver foil, 40 μm thick Ce3Al metallic glass ribbon, and 3 mm thick poly(methyl methacrylate) (PMMA) backer window for use with input laser energies varying from 100 to 2000 mJ and corresponding estimated peak pressures of 1.4 to 4.1 GPa in Ce3Al. At shock pressures below ∼1.8 GPa (300 mJ laser input energy), samples were recovered showing no obvious deformation or structural changes evidenced via XRD analysis. At higher laser energies and shock pressures above the elastic limit, samples were recovered showing visible deformation and crystallization evidenced by Rietveld analysis of diffraction patterns. The corresponding velocity profiles also showed a stepped wave structure, increasing in magnitude with energy. The overall results reveal possible densification of the glass due to delocalization of 4f electrons in Ce at lower laser shock pressures and increased crystallization with preferred orientation and distortion of the nanocrystals at higher shock compression conditions. [ABSTRACT FROM AUTHOR]

The nanometer size of CdTe quantum dots (QDs) and their unique optical properties, including size-tunable narrow photoluminescent emission, broad absorption, fast photoluminescence decay, and negligible light scattering, are ideal features for spectrally tagging the shock response of localized regions in highly heterogeneous materials such as particulate media. In this work, the timeresolved laser-excited photoluminescence response of QDs to shock-compression was investigated to explore their utilization as mesoscale sensors for pressure measurements and in situ diagnostics during shock loading experiments. Laser-driven shock-compression experiments with steady-state shock pressures ranging from 2.0 to 13 GPa were performed on nanocomposite films of CdTe QDs dispersed in a soft polyvinyl alcohol polymer matrix and in a hard inorganic sodium silicate glass matrix. Time-resolved photoluminescent emission spectroscopy was used to correlate photoluminescence changes with the history of shock pressure and the dynamics of the matrix material surrounding the QDs. The results revealed pressure-induced blueshifts in emitted wavelength, decreases in photoluminescent emission intensity, reductions in peak width, and matrix-dependent response times. Data obtained for these QD response characteristics serve as indicators for their use as possible time-resolved diagnostics of the dynamic shock-compression response of matrix materials in which such QDs are embedded as in situ sensors. [ABSTRACT FROM AUTHOR]

The shock-compression response of Ni+Al multilayered thin foils is investigated using laseraccelerated thin-foil plate-impact experiments over the pressure range of 2 to 11 GPa. The foils contain alternating Ni and Al layers (parallel but not flat) of nominally 50 nm bilayer spacing. The goal is to determine the equation of state and shock-induced reactivity of these highly reactive fully dense thin-foil materials. The laser-accelerated thin-foil impact set-up involved combined use of photon-doppler-velocimetry to monitor the acceleration and impact velocity of an aluminum flyer, and VISAR interferometry was used to monitor the back free-surface velocity of the impacted Ni+Al multilayered target. The shock-compression response of the Ni+Al target foils was determined using experimentally measured parameters and impedance matching approach, with error bars identified considering systematic and experimental errors. Meso-scale CTH shock simulations were performed using real imported microstructures of the cross-sections of the multilayered Ni+Al foils to compute the Hugoniot response (assuming no reaction) for correlation with their experimentally determined equation of state. It was observed that at particle velocities below ~150 m/s, the experimentally determined equation of state trend matches the CTH-predicted inert response and is consistent with the observed unreacted state of the recovered Ni+Al target foils from this velocity regime. At higher particle velocities, the experimentally determined equation of state deviates from the CTH-predicted inert response. A complete and self-sustained reaction is also seen in targets recovered from experiments performed at these higher particle velocities. The deviation in the measured equation of state, to higher shock speeds and expanded volumes, combined with the observation of complete reaction in the recovered multilayered foils, confirmed via microstructure characterization, is indicative of the occurrence of shock-induced chemical reaction occurring in the time-scale of the high-pressure state. TEM characterization of recovered shockcompressed (unreacted) Ni+Al multilayered foils exhibits distinct features of constituent mixing revealing jetted layers and inter-mixed regions. These features were primarily observed in the proximity of the undulations present in the alternating layers of the Ni+Al starting foils, suggesting the important role of such instabilities in promoting shock-induced intermetallic-forming reactions in the fully dense highly exothermic multilayered thin foils. [ABSTRACT FROM AUTHOR]