We conducted three Hugoniot and release experiments on copper on the Z machine at Hugoniot stress levels of 0.34 and 2.6 TPa, using two-layer copper/aluminum impactors traveling at 8 and 27 km/s and Z-quartz windows. Velocity histories were recorded for 4 samples of different thicknesses and 5 locations on the flyer plate (3 and 4 for the first two experiments). On-sample measurements provided Hugoniot points (via transit time) and partial release states (via Z-quartz wavespeed). Fabrication of the impactor required thick plating and several diamond-machining steps. The lower-pressure test was planned as a 2.5 TPa test, but a failure on the Z machine degraded its performance; however, these results corroborated earlier Cu data in the same stress region. The second test suffered from significant flyer plate bowing, but the third did not. The Hugoniot data are compared with the APtshuler/Nellis nuclear-driven data, other data from Z and elsewhere, and representative Sesame models.
Furnish, Michael D.; Shulenburger, Luke S.; Desjarlais, Michael D.; Fei, Yingwei F.
We have conducted a series of ride-along experiments on the Z facility to ascertain the Hugoniot of silica centered in the stishovite phase over a range 0.4 - 1.0 TPa, together with partial release states produced at the interface between the sample and a fused silica window. The stishovite samples were synthesized in a large-volume multi-anvil press at 15 GPa and 1773 K, with an initial density of 4.29 gm/cc. The new Z experiments on stishovite fill in a gap between gas gun experiments and NIF experiments. The states are compared with the Hugoniots of quartz and fused silica for inferences as to EOS. They are generally consistent with Sesame 7360 predictions. Sound speed constraints from these data are discussed. The new Hugoniot data cross over the melting curve of stishovite; together with the partial-release data and predictions from density-functional theory modeling, they provide insights into the properties of solid and liquid under extreme conditions. These data are fundamentally important for understanding the interior of silicate-based super-Earths.
Howard, Marylesa; Diaz, Abel; Briggs, Matthew E.; Crawford, Kristen; Dolan, Daniel H.; Furlanetto, Michael R.; Furnish, Michael D.; Holtkamp, David B.; La Lone, B.M.; Strand, Oliver T.; Stevens, Gerald D.; Tunnell, Thomas W.
Photonic Doppler Velocimetry is an interferometric technique for measuring the beat frequency of a moving surface, from which the calculated velocity profile of the surface can be used to describe the physical changes the material undergoes after high-impact shock. Such a technique may also be used to characterize the performance of small detonators and determine the time at which the surface began moving. In this work, we develop a semi-automated technique for extracting the time of initial movement from a normalized lineout of the power spectrogram near the offset frequency of each probe. We characterize the response bias of this method and compare with the time of initial movement obtained by hand calculation of the raw voltage data. Results are shown on data from shock experiments such as gas gun setups and explosives-driven flyer plates.
Low carbon, high strength steel alloys such as Vascomax steels are used in a wide variety of extreme environments due to their high strength, high fracture toughness, and stability over a wide range of temperatures. In this study, Vascomax® C250 steel was dynamically characterized in compression using Kolsky compression bar techniques at two strain rates of 1000 and 3000 s-1. A pair of impedance-matched tungsten carbide platens were implemented to protect damage to the bar ends. The tungsten carbide platens were experimentally calibrated as system compliance which was then properly corrected for actual specimen strain measurements. In addition, elastic indentation of the high-strength compression sample into the platens was also evaluated and showed negligible effect on the specimen strain measurements. The Vascomax® C250 steel exhibited strain-rate effects on the compressive stress-strain curves. The dynamic yield strength was approximately 18% higher than quasi-static yield strength obtained from hardness tests. The dynamic true stress-strain curves of the Vascomax® C250 steel in compression were also computed and then compared with the previously obtained true tensile stress-strain curves at the same strain rates. The Vascomax® C250 steel exhibited a reasonable symmetry in dynamic compression and tensile stress-strain response. However, the fracture strains in dynamic compression were smaller than those in dynamic tension probably due to different fracture mechanisms in the different loading modes.
We applied MBBAY high fluence pulsed radiation intensity driven momentum transfer analysis to calculate X-ray momentum coupling coefficients CM=(Pa s)/(J/m2) for two simplified comet analog materials: i) water ice, and ii) 70% water ice and 30% distributed olivine grains. The momentum coupling coefficients (CM) max of 50×10−5 s/m, are about an order of magnitude greater than experimentally determined and computed MBBAY values for meteoritic materials that are analogs for asteroids. From the values for comet analog materials we infer applied energies (via momentum transfer) required to deflect an Earth crossing comet from impacting Earth by a sufficient amount (~1 cm/s) to avert collision ~a year in advance. Comet model calculations indicate for CM=5×10−4 s/m the deflection of a 2 km comet with a density 600 kg/m3 by 1 cm/s requires an applied energy on the target surface of 5×1013 J, the equivalent of 12 kT of TNT. Depending on the geometrical configuration of the interaction the explosive yield required could be an order of magnitude higher.
Vascomax® maraging C250 and C300 alloys were dynamically characterized in tension with Kolsky tension bar techniques. Compared with conventional Kolsky tension bar experiments, a pair of lock nuts was used to minimize the pseudo stress peak and a laser system was applied to directly measure the specimen displacement. Dynamic engineering stress–strain curves of the C250 and C300 alloys were obtained in tension at 1000 and 3000 s−1. The dynamic yield strengths for both alloys were similar, but significantly higher than those obtained from quasi-static indentation tests. Both alloys exhibited insignificant strain-rate effect on dynamic yield strength. The C300 alloy showed approximately 10 % higher in yield strength than the C250 alloy at the same strain rates. Necking was observed in both alloys right after yield. The Bridgman correction was applied to calculate the true stress and strain at failure for both alloys. The true failure stress showed a modest strain rate effect for both alloys but no significant difference between the two alloys at the same strain rate. The C250 alloy was more ductile than the C300 alloy under dynamic loading.
The line-imaging ORVIS or VISAR provides velocity as a function of position and time for a line on an experimental setup via a streak camera record of interference fringes. This document describes a Matlab-based program which guides the user through the process of converting these fringe data to a velocity surface. The data reduction is of the "fringe trace" type, wherein the changes in velocity at a given position on the line are calculated based on fringe motion past that point. The analyst must establish the fringe behavior up front, aided by peak-finding routines in the program. However, the later work of using fringe jumps to compensate for phase problems in other analysis techniques is greatly reduced. This program is not a standard GUI construction, and is prescriptive. At various points it saves the progress, allowing later restarts from those points.
Material response to dynamic loading is often dominated by microstructure (grain structure, porosity, inclusions, defects). An example critically important to Sandia's mission is dynamic strength of polycrystalline metals where heterogeneities lead to localization of deformation and loss of shear strength. Microstructural effects are of broad importance to the scientific community and several institutions within DoD and DOE; however, current models rely on inaccurate assumptions about mechanisms at the sub-continuum or mesoscale. Consequently, there is a critical need for accurate and robust methods for modeling heterogeneous material response at this lower length scale. This report summarizes work performed as part of an LDRD effort (FY11 to FY13; project number 151364) to meet these needs.
In support of LLNL efforts to develop multiscale models of a variety of materials, we have performed a set of eight gas gun impact experiments on 2169 steel (21% Cr, 6% Ni, 9% Mn, balance predominantly Fe). These experiments provided carefully controlled shock, reshock and release velocimetry data, with initial shock stresses ranging from 10 to 50 GPa (particle velocities from 0.25 to 1.05 km/s). Both windowed and free-surface measurements were included in this experiment set to increase the utility of the data set, as were samples ranging in thickness from 1 to 5 mm. Target physical phenomena included the elastic/plastic transition (Hugoniot elastic limit), the Hugoniot, any phase transition phenomena, and the release path (windowed and free-surface). The Hugoniot was found to be nearly linear, with no indications of the Fe phase transition. Releases were non-hysteretic, and relatively consistent between 3- and 5-mmthick samples (the 3 mm samples giving slightly lower wavespeeds on release). Reshock tests with explosively welded impactors produced clean results; those with glue bonds showed transient releases prior to the arrival of the reshock, reducing their usefulness for deriving strength information. The free-surface samples, which were steps on a single piece of steel, showed lower wavespeeds for thin (1 mm) samples than for thicker (2 or 4 mm) samples. A configuration used for the last three shots allows release information to be determined from these free surface samples. The sample strength appears to increase with stress from ~1 GPa to ~ 3 GPa over this range, consistent with other recent work but about 40% above the Steinberg model.