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Two types of Mg-Cu composition system graded density impactors used for complex loading (shock loading and quasi-isentropic compression) are designed by the elastic-plastic hydrodynamic method in this paper. Mixtures of metal powders in the Mg-Cu system are cast into a series of 17 and 25 uniform compositions ranging from 100% Mg to 100% Cu. The graded density impactors are launched to the stationary 10 μm aluminum film and 12 mm LiF window targets by a two-stage light-gas gun in the National Key Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, CAEP, and the resulting wave profiles are measured with the DISAR system. Hydrodynamic simulation results are perfectly consistent with the experiments. Our work in this paper will set up a foundation for further research of controllable loading/releasing routes and rate experiments in the future.

We designed an Mg-W functionally graded-density materials system with two different sequences of density–thickness distributions and fabricated disk-like pellets with the graded-density materials by elaborate stacking of different metal powder layers, followed by a one-step hot-pressure sintering process. The microstructures of the sintered pellets were characterized using a scanning electronic microscope and a scanning acoustic microscope. The pellets were used as graded-density impactors (GDIs) to test their capabilities to produce complex particle-velocity wave profiles along a specified thermodynamic path. The wave profile was obtained from reverse-impact experiments using a two-stage light gas gun in which the GDI flyer impacted a lithium fluoride window. The particle-velocity history at the impact surface of the LiF window was deduced from the interference fringe numbers of the distance interferometer system for any reflector records. For GDIs consisting of nine composition layers of graded-density materials, the particle velocity profiles displayed combined shock loading and quasi-isentropic compressing and release processes. The impactor, consisting of 12 composition layers, produced wave profiles that contained shock loading, quasi-isentropic reloading, controlled releasing, and recompressing and released processes. The wave profiles simulated using a hydrodynamic computer model developed in house agree well with the experimental results as well as other theoretical results.

Several problems encountered in shock temperature measurements for metals using optical radiometry were discussed in detail. The influences of the driver/film gap upon the observed interface temperature history were formulated analytically, and the temperature relaxation behaviors at the film/window interface were also characterized. We found that the energy deposition at the driver/film gap would influence to varied degrees the film/window interface temperature profile unless the film deposited on the window can be regarded to have an infinite thickness. Modeling calculations showed that at shock pressures of a few megabars, the observed interface temperature of iron would be at least 300–600 K higher, relative to the prediction from the Grover model, provided that the gap and film were both 1 ∼ 2 pm thick. Additionally, a metal-plate sample was used to measure a reliable shock temperature based on one-dimensional heat conduction model for the plate-sample(driver)/ pm-gap/window setup we propose...

Dynamic strength behavior of Zr51Ti5Ni10Cu25Al9 bulk metallic glass (BMG) up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirming the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.

Equations of state of metals are important issues in earth science and planetary science. A major limitation of them is the lack of experimental data for determining pressure-volume and temperature of shocked metal simultaneously. By measuring them in a single experiment, a major source of systematic error is eliminated in determining from which shock pressure release pressure originates. Hence, a non-contact fast optical method was developed and demonstrated to simultaneously measure a Hugoniot pressure-volume (P(H)-V(H)) point and interfacial temperature T(R) on the release of Hugoniot pressure (P(R)) for preheated metals up to 1000 K. Experimental details in our investigation are (i) a Ni-Cr resistance coil field placed around the metal specimen to generate a controllable and stable heating source, (ii) a fiber-optic probe with an optical lens coupling system and optical pyrometer with ns time resolution to carry out non-contact fast optical measurements for determining P(H)-V(H) and T(R). The shock response of preheated tantalum (Ta) at 773 K was investigated in our work. Measured data for shock velocity versus particle velocity at an initial state of room temperature was in agreement with previous shock compression results, while the measured shock data between 248 and 307 GPa initially heated to 773 K were below the Hugoniot evaluation from its off-Hugoniot states. Obtained interfacial temperatures on release of Hugoniot pressures (100-170 GPa) were in agreement with shock-melting points at initial ambient condition and ab initio calculations of melting curve. It indicates a good consistency for shock melting data of Ta at different initial temperatures. Our combined diagnostics for Hugoniot and temperature provides an important approach for studying EOS and the temperature effect of shocked metals. In particular, our measured melting temperatures of Ta address the current controversy about the difference by more than a factor of 2 between the melting temperatures measured under shock and those measured in a laser-heated diamond anvil cell at ∼100 GPa.

Shock wave compression experiments were conducted on a Zr-based bulk metallic glass (BMG, Zr51Ti5Ni10Cu25Al9 in atomic percent) up to 110 GPa. Time-resolved free-surface velocity profiles were measured in a shock stress range from 18 to 28 GPa with velocity interferometer techniques. The shock Hugoniot data in a shock stress range from 53 to 110 GPa were obtained by using electric pin techniques. The time-resolved wave profiles showed a distinct two-wave structure consisting of an elastic precursor followed by a plastic wave. Based on the obtained wave profiles, the Hugoniot elastic limits were determined to be 6.9 to 9.6 GPa. The shock wave velocity (Ds) vs. particle velocity (up) Hugoniot data in a shock stress range from 18 to 110 GPa were linearly fitted by Ds=(4.241±0.035)+(1.015±0.024)up. No evidence of phase transition was found in the performed shock experiments of the Zr-based BMG.

LiF single crystal was used as transparent window (anvil) to tamp the shock-induced free surface expansion of Ta specimen, and the Ta/LiF interface temperature was measured under shock compression using optical pyrometry technique. The shock temperatures and/or melting temperatures of Ta up to ∼400 GPa were extracted from the observed interface temperatures based on the Tan–Ahrens’ model for one-dimensional heat conduction across metal/window ideal interface in which initial melting and subsequent solidification were considered under shock loading. The obtained data within the experimental uncertainties are consistent with the results from high-pressure sound velocity measurements. The temperature of the partial melting on Ta Hugoniot is estimated to be ∼9700 K at 300 GPa, supported by available results from theoretical calculations.

Unloading wave profile measurements using the velocity interference system for any reflector technique were performed on LY12 Al over shock stress ranging from ∼20to∼100GPa, from which longitudinal and bulk sound velocities along the quasielastic release path were evaluated. Based on the intrinsic relations under uniaxial strain conditions, the effective shear modulus defined by Cochran and Guinan (Lawrence Livermore National Laboratory Report No. UCID-17105, 1976) was correlated to the longitudinal and bulk sound velocities. Results show that the effective shear modulus calculated from the measured sound velocities decreases rapidly with the release stress and can be expressed approximately as a linear function of the release stress; the slope of the linear function depends the initial shock-loading stress. By using this linear function of the effective shear modulus, the performed numerical simulations well reproduce the release wave traces of the Al alloys observed in the present work and reported in l...

The shock compression response of nano-Fe powder (∼25nm) pressed to ∼35% theoretical maximum density was determined based on shock stress and wave velocity measurements using piezoelectric stress gauges. The obtained data show a discontinuity in shock wave velocity plotted against particle velocity and an inflexion in specific volume from compression to expansion with increasing shock stress. It is found that the Hugoniot of 25nm Fe powder cannot be fully described using analytical models that are otherwise capable of predicting the Hugoniot of micron-sized powder or highly porous materials.

The Hugoniot of preheated metal is related with its principal Hugoniot by means of the Gruneisen equation of state and the Rankine-Hugoniot equation. Modeling calculations show that the preheating lowers to a certain extent the shock impedance. The evaluated Hugoniot of preheated Mo is comparable with the available experimental data. Hugoniots of 6061-T6 Al flyers of different preheat temperatures in reported Hugoniot experiments on Z pinch [Knudson et al., J. Appl. Phys. 94, 4420 (2003)] are calculated, and the determined shock states of 6061-T6 Al using the impedance-match method are consistent with the reported results. This approach allows a reasonable evaluation for Hugoniot of the preheated metal mainly from its principal Hugoniot.

Based on the model that the high-pressure melting temperatures of metals approximately equal the experimentally measured interface temperatures between the metallic plate sample and the transparent window when shock- and/or release-induced melting falls into the mixed phase region, we proposed a method to determine the melting temperatures of metals under megabars of shock compression. Experiments were conducted by using the oxygen-free high-conductivity copper, and pure iron plate sample with single-crystal lithium fluoride windows. Results showed that the measured melting temperatures are in good agreement with reported theoretical calculations.