Aluminum Flyer Plates Research Articles

High-Strain Rate Spall Strength Measurement for CoCrFeMnNi High-Entropy Alloy

In this study, we experimentally investigate the high stain rate and spall behavior of Cantor high-entropy alloy (HEA), CoCrFeMnNi. First, the Hugoniot equations of state (EOS) for the samples are determined using laser-driven CoCrFeMnNi flyers launched into known Lithium Fluoride (LiF) windows. Photon Doppler Velocimetry (PDV) recordings of the velocity profiles find the EOS coefficients using an impedance mismatch technique. Following this set of measurements, laser-driven aluminum flyer plates are accelerated to velocities of 0.5–1.0 km/s using a high-energy pulse laser. Upon impact with CoCrFeMnNi samples, the shock response is found through PDV measurements of the free surface velocities. From this second set of measurements, the spall strength of the alloy is found for pressures up to 5 GPa and strain rates in excess of 106 s−1. Further analysis of the failure mechanisms behind the spallation is conducted using fractography revealing the occurrence of ductile fracture at voids presumed to be caused by chromium oxide deposits created during the manufacturing process.

A compact pulsed power driver with precisely shaped current waveforms for magnetically driven loading experiments.

Magnetically driven loading techniques based on high current pulsed power drivers are very important tools for researching material dynamic behaviors and high-pressure physics. Based on the technologies of a Marx generator energy storage and low impedance coaxial cable energy transmission, a compact high current pulsed power driver CQ-7 was developed and established at the Institute of Fluid Physics, China Academy of Engineering Physics, which can generate precisely shaped current waveforms for magnetically driven loading experiments. CQ-7 is composed of 256 two-stage Marx generators in parallel with low impedance, high voltage coaxial cables for current output. The 256 Marx generators are divided into 16 groups, and each separate group can be individually triggered to discharge and shape currents in sequence by a low jitter, high voltage pulse trigger with 16 output signals. The electrical parameters of CQ-7 are a capacitance of 20.48 µF, an inductance of 4.12 nH, and a resistance of 3.35 mΩ in a short circuit. When working at the charging voltage of ±40-±60kV, CQ-7 can deliver a peak current from 5 to 7 MA to the short-circuit loads with a rising time of 400-700ns at different discharging time sequences. Two different experiments were conducted to test the performance of CQ-7: magnetically driven high velocity flyer plates and solid liner implosion. The results show that CQ-7 can accelerate the aluminum flyer plate with a size of 12 × 8 × 1mm3 to more than 7.5 km/s and uniformly drive the aluminum liner with an inner diameter of 6.2mm and a thickness of 0.4mm to more than 9.5 km/s. Furthermore, these experiments indicate that CQ-7 is a robust platform for material dynamics and high-pressure physics.

Investigation of structure and mechanical properties under quasi-static and planar impact loading of aluminum composite reinforced with Al2O3 nanoparticles of different shape

We report on an investigation of the structure and mechanical properties under quasi-static and planar impact loading of Al-based nanocomposites reinforced with alumina nanoparticles of ball, plate and sheet shape fabricated through accumulative roll bonding (ARB) for 4 and 10 cycles. The distribution of the nanoparticles and structural characteristics of the matrix were revealed using transmission electron microscopy. The microhardness, ultimate and yield strengths and ductility under tension at the strain rate of 1 × 10−3 s−1 were measured as mechanical characteristics under the quasi-static loading. The maximum pressure of the impact compression, Hugoniot elastic limit and spall strength were calculated using the free surface velocity data recorded during the impact by aluminum flyer-plates with the impact velocity of 630 ± 30 m/s. Our results show that nanoparticles tend to agglomeration inside the composite. The size of agglomerates depends on the nanoparticle shape and a number of ARB cycles. Only the part of the ball-shaped nanoparticles can be distributed uniformly as separate nanoparticles after 10 ARB cycles. The introduction of the nanoparticles into aluminum assists in the structural refinement in the nanocomposites relative to alumina-free aluminum. This effect is mostly exhibited in the composite reinforced with the ball-shaped nanoparticles, some of which are distributed separately. The nanoparticle of different shape affects the mechanical properties ambivalently under both quasi-static and shock-wave conditions due to their various distribution in the matrix and different properties of the agglomerates. The spall strength decreases with the nanoparticle introduction because the particles and their agglomerates are the stress concentrators and crack origins.

Shock wave compressibility of composite materials based on aramid fibers

Using a VISAR laser interferometer, the experiments on investigation of the shock wave structure, spall strength and determination of Hugoniot parameters were performed for two composite materials based on the aramid fibers. Textolite and Kevlar were made using the same epoxy resin and aramid fibers, but had a different structure - unidirectional fibers and plies of woven fibers, respectively. The density of these materials is approximately 1.27 g/cm3. To study the shock wave compressibility of composite materials under high pressure, the explosive propellant charges were used to provide a flat throw of aluminum flyer plates with velocities from 0.7 to 5.05 km/s. As a result of experiments, particle velocity profiles on the composite/water boundary were obtained. On the velocity profiles for kevlar and textolite with transverse orientation of the fibers, after the initial shock jump, oscillations are observed due to the heterogeneous structure of the investigated materials. Unlike the composite materials with transverse orientation of the fibers, in the case when a shock wave propagates along the fibers, a two-wave configuration is recorded, which is due to the anisotropic structure of material. It was found that Hugoniots of composites with perpendicular orientation of the fibers are parallel to each other and differ only in the first coefficient determined by the sound speed of the material. Also a study of spall strength of textolite and Kevlar was performed. It was found for both materials that the value of spall strength along the fibers is higher than that for the transverse direction.

Sound velocity, shear modulus, and shock melting of beryllium along the Hugoniot

Magnetically launched flyer plates were used to investigate the shock response of beryllium between 90 and 300 GPa. Solid aluminum flyer plates drove steady shocks into polycrystalline beryllium to constrain the Hugoniot from 90 to 190 GPa. Multilayered copper/aluminum flyer plates generated a shock followed by an overtaking rarefaction which was used to determine the sound velocity in both solid and liquid beryllium between 130 and 300 GPa. Disappearance of the longitudinal wave was used to identify the onset of melt along the Hugoniot and measurements were compared to density functional theory calculations to explore the proposed hcp-bcc transition at high pressure. The onset of melt along the Hugoniot was identified at $\ensuremath{\sim}205\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, which is in good agreement with theoretical predictions. These results show no clear indication of an hcp-bcc transition prior to melt along the beryllium Hugoniot. Rather, the shear stress, determined from the release wave profiles, was found to gradually decrease with stress and eventually vanish at the onset of melt.

Quasi-static and shock-wave loading of ultrafine-grained aluminum: effect of microstructural characteristics

The interrelation between microstructural characteristics and mechanical properties under quasi-static and shock-wave (dynamic) loading was investigated in ultrafine-grained aluminum processed by accumulative roll bonding (ARB) for 4, 7, 10 and 14 cycles. The microstructural parameters such as the size of the elements of grain–subgrain structure, grain size and fraction of high-angle grain boundaries were obtained using transmission electron microscopy (TEM) and electron back scatter diffraction (EBSD). Indentation and tensile tests at the strain rate of 1 × 10−4 s−1 were applied as the quasi-static loading, the impact by aluminum flyer-plates with the impact velocity of 620 ± 30 m s−1 was the shock-wave loading. The strain rate in the rarefaction wave before spall fracture was 2 × 105–7 × 105 s−1 in the latter case. It is shown that the dislocation substructures and low-angle subboundaries significantly affect the strength properties under quasi-static conditions, while the grain size (the areas bounded by only high-angle boundaries) and fraction of high-angle grain boundaries mainly define the dynamic strength properties. The different influence of the microstructural characteristics on the quasi-static and dynamic mechanical properties is related to the easier dislocation cross-slip under high strain rates.

Microstructural and Phase Composition Differences Across the Interfaces in Al/Ti/Al Explosively Welded Clads

The microstructure and phase composition of Al/Ti/Al interfaces with respect to their localization were investigated. An aluminum-flyer plate exhibited finer grains located close to the upper interface than those present within the aluminum-base plate. The same tendency, but with a higher number of twins, was observed for titanium. Good quality bonding with a wavy shape and four intermetallic phases, namely, TiAl3, TiAl, TiAl2, and Ti3Al, was only obtained at the interface closer to the explosive material. The other interface was planar with three intermetallic compounds, excluding the metastable TiAl2 phase. As a result of a 100-hour annealing at 903 K (630 °C), an Al/TiAl3/Ti/TiAl3/Al sandwich was manufactured, formed with single crystalline Al layers. A substantial difference between the intermetallic layer thicknesses was measured, with 235.3 and 167.4 µm obtained for the layers corresponding to the upper and lower interfaces, respectively. An examination by transmission electron microscopy of a thin foil taken from the interface area after a 1-hour annealing at 825 K (552 °C) showed a mixture of randomly located TiAl3 grains within the aluminum. Finally, the hardness results were correlated with the microstructural changes across the samples.

Absolute equation of state measurement of aluminum using laser quasi-isentropic-driven flyer plate

AbstractIn this paper, we perform an absolute equation of state (EOS) measurement on the principal Hugoniot of aluminum using a near-symmetric impact method. The flyer plates are accelerated to high velocities using the laser-ramp-driven method. An aluminum flyer plate of ~25 µm is accelerated to the velocity range from 4 to 12 km/s. Then the aluminum flyer plate propagates across a vacuum gap and impacts with an aluminum step target. A line-imaging optical recording velocity interferometer for any reflector (ORVIS) is used to measure the aluminum flyer plate and the shock velocity simultaneously. Aluminum EOS data were measured with pressures range from 50 to 200 GPa. This absolute EOS measurement method may be used for studying a variety of materials.

Microstructure of CrMnNi Cast Steel After Explosive-Driven Flyer-Plate Impact at Room Temperature and Below

A low-carbon metastable austenitic CrMnNi cast steel was investigated under shock conditions in a flyer-plate impact test. The samples were impacted by aluminum flyer-plates with impact velocities of 620 ± 30 m/s. Depending on deformation temperature and strain rate, the material exhibited different deformation mechanisms (dislocation glide, martensitic transformation, and mechanical twinning), which determined the microstructural evolution and mechanical behavior. Flyer-plate impact tests were carried out at 213 K and 293 K (−60 °C and +20 °C). A soft recovered sample revealed microstructural changes directly after impact. The subsequent microstructural investigations via light-optical microscopy and scanning electron microscopy revealed that transformation-induced plasticity (TRIP effect) was the primary deformation mechanism. Moreover, it was possible to quantify the martensite volume fraction by different methods and to identify the hcp e-martensite phase as an intermediate transformation stage. A decrease in temperature also increased the driving force for the martensitic transformation.

On the scaling of the magnetically accelerated flyer plate technique to currents greater than 20 MA

In this article we discuss scaling the magnetically accelerated flyer plate technique to currents greater than is available on the Z accelerator. Peak flyer plate speeds in the range 7-46 km/s are achieved in pulsed power driven, hyper-velocity impact experiments on Z for peak currents in the range 8-20 MA. The highest (lowest) speeds are produced using aluminum (aluminum-copper) flyer plates. In either case, the =1 mm thick flyer plate is shocklessly accelerated by magnetic pressure to ballistic speed in =400 ns; it arrives at the target with a fraction of material at standard density. During acceleration a melt front, due to resistive heating, moves from the drive-side toward the target-side of the flyer plate; the speed of the melt front increases with increasing current. Peak flyer speeds on Z scale quadratically (linearly) with current at the low (high) end of the range. Magnetohydrodynamic simulation shows that the change in scaling is due to geometric deformation, and that linear scaling continues as current increases. However, the combined effects of shockless acceleration and resistive heating lead to an upper bound on the magnetic field feasible for pulsed power driven flyer plate experiments, which limits the maximum possible speed of a useful flyer plate to < 100 km/s.

High velocity flyer plates launched by magnetic pressure on pulsed power generator CQ-4 and applied in shock Hugoniot experiments.

High velocity flyer plates with good flatness and some thickness have being widely used to the field of shock physics for characterizations of materials under dynamical loading. The techniques of magnetically driven high-velocity flyer plates are further researched based on our pulsed power generators CQ-4 and some good results got on Sandia's Z machine. With large current of several mega-amperes, the loading surface of electrode panel will suffer acute phase transitions caused from magnetic diffusion and Joule heating, and the thickness and flatness of the flyer plates will change with time. In order to obtain the flyer plates with high performances for shock physics, some researches on electrode panels were done by means of LS-DYNA980 software with electro-magnetic package. Two typical configurations for high velocity flyer plates were compared from distribution uniformity of magnetic field in simulation. The results show that the configuration with counter-bore with "notch" and "ear" is better than the other. Then, with the better configuration panels, some experiments were designed and done to validate the simulation results and obtain high velocity flyer plates with good flatness for one-dimensional strain shock experiments on CQ-4. The velocity profiles of the flyer plates were measured by displacement interferometer systems for any reflectors. And the planarity of flyer plates was measured by using the optical fiber pins array for recording the flyer arrival time. The peak velocities of 8.7 km/s with initial dimension of 10 × 7.2 × 0.62 mm for aluminum flyer plates have been achieved. And the flyer plate with initial size of 12 × 9.2 × 0.73 mm was accelerated to velocity of 6.5 km/s with the flatness of less than 11 ns in the central region of 6 mm in diameter and the effective thickness of about 0.220 mm. Based on these work, the symmetrical impact experiments were performed to obtain the high accuracy Hugoniot data of OFHC (oxygen free high conductance) copper on CQ-4. The experimental results agree well with previous experiment's data given by Mcqueen and Marsh [J. Appl. Phys. 31, 1253 (1960)] and Mitchell and Nellis [J. Appl. Phys. 52, 3363 (1981)], and the experimental uncertainty of shock wave velocity is less than 2.4%.

Recent advances in hyper-velocity flyer launch experiments on PTS

Magnetically driven loading technology is to load the large pulse current to the test area through the pulsed power, which forms a smooth magnetic pressure rising over time to achieve a quasi-isentropic compression of sample and hyper-velocity flyer launch. Based on the output characteristics and parameters of PTS accelerator, two types of hyper-velocity flyer launch experiments with different load configurations, such as the load, flyer plates size, current waveform and diagnostic systems etc, are designed and tested. LY12 aluminum flyer plates with dimensions of 10 mm0.725 mm was launched by single-sided stripline load configuration to 11.5 km/s while the magnetic drive load pressure is near 0.9 10^5 MPa. Simulation and experimental results agrees well with those of in the flyer launch process and the ultimate velocity. Further simulation shows that the launch velocity of aluminum flyer plates with dimensions of 8.5 mm1 mm is expected to exceed 15 km/s under the program of optimizing the structural parameters and regulation. The design and experiment technology of hyper-velocity flyer launch based on multi-branch pulsed power generator has been mastered during the designs and experiments.

Carbon dioxide shock and reshock equation of state data to 8 Mbar: Experiments and simulations

We present density functional theory (DFT) simulations and shock-reshock experiments for liquid carbon dioxide (CO${}_{2}$) in the range 100 to 800 GPa. The simulations support the previously suggested dissociation threshold around 50 GPa [W. J. Nellis et al., J. Chem. Phys. 95, 5268 (1991)] for shocked liquid CO${}_{2}$ and describe a very steep Hugoniot past dissociation. We performed the shock-reshock experiments using the Sandia Z machine. The Z machine magnetically accelerated aluminum flyer plates to shock compress cryogenic liquid CO${}_{2}$ to 550 GPa and attained reshock states up to 840 GPa. The plate impact experiments combined with well-characterized impedance matching standards and laser velocimetry results in high-accuracy measurements of the principal Hugoniot and reshock states of liquid CO${}_{2}$. The experimental results validated the DFT simulations at extreme conditions and the combination of experiment and DFT provide reliable data for evaluating existing and constructing future wide-range equations of state models for molecular compounds such as CO${}_{2}$.

A 4 MA, 500 ns pulsed power generator CQ-4 for characterization of material behaviors under ramp wave loading

A pulsed power generator CQ-4 was developed to characterize dynamic behaviors of materials under ramp wave loading, and to launch high velocity flyer plates for shock compression and hypervelocity impact experiments of materials and structures at Institute of Fluid Physics, China Academy of Engineering Physics. CQ-4 is composed of twenty capacitor and primary discharge switch modules with total capacitance of 32 μF and rated charging voltage of 100 kV, and the storage energy is transmitted by two top and bottom parallel aluminum plates insulated by twelve layers of polyester film with total thickness of 1.2 mm. Between capacitor bank and chamber, there are 72 peaking capacitors with total capacitance of 7.2 μF and rated voltage of 120 kV in parallel, which are connected with the capacitor bank in parallel. Before the load, there is a group of seven secondary self-breaking down switches connected with the total circuit in series. The peaking capacitors and secondary switches are used to shape the discharging current waveforms. For short-circuit, the peak current of discharging can be up to 3 ~ 4 MA and rise time varies from 470 ns to 600 ns when the charging voltages of the generator are from 75 kV to 85 kV. With CQ-4 generator, some quasi-isentropic compression experiments under ramp wave loadings are done to demonstrate the ability of CQ-4 generator. And some experiments of launching high velocity flyer plates are also done on CQ-4. The experimental results show that ramp wave loading pressure of several tens of GPa on copper and aluminum samples can be realized and the velocity of aluminum flyer plate with size of 10 mm × 6 mm × 0.35 mm can be accelerated to about 11 km/s and the velocity of aluminum flyer plate with size of 10 mm × 6 mm × 0.6 mm can be up to about 9 km/s, which show that CQ-4 is a good and versatile tool to realize ramp wave loading and shock compression for shock physics.

Optic-microwave mixing velocimeter for superhigh velocity measurement

The phenomenon that a light beam reflected off a moving object experiences a Doppler shift in its frequency underlies practical interferometric techniques for remote velocity measurements, such as velocity interferometer system for any reflector (VISAR), displacement interferometer system for any reflector (DISAR), and photonic Doppler velocimetry (PDV). While VISAR velocimeters are often bewildered by the fringe loss upon high-acceleration dynamic process diagnosis, the optic-fiber velocimeters such as DISAR and PDV, on the other hand, are puzzled by high velocity measurement over 10 km/s, due to the demand for the high bandwidth digitizer. Here, we describe a new optic-microwave mixing velocimeter (OMV) for super-high velocity measurements. By using currently available commercial microwave products, we have constructed a simple, compact, and reliable OMV device, and have successfully obtained, with a digitizer of bandwidth 6 GH only, the precise velocity history of an aluminum flyer plate being accelerated up to 11.2 km/s in a three stage gas-gun experiment.

Magnetically driven hyper-velocity launch capability at the Sandia Z accelerator

The intense magnetic field generated by the Z accelerator at Sandia National Laboratories is used as a pressure source for material science studies. A current of ∼20 MA can be delivered to the loads used in experiments on a time scale of ∼100–600 ns. Magnetic fields (pressures) exceeding 1200 T (600 GPa) have been produced in planar configurations. In one application we have developed, the magnetic pressure launches a flyer plate to ultra-high velocity in a plate impact experiment; equation of state data is obtained on the Hugoniot of a material that is shock compressed to multi-megabar pressure. This capability has been enhanced by the recent development of a planar stripline configuration that increases the magnetic pressure for a given current. Furthermore, the cross sectional area of a stripline flyer plate is larger than in previous coaxial loads; this improves the planarity of the flyer thereby reducing measurement uncertainty. Results of experiments and multi-dimensional magneto hydrodynamic (MHD) simulation are presented for ultra-high velocity aluminum and copper flyer plates. Aluminum flyer plates with dimensions ∼25 mm by ∼13 mm by ∼1 mm have been launched to velocities up to ∼45 km/s; for copper the peak velocity is ∼22 km/s. The significance of these results is that part of the flyer material remains solid at impact with the target; an accomplishment that is made possible by shaping the dynamic pressure (current) ramp so that the flyer compresses quasi-isentropically (i.e., shocklessly) during acceleration.

Magnetic acceleration of aluminum foils for shock wave experiments

Scaled experiments studying the interaction of shock waves with inhomogeneous background media are essential for understanding many astrophysical phenomena, since they can be used to test analytical theories and simulation codes. We are currently developing such experiments at the Nevada Terawatt Facility. We are using a pulsed power generator (1 MA peak current) to accelerate thin aluminum flyer plates. By impacting these foils on low-density foam targets, we will be able to carry out scaled experiments. We have demonstrated velocities of up to 8 km/s for 50 μm thick aluminum flyers, and are planning to further increase the flyer velocities. We have also carried out first impact tests with transparent polycarbonate targets. Several improvements for our setup are currently in planning, and these improvements will enable us to design scaled experiments for our facility.

Surface coating by diamond particles on an aluminum substrate by underwater shock wave

A new method for surface coating of an aluminum plate by diamond particles is developed. Underwater shock wave derived from the detonation of an explosive acts to accelerate an aluminum flyer plate to a desired velocity, the flyer plate collides with diamond particles and an aluminum base plate. Diamond particles are penetrated into aluminum. A diamond rich layer which of about 200 μm in depth was generated and the volume fraction of diamond was observed to gradually decrease from top to bottom. A simplified numerical simulation for observation of aluminum deformation at the collision was performed using Ls-Dyna software.

The compact capacitor bank CQ-1.5 employed in magnetically driven isentropic compression and high velocity flyer plate experiments

Based on the low inductance capacitor, the parallel-plate transmission line, and the explosive network closing switch, a compact pulsed power generator CQ-1.5 has been developed at the Institute of Fluid Physics and is capable to deliver a current of peak of 1.5 MA within rise time of 500-570 ns into a 2-3 nH inductive load. The work is motivated to do isentropic compression experiments (ICEs) on metals up to 30-50 GPa and to launch flyer plates at velocities over 8 kms. The experiments were conducted with the diagnostics of both Doppler pin system and velocity interferometer system for any reflectors, and the measured free surface velocity histories of ICE samples were treated with a backward integration code. The results show that the isentropes of Cu and Al samples under 35 GPa are close to their Hugoniots within a deviation of 3%. The LY12 aluminum flyer plates were accelerated to a velocity over 8.96 kms.

Magnetically accelerated, ultrahigh velocity flyer plates for shock wave experiments

The intense magnetic field produced by the 20 MA Z accelerator is used as an impulsive pressure source to accelerate metal flyer plates to high velocity for the purpose of performing plate impact, shock wave experiments. This capability has been significantly enhanced by the recently developed pulse shaping capability of Z, which enables tailoring the rise time to peak current for a specific material and drive pressure to avoid shock formation within the flyer plate during acceleration. Consequently, full advantage can be taken of the available current to achieve the maximum possible magnetic drive pressure. In this way, peak magnetic drive pressures up to 490 GPa have been produced, which shocklessly accelerated 850μm aluminum (6061-T6) flyer plates to peak velocities of 34km∕s. We discuss magnetohydrodynamic (MHD) simulations that are used to optimize the magnetic pressure for a given flyer load and to determine the shape of the current rise time that precludes shock formation within the flyer during acceleration to peak velocity. In addition, we present results pertaining to plate impact, shock wave experiments in which the aluminum flyer plates were magnetically accelerated across a vacuum gap and impacted z-cut, α-quartz targets. Accurate measurements of resulting quartz shock velocities are presented and analyzed through high-fidelity MHD simulations enhanced using optimization techniques. Results show that a fraction of the flyer remains at solid density at impact, that the fraction of material at solid density decreases with increasing magnetic pressure, and that the observed abrupt decrease in the quartz shock velocity is well correlated with the melt transition in the aluminum flyer.