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Brittle materials such as glasses and polycrystalline ceramics are attractive for armor materials and for aerospace applications because of their high compressive strengths and their lower densities than metals. Leaded glasses exhibit lower Young’s modulus and slow crack growth exponent as compared to lead free soda-lime silica glass or high purity glasses such as fused silica allowing this to be an excellent candidate for these applications. A series of experiments utilizing the 90 mm bore single-stage powder gun has probed the planar (uniaxial strain) impact response of leaded silica glasses that were subjected to peak shock stress up to 22 GPa. The material studied was a potash-soda-lead glass with approximately 30% lead by weight and a density of 3.034 g/cm3. Glass samples of 25 mm diameter and of two different thicknesses (3 mm and 7 mm) were used for these experiments. Velocity interferometry data acquired during this investigation have been evaluated to determine dynamic yield strength (Hugoniot elastic limit) and shock Hugoniot state of the glass.

The phase transition of crystalline and amorphous silica materials to a stishovite-like high-pressure phase has received considerable interest. While most work has focused on pure SiO2 glass (fused silica), studies identifying a similar high-pressure phase transformation in soda-lime glass have not been performed. Marked differences in the network structure and compressibility of soda-lime glass as compared to fused silica raise questions as to how a stishovite transition might manifest in these glasses. In this work, new plate impact experiments on soda-lime glass have been performed to ∼110 GPa to measure the Hugoniot response in the high-pressure regime. Results of these tests were unable to find evidence of a transition to a high-pressure polymorph under shock loading. A glass constitutive model is proposed to capture this newly measured high-pressure response. Good agreement between time resolved measurements and simulation results from the CTH hydrocode with this model implemented are shown, along with additional insights into the apparent glass behavior.

The work presented in this paper details both an experimental program and an associated numerical modeling effort to characterize and predict the ballistic response of S-2 glass/SC15 epoxy composite panels. The experimental program consisted of ¼ inch diameter soft carbon steel spheres impacting ¼ and ½ inch thick flat composite panels at velocities ranging from 220 to 1570 m/s. High speed cameras were used to capture the impact event and resulting residual velocity of the spheres for each test configuration. After testing, each panel was inspected both visually and with ultrasonic C-scan techniques to determine the extent and depth of damage imparted on the panel by the impactor. The numerical modeling efforts utilized the anisotropic multi-constituent composite model (MCM) within the CTH shock physics hydrocode. The MCM model allows for evaluation of damage at the constituent level through continuum averaged stress and strain fields. The model also accounts for the inherent coupling of the equation of state and strength response that occurs in anisotropic composite materials. Finally, the simulation results are compared against the experimentally measured residual velocity as a quantitative metric and against the measured damage extent and patterns as a qualitative metric. The comparisons show good agreement in residual velocity and damage extent.

The high-pressure dynamic response of titanium dioxide (TiO 2) is not only of interest because of its numerous industrial applications but also because of its structural similarities to silica (SiO 2). We performed plate impact experiments in a two-stage light gas gun, at peak stresses from 64 to 221 GPa to determine the TiO 2 response along the Hugoniot. The lower stress experiment at 64 GPa shows an elastic behavior followed by an elastic–plastic transition, whereas the high stress experiments above 64 GPa show a single wave structure. Previous shock studies have shown the presence of high-pressure phases (HPP) I (26 GPa) and HPP II (100 GPa); however, our data suggest that the HPP I phase is stable up to 150 GPa. Using a combination of data from our current study and our previous Z-data, we determine that TiO 2 likely melts on the Hugoniot at 157 GPa. Furthermore, our data confirm that TiO 2 is not highly incompressible as shown by a previous study.

This article details the implementation and application of the glass-specific computational constitutive model by Holmquist and Johnson (J Appl Mech 78:051003, 2011) to simulate the dynamic response of soda-lime glass under high rate and high pressure shock conditions. The predictive capabilities of this model are assessed through comparison of experimental data with numerical results from computations using the CTH shock physics code. The formulation of this glass model is reviewed in the context of its implementation within CTH. Using a variety of experimental data compiled from the open literature, a complete parameterization of the model describing the observed behavior of soda-lime glass is developed. Simulation results using the calibrated soda-lime glass model are compared to flyer plate and Taylor rod impact experimental data covering a range of impact and failure conditions spanning an order of magnitude in velocity and pressure. The complex behavior observed in the experimental testing is captured well in the computations, demonstrating the capability of the glass model within CTH.

Composite materials are used as alternatives to conventional metallics in a multitude of applications including military ground vehicles, aircraft, space launch and re-entry vehicles and even personnel protection where weight savings are critical. In application, these materials are susceptible to high velocity impacts from various threats and it is essential that the response of these materials, under relevant conditions, be understood in order to provide optimized effective designs. This work details an on-going effort to validate the anisotropic multiple constituent model (MCM) within the CTH hydrocode. Within the CTH framework, the anisotropic MCM model is coupled with an equation of state (EOS) and provides continuum averaged stress and strain fields for each constituents (fiber and resin) of a composite microstructure from which progressive damage evaluations can be performed. In this paper we focus on recent validation efforts where woven S2/SC15 (glass/epoxy) composite panels were impacted with steel spheres at various impact velocities and angles of obliquity. The experimental testing was performed at the Shock Thermodynamics Applied Research (STAR) Facility at Sandia National Laboratories to provide data for further validation of the MCM model under oblique impact conditions. Oblique impacts result in stress fields which exercise the anisotropy of the strength model and the EOS coupling of the MCM model more robustly. Results are presented for both the CTH MCM model predictions and the experimental testing. The primary comparison metrics evaluated are the predicted and observed damage extent, overall damage pattern, and residual velocity of the projectile.

For armor applications, ceramic materials are often useful due to their high dynamic strength. In some instances, in addition to high strength, the armor must also be transparent, which significantly limits the choices of materials. Materials in the aluminum oxide–aluminum nitride family (including Al2O3 and AlON) are both strong and transparent. Only the end compound AlN is opaque. In this paper, the dynamic response to shock loading is examined for these materials to better understand the material response. Despite the chemical similarities, significant differences exist in the shock response and will be discussed.

The recently developed Magnetically Applied Pressure-Shear (MAPS) experimental technique to measure material shear strength at high pressures on magneto-hydrodynamic (MHD) drive pulsed power platforms was fielded on August 16, 2013 on shot Z2544 utilizing hardware set A0283A. Several technical and engineering challenges were overcome in the process leading to the attempt to measure the dynamic strength of NNSA Ta at 50 GPa. The MAPS technique relies on the ability to apply an external magnetic field properly aligned and time correlated with the MHD pulse. The load design had to be modified to accommodate the external field coils and additional support was required to manage stresses from the pulsed magnets. Further, this represents the first time transverse velocity interferometry has been applied to diagnose a shot at Z. All subsystems performed well with only minor issues related to the new feed design which can be easily addressed by modifying the current pulse shape. Despite the success of each new component, the experiment failed to measure strength in the samples due to spallation failure, most likely in the diamond anvils. To address this issue, hydrocode simulations are being used to evaluate a modified design using LiF windows to minimize tension in themore » diamond and prevent spall. Another option to eliminate the diamond material from the experiment is also being investigated.« less

Magnetically-applied pressure-shear (MAPS) is a recently developed technique to directly measure material shear strength using magnetohydrodynamic (MHD) pulsed power platforms [1,2]. The method has been prototyped on Sandia's Veloce pulser, but was limited to strength measurements at modest pressures of ~10 GPa. Our present aim is to develop MAPS into a robust technique to measure strength at higher pressures achievable on Sandia's Z pulsed power machine.

Pressure-shear experiments were performed on granular tungsten carbide and sand using a newly-refurbished slotted barrel gun. The sample is a thin layer of the granular material sandwiched between driver and anvil plates that remain elastic. Because of the obliquity, impact generates both a longitudinal wave, which compresses the sample, and a shear wave that probes the strength of the sample. Laser velocity interferometry is employed to measure the velocity history of the free surface of the anvil. Since the driver and anvil remain elastic, analysis of the results is, in principal, straightforward. Experiments were performed at pressures up to nearly 2 GPa using titanium plates and at higher pressure using zirconium plates. Those done with the titanium plates produced values of shear stress of 0.1-0.2 GPa, with the value increasing with pressure. On the other hand, those experiments conducted with zirconia anvils display results that may be related to slipping at an interface and shear stresses mostly at 0.1 GPa or less. Recovered samples display much greater particle fracture than is observed in planar loading, suggesting that shearing is a very effective mechanism for comminution of the grains.

Magnetically-Applied Pressure-Shear (MAPS) is a new experimental technique to measure material shear strength at high pressures and has been developed for use on MHD driven pulsed power platforms [1]. By applying an external static magnetic field to the sample region, the MHD drive directly induces a shear stress wave in addition to the usual longitudinal stress wave. Strength is probed by passing this shear wave through a sample material where the transmissible shear stress is limited to the sample strength. The magnitude of the transmitted shear wave is measured via a transverse velocity interferometry system (VISAR) from which the sample strength is determined [2]. This paper presents and analyzes the 2D MHD simulations used to design the MAPS experiments.

A new experimental technique to measure material shear strength at high pressures has been developed for use on magneto-hydrodynamic (MHD) drive pulsed power platforms. By applying an external static magnetic field to the sample region, the MHD drive directly induces a shear stress wave in addition to the usual longitudinal stress wave. Strength is probed by passing this shear wave through a sample material where the transmissible shear stress is limited to the sample strength. The magnitude of the transmitted shear wave is measured via a transverse VISAR system from which the sample strength is determined.

The behavior of a shocked tungsten carbide / epoxy mixture as it expands into a vacuum has been studied through a combination of experiments and simulations. X-ray radiography of the expanding material as well as the velocity measured for a stood-off witness late are used to understand the physics of the problem. The initial shock causes vaporization of the epoxy matrix, leading to a multi-phase flow situation as the epoxy expands rapidly at around 8 km/s followed by the WC particles moving around 3 km/s. There are also small amounts of WC moving at higher velocities, apparently due to jetting in the sample. These experiments provide important data about the multi-phase flow characteristics of this material.

Material heterogeneity appears to give rise to variability in the yield behavior of ceramics and metals under shock loading conditions. The line‐imaging VISAR provides a way to measure this variability, which may then be quantified by Weibull statistics or other methods. Weibull methods assign a 2‐parameter representation of failure phenomena and variability. We have conducted experiments with tantalum (25 and 40 μm grains) and silicon carbide (SiC‐N with 5 μm grains). The tantalum HEL variability did not depend systematically on peak stress, grain size or sample thickness, although the previously observed precursor attenuation was present. SiC‐N HEL variability within a single shot was approximately half that of single‐point variability in a large family of shots; these results are more consistent with sample‐to‐sample variation than with variability due to changing shot parameters.

This study is best characterized as new technology development for implementing new sensors to investigate the optical characteristics of a rapidly expanding debris cloud resulting from hypervelocity impact regimes of 7 to 11 km/s. Our gas guns constitute a unique test bed that match operational conditions relevant to hypervelocity impact encountered in space engagements. We have demonstrated the use of (1) terahertz sensors, (2) silicon diodes for visible regimes, (3) germanium and InGaAs sensors for the near infrared regimes, and (4) the Sandia lightning detectors which are similar to the silicon diodes described in 2. The combination and complementary use of all these techniques has the strong potential of ''thermally'' characterizing the time dependent behavior of the radiating debris cloud. Complementary spectroscopic measurements provide temperature estimates of the impact generated debris by fitting its spectrum to a blackbody radiation function. This debris is time-dependent as its transport/expansion behavior is changing with time. The rapid expansion behavior of the debris cools the cloud rapidly, changing its thermal/temperature characteristics with time. A variety of sensors that span over a wide spectrum, varying from visible regime to THz frequencies, now gives us the potential to cover the impact over a broader temporal regimemore » starting from high pressures (Mbar) high-temperatures (eV) to low pressures (mbar) low temperatures (less than room temperature) as the debris expands and cools.« less

This study details and demonstrates a strain-based criterion for the prediction of polymer matrix composite material damage and failure under shock loading conditions. Shock loading conditions are characterized by high-speed impacts or explosive events that result in very high pressures in the materials involved. These material pressures can reach hundreds of kbar and often exceed the material strengths by several orders of magnitude. Researchers have shown that under these high pressures, composites exhibit significant increases in stiffness and strength. In this work we summarize modifications to a previous stress based interactive failure criterion based on the model initially proposed by Hashin, to include strain dependence. The failure criterion is combined with the multi-constituent composite constitutive model (MCM) within a shock physics hydrocode. The constitutive model allows for decomposition of the composite stress and strain fields into the individual phase averaged constituent level stress and strain fields, which are then applied to the failure criterion. Numerical simulations of a metallic sphere impacting carbon/epoxy composite plates at velocities up to 1000 m/s are performed using both the stress and strain based criterion. These simulation results are compared to experimental tests to illustrate the advantages of a strain-based criterion in the shock environment.