The Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) test was developed at LANL by Gray and coworkers to probe the tensile response of materials at large strains (>1) and high strain-rates (>1,000/s) by firing projectiles through a conical die at 300–700m/s. This technique has recently been applied to various polymers, such as the fluoropolymers PTFE (Teflon) and the chemically similar PCTFE, which respectively exhibited catastrophic fragmentation and distributed dynamic necking. This work details investigations of the Dyn-Ten-Ext response of high density polyethylene, both to failure and sub-critical conditions. At large extrusion ratios (~7.4) and high velocities, such as those previously employed, HDPE catastrophically fragmented in a craze-like manner in the extruded jet. At more modest extrusion ratios and high velocities the specimen extruded a stable jet that ruptured cleanly, and at lower velocities was recovered intact after sustaining substantial internal damage. Thermomechanical finite element simulations showed that the damage corresponded to a locus of shear stress in the presence of hydrostatic tension. X-ray computed tomography corroborated the prediction of a shear damage mechanism by finding the region of partially damaged material to consist of macroscopic shear-mode cracks nearly aligned with the extrusion axis, originating from the location of damage inception.

Observations of unit cell compression or decomposition during dynamic shock loading requires the implementation of a probe capable of penetrating an opaque and evolving sample at elevated pressures and temperatures. By pairing synchrotron generated high energy X-rays and gas gun driven plate impact, we were able to study the evolution of the structure in polytetrafluoroethylene (PTFE) at pressures spanning 1.84–52.9 GPa. Under the planar, one-dimensional, shockwave, the polymer was forced into an anisotropic conformation, in which the polymer chains assembled parallel to the shockwave. PTFE initially has a hexagonal crystal structure (Phase IV), once it was compressed above ~0.5 GPa it had a conformational change to the orthorhombic crystal structure (Phase III). The compression of the polymer chains was observed by X-ray diffraction, where the PTFE (110) peak shifted to higher q with increased pressure; polymer chain compression was still observed at 30.0 GPa. The highest pressure shot, at 52.9 GPa, above the reactants to products transition region, showed no new carbon species formation within the given time window and q -range. By following the orthorhombic lattice diffraction peak, we were able to calculate the Hugoniot loci of the crystalline and amorphous parts for each dynamic event (LA-UR-22-31436).

Abstract Prewar work on the hydrodynamics of explosives and U.S./UK scientific cooperation well beyond Los Alamos contributed to the design of the explosive lenses for the Trinity gadget. Researchers were deliberately brought together and encouraged to share ideas by the leaders of the wartime laboratory. James Tuck, one of the British mission scientists, made particularly interesting contributions in this area, but this paper is not a claim of British or any other individual parentage. Rather, it highlights the importance of collaboration at Los Alamos and more widely.

The response of Viton B, a fluorinated tripolymer, to one dimensional shock loading has been investigated using manganin stress gauges as the diagnostic. These have been mounted such that they are sensitive to both the longitudinal and lateral components of stress. In the case of the longitudinal gauges, mounting at multiple locations within the target assembly also allows measurement of shock and release velocities as well. Results show that in terms of shock velocity and stress and shear strength, results from Viton B lie a little higher than the corresponding results for polytetrafluoroethylene (PTFE), but more similar to those of polyvinylidene difluoride (PVDF). However, in terms of the release velocity, the behaviour of Viton B is more akin to PTFE. We believe that there are two competing mechanisms at play; an electrostatic repulsion between chains due to the presence of electronegative fluorine atoms that acts against interchain interactions (hence the low shock and high release velocities) and interchain entanglement (tacticity) due to the presence of trifluoromethyl side groups on one of the monomer sub units. This will result in a greater shock velocity and increase in shear strength behind the shock front (when compared to PTFE) as adjacent polymer chains physically interact via entanglement. This should reduce the release velocity for similar reasons; however the release behaviour of Viton B and PTFE is similar. We thus suggest that the electrostatic repulsion between chains may be acting over a longer length scale than interchain entanglement.

Professor John Edwin Field passed away on October 21st, 2020 at the age of 84. Professor Field was widely regarded as a leader in high-strain rate physics and explosives. During his career in the Physics and Chemistry of Solids (PCS) Group of the Cavendish Laboratory at Cambridge University, John made major contributions into our understanding of friction and erosion, brittle fracture, explosives, impact and high strain-rate effects in solids, impact in liquids, and shock physics. The contributions made by the PCS group are recognized globally and the impact of John’s work is a lasting addition to our knowledge of the dynamic effects in materials. John graduated 84 Ph.D. students and collaborated broadly in the field. Many who knew him attribute their success to the excellent grounding in research and teaching they received from John Field.

This article is set during the 1944 and 1945 final push to complete Project Y -- the Manhattan Project at Los Alamos -- and focuses primarily on overcoming the challenge of creating and demonstrating a successful convergent explosive implosion to turn a subcritical quantity of plutonium into a critical mass. The critical mass would then efficiently yield kilotons of trinitrotoluene (TNT)-equivalent energy in about a microsecond, demonstrating the implosion atomic bomb concept. This work culminated in the Trinity atomic test near Alamogordo on July 16, 1945. This implosion effect demarcated the approach to explosive science and technology the Laboratory has followed ever since, including development of high-explosive synthesis and formulation, small and large test and diagnostic facilities, shock dynamics theory, high-explosive system design engineering, and three-dimensional implosion modeling and simulation using some of the fastest computers in the world. This work also ushered in a period of broader application of precision high explosives in conventional munitions, demolition, mining and oil exploration, and space travel.

Los Alamos National Laboratory has a long history of developing and fielding high explosive pulsed power (HEPP) components and systems. In recent years, the Ranchero flux compression generator (FCG or generator) has been modified for improved high current performance, and a new helical flux compression generator (HFCG), the MK-X, has been designed to provide higher initial flux for Ranchero FCGs than can be achieved with the existing capacitor bank at Los Alamos HEPP test facilities. Integrating these two FCGs into a system is the focus of current development, and the first full system test has been performed. The system consists of a MK-X coupled efficiently to an R43S6 FCG with an exploratory pulse forming network (PFN) connecting the FCGs to the load. "R43S6" has become the shorthand designation for a Ranchero module with a 43 cm coaxial section and a Swooped output using a 6 inch diameter coaxial high explosive charge. The goal is to deliver ~50 MA to physics loads on microsecond time scales, and the following material illuminates the design philosophy and summarizes the outcome of the discussions and tests. Analysis of test data is still in progress, and a preliminary synopsis of results is given. Details of our PFN work are given by Gianakon [1] in this conference.

An internal state variable (ISV) model for polyether ether ketone (PEEK) is developed to capture experimental measurements conducted below its glass transition temperature. The model is based on the response of two relaxing components put in parallel, one having a back stress response that softens with plastic flow. This softening allows reproducing both monotonic and cyclic loading, and is possibly associated with detangling, melting of network junctions, and/or change in crystallinity. The resulting model, which is thermodynamic and multidimensional, was used to capture the response of PEEK 450G using thermal expansion (23 degrees C to 120 degrees C), heat capacity (-40 degrees C to 140 degrees C), monotonic extension and compression (-85 degrees C to 150 degrees C; 0.0001 s(-1) to 3000 s(-1); strains up to 40-80%), equilibrium stress measurements in compression (23 degrees C to 120 degrees C; strains up to 60%), and ultrasonic longitudinal and shear wave speed measurements along and transverse to the directions of compression (23 degrees C to 120 degrees C; up to 50% plastic compression). The model is compared to the response under monotonic and cyclic shear and internal dissipation is assessed using the equivalent adiabatic temperature rise.

The well-known Taylor cylinder impact test, which follows the impact of a flat-ended cylindrical rod onto a rigid stationary anvil, is conducted over a range of impact speeds for two polymers, polymethylmethacrylate (PMMA) and polycarbonate (PC). Experiments and modeling were developed to capture the deformation and fracture behavior of the cylinders after impact. The Taylor impact loading geometry imposes high levels of pressure and shear loading at impact velocities above a critical value. Introduction of shear stress at the rod-anvil interface was achieved in a new constitutive model by varying of conditions using a mediating material at the interface. This study showed a region in which there was spatial and temporal variation of both longitudinal and radial deformation that provided evidence of different failure modes.

The response of simple polymers to shock loading is governed by a number of factors such as the complexity of the polymer chains and nature of the atoms attached to the main carbon-carbon backbone. In the case of polyethylene based materials such as polyethylene, polypropylene and polytetrafluoroethylene the competing effects of inter chain tangling (tacticity) and electrostatic repulsion between adjacent polymer chains have been shown to have a profound effect on shock velocity, release velocity and shear strength development. In this work, we apply these considerations to a commercially available fluoro-tripolymer, Viton-B, where all these molecular features are present.

The well-known Taylor cylinder impact test, which follows the impact of a flat-ended cylindrical rod onto a rigid stationary anvil, is conducted over a range of impact speeds for two polymers, polytetrafluoroethylene (PTFE) and polyetheretherketone (PEEK). In previous work, experiments and a model were developed to capture the deformation behaviour of the cylinder after impact. These works showed a region in which spatial and temporal variation of both longitudinal and radial deformation provided evidence of changes in phase within the material. In this further series of experiments, this region is imaged in a range of impacted targets at the Diamond synchrotron. Further techniques were fielded to resolve compressed regions within the recovered polymer cylinders that showed a fracture zone in the impact region. The combination of macroscopic high-speed photography and three-dimensional X-ray imaging has identified the development of failure with these polymers and shown that there is no abrupt transition in behaviours but rather a continuous range of responses to competing operating mechanisms. The behaviours noted in PEEK in these polymers show critical gaps in understanding of polymer high strain-rate response.

Use of polymers in defense, aerospace and industrial applications under extreme loading conditions makes prediction of the behavior of these materials very important. Crucial to this is knowledge of the physical damage response in association with phase transformations during loading and the ability to predict this via multi-phase simulation accounting for thermodynamical non-equilibrium and strain rate sensitivity. The current work analyzes Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) experiments on polytetrafluoroethylene (PTFE). In particular, the phase transition during loading and subsequent tension are analyzed using a two-phase rate sensitive material model implemented in the CTH hydrocode. The calculations are compared with experimental high-speed photography. Deformation patterns and their link with changing loading modes are analyzed numerically and correlated to the test observations. It is concluded that the phase transformation is not as critical to the response of PTFE under Dyn-Ten-Ext loading as it is during the Taylor rod impact testing.

The well-known Taylor cylinder impact test, that follows the impact of a flat-ended cylindrical rod onto a rigid stationary anvil, is conducted over a range of impact speeds for two polymers, PTFE and PEEK. In previous work experiments and a model were developed to capture the deformation behaviour of the rod after impact. A distinctive feature of these works was that a region in which both spatial and temporal variation of both longitudinal and radial deformation showed evidence of changes in phase within the material. This region is X-ray imaged in a range of impacted targets at the I13 Imaging and Coherence beam line at the Diamond synchrotron. Further techniques were fielded to resolve compressed regions within the recovered polymer cylinders that showed a fracture zone in the impact region. This shows the transit of damage from ductile to brittle failure results from previously undetected internal failure.

With the development of new methods for the characterization of equilibrium stress through cyclic loading, it is now possible to follow the evolution of back stress during the nonlinear deformation of polymers. Experiments on PEEK and PC below the glass-transition temperature indicate a back stress that may evolve with plastic deformation, and which is substantially different from that seen during the response in the rubbery range. In particular, the back stress during the response of PC shows the characteristic post-yield softening, possibly indicating that the observed post-yield softening in the response comes from the back stress. This is not seen in PEEK, which also shows no substantial post-yield softening. The equilibrium stress plays a central role in modeling both the quasi-static and dynamic response of PEEK.

Traditional viscoelastic models for describing polymer response during large deformations are normally designed to capture the response during monotonic loading and typically have difficulty capturing the response after a reversal of the deformation process. In particular, most models pay little attention to capturing the equilibrium stress, the anisotropy developed after plastic flow in the elastic response, and the characteristics of the yield and subsequent flow after reversal of the loading. To characterize these events, the thermo-mechanical response of PEEK is studied during shear histories that have one or more points at which the strain rate is reversed. In particular, using digital image correlation (DIC) methods, the response of PEEK is captured during processes that subject the material to histories that reverse the straining direction one or more times. These studies show that the response of PEEK in monotonic loading is very different from that observed after reversing the loading, and also from that observed in further cycling. Yet, after multiple cycles of loading and reverse loading, if the loading is then continue beyond the point that loading reversal was initiated in the cycling, the response after this point returns to that of the initial monotonic loading.

An application of nuclear physics, a facility for using protons for flash radiography, has been developed at the Los Alamos Neutron Science Center (LANSCE). Protons have proven far superior to high energy x-rays for flash radiography because of their long mean free path, good position resolution, and low scatter background. Although this facility is primarily used for studying very fast phenomena such as high explosive driven experiments, it is finding increasing application to other fields, such as tomography of static objects, phase changes in materials and the dynamics of chemical reactions. The advantages of protons are discussed, data from some recent experiments will be reviewed and concepts for new techniques are introduced.

Poly-ether-ether-ketone (PEEK) is a high-performance semi-crystalline polymer with mechanical and thermal stability characteristics that are superior to most tough polymers. The mechanical characteristics of this polymer are modeled over a broad range of mechanical loading conditions using a thermodynamically consistent modeling process. This preliminary model, which ignores the thermal response and the possible recrystallization of this material during loading, shows an outstanding ability to capture the multidimensional nonlinear response of PEEK up to 60 % compression, with loading rates from 0.0001 to 3000 1/s at room temperature. The model includes the measured anisotropy in the wave response that develops with plastic flow, captures the evolution of the measured equilibrium stress, and correctly matches the evolution of the tangent modulus at equilibrium. This broad range of rates and experimental conditions are achieved by using a two-element nonlinear thermodynamically-consistent model.