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Electrically exploded wires find uses throughout high-energy physics. For example, they are commonly used as high-temperature sources, X-ray generators, and in precision timing detonators. However, the detailed and complete physics that occurs is complex and still poorly understood. A full mechanistic description of these complex phenomena is beyond the scope of a single paper. Instead, we focus on the formation of metal vapor and its transition to plasma. This single transition is commonly assumed to comprise “bridge-burst”. We use a suite of diagnostics including a novel, fiber-based, high-speed, optical pyrometer to better characterize this transition. The primary finding from this project is that peak light output from an exploding wire does not temporally match the peak temperature. Additionally, it is found that peak light does not align with peak bridge-burst voltage and that the peak temperature is not voltage-dependent. These findings are non-intuitive and will allow for the correction of false assumptions previously made about this topic.

The apparent simplicity of the drop-weight apparatus for explosive sensitivity testing hides the reality that it is actually a complex integrated test of both ignition and growth of deflagration. Although the drop-weight test is undeniably a useful screening test for explosive properties, a misunderstanding of the technique’s limitations has blinded many researchers to its limited wider applicability. This monograph discusses how the test actually works, the significant engineering difficulties with standardization between machines, which types of explosives are suited to the test and which are not, and finally offers a few suggestions for alternatives when a more quantified understanding of a material’s response is required for other applications.

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.

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 °C to 120 °C), heat capacity (−40 °C to 140 °C), monotonic extension and compression (−85 °C to 150 °C; 0.0001 s−1 to 3000 s−1; strains up to 40–80%), equilibrium stress measurements in compression (23 °C to 120 °C; strains up to 60%), and ultrasonic longitudinal and shear wave speed measurements along and transverse to the directions of compression (23 °C to 120 °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.

It is known that PBX 9502 changes sensitivity and performance as a function of temperature, presumably due to changes in void morphology and density. These experiments have examined both the velocity of detonation (VOD) and reaction zone profile (particle velocity vs. time) as a function of pressed density. The rate sticks are 2 inches in diameter with an aspect ratio of 1:8. The reaction zone profile was characterized by photonic Doppler velocimetry (PDV) at an aluminized lithium fluoride window and VOD was measured by both piezoelectric pins and time domain reflectometry (TDR). The density range examined was 1.700 - 1.895 g/cc (1.895 is production density). The results obtained are compared to those of in-situ heated rate stick experiments, and the void structure was characterized by small-angle neutron scattering (SANS) methods in order to quantify changes in morphology.

The minimum energy required after bridge-burst to function a commercially available RP-1 exploding bridgewire detonator with a gold bridgewire was investigated using two capacitor discharge units (CDUs) making use of state-of-the-art on/off high-voltage high-current switches. Both switches are capable of shutting off the current flow in ≈ 100 ns and the conduction time was varied systematically to limit the duration of electrical energy delivered from the CDU until a detonation go/no-go threshold was reached. It was found that the minimal extra electrical energy required for a soft-fire (a statistically marginal go) was approximately half that required for a hard-fire (a definite go). The measured energy required to function the RP-1 detonator from the 11.5 kV CDU was approximately 20 mJ greater than for the 600 V CDU, and it is postulated that this was due to arcing across the detonator terminals and an associated current shunt that was not efficient at depositing energy conducive to detonator functioning. Measurements of the bridgewire temperatures bursting in air showed that the maximum temperature reached was consistent ( ≈ 18 kK) when sufficient energy was delivered that the detonator functioned (either soft- or hard-fire), but that the temperature for a sub-threshold bridgewire burst was significantly cooler at approximately 8 kK. Furthermore, it was demonstrated that the intensity of the light emitted at burst scaled with deposited energy. A related finding is that the light emission from the bridgewire peaks some tens of nanoseconds after both peak voltage and peak electrical power.

This paper describes a series of experiments performed on a specific design of an explosively driven metallic plate launcher. While endeavoring to keep the detonation front, and hence the flyer, flat, the design makes use of two features that lessen the explosive mass required and reduce the propensity for generating spall in the flyer. Several variations on a standard design were fielded, not so much because they were ideally suited to the intended purpose (worst-case fragment attack simulations into cased explosive assemblies), but so that the predictions made by computer models on this slightly abnormal explosively driven system could be compared with reality. In this manner, the predictive capability of the code could be verified for subsequent design variations optimized for specific applications. The design used here had a 63.5 mm diameter flyer that was 6.35 mm thick. The leading center section (≈25 mm) was flat to better than 1 mm in all cases and to 0.1-0.2 mm in optimal situations. Greater curvature and oscillation was seen towards the periphery of the flyer. This paper concentrates on the experimental program rather than the still-ongoing computational modeling efforts.

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.

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.

In order to improve understanding of how aluminum contributes in non-ideal explosive mixtures, cast-cured formulations have been analyzed in a series of cylinder tests and plate-pushing experiments. This study describes the contribution of 15 % aluminum (median size of 3.2 μm) vs. lithium fluoride (an inert substitute for aluminum

Extreme piezoresistivity was discovered in a silicone/nickel nanostrand (silicone/NiNs) nanocomposite. A novel technique was developed to study the charge transport phenomena responsible for the piezoresistive mechanism in the silicone/NiNs system using conductive nanoindentation. A quantum mechanical tunneling (QMT)/percolation model was developed, which bridges the gap between quantum effects at the nanoscopic scale and bulk material response at the macroscopic scale. The predictions of this model are compared to experimental measurements.

Dynamic x-rays have been used to follow the deformation ahead of a steel ball fired into a mock-up of a generic cylindrical rocket motor. The impact was arranged to intersect a sparse lead powder layer within the mock explosive that created a random speckle pattern on x-ray film. Three different digital image correlation programs are compared to examine any sensitivity to the sub-optimal speckle pattern produced by the lead powder. An identical output data reduction method was used in all cases to aid comparison. All three correlation methods were able analyze the deformation, but all had intricacies that would require more detailed optimization of the data reduction in order to fully exploit the technique. Quantitative analysis showed that the three methods agreed closely in estimations of rigid body displacements between a pair of representative x-ray images. It was discovered that the deformation caused by the ball impact was highly localized and the useful data available about the deformation pattern was sparse. This limits the applicability of this technique to this specific application. Extensive cracking was not observed that would have aided the development of computer-based models for prediction of such impact events. The x-ray technique was however excellent for determining the ball position as a function of time after impact.

Doppler velocimetry is used extensively to measure velocities in dynamic experiments, but Doppler shifts of ≈1.3 GHz/km/s demand expensive digitizers. We discuss methods leveraging frequency down-mixing to reduce digitization requirements and costs.

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.

The current work deals with mixed-mode-I/II fracture in polytetrafluoroethylene (PTFE). Mode-I fracture in PTFE 7C has previously been shown to exhibit strong phase dependence with a brittle-to-ductile transition associated with the room temperature phase transitions. Increases in fracture toughness around room temperature and above result from the onset of stable fibril formation bridging the crack plane and increased plastic energy dissipation. Mixed-mode-I/II loading conditions are achieved using a modified compact tension specimen with Arcan type fixtures. The fracture toughness δVC of PTFE 7C exhibits a 42% decrease from pure mode-I to near mode-II loading due to a marked decrease in fibril formation.

Strain measurements by neutron diffraction are employed as an in situ technique to obtain insight into the deformation modes of crystalline domains in a deformed semi-crystalline polymer. The SMARTS (Spectrometer for MAterials Research at Temperature and Stress) diffractometer has been used to measure the crystalline lattice displacements in polytetrafluoroethylene (PTFE) for crystalline phase IV (at room temperature) in tension and compression and for crystalline phase I (at 60°C) in compression. The chemical structure of PTFE, -(C2F4)-n, makes it ideally suited for investigation by neutron methods as it is free of hydrogen that results in limited penetration depths and poor diffraction acquisition in most polymers. Deformation parallel to the prismatic plane normals is shown to occur by inter-polymer chain compression with a modulus ∼10× bulk, while deformation parallel to the basal plane normal occurs by intra-polymer chain compression with a modulus ∼1000× bulk, corresponding with theoretical values for a PTFE chain modulus. Deformation parallel to the pyramidal plane normals is accommodated by inter-polymer chain shear.

The current work presents the characterization and comparison of the mechanical response of three different industrial forms of polyethylene. Specifically, high-density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), and cross-linked polyethylene (PEX) were tested in compression as a function of temperature (−75 to 100°C) and strain-rate (10−4 to 2,600 s−1). The responses of UHMWPE and PEX are very similar, whereas HDPE exhibits some differences. The HDPE samples display a significantly higher yield stress followed by a flat flow behavior. Conversely UHMWPE and PEX both exhibit significant strain hardening after yield. The temperature and strain-rate dependence are captured by simple linear and logarithmic fits over the full range of conditions investigated. The yield behavior is presented in terms of an empirical mapping function that is extended to analytically solve for the mapping constant. The power-law dependence on strain-rate observed in some polymers is explained using this mapping function.

The mechanical properties of PEEK 450G have been extensively investigated. The compressive properties were measured at strain rates between 1 × 10 −4 and 3000 s −1 and temperatures between −85 and 200 °C. The tensile properties were measured between the strain rates of 2.7 × 10 −5 and 1.9 × 10 −2 s −1 and at temperatures between −50 and 150 °C. The Taylor impact properties were investigated as a function of velocity and various large-strain compression tests were undertaken to explain the results. The fracture toughness was investigated as a function of temperature and compared with previous literature. Additionally, the fracture surfaces were studied by microscopy. As with all semi-crystalline polymers the mechanical response is a strong function of the strain rate and testing temperature. A previously reported phenomenon of darkening observed in Taylor impacted samples is shown to be due to reduced crystallinity brought about by large compressive strain. For samples deformed to large compressive strains using a variety of techniques and strain-rates the measured Vickers hardness was found to decrease in accordance with reduced crystallinity measured by other techniques.

Los Alamos “Ranchero” Magnetic Flux Compression Generators (FCGs) have been used to power imploding liner loads. The fundamental FCG design is based on a cylindrical detonation system that expands the armature simultaneously into a coaxial generator volume and has been shown to generate currents as high as 76 MA. Analysis of the 76 MA test results revealed a weakness in the design at the output glide plane. To prevent premature shorting at the output current slot of the generator, the armature/glide plane interface was originally designed to lag the leading edge of the armature. However, 2D-MHD calculations reveal that at very high currents a magnetically driven aneurism develops in this lagging section which reduces the performance of the generator. A new model Ranchero is being developed to correct this weakness and provide enhanced performance. In the new model, the output glide plane is eliminated and the armature is extended along the FCG axis, with its radius increasing along a curve until it reaches the current output slot. A cylindrical detonation system of the type required for earlier designs continues to be used, and the high explosive (HE) in the extended section is detonated by the last point of the cylindrical detonator. The stator of the FCG is contoured, allowing the contact point of the armature to zipper from the input to the output end in the last few μs of flux compression. In addition, the new model Ranchero is intended to use PBX 9501 (9501) for the HE and also remove the smoothing layer, which has been part of all Ranchero HE systems to date. Both of these factors lead to increased performance. 9501 is more energetic than the PBXN 110 used in Ranchero generators to date, and both calculations and experiments have shown that the smoothing layer is not needed when the detonator point spacing is 18 mm. Tests of original model Rancheros using PBXN 110 castable HE, with an imbedded smoothing layer, demonstrated an armature expansion velocity of 3.1 mm/μs. Further tests show that removal of the smoothing layer increases the speed to 3.3 mm/μs, and replacement of the cast PBXN 110 with 9501 without a smoother gives a velocity of 3.8 mm/μs. Designs, concerns, and experimental results facilitating the new model Ranchero are presented. In addition, performance estimates are given for the initial imploding liner tests to be conducted, and further computational details are presented in a companion paper given by C. L. Rousculp and others at this conference.

Polychlorotrifluoroethylene (PCTFE), also known as Kel-F 81, is a semi-crystalline fluoropolymer. Although it has been employed in a wide range of cryogenic components, valve seats, seals, and microelectronics packaging, its mechanical behavior has received limited coverage in the literature. In this work, we present the tensile and compressive constitutive response of PCTFE for a range of temperatures (−85 to 150 °C) and strain rates (1 × 10−4–2.9 × 103 s−1). Both large-strain experiments based on flow stress and small-strain dynamic mechanical analysis (DMA) using the elastic modulus exhibit a strong increase in the glass transition temperature, Tg, with increasing strain rate. The quasistatic fracture behavior of PCTFE is presented using J-integral fracture experiments. Finally, a discussion of the implication of the constitutive and damage responses of PCTFE on impact failure modes observed in Taylor impact experiments is presented.

The extremely low coefficient of friction and biocompatibility provided by the inert nature of polytetrafluoroethylene (PTFE) have lead to its application in a wide range of biological implants ranging from single component PTFE structures to sliding contact pads in complex joints. In vivo fracture has been identified as a major cause of failure in these implants. It has recently been shown that the fracture behavior of PTFE undergoes transitions from brittle-fracture below 19 -C to ductile-fracture with fibril formation and large-scale plasticity over 30 -C associated with crystalline phase transformations. In this paper the formation of fibrils and an associated increase in JIC fracture toughness are revealed to be restricted by an increase in crystalline content in PTFE. [LAUR 05-2223] D 2005 Elsevier B.V. All rights reserved.

Fluoropolymers posses several advantageous properties for load-bearing structural components including higher strength at elevated temperatures and higher toughness at lowered temperatures. Stress-strain studies have been conducted on two homopolymers (Teflon (PTFE) and KEL-F 81 (PCTFE)) and two copolymers (KEL-F 800 and THV 500G) as a function of temperature and strain rate. A split-Hopkinson pressure bar (SHPB) was used to achieve a strain rate of ∼3200/s in compression, while screw-driven testing machines afforded a strain rate of 0.001/s. A tensile split-Hopkinson pressure bar (T-SHPB) was used for testing at strain rates of 800/s in tension. To address the large strains to failure (up to 700% extension) an optical extensometer was employed for a strain rate of0.005/s in tension. The effects of temperature and strain rate for this family of polymers is presented in detail, including an observed shift in glass transition (T g ) to higher temperatures with increased strain rate and rate insensitivity of thermally-induced phase transitions.

Under repeated tensile strain, many particle-filled polymers such as silica-filled polydimethylsiloxane (PDMS), exhibit a reduction in stress after the initial extension, the so-called Mullins effect, and the mechanism(s) responsible for this is considered to be a major unsolved mystery of polymer physics. We report here the first observation of the absence of this effect in cross linked, silica-filled PDMS when the second strain axis is perpendicular to the initial strain axis. This result poses a challenge for existing theories. We propose a mechanism to account for the Mullins effect that is consistent with our experimental observations.

Commercial purity aluminum AA1050 was subjected to one of two equal channel angular extrusion (ECAE) routes. Route “A” is defined as no rotation between passes and route “C” is rotated 180° between extrusion passes. The resulting microstructures have similar grain sizes but relatively different grain boundary structures. The microstructure processed by route “A” has approximately 70% high angle boundaries (HABs), while the route “C” has approximately 40% HABs. The boundary structure plays an important role in the mechanical properties of the material because these boundaries act as a source and sink of dislocations. Mechanical tests conducted on these two microstructures at intermediate and dynamic strain rates at both 77 and 298 K are compared with the results of material tested at quasi-static strain rate.

Samples of DuPont 7A and 7C Teflon (PTFE, poly(tetrafluoroethylene)) were tested in tension at strain-rates between 2×10 −4 and 0.1 s −1 and temperatures between −50 and 150 °C. Additionally, using a Hopkinson bar, a temperature series was undertaken in tension between −50 and 23 °C at a strain rate of 800 s −1 . To investigate the small-strain response, strain gauges were used to measure axial and transverse strain allowing the Poisson ratio to be calculated. The effect of crystallinity was investigated using 7C material thermally processed to produce more amorphous material. As expected, the tensile mechanical properties of PTFE are significantly affected by strain-rate and temperature, but only to a limited extent by crystallinity. The Poisson ratio at small strains was found to differ in tension (≈0.36) and compression (≈0.46). Failure behavior and microstructure were correlated to temperature induced phase transitions.

In the design mode of operation, TATB-­based PBXs, such as PBX 9502 or LX-­17, are promptly initiated by a detonator and booster system. In abnormal situations, such as accidents, a wide variety of non-­design-­mode insults can arise and it is desirable that these do not produce detonation but rather that, at most, they lead to a low chemical energy release. The most significant abnormal hazard is the direct shock initiation threat arising from high-­velocity fragment impact. This is quite well defined and may result in a detonative response if the fragment is large enough and fast enough. However, it is of considerably greater significance to the safety envelope of these explosives whether they are at all capable of DDT (deflagration-­to-­detonation transition), either at ambient or elevated temperatures since accidental insults to the explosive, either mechanical or thermal, that may produce local burning are both more numerous and more likely than shock loading. The purpose of this document is to demonstrate, based on the accumulated body of conservative experimental testing, that in explosive geometries and masses relevant to the Weapons Program, TATB-­based PBXs do not present a deflagration-­to-­detonation transition (DDT) hazard at any temperature. This is a significant statement since itmore » removes detonative outcome concerns from the majority of insult scenarios on TATB-­based charges. It does not address the response of included detonator and booster assemblies, the response of which must be considered separately.« less

LA-19.4-CT-3 (CT-3) was the third camera test in a series beginning in 1/11, which diagnose the performance of 6 mm thick, 6061 T-0 Al Ranchero armatures. [The test LA-43-CT-2 (CT-2) is described in LA-UR-14-21983.] The goal of CT-3 was to verify that PBX-9501, with 18 mm point spacing and no smoothing layer, could be used for Ranchero generator armatures in place of PBXN-110, which had been used in all previous Ranchero applications. CT-1 and CT-2 both had 43 cm long slapper detonator systems imbedded in the cast PBXN-110 explosive, but manufacturing a charge for a similar 9501 test was not cost effective. Instead, a single cylinder of 9501, 19.368 cm long and 15.494 cm (6.100”)in diameter, had a groove machined to accommodate a row of 11 SE-1 detonators with 18 mm point spacing along the mid-plane of the cylinder. The expansion of the armature looks like a slapper assembly along almost ½ of the circumference, and provides adequate proof of concept. Removing the smoother from PBXN-110-driven armatures increased the armature velocity from 3.1 mm/μs to 3.3 mm/μs, as seen in CT-2, and the velocity measured on CT-3 increased to 3.8 mm/μs. In addition, the camera records show that the surfacemore » of the armature is smooth enough, and free from ruptures for an expansion of greater that 2X. The advantage of using 9501 is that it precludes concerns about blow-outs seen when bubbles are left in the cast material, and gives extra velocity. The disadvantage is that the machined explosives are more expensive.« less

A multilayer dielectric coating deposited on the endface of a single-mode fiber is used as an optical sensor for high pressures. The reflectance of the coating decreases by 10% for a pressure of 710 MPa.

A Ranchero flux compression generator (FCG) was recently tested at the 76 MA level. Ranchero generators were designed to be cost effective high current devices, and a variety of configurations have been tested. The Ranchero armature is a 152 mm diameter aluminum cylinder with a 6 mm thick wall. The high explosive (HE) is detonated simultaneously on axis, and the armature is expanded by a factor of two. At the final 300 mm diameter, the circumference is over 950 mm, which has been anticipated to accommodate currents approaching 100 MA. The test was performed with a 43 cm long module having an initial inductance of 56 nH, and a load inductance of 0.55 nH, consisting of a short load feed slot and probe grooves. A 12 mF capacitor bank at ~16.5 kV provided the initial 3.75 MA seed current. The performance of the generator with this load was calculated using a 2D MHD ALE code, and agreement was excellent. Generator design, test data, and details of the MHD calculations are given. The most important aspect of the results is verification of codes at the 76 MA level. The same codes do not show excessive losses up to the 100 MA level, and it is a much smaller extrapolation to that level at this time.

Modeling of thermal and mechanical events in high-explosive materials is complicated by the composite nature of the material, which experiences viscoelastic and plastic deformations and sustains damage in the form of microcracks that can dominate its overall behavior. A mechanical event of interest is projectile interaction with the material, which leads to extreme local deformation and adiabatic heating, which can potentially lead to adverse outcomes in an energetic material. Simulations of such an event predicted large local temperature rises near the path of a spherical projectile, but these were experimentally unconfirmed and hence potentially non-physical. This work concerns the experimental verification of local temperatures both at the surface and in the wake of a spherical projectile penetrating a mock (unreactive) high-explosive at ~700 m/s. Fast response thermocouples were embedded radially in a mid-plane of a cylindrical target, which was bonded around the thermocouples with epoxy and recorded by an oscilloscope through a low-pass filter with a bandwidth of 500 Hz. A peak temperature rise of 70 K was measured both at the equator of the projectile and in its wake, in good agreement with the temperature predicted in the minimally distorted elements at those locations by a finite element model in ABAQUS employing the ViscoSCRAM constitutive model. Further work is needed to elucidate the extreme temperature rises in material undergoing crushing or fragmentation, which is difficult to predict with meshed finite element methods due to element distortion, and also challenging to quantify experimentally.

A quadrature interferometer used in a free-field measurement mode has, with the aid of a high directivity horn antenna, been successfully used to measure the detonation front of PBX-9501 within a dielectric can. Using the known length of explosive, a relative dielectric permittivity of 3.84 has been calculated for the 34 GHz frequency used. Using this value, the displacement vs. time of the detonation front can be found and hence the velocity of detonation may be calculated. This technique shows good promise as a method of measuring the run-to-detonation distance in explosives using a totally non-contacting technique.

Polyurea was investigated under Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) loading where spherical projectiles were propelled at 440 to 509 ms-1 through a conical extrusion die with an area reduction of 87%. Momentum of the leading edge imposes a rapid tensile deformation on the extruded jet of material. Polyurea is an elastomer with outstanding high-rate tensile performance of interest in the shock regime. Previous Dyn-Ten-Ext work on semi-crystalline fluoropolymers (PTFE, PCTFE) elucidated irregular deformation and profuse stochastic-based damage and failure mechanisms, but with limited insight into damage inception or progression in those polymers. The polyurea behaved very differently; the polymer first extruded a jet of apparently intact material, which then broke down via void coalescence, followed by fibrillation and tearing of the material. Most of the material in the jet elastically retracted back into the die, and only a few unique fragments were formed. The surface texture of all failed surfaces was found to be tortuous and covered with drawn hair-like filaments, implying a considerable amount of energy was absorbed during damage progression.

Ranchero is a coaxial magnetic flux compression generator (FCG) initiated simultaneously on-axis, which is intended to produce currents approaching 100 MA. We continue with both applications and development, striving for both cost effectiveness and high performance. In this paper we discuss on-going work, provide details of the sophisticated detonation system, and show high current predictions from our active modeling effort. We intend further tests that will push the limits of Ranchero performance.

We have measured dynamic and quasi-static mechanical properties of C-4 and Primasheet P1000 explosive materials to provide input data for modeling efforts. Primasheet P1000 is a pentaerythritol tetranitrate-based rubberized explosive. C-4 is a RDX-based moldable explosive. Dynamic measurements included acoustic and split-Hopkinson pressure bar tests. Quasi-static testing was done in compression on a load frame and on a dynamic mechanical analyzer. Split-Hopkinson and quasi-static tests were done at five temperatures from -50°C to 50°C. Acoustic velocities were measured at, above, and below room temperature.