Electromagnetic Particle Velocity Gauges Research Articles

Shock Initiation Characteristics of CL-20-Based Cast Cured Explosives with High Aluminum and Ammonium Perchlorate Contents

Abstract The addition of a large amount of aluminum and ammonium perchlorate will change the sensitivity of the explosive. At present, there is lack of deep understanding of the shock initiation characteristics of CL-20 based mixed explosives with high aluminum and AP contents, which is important for the optimization of the explosive components and safety use. In this paper, the electromagnetic particle velocity gauges were embedded in the wedge-shaped explosive to measure the particle velocity during shock initiation, and then numerical simulation model was constructed, based on the experimental data, the parameters of reaction rate model and equation of state were calibrated. By combining experiments and numerical simulations, the shock initiation characteristics and effects of aluminum and ammonium perchlorate contents on the initiation process were investigated. Results show that the two kinds CL-20-based cast cured explosives with high aluminum and AP contents are more sensitive than PBXW-115. The change of aluminum and ammonium perchlorate significantly changed the shock initiation behavior, which could lead to intersection point in the Pop relationship. Based on the characteristics of shock initiation, it can be inferred that the shock initiation process of explosives follows different mechanisms under low and high pressure. Under relatively low pressure, the shock initiation process of explosives is mainly dominated by the formation and growth of “hotspots”, while under higher pressure, the rapid reaction of CL-20 itself will dominate the initiation and rapid growth of detonation.

Experimental and numerical study of shock-to-detonation transition in tri-amino-tri-nitro-benzene explosive with temperature effects

ABSTRACT The present work completed a series of one-dimensional plate impact experiments combined with an temperature control system, which could study the temperature effects on shock initiation characteristics of the tri-amino-tri-nitro-benzene (TATB)-based explosives. Buildup to detonation was measured with aluminum-based electromagnetic particle velocity (EMV) gauge technique, and the shock tracker gauges recorded the change in position of shock wave in the explosive sample over time. As temperature cooling to −20°C, the fitting line of Hugoniot had an obvious inflection point, and the run distance to detonation became longer than ambient temperature under the same initiation pressure, indicating that the explosives became less sensitive. Finally, the numerical simulation of the shock initiation process for explosives was performed by the Arrhenius, Wescott, Stewart, and Davis (AWSD) reaction rate model . The results indicated that the AWSD reaction rate model based on the impact temperature and pressure can better simulate the shock-to-detonation transition at different temperatures by only one set of model parameters.

Experimental investigation of shock response to an insensitive explosive under double-shock wave

A new integrated velocimetry system that includes terahertz-wave-based Doppler velocimetry (TDV) and a multiplied electromagnetic particle velocity gauge (EMV) is demonstrated by measuring the particle velocity history and the corresponding shock-to-detonation transition (SDT) distance in double-shock experiments of insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-2. This system overcomes the defects in resolution, testing distance, particle velocity measurement history, and shock-wave capture when TDV or EMV are used separately in double-shock experiments. The effectiveness of the integrated velocimetry system is verified via double-shock experiments, and the deviation of shock wave displacement is less than 6%. Furthermore, the desensitization effects of TATB-2 are determined by comparing the initiation behavior for the double-shock and sustained-pulse experiments. Results indicate that the longer the time of the unreactive preshock wave, the stronger the desensitization effects. Further, the reactive main shock wave in the double-shock experiment can weaken the desensitization effects of the double-shock wave.

Dynamic Behavior of Clay with different Density under Planar Impact

The dynamic behaviour of clay with different initial density was researched by a single-stage light gas gun. Soil samples with four initial density (1.7, 1.8, 1.9 and 2.0 g/cm3) were investigated in this study, the water content, graininess and raw material of which were the same. Four electromagnetic particle velocity gauges were embedded directly into each sample, which was compressed by clay powder. And the motions of shock wave were detected by these gauges. Typical waveforms of the particle velocity and the Hugoniot data of the experiments were presented. The dynamic stress-strain relation could be determined by the Lagrangian analysis method which was utilized to the four particle velocity waveforms. The results show that, the initial density was possibly the most important factor to affect the dynamic behaviour of soft clay soil under intense dynamic load compared with the water content.

Polysulfone shock compressed above the decomposition threshold: Velocimetry and modeling of two-wave structures

Polysulfone was shock loaded to pressures of 14.6–26.2 GPa in a series of gas gun-driven plate-impact experiments measuring material response with embedded electro-magnetic particle velocity gauges and optical velocimetry. The embedded electro-magnetic particle velocity gauges did not show a distinct two-wave structure but did show rounding that suggested a reaction but not a distinct separation of the reactants and product waves. In contrast, the transmission experiments fielded with optical velocimetry, with product pressures ranging from 21.0 to 26.2 GPa, showed well-defined two-wave structures due to shock-driven chemical decomposition of the polymer to products at a higher density. Distinct two-wave structures have not previously been published in literature during polymer compression; here, we observed these two-wave structures at both the polymer/lithium fluoride and polymer/polymethylmethacrylate interfaces. Hydrodynamic simulations of the experiments were performed using a newly constructed SESAME equation of state (EOS) for the polymer, a thermochemical EOS for the decomposition products, and an Arrhenius reaction rate model for the kinetics of the reaction. Simulation results also demonstrated two-wave structures but were unable to quantitatively reproduce either the embedded gauge or optical velocimetry data.

WGT: A mesoscale-informed reactive burn model

Polymer bounded explosives (PBXs) consist of energetic crystals coated with a polymer binder. These materials exhibit a highly heterogeneous microstructure. The initiation of the detonation phenomenon in PBXs is believed to be generated at the microstructure scale through hotspots. Hence, many of the explosives properties (initiation, desensitization, etc.) are understood as a direct consequence of their microstructure. Mesoscale modeling directly addresses the physics of hotspot formation. Unfortunately, high computational cost prevents their use on laboratory-sized and large scale experiments. In practice, continuum-scale models remain mandatory. We describe a new reactive burn model, named WGT, aiming to represent, at the continuum scale, some of the complexity of the PBX’s microstructure. The initiation regime is driven by the shock temperature and results from surrogate modeling of the kinetics of a heterogeneous nucleation and growth model. The other regimes follow the formulation of the WHS2D2 reactive burn model and are driven by the local temperature. This model was calibrated on experimental results for PBX 9502 available in the literature, such as detonation velocity–curvature laws, Pop-plot data, or embedded electromagnetic particle velocity gauges. The model was also tested against desensitization and propagation data.

Double Shock Experiments on PBX Explosive JOB‐9003

AbstractOne‐dimensional plate impact experiments have been performed to study the double shocks to detonation transition and Hugoniot state in the HMX‐based explosive JOB‐9003. The flyer was a combination of sapphire and Kel‐F, which can pass two different pressure waves into PBX Explosive JOB‐9003 sample after the impact. The particle velocities at interface and different depths in the JOB‐9003 sample were measured with Al‐based electromagnetic particle velocity gauge technique, thus obtaining particle velocity‐time diagram. According to the diagram, the corresponding Hugoniot state can be determined based on the particle velocity and shock wave velocity in the sample. Comparing with sustained pulse experiments, PBX Explosive JOB‐9003 shows desensitization feature due to the pre‐pressed shock wave.

Experimental investigation of the reaction-build-up for plastic bonded explosive JOB-9003

In order to measure the shock initiation behavior of JOB-9003 explosives, Al-based embedded multiple electromagnetic particle velocity gauge technique has been developed. In addition, a gauge element called the shock tracker has been used to monitor the progress of the shock front as a function of time, thus providing a position–time trajectory of the wave front as it moves through the explosive sample. The data is used to determine the position and time for shock to detonation transition. All the experimental results show that the rising-up time of Al-based electromagnetic particle velocity gauge is very short (<20 ns); the reaction-build-up velocity profiles and the position–time for shock to detonation transition of HMX-based plastic bonded explosive (PBX) JOB-9003 with 1–8 mm depth from the origin of the impact plane under different initiation pressures were obtained with high accuracy.

Reaction Buildup of PBX Explosives JOB-9003 under Different Initiation Pressures

ABSTRACTAluminum-based embedded multiple electromagnetic particle velocity gauge technique has been developed in order to measure the shock initiation behavior of JOB-9003 explosives. In addition, another gauge element called a shock tracker has been used to monitor the progress of the shock front as a function of time, thus providing a position-time trajectory of the wave front as it moves through the explosive sample. The data are used to determine the position and time for shock to detonation transition. All the experimental results show that: the rising-up time of Al-based electromagnetic particle velocity gauge was very fast and less than 20 ns; the reaction buildup velocity profiles and the position-time for shock to detonation transition of HMX-based PBX explosive JOB-9003 with 1–8 mm depth from the origin of impact plane under different initiation pressures are obtained with high accuracy.

Shock Initiation of the CL-20-Based Explosive C-1 Measured with Embedded Electromagnetic Particle Velocity Gauges

Hexanitrohexaazaisowurtzitane (CL-20) is a high-energy material with high shock sensitivity. The evolution of shock into the detonation of CL-20 deserves academic attention and research. An embedded electromagnetic particle velocity gauge was used to study the shock initiation of detonation in a pressed solid explosive formulation, C-1, containing 94 wt-% epsilon phase CL-20 and 6 wt-% fluororubber (FPM). In conventional experiments, the magnetic field was generated using a pair of electromagnets with a complex structure and operation. A new device was designed to solve complex problems. This device comprised NdFeB magnets, pole shoes and magnetic yokes; using this technique, a uniform magnetic field could be created. A series of shock initiation experiments on high-explosive C-1 was performed, and the explosive samples were initiated at different intensity input shocks by an explosive driven flyer plate. In situ magnetic particle velocity gauges were utilized to detail the growth from an input shock to detonation, and the attenuation of particle velocity in unreacted C-1 was also obtained in low-intensity shock initiation experiments. Hugoniot data for C-1 in the form of shock velocity D vs. particle velocity Up were obtained. A simulation model for shock initiation of C-1 was established, and the particle velocity data from several experiments were used to determine the parameters required for the unreacted equation of state and ignition and growth reactive flow model for C-1. These coefficients were then applied in the calculation of the initial shock pressure−distance to detonation relationship (Pop-plot) for the explosive. Based on the results of experiments and simulations, the shock sensitivity characteristic of C-1 was described.

A new approach for Hugoniot equation of state of polycarbonate

The plate impact experiment is an important way to measure the equation of state of solid material in high pressure. However, traditional methods always have some defects, such as high failure rate, indefinite and inaccurate result in the test, and lack of comparison. Meanwhile, few of published data concerned the high strain rate behavior of polycarbonate during shock loading. In the present study, a new approach was therefore carried out to obtain the equation of state of polycarbonate material in a single-stage gas gun, which consists of asymmetric impact technology, manganin gauges, PVDF, electromagnetic particle velocity gauges and electrical pins. The least square method was used to analyze the fitting goodness and scatter degree of the single and the combined method respectively. The results showed that manganin gauges have the best property of stability, followed by particle velocity gauges, PVDF gauges and electrical pins. Compared with other single method, the combined method can improve the accuracy of measurement in a relatively less number of experiments than previous data. At last, the D−u Hugoniot curve of polycarbonate in high pressure was gained, and the manganin gauges were calibrated by the experimental data.

Gas gun ramp loading of Kel-F 81 targets using a ceramic graded areal density flyer system

Kel-F 81 (PCTFE/Polychlorotrifluoroethylene) polymer targets were subjected to ramp loadings generated by a ceramic flyer accelerated into the targets by a gas gun in the plate impact configuration. This approach used a ceramic graded areal density flyer in conjunction with a ceramic buffer plate to induce a ramp loading in the target. The flyer was comprised of a rapid prototyped alumina ceramic. The loading was observed with embedded electromagnetic particle velocity gauges (PV gauges) with the results compared with ANSYS Autodyn™ hydrocode simulations. Experimental results show that ramp loadings of varying duration and magnitude were induced into the target. These loadings can be described as shockless compressions leading to shocked states within the material. In addition, numerical simulations provided further insight into the loading approach – with good agreement found with experimental data, opening the potential to design more complex loading systems in future.

Shock initiation of the TATB-based explosive PBX 9502 cooled to 77 Kelvin

We present gas-gun driven plate impact shock initiation experiments on the explosive PBX 9502 (95 weight percent triaminotrinitrobenzene, 5 weight percent Kel-F 800 binder) cooled to liquid nitrogen temperature, 77K. PBX 9502 samples were cooled by flowing liquid nitrogen through a sample mounting plate and surrounding coil. Temperatures were monitored using embedded and surface mounted thermocouples. Reactive flow was measured with embedded electromagnetic particle velocity gauges. Wave profiles from the particle velocity gauges show that, even at 77K, shock initiation in PBX 9502 retains a heterogeneous or "hot-spot" character. The "Pop-plot," or distance to detonation, xD, vs. impact pressure, P, is log10(xD) = 4.9 − 3.3log10(P).

Ramp wave generation using graded areal density ceramic flyers and the plate impact technique

A requirement exists to generate realistic insults in energetic targets, for example ramp loadings leading to shock waves. This paper examines the development of a ceramic flyer ramp wave generation technique. Ceramic stereolithography was used to produce fully-dense, graded areal density alumina ceramic flyers. These flyers consisted of multiple square pyramids arranged on a solid base. The gas gun plate impact and electromagnetic particle velocity gauge techniques were used to observe the ramp waves generated when the flyers impacted a Kel-F 81 polymer target. Ramp waves of varying properties were successfully generated in the targets, and good agreement was obtained with 3D hydrocode modelling.

Shear Wave Attenuation and its Micro-Mechanism of Polymers

The impact shear response of crystallized polypropylene under combined compression and shear loading was studied by using an inclined gas gun and electro-magnetic particle velocity gauges. The experimental results show that the transverse wave velocity increases nonlinearly with the impact velocity, indicating its shear behavior is strongly related to the hydrostatic pressure. Remarkable shear wave attenuation occurs near the impact surface when the impact velocity and inclination angle reach the critical value. The micro-observation of recovered samples with a polarized optical microscope reveals that there exists a melting layer of about 2-3μm thick, i.e. adiabatic shear failure layer, very near the impact surface (about 5μm) which causes the shear wave attenuation.

Measurements of shock initiation in the tri-amino-tri-nitro-benzene based explosive PBX 9502: Wave forms from embedded gauges and comparison of four different material lots

We have completed a series of ambient temperature (23±2°C) shock initiation experiments on four lots (batches) of the insensitive high explosive PBX 9502. PBX 9502 consists by weight of 95% dry-aminated tri-amino-tri-nitro-benzene (TATB) and 5% of the plastic binder Kel-F 800, a 3∕1 copolymer of chloro-trifluoro-ethylene and vinylidene-fluoride. Two of the four lots were manufactured using the “virgin” process. Both of these lots had few fine TATB particles. One virgin lot was stored the majority of its life (&amp;gt;15yr) as a molding powder and pressed as a 240mm diameter by 130mm thick cylinder. The other virgin lot was stored the majority of its life as a hollow hemispherical pressing. Two lots were manufactured using the “recycle” process and had many fine TATB particles. One recycled lot was stored the majority of its life as a molding powder, while the other was stored as a pressed charge. Shock initiation experiments were performed using precisely characterized planar shocks generated by impacting an explosive sample with a projectile accelerated in a two-stage gas gun. The evolution of the shock into a detonation was measured using 10 or 11 embedded electromagnetic particle velocity gauges and three “shock tracker” gauges. Results include the following: (1) high quality particle velocity wave forms which should be useful for calibrating reactive burn models, (2) no difference in the sustained shock initiation response between lots regardless of material processing or storage history, (3) responses for all lots equivalent to those measured by Dick et al. [J. Appl. Phys. 63, 4881 (1988)], additional Hugoniot and Pop-plot data for PBX 9502, and (5) the short shock response which, when compared to the sustained shock response, shows no extension in the run distance unless the rarefaction overtakes the shock front prior to the distance it would have run towards a detonation as a sustained shock.

Shock Initiation of Energetic Materials at Different Initial Temperatures (Review)

Shock initiation is one of the most important properties of energetic materials, which must transition to detonation exactly as intended when intentionally shocked and not detonate when accidentally shocked. The development of Manganin pressure gauges that are placed inside the explosive charge and record the buildup of pressure upon shock impact has greatly increased the knowledge of these reactive flows. This experimental data, together with similar data from electromagnetic particle velocity gauges, has allowed us to formulate the Ignition and Growth model of shock initiation and detonation in hydrodynamic computer codes for predictions of shock initiation scenarios that cannot be tested experimentally. An important problem in shock initiation of solid explosives is the change in sensitivity that occurs upon heating (or cooling). Experimental Manganin pressure gauge records and the corresponding Ignition and Growth model calculations are presented for two solid explosives, LX-17 [92.5% triaminotrinitrobenzene (TATB) with 7.5% Kel-F binder] and LX-04 [85% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX) with 15% Viton binder] at several initial temperatures.

S-wave tracing technique to investigate the damage and failure behavior of brittle materials subjected to shock loading

To reveal the intrinsic rules of dynamic damage and failure behavior for brittle materials subjected to shock loading, a so-called transversal shear wave tracing technique (SWT) is proposed and discussed in detail in the present paper based on the wave propagation theory and the combined compression–shear impact technique. The idea of the SWT method is to diagnose the material state at real time by measuring the propagation features of loading and unloading shear waves. By using SWT technique, the preliminary experimental results of fiber-reinforced cement (FCEM) with electromagnetic particle velocity gauges embedded in the sample at different locations are reported and analyzed. By tracing the shear wave propagation, it is found that the amplitude and speed of unloading shear wave (S −) are related to the damage degree of the material. Particularly, S − vanishes when impact velocities exceed 197 m/s, which discloses clearly a transition point from damage state to failure state of FCEM. It is significant for there is no obvious cusp to indicate such transition on the Hugoniot of FCEM. Some further studies are needed for understanding and developing of SWT method.

Time-dependent inelastic deformation of shocked soda-lime glass

Plate impact experiments were carried out to understand inelastic deformation in soda-lime glass shocked between 3 and 10.8GPa. In-material, wave profile measurements were obtained using longitudinal and lateral stress gauges (4.6–10.8GPa), and electromagnetic particle velocity gauges (2.9–6GPa) at comparable sample thicknesses. The 4.6 and 6GPa experiments revealed time-dependent material inelastic response along with time-dependent loss of material strength. Because of the unsteady, two wave structure observed in the longitudinal wave profiles in conjunction with the time-dependent changes in the lateral stress data, previous interpretations of the shocked soda-lime glass response in terms of a propagating failure wave are not valid. At higher peak stresses (∼10GPa), the experimental results do not display time-dependent strength loss. The shock wave response of soda-lime glass over the 4–10GPa range is complex, and material strength and inelastic deformation features depend significantly on the peak stress. Using the experimental results, a phenomenological continuum model incorporating the various material phenomena was developed. Wave profile simulations using the continuum model show reasonable overall agreement with the experimental profiles at different stress levels. Because of the approximate nature of the continuum model, all of the experimental details were not reproduced in the wave propagation simulations. It is likely that around and above 10GPa, other material phenomena not included in our model may need to be considered.

Dynamic compression-shear loading with in-material interferometric measurements

The present article introduces a new technique for window interferometry in the case of combined normal and shear wave motion. The method can, in principle, be used for micromechanical studies of damage and inelasticity in a variety of materials. Preliminary tests conducted on brittle materials indicate the feasibility of the technique and its advantages over other in-material measurements using embedded manganin gauges or electromagnetic particle velocity gauges. An analysis of the interferometric signals, incorporating variations in the index of refraction of the window material, is used in the interpretation of the velocity histories. The suitability of the technique in the study of dynamic failure and material instabilities is presented. Furthermore, the use of the in-material measurement technique in the design of pressure-shear recovery experiments is described.