Elizabeth Francois

Methods for Characterizing and Comparing Populations of Shock Wave Curves

At Los Alamos National Laboratory, engineers conduct experiments to evaluate how well detonators and high explosives work. The experimental unit, often called an “onionskin,” is a hemisphere consisting of a detonator and a booster pellet surrounded by high explosive material. When the detonator explodes, a streak camera mounted above the pole of the hemisphere records when the shock wave arrives at the surface. The output from the camera is a two-dimensional image that is transformed into a curve that shows the arrival time as a function of polar angle. The statistical challenge is to characterize the population of arrival time curves and to compare the baseline population of onionskins to a new population. The engineering goal is to manufacture a new population of onionskins that generate arrival time curves with the same shape as the baseline. We present two statistical approaches that test for differences in mean curves and provide simultaneous confidence bands for the difference: (i) a B-Spline basis approach and (ii) a Bayesian hierarchical Gaussian process approach. In problems that involve complex modeling with modest sample sizes, it is important to apply multiple approaches with complementary strengths such as these to determine whether all approaches provide similar results. Solid performances of the two approaches are demonstrated on several simulations that were constructed to mimic the actual onionskin analysis. Finally, an analysis of onionskin data is presented. This article also has supplementary materials available online.

Modeled Diagnostics For Detonator Characterization

A novel diagnostics method to measure the detonation electric effect was tested and verified against computerized models. Where standard diagnostics are used to measure currents, timings, and other particularly useful quantities, a novel copper antenna was created in order to detect and measure RF-signals (radio frequency) from high explosives (HE). With detonation velocities, pressures, and arrival times resolved from multiple diagnostics, including Rogowski coils5, Polyvinylidene Fluoride (PVDF) gauges, and Current Viewing Resistors (CVR), models created with ALE3D Hydro Codes then predict detonator performance and further qualify the copper antenna’s integrity as a capable diagnostic in quantifying RF emissions.A novel diagnostics method to measure the detonation electric effect was tested and verified against computerized models. Where standard diagnostics are used to measure currents, timings, and other particularly useful quantities, a novel copper antenna was created in order to detect and measure RF-signals (radio frequency) from high explosives (HE). With detonation velocities, pressures, and arrival times resolved from multiple diagnostics, including Rogowski coils5, Polyvinylidene Fluoride (PVDF) gauges, and Current Viewing Resistors (CVR), models created with ALE3D Hydro Codes then predict detonator performance and further qualify the copper antenna’s integrity as a capable diagnostic in quantifying RF emissions.

Initiation of Insensitive High Explosives Using Multiple Wave Interactions

Insensitive High Explosives (IHEs) increase safety in many types of uses. However, the safety comes at the cost of performance. Initiation of IHE requires large boosters and powerful detonators as well. Multipoint initiation is being utilized to exploit explosive wave interactions to create overdriven states, greatly facilitating the initiation of IHEs. This concept builds from recent explosive experiments where the minimum spot size for single-point initiation in PBX 9502 was determined. Below this threshold, PBX 9502 could not be initiated. This was then expanded to three initiation points, which were smaller than this threshold. Measurements of the velocity and pressure of the wave interactions were collected using Photon Doppler Velocimetry (PDV). Not only was initiation observed, but the resulting pressures at the double and triple points were found to be above the CJ state for PBX 9502. Based on these results, further tests were conducted to isolate and measure the longevity and pressure of this phenomenon using a series of cutback tests.Insensitive High Explosives (IHEs) increase safety in many types of uses. However, the safety comes at the cost of performance. Initiation of IHE requires large boosters and powerful detonators as well. Multipoint initiation is being utilized to exploit explosive wave interactions to create overdriven states, greatly facilitating the initiation of IHEs. This concept builds from recent explosive experiments where the minimum spot size for single-point initiation in PBX 9502 was determined. Below this threshold, PBX 9502 could not be initiated. This was then expanded to three initiation points, which were smaller than this threshold. Measurements of the velocity and pressure of the wave interactions were collected using Photon Doppler Velocimetry (PDV). Not only was initiation observed, but the resulting pressures at the double and triple points were found to be above the CJ state for PBX 9502. Based on these results, further tests were conducted to isolate and measure the longevity and pressure of this phe...

Initiation train experiments to enable detonator diagnostics

A measurement of when the detonator breaks out and lights an initiation train has been a desirable diagnostic for both modelers and experimentalists alike. A detonator diagnostic has been developed using magnet wire circuit to transmit a signal when the detonation wave breaks the cup. This is used to establish time zero for a variety of types of shots. This paper describes the design and testing challenges of this diagnostic, and the tests conducted to prove the concept. The value of this diagnostic is that it is an in situ measurement, meaning it can easily be housed inside the booster counterbore on the detonator face. It provides an unambiguous measurement of time zero, when coupled with diagnostics that supply detonator bridge burst information.

Final report for SERDP WP-2209 Replacement melt-castable formulations for Composition B

Abstract : Objective. Composition B is a melt-cas Objective. Composition B is a melt-castable explosive formulation incorporating TNT and RDX. Both of these components have undesirable environmental impacts from production and use. The desired outcome of this work was the selection of an explosive material to replace Comp-B that would preserve the beneficial attributes of that explosive without the negative environmental ramifications table explosive formulation incorporating TNT and RDX. Both of these components have undesirable environmental impacts from production and use. The desired outcome of this work was the selection of an explosive material to replace Comp-B that would preserve the beneficial attributes of that explosive without the negative environmental ramifications.

Reactive flow calibration for diaminoazoxyfurazan (DAAF) and comparison with experiment

Diaminoazoxyfurazan (DAAF) has a number of desirable properties; it is sensitive to shock while being insensitive to initiation by low level impact or friction, it has a small failure diameter, and its manufacturing process is inexpensive with minimal environmental impact. In light of its unique properties, DAAF based materials have gained interest for possible applications in insensitive munitions. In order to facilitate hydrocode modeling of DAAF and DAAF based formulations, we have developed a set of reactive flow parameters which were calibrated using published experimental data as well as recent experiments at LANL. Hydrocode calculations using the DAAF reactive flow parameters developed in the course of this work were compared to rate stick experiments, small scale gap tests, as well as the Onionskin experiment. Hydrocode calculations were compared directly to streak image results using numerous tracer points in conjunction with an external algorithm to match the data sets. The calculations display ...

Front curvature and rate stick data on formulations containing DAAF, TATB, RDX and HMX including diameter and temperature effects

A test series was conducted on formulations containing TATB and RDX (PBXN-7), TATB and HMX (PBXW-14) and DAAF and HMX where corner turning and detonation propagation data were measured. Corner turning is a function of temperature and can be used to evaluate the completeness of explosive work. In order to show cold temperature performance behavior, this test was developed to compare the front curvature of these materials at a variety of diameters, explosive compositions, and temperatures. Shots were fired at ambient and -55 °C. The test apparatus developed for this lends itself to streak imaging across the pellet face, and time of arrival scope data from magnet wire embedded between the pellets. The test set up, fixturing and data analysis will be discussed. The results of the shots showed interesting diameter effects on the detonation velocity of the formulations and gave an excellent comparison of the relative curvatures as a function of temperature.