New processing technologies are allowing researchers, industry and academia to probe new materials space not previously achievable. These technologies include additive manufacturing and Resonant Acoustic® Mixing (RAM) which are being demonstrated to reduce processing times, environmental impact and of course cost. With the introduction of any new technology it is imperative that users, managers and national bodies provide the resources and time to determine, understand and provide guidance associated with the safe operating envelope. Combining the RAM with energetic materials requires numerous steps and iterations to generate the required knowledge. This paper is divided into three parts; the first provides a comparison of existing process technologies for energetic materials and how the community has approached using RAM for each of the energetic material sectors. The second part of the paper provides a summary of a review on how RAM users had provided safety assurance in using the technology with energetic materials. The third part covers how the community is using fundamental and applied research to continue in understanding the technology and where the benefits may lie. It is noted that this field is young therefore information contained herein will change in the future.
Dynamic measurements of shock and detonation velocities are performed using long chirped fiber Bragg gratings (CFBGs). Such thin probes, with a diameter of typically 125 µm or even 80 µm can be directly inserted into high-explosive (HE) samples or simply glued laterally. During the detonation, the width of the optical spectrum is continuously reduced by the propagation of the wave-front, which physically shortens the CFBG. The light power reflected back shows a ramp-down type signal, from which the wave-front position is obtained as a function of time, thus yielding a detonation velocity profile. A calibration procedure was developed, with the support of optical simulations, to cancel out the optical spectrum distortions from the different optical components and to determine the wavelength-position transfer function of the CFBG. The fitted slopes of the X–T diagram give steady detonation velocity values which are in very good agreement with the classical measurements obtained from discrete electrical shorting pins (ESP). The main parameters influencing the uncertainties on the steady detonation velocity value measured by CFBG are discussed. To conclude, different HE experimental configurations tested at CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives) are presented: bare cylindrical sticks, wedges for shock-to-detonation transitions (SDT), spheres, a cast-cured stick around a CFBG, and a detonation wave-front profile configuration.
PBXs are complex composites geometrically (irregularly shaped grains vary greatly in size), and constitutively (grains are anisotropic, twin and fracture). Heterogeneity at the grain scale results in localized damage and the creation of hot spots. To develop accurate, quantitative and predictive models it is imperative to develop a sound physical understanding of the grain scale material response. Numerical simulation is a useful tool to further model development. Here an inherent advantage of a particle method in discretizing geometrically complex materials is exploited to import three-dimensional material configurations from x-ray microtomography data, i.e. "real" microstructures. Numerical simulations determine representative volume element size and generate statistics on grain scale strain heterogeneity. These statistics calibrate the Stochastic Transformation Field Analysis bulk constitutive model.
In recent years, the phenomena occurring during shock wave propagation in spatial structures have been studied to characterize more accurately and to minimize the effects of pyrotechnical sources. As part of a program managed by the Centre National d'Etudes Spatiales (CNES, the French space agency), SNPE Matériaux Energétiques (SME) and MBDA France collaborated in a study to understand the mechanisms of shock wave propagation induced by the detonation of a linear pyrotechnical source. The focus of the study was on structures representative of space launcher structures such as those used for the Ariane 5 launcher. Various experiments were performed with metallic and composite plates, and two types of measurement devices (strain gauges and accelerometers) were investigated. Additional out-of-plane velocity and displacement measurements were provided by laser vibrometers, and displays of the separation of the plates were provided by a high-speed camera (up to 4800 feet/second). Signals treatment provided bending and compression strain describing plate mechanical responses. The apparatus used and the associated concerns that arose during the firings also are discussed.
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