ANDROMEDE

The understanding of the transition processes in energetic materials is essential for safety and performances. The classical diagnostics give localized and dispersed measurements (such as contact pins, magnetic gauges and piezo-resistive gauges for the stress measurements). The use of fiber optics (drilled fibers, fibered Doppler Interferometer, Bragg gratings) offers weakly disruptive, electromagnetic immunity, and excellent spatial resolution, especially for continuous measurement. The ANDROMEDE project (Nanosecond data analysis by fiber Bragg grating in energetic materials) is a basic research project, including CEA LIST, CEA Gramat and SME (Groupe SAFRAN). ANDROMEDE aims to open new fields in dynamic measurement with fiber Bragg gratings using ultra-fast spectrometry. CEA LIST and CEA Gramat have already obtained a experimental feedback on the detonation velocity with Fiber Bragg gratings. The goal of the project is to achieve the measurement of the shock velocity and pressure distributions. For this purpose, two optoelectronic diagnostics with sub –millimeter spatial resolution will be developed and tested on specific experimental setups. The objective of the ANDROMEDE project is to reveal these transition processes by using a silica fiber Bragg grating sensor within the energetic or inert material. The choosen fiber optics have a fragile breaking threshold of 16 GPa under shock. Under this value, the use of such a fiber will allow to reach the pressure data by a spectral shift measurement due to the shock front in the Bragg grating. This technique gives also the shock duration and the shock velocity can be deduced. Above 16 GPa, the fiber breaking occurs, the reactive shock velocity is obtained by a “potentiometric” method linking the reflected laser signal amplitude with the shock position versus time. The shock curvature will be measure by the integration of several fibers within the high explosive cross section. This new diagnostic is a breakthrough in the field of dynamic metrology. The ANDROMEDE project aim to reach a new technological knowledge step for the understanding of the transient phenomena in energetic materials and especially to characterize the energetic thresholds with the measure of the continuous evolution of these physical parameters. With this work, a better design of initiation devices, boosters and main charges will be possible. Moreover, this project will push forward the new field of dynamic spectrometry. Several development axis will be evaluated: the small scale model design with instrumented gauges for vulnerability industrial structure studies on dynamic solicitations, for the characterization of the Combustion-Deflagration-Detonation Transition in energetic powder containers, and the study of gas and dust cloud explosions.