Optical fiber metrology for detonation velocity measurements

摘要

Small explosive samples, more and more, are used due to the limited quantity of raw materials in research and development projects. Detonation velocity is the most used parameter to characterize the process of detonation front propagation. Many methods based on electrical or optical phenomena have been developed. Most of them need very expensive apparatus, hard to calibrate or to synchronize. The less intrusive and precise are optical methods based on fast streak cameras, or using optical fibers connected to fast opto-electronic converters. The optical methods have the advantage that can be used under magnetic fields. This work presents a new handled and cheap technique based in optical fibers connected to an opto-electronic converter and to a digital recording system. This technique was developed and characterized in two metrological configurations: (J) measuring and recording the rising emitting light (REL) from thermal radiation of the detonation front; (2) measuring and recording extinguishment of laser light (ELL), conducted by the fibers before the cut event, generated by the detonation or shock propagation in optical media. Correlating gap distances and delay times in two or more fibers, placed in parallel positions, is the most used configuration. These metrological configurations were used to calculate the detonation velocity of small PBX samples (seismoplast) with good precision. The last method presents the advantage of the recorded signal is independent of detonation self-radiative process and allows the measurement of shock wave propagation in an inert material The experimental results for detonation front velocity were obtained with a resolution of 0.5 to 2%. This study opens a way to apply this technique in the ELL mode, for measuring the pressure induced in an inert target by the detonation wave, as well as to characterize the copper cylinder test.