Master of Science (MS)
The impact of high-speed (500-1500 m/s), laser driven micro-fliers with thin energetic targets (10-100 956;m) is being examined to characterize impact-induced heating and combustion of these materials. Aluminum fliers are propelled by a laser into a thin metallic target plate having a layer of energetic material deposited on its backside. Mass spectrometry is performed in vacuo on the energetic side to interrogate the shock-induced chemistry of the energetic material. It is important to ignite and possibly detonate the energetic material without perforation of the target plate avoiding contamination of the vacuum chamber. To guide development of these experiments, a low-order (zero-dimensional) model is formulated to estimate ballistic performance for large dimensional parameter spaces in a computationally inexpensive manner. The imaging of post-impact target coupons gives insight into deformation and failure modes of the target plate. The model accounts for both the early-time system response with 1-D shock relations and the late-time response with quasi-static strength of flat plates. The model is validated against impact data for larger scale flier-target configurations, and gives predictions for micro-scale configurations. The post-impact target plates show that the system behavior is stochastic in nature. Thus, a method for propagating input uncertainty is presented to estimate the uncertainty in model output variables, and a sensitivity study is performed to highlight dependence of the system response on input parameters. Model output is most sensitive to the ratio of flier width to diameter. Predictions are performed for energetic materials including HMX (C4H8N8O8), TNT (C7H5N3O6), and PETN (C5H8N4O12) over the initial flier velocity - flier thickness parametric plane for given target thicknesses to produce ballistic initiation maps to identify configurations for which initiation of energetic material may occur without perforation of the target plate. Because of the high critical shock initiation energy of HMX (150 J/cm2) and TNT (77 J/cm2), it is difficult to identify micro configurations that result in initiation. However, such configurations were found for PETN which has a lower critical shock energy (5.03 J/cm2). The area of the region for initiation increases with increasing target thickness for these configurations.
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Fry, Mark B., "Low-order modeling of micro-flier impact with thin stationary energetic targets" (2012). LSU Master's Theses. 1754.