122 J.H. Campbell et al. have transients of microseconds or less. This near-field energy is distributed over a wide range of frequencies and is typically not dominated by a few selected frequencies. The energy deposition time for a pyrotechnic event is very small and does not strongly excite the rigid body modes of the structure. The resulting stress waves, from the explosives, propagate through the test article and high-frequency energy is gradually attenuated due to various material and structural damping mechanisms. That high-frequency energy is then transferred or coupled into the lower frequency modes of the structure. Unlike the results from the sub-scale laboratory tests, multiple inputs had some effect on the desired output depending on where the sensors were located. For the tri-axial block, there was no relationship with individual and simultaneous inputs in the time domain. For every configuration, the X, Y, and Z simultaneous input test had the second lowest magnitude of the 4 tests. Configuration 4 should be larger than the other 3 configurations if there was a direct mapping function between an impact hammer and pyroshock input (Fig. 12.10). Similar to the sub-scale laboratory test, multiple inputs had an impact on many of the sensors located on the plate. The topright corner sensor that is common among all of the configurations maintained the highest magnitude with the simultaneous input test. The combination of the single inputs may equal the Configuration 4 input but further analysis will be required. This was the same for two other sensors in Configuration 1 and 2. For the most part, there are some locations where the superposition of single inputs does tend to lead the correlating multiple input magnitude. However, this is not evident as a trend for the test series. Figure 12.11 shows some circumstances where the first 3 test series contain acceleration magnitudes lower than the 4th configuration. The possibility exists that, for these configurations, the superposition of single impacts may equate to a multiple impact. Fig. 12.10 Single and multiple inputs for tri-axial block. (a) Single and multiple inputs (X direction); (b) single and multiple inputs (Y direction); (c) single and multiple inputs for tri-axial block
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