Compaction of Porous Beds

Dynamic Compaction of Inert Porous Beds

“…The difficulty of compacting melamine relative to Teflon 7C is in agreement with quasi-static data. 5 A comparison for Teflon 7C of dynamic pressure versus density with quasi-static data indicated that dynamic compaction required about twice the quasi-static pressure to achieve the same density. Such a comparison for melamine was not possible because of the significant density gradient in dynamic experiments that was attributed to wall friction, which according to quasi-static data in a polished steel tube, 5 is an order of magnitude greater than for Teflon 7C.…”

“…5 A comparison for Teflon 7C of dynamic pressure versus density with quasi-static data indicated that dynamic compaction required about twice the quasi-static pressure to achieve the same density. Such a comparison for melamine was not possible because of the significant density gradient in dynamic experiments that was attributed to wall friction, which according to quasi-static data in a polished steel tube, 5 is an order of magnitude greater than for Teflon 7C. However, treating melamine quasi-static data as a Hugoniot curve and then calculating parameters for comparison with dynamic measurements indicated that melamine compaction may not be rate sensitive, at least not to the extent that Teflon 7C is.…”

“…As shown in the Appendix, significant gas flow along the inner wall requires some radial compaction to form an annulus at the wall. Thus the porous bed maintained contact with the inner tube wall and was restrained by friction, which according to quasi-static data 5 is an order of magnitude higher than for Teflon 7C.…”

“…For both Shots S92 and S89-4, the initial pressure build-up was small enough in magnitude to be elastic loading of the porous bed according to quasi-static data. 5 Relative to the first detection of luminosity at the ignitor interface, the arrival of the CF at the far boundary was about 600 us later than that in Shots S78 and 589-4. This, in conjunction with the later start of the CF (-500 p s), indicates that the CF velocity was nearly the same as in Shots S78 and S89-4, as expected because CF velocity is a weak function of pressure (see Chapter 4).…”

“…The inert materials were chosen to represent the variation in mechanical behavior that occurs for plastic bonded explosives and propellants and crystalline explosives. These experiments were part of a research effort 5 that also included: 1) quasi-static compaction measurements of the same materials in order to obtain relationships for intragranular stress versus porous bed density, and 2) the use of these relationships as a compaction law in a numerical model which successfully simulated the dynamic compaction experiments. …”