Explosive compaction

Following detonation of the charges, some immediate ground heave or small settlements occurs around individual blast holes. Nothing is then apparent at ground surface for at least several minutes or, in the case of fine sand, tens of minutes then the ground starts to settle, and continues to settle for upwards of an hour. Compaction induced by explosives is not over the few seconds of explosive detonation 

Induced vibrations on nearby structures need to be controlled where blast densifi-cation is carried out in developed areas. Blasting within 30-40 m of existing structures requires a reduction in the charge weights per deck (involving a reduction in 

Design of the appropriate charge delays between adjacent decks in each borehole and between adjacent boreholes is carried out using the following process  

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Figure 6.13. Experimental arrangement of the hot-explosive compaction method for the preparation of consolidated Ni-Al alloys (after Kecskes etal. 2004). (a) Precursor powder sample inside a steel-tube container placed in, (b) an asbestos thermal insulation sheet (c) a concentric card-box filled with the powdered explosive (80% NH4NO3 + 20% TNT) (d) threaded steel plugs serving as contacts for the preliminary heating and to be lifted off just before detonating the explosive (e) detonating cords.

Interstitial Gas on the Shock Sensitivity of Low Explosive Compacts , Ibid, 349-58(1965) 13) Marjorie W. Evans et al, Shock Initiation of Low-Density Pressing of Ammonium Perchlorate , Ibid, 359-71 14) Donna Price T.P. 

Transition of combstn to deflgrn in expls. Combstn of powdered expls at high constant pressures) 11) J. Eadie, "The Effect of Wax on the Shock Sensitivity of Explosive Compacts , 4thONRSympDeton(l965), 399-403 12) J.E. Hay et al, "The Effect of Physical and Chemical Properties on the Sensitivity of Liquid Explosives , 4thONRSympDeton... 

M.C. Chick, "The Effect of Interstitial Gas on the Shock Sensitivity of Low Density Explosive Compacts , 4th ONRSympDeton (1965), pp 349-58 [A small scale gap test, briefly described on pp 350-51, has been used to investigate the role played by interstitial gases in the shock initiation of granular cylindrical charges of HMX (p = 1.14g/cc with 40% voids) and PET tf (p =... 

Modes a), b) c) presumably operate in the usual impact and/or friction initiation of pressed solid explosives, and modes a) b) in the impact and/or friction initiation of liquid explosives. Modes e), f)> g) h) operate in the shock initiation (and possibly the propagation) of detonation in solid explosive compacts or explosive liquids containing inhomogeneities. 

Hydrodynamic hot spots. For initiation via impact, characteristic times are of the order of several hundred microseconds and explosion usually starts with a deflagration which can turn into a detonation (Refs 1 5). For this process the heat flow described above appears to be adequate. However, for initiation of detonation, in granular explosive compacts or explosive liquids containing inhomogeneities, via shock the characteristic times are entirely too short for any appreciable heat flow from the hot spot to the surrounding explosive (Ref 6). 

If, as stated above, Pcr lOkbar, then the question arises how stresses of this magnitude can be generated by impact in explosive compacts whose compressive strengths are about 100 fold less than Pcr. For unconfmed explosive compacts (in Kholevo No 2) this can only occur with thin explosive compacts, ie with explosive layers whose h/EKrelation between, Ou> the ultimate compressive strength of the explosive compact the average stress, Fu, at which the compact fails via brittle fracture (in compression) is ... 

Explosive Compaction. See under Explosive Fabrication of Metals... 

Explosively compacted materials, such as Ti and steel, have produced small pellets, ca 1 x 1 inch, having densities of over 95% of theoretical without a sintered operation. 

Niiler, A., Kecskes, L. J., and Kottke, T., Consolidation of combustion synthesised materials by explosive compaction, Proceedings of the First US-Japanese Workshop on Combustion Synthesis, Tokyo, Japan, 53 (1990). 

In an explosive compact voids exist between the grains, and during shock or impact the voids collapse rapidly. Any plastic flow of material may also aid in sealing the gases in the spaces. The adiabatic heating process is, therefore, likely to be of major importance in providing hot spots and initiating fast decomposition in explosives of less than theoretical density. 

Nariman-Zadeh, N., Darvizeh, A., Felezi, M. E., and Gharababaei, H. (2002). Polynomial modeling of explosive compaction process of metallic powders using GMDH-type neural networks and singular value decomposition. Ma/er Sci. Eng. 10, 727-744. 

Figure 7.20 Example of (a) explosive compaction loading (after Stewart Hodge, 1988) and (b) achieved change in CPTresistance (after Rogers et al, 1990).

Figure 8.56 below (from Gohl et al, 2000) compares the laboratory data on Fuji River sand, the line labelled as after Ishihara Yoshimine, 1991 with the measured results achieved using explosive compaction. The Fuji River data is a lower bound to the explosive compaction case-histories, likely because the Fuji River sand is the least compressible soil in the figure. This figure is for the maximum strains following full liquefaction, which is the limiting case for consolidation. 

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