Munroe Jets

Munroe jets are formed by the oblique interaction of detonation products from two explosive charges separated by an air gap. The jet consists of a high velocity jet of low density precursor gases and particles that travel faster than the primary jet which is a high pressure regular shock reflection. 

The Los Alamos PHERMEX Data Volumes contain 40 radiographs taken by Douglas Venable in the 1960 s of Munroe jets generated by Composition B explosive charges separated by 0.5 to 8 cm of air. In several of the experiments the Munroe jets interacted with thin Tantalum foils and with aluminum plates. The complete list of the Munroe jet shots is on pages 23-24 of reference 15 and the Los Alamos Data Volumes are on the CD-ROM. 

Davis and have performed an extensive test series studying the damage to steel witness plates by a detonation running in PBX-9502 with small gaps. 

The experimental study examined the damage on metal plates resulting from small gaps in explosive charges. The 2-inch square by 1-inch thick PBX-9502 blocks were placed on a 1-inch by 4-inch diameter 304 steel witness plate. The blocks were separated by Plexiglas shims to form an air gap of 1 mm thickness. The PBX-9502 blocks were initiated from the top by an SE-1 detonator and a 1/4 inch thick PBX-9501 booster. 

The plate dent experiments are so difficult to understand or model that reference 16 did not consider Munroe jets as a mechanism for the formation of the dents or connect the results of the experiments with the PHERMEX Munroe jet data base. Such experiments are similar to attempting to do biology from road kill. 

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The air bubbles produce a type of micro-Munroe jet oriented in the direction of the shock. 

Douglas Venable developed the X-Ray machine PHERMEX and applied it to many problems of shock and detonation wave physics in the 1960 s. In this chapter we will use the NOBEL code to model some of his classic PHERMEX experimental observations of Munroe jets. Most of our current understanding and modeling of detonation wave corner turning depends upon the PHERMEX experiments of Venable. 

The geometry of the PHERMEX Munroe jet experiments is shown in Figure 6.23. The Munroe jet was formed by the interaction of the detonation products from two Composition B-3 explosive charges separated by an air gap 1 cm wide. The charges are initiated by 2.54 cm of Composition B-3 initiated by a P-081 lens. 

Figure 6.23 Experimental geometry for studying Munroe jets.

Explosive interfaces or defects such as cracks will result in Munroe jets which can cause significant damage to adjacent metals. The Munroe jets formed by etchings on explosive surfaces can result in remarkable sketches such as the metal plate image of Alfred Nobel made during his lifetime shown in Figure 6.34. The NOBEL code described in this chapter uses the Nobel image as its symbol. 

Figure 6.34 The metal etching of Alfred Nobel generated by Munroe jets created by sketches on the explosive surface in contact with a metal plate.

Figure 6.36 The witness plate and a cross section across the trench left in the steel plate by the Munroe jet created by a 0.1 cm gap between two PBX-9502 charges.

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