Untitled - Sciencemadness Dot Org

SHOCK INITIATION PROPERTIES
Fig. 4.21. Minimum priming charge
test assembly.
Resin 93-022, Sylgard 182). This material was chosen because it can be loaded
readily into the cavity, and it propagates a detonation in quite small diameters of
test explosives. The l/2-in.-thick brass plate that covers the assembly partly con-
fines the explosive react,ion and also serves as a locating ring for the 2-grain/ft mild
detonating fuse (MDF) that carries the detonation from the detonator to the XTX
8003.
The quantity varied is the diameter of the hemispherical cavity, and hence the
volume and weight of the XTX 8003 booster. This is done by using a set of end mills
whose tips have been ground so that they form cavities of the desired sizes. The
cavity is filled by weighing out the required quantity of XTX 8003 (1.53-g/cm3
loading density), rolling it into a ball, and pressing it into place.
The weight of XTX 8003 is increased and decreased in logarithmic steps of 0.1 log
units, starting with 1.53 mg, until the quantity of XTX 8003 required to detonate
the test charge in half the trials is found.
4.4 Rifle Bullet Test. Three tests have been used at LASL to determine the
response of explosives to attack by rifle bullets.
In the first test, a bare, 2-in.-diam by 3-in-long cylinder is placed in the V-notch
of a plastic holder that rests on a steel plate. The projectile, a go-grain steel
cylinder, roughly 0.3 in. in diameter and 0.5 in. long, is fired at the end of t,he charge
by a .30 caliber rifle. The approximate bullet velocity is measured with velocity
screens. A microphone or pressure transducer that measures the overpressure
created by an event usually indicates either no overpressure or a pressure
characteristic of a detonation. Results are expressed in terms of a critical velocity,
Vcrit; the minimum velocity at which detonations were observed, V,,, min; and the
maximum velocity at which no reactions were observed, Vinert ,,,ax. This test is
another shock sensitivity test. The bullet velocity is an indirect indicator of the
shock pressure required to initiate detonation.
In the second and third tests, the explosive is confined in a l- by I.5-in. pipe nip-
ple or a l-pint cardboard carton, respectively. Standard .30 and .50 caliber bullets
weighing 153 and 700 grains are fired at velocities of 2755 and 2840 ft/s to attack the
explosive. (In these tests the pipe nipple confinement is used for explosives cast or
pressed to more than 95% of their crystal densities. The cardboard carton confine-
434