New Gap Sensitivity Methods For Explosives

It seems that there is no book that treats the measurement of the physical pa rameters of explosives as its only subject, although limited information is avail able in a number of books. Therefore, I have tried to bridge this gap in the lit erature with this book. A large number of various physical parameters have to be determined ex perimentally in order to test or characterise an explosive. Various physical principles have been applied for such measurements. Accordingly, a large number of different experimental methods exist, as well as various testing appa ratuses and procedures. On the other hand, great progress has been made recently in the study of detonation phenomena. New measuring techniques can assess extremely short processes to below nanoseconds scale. They make it possible to determine im portant parameters in detonation physics. I have made a great attempt to cover the available literature data on the subject. Because it would be a highly demanding task to include in a single volume all the methods that are in use by various testing agencies, I have tried to give primarily the principles for determination of individual physical pa rameters of explosives by different measuring methods as well as data treatment procedures.

A revised small scale gap test (SSGT) has been developed. It employs a 1.4-inch long, 0.2-inch diameter RDX column loaded in a brass cylinder as a donor. The acceptor is of similar configuration. The sensitivity of the explosive loaded in the acceptor is determined by the test as a function of the thickness of the lucite barrier which is used to moderate the donor output. The mean firing sensitivity, for instance, is determined from the thickness of lucite at which 50% response would be expected. By revision of methods and design, and by careful control of the loading and the testing conditions, the resolution of the revised SSGT has been improved by a factor of 4 to 5 over that of the original SSGT.

This report describes a method whereby the sensitivity of explosives to initiation by other explosives may be evaluated when only a small sample of the explosive is available. Cylindrical brass containers 1" in diameter and l/4" long8 with 0.100" diamieter centrally drilled holes were used to contain the explosive to be tested. The use of such small columns makes it possible to obtain statistically valuable data from small amounts of explosive. The depth of a dent in a steel block placed at the back of the explosive column was used as a criterion to determine whether the shot was a fire or misfire. The order of decreasing sensitivity of the five explosives tested was found to be RDX, tetryl, Comp B, TNT and Comp A. This is in agreement with results of stmilar larger scale experiments.

The report describes a small scale gap test (SSGT) used at MRL for the assessment of shock sensitivity of high explosives. Details of the test assembly, procedure and analysis of results, along with results for a range of explosives and explosive compositions are presented. A specially designed explosive firing cell is also described. The MRL SSGT has proved to be a simple, convenient and relatively cheap method for the assessment of shock sensitivity. Results are reproducible and provide a good indication of relative shock sensitivity.