2018 Insensitive Munitions & Energetic Materials Technology Symposium
Portland, OR
Gap Test Calculations and Correlations
Ernest L. Baker, V. Pouliquen, M. Voisin and M. Andrews
Munitions Safety Information Analysis Center (NATO), Brussels, Belgium
NEWGATES (New Excel Worksheets on GAp TESts)is a large data base and
computational tool for gap test data. NEWGATES includes pressure calibration curves
for the various gap tests based on test results, numerical simulations and analytical
calculations. NEWGATES can also calculate the shock pressure transmitted in the
tested energetic using the attenuator material Hugoniot and tested energetic unreacted
Hugoniot. We have conducted studies investigating laboratory test characteristics
correlations. Correlations found included: NOL-SSGT to NOL-LSGT, NOL-LSGT to
critical diameter, critical diameter to Held criteria and NOL-LSGT to density for a given
explosive. The Gurney energy, the Figure of Insensitiveness of the Rotter Impact test,
the detonation velocity and the detonation pressure characteristics do not provide any
correlation relationship with the gap test results or critical diameter. Most recently,
NEWGATES has been modified to include an improved NOL small scale to large scale
gap test correlation and a critical diameter estimation calculation.
INTRODUCTION
The Munitions Safety Information and Analysis Center (MSIAC) has developed a number of
safety related computational tools, including NEWGATES (New Excel Worksheets on GAp
TESts) [1] which is a large data base and computational tool for gap test data. NEWGATES
currently contains information about 10 gap tests (dimensions, scope, principles); pressure
calibration curves; time calibration curves; shock curvature calibration curves; 1455 gap test
results; and over 250 Hugoniots. In order to reduce the cost, time and risks involved in the
conception of an explosive researchers have often tried to determine ways to predict the
sensitivity properties of an explosive. We have conducted studies investigating laboratory test
characteristics correlations [2], including the NEWGATES gap test data. The explosive
characteristics investigated included the Held criterion, the weight percentage of RDX, the
composition density, the composition, the Gurney energy, the Rotter impact test and the
detonation state properties.
ATTENUATOR AND ACCEPTOR GAP TEST PRESSURES
Reported gap test “incident pressures” represent the shock pressure in the attenuator material
just before it shocks the energetic material being tested. As the shock pressure is reduced as it
passes through the attenuator, a pressure calibration curve is required [3,4]. Figure 1 presents a
general diagram of a gap test and calibration curves for the Naval Ordnance Laboratory – Large
Scale Gap Test (NOL-LSGT). Donor-produced shock pressures are sustained at higher levels
for longer distances as either the test diameter or confinement is increased. This makes the
calibration curve highly test dependent. NEWGATES includes pressure calibration curves for the
various gap tests based on test results, numerical simulations and analytical calculations.
