Large-scale gap test

Pentolite at d 1.56g/cc is used as the standard donor charge in the NOL Large Scale Gap Test" (Ref 10)... 

Price, D. und Jaffe, J. Large Scale Gap Test Interpretation of Results for Propellants, ARS-Journal 31, 595-599 (1961)... 

D) Large Scale Gap Test used at LASL is a modified version of test described by Cachia Whitbread (Ref 37b). It uses unconfined samples, 0.5 inch diam x 1.5 in long. A similar test is described by Donna Price (Ref 80) (See also Ref 47a)... 

In the past these tests were rather qualitative and one of the chief disadvantages was the lack of knowledge of the pressure transmitted to the acceptor. With the advent of calibration, however, the significance of gap tests was greatly increased. After discussing briefly the work on calibration done by various scientists between the years 1949 1965. Liddiard Price stated that the purpose of their work was to use the improved experimental and data reduction techniques developed in the few years prior to 1965 in order to obtain a calibration with the best data available. The report describes two test assemblies "NOL Standardized Gap Test [Fig 1(A)land "Modified Gap Test [Fig 1(B)]. The "Standardized Test , also known as "LSGT (Large Scale Gap Test), is described in Refs 48 54. For description of "NOL Modified Test , see Refs 59 68 Other modification developed at NOL is described in Ref 52... 

Donna Price T.P. Liddiard, Jr, "The Small Scale Gap Test Calibration and Comparison with the Large Scale Gap Test", NOLTR 66-87(1966), White Oak, Maryland [The SSGT, first described in 1952 by Dim-mock, Jr (Ref 26), has been used in its modified form, described in 1961 by Ayres (Ref... 

Detonation, Large-Scale Gap Test. See Ref 42 under Detonation (and Explosion), Experimental Procedures... 

Jaffe, "Large Scale Gap Test Interpretation of Results for Propellants , ARS-J 31, 595-96(1961) C) I. Jaffe, R. Beauregard A. Amster, "Determination of the Shock Pressure Required to Initiate Detonation of an Acceptor in the Shock Sensitivity Test , ARS-J 32, 22-5(1962) D) J. Toscano, I. Jaffe G. Robertson, "Large Scale Sensitivity Test Comparison of Tetryl and Pentolite Donors , AIAA-J 1,... 

Halved Cartridge Gap Method (Vol 1, p XIV Large Scale Gap Test (LSGT) (Vol 4, p D318-R Fig 2 on p D319-L. Also p D324)... 

The reader is referred to Ref 1 for a voluminous compilation of detonation properties (detonation velocity and diameter effect, cylinder test performance, plate dent test and detonation failure thickness), shock initiation properties (wedge test data and small and large - scale gap tests), and sensitivity tests (skid test, large-scale drop test or spigot test and spark sensitivity) relevant to LASL research expls Refs 1) T.R. Gibbs A. Popolato, LASL Explosive Property Data , Univ of California Press, Berkeley (1980) 2) B.M. Dobratz,... 

There are several variants of the gap test (Aubert et al., 1989 Foan and Coley, 1981 Foster et al, 1985 Grief et al, 1985 Hollenberg, 1986 Keefe, 1981 Large Scale Gap Test, 1987 Mesure du pouvoir d amorcage methode du gap test, 1975 Sanchidrian, 1993). The main difference among them is in the size of the donor (booster) and acceptor (tested explosive) charges. This difference arises because the tests must be performed with shock waves not only of different pressures but also of different duration of the shock wave positive phase. Thus, for example, when increasing the donor and acceptor diameters from 50 to 200 mm, the shock wave positive phase duration may increase fi-om a few to nearly 50 milliseconds. 

The US Naval Ordnance Laboratory s (NOL) large-scale gap test is illustrated in Figure 2.27. 

Large Scale Gap Test (U.S. Naval Ordnance Laboratory Method), MIL-STD-650, MethodT 513.1 (1987). 

Kamlet, M. J. and Adolph, H. G. (1979) Propellants Explosives Pyrotech. 4,30. Price, D. and Liddiard, Jr., T. P. (1966) The Small Scale Gap Test Calibration and Comparison with Large Scale Gap Test, NOLTR 66-87. 

To test these theoretical predictions a number of initiation experiments using both a modified version of the NOL large scale gap test and also the Rotter drop weight impact test have been conducted. The experimental details of these tests have been described in a previous publication (Ref 22). 

Weston et al. [1] have considered relationships among various shock sensitivity tests and Price [2-4] has considered a variety of factors important in shock sensitivity tests. Among the more sensitive explosives, correlations tend to be satisfactory between tests that rely on shock initiation. It is important to understand the critical factors in each test (small scale gap test, large scale gap test,... 

The relative shock sensitivities of explosive compositions are commonly assessed by means of gap tests. In these tests, the shock from a standard donor explosive is transmitted to the test explosive through an inert barrier (the so called gap ). The shock sensitivity of the test explosive is characterized by the gap thickness for which the probability of detonation is 50%. In reference 26, the Los Alamos standard gap test and the Naval Ordnance Laboratory (NOL) large scale gap test were modeled using the 2DE code with Forest Fire burn rates. The Los Alamos gap test uses Dural for the inert barrier while the NOL gap test uses Plexiglas. The test explosive is unconflned in the Los Alamos gap test. In the NOL gap test the test explosive is confined with steel. The model showed good agreement between the calculated and experimental gap test values for PBX-9404, PBX-9502, Pentolite, Composition B, and an HMX based propellant, VTQ-2. 

LANL large scale gap test 1.715 (pressed) 3.5 no explosions... 

---