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An analysis was performed of Small Gap Test (SSGT) sensitivity data using nonreactive shock Hugoniots, and a recently developed concept which relates sensitivity to porosity. The basic idea of the concept is that detonation is achieved, regardless of porosity, when a critical thermal energy is induced into the explosive by shock. This analysis supports the validity of this notion, both for TATB-like explosives, for which it was conceived, and for other explosive materials as well.
Recent information is summarized and applied to a more quantitative interpretation of shock sensitivity (gap) test values than previously available. It was found that a GO in this test means that the witness plate is subjected to a shockwave of 95 kbar pressure or more; a NO GO for high energy explosives and propellants most probably occurs because of the physical condition of the test material. Sensitivity ordering by shock amplitude at the end of the gap was the same as that obtained from induced pressures in ten materials for which the comparison could be made. The appendix compares gap and wedge test results for explosives; the comparison suggests that both are part of a continuous curve showing the shock initiation behavior of the material at varying pressure levels. (Author).
Numerical simulations of eight inch (203 mm) diameter gap test experiments employing heavily confined donors have been conducted. They reveal that strong convergence of lateral rarefaction waves results in transmitted shocks with latent high pressure regions which exceed the amplitude of the leading edge of the shock wave, and are transmitted into the gap attenuator. Since gap tests are calibrated using TOA measurement of the transmitted shock wave, into the attenuating material, the complex wave structure may lead to erroneous gap pressure assignments in the eight inch gap test. These simulations further indicate that this complex shock wave structure is attributable to the heavy steel case confinement, as donors without it exhibit minimal perturbations from lateral rarefaction. This results in a transmitted shock which is characterized by a smooth time decay profile. Therefore a new eight inch gap test using uncased Comp-B donors was developed, calibrated, and evaluated. TNT and AFX-1100 were used as baseline standard acceptors. The test is designated the 'Super Large Scale Gap Test' (SLSGT). Results indicate that the sensitivity of TNT to shock initiation is somewhat greater than previously observed.