Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session B01: DDT and HotspotsFocus Recordings Available
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Chair: Bradley White, Lawrence Livermore Natl Lab Room: Anaheim Marriott Platinum 5 |
Monday, July 11, 2022 9:15AM - 9:45AM |
B01.00001: Deflagration-to-Detonation Transition (DDT) in Granular HMX in Two Dimensions Invited Speaker: Gary R Parker There are sound reasons to question whether historical (quasi) 1-dimensional DDT tube tests, from which our best DDT models have been developed, have captured all of the physics required to precisely describe the complex process of deflagration-to-detonation transition, especially as it evolves in three dimensions. Foremost is the fact that a burning column of explosive, mechanically constrained inside a tube, is prohibited from experiencing divergence in the stress forces and flows and, therefore, misses the effects of tensile fracture and flame intrusion into the deflagrating explosive part. Consequently, tests with tube geometry likely preclude, or underrepresent, phenomena associated with crack burning and their effects on deflagration propagation and mass-burn-rate enhancement. To investigate how fracture and flow divergence affect the DDT process in >1 dimension, we designed a suite of strongly confined 2-dimensional DDT tests containing thin (2 mm) HE slabs, where ignition location and slab shape (e.g., circle, ellipse and wedge) were varied. The reaction vessels had transparent windows enclosing the explosive’s top surface and high-speed cameras were used to observe luminous flames, fracture and compaction of the explosive, as well as detonation transition and propagation. Some tests included fluorescent particle trackers for measurement of bed strain. In all cases, DDT was the result of constructive pressure wave interactions, either by reflection at the confinement interface, or at the intersection of colliding waves, to produce an amplified shock of sufficient strength to initiate detonation. This detail offers a significant refinement to the final steps of the widely accepted mechanism for DDT. We will present novel image data and analysis describing the important differences in the mechanism for DDT in multiple dimensions. We will also discuss how our new DDT model may improve understanding of DDT in 1-dimensional DDT tube geometry. |
Monday, July 11, 2022 9:45AM - 10:00AM |
B01.00002: Effect of Confinement Thickness on the Deflagration to Detonation Transition of an HMX-based High Explosive. Christopher Miller, Bradley W White, John E Reaugh, Joseph Tringe Accurately modeling the the deflagration-to-detonation transition (DDT) in high eplosives is a critical step towards making effective predictions about the safety of energetic materials. DDT is influenced by a combination of material properities and environmental factors, including confinement strength, and their relative importance has yet to be fully quantified. In this study, we use HERMES (High Explosive Response to MEchanical Stimulus) model to simulate the thermite-ignitor driven DDT in LX-10 and Class I HMX powder confined in a steel tube. The influence of the confinement tube wall thickness as a function of DDT run distance is calculated and compared to available results in the literature. A comparison of both 2D and 3D HERMES model results is also presented. |
Monday, July 11, 2022 10:00AM - 10:15AM |
B01.00003: Extension of the xHVRB Reactive Burn Model for Graded Density Explosives Leah W Tuttle, David L Damm A new capability for modeling graded density reactive flow materials in the shock physics hydrocode, CTH, is demonstrated here. Previously, materials could be inserted in CTH with graded material properties, but the sensitivity of the material was not adjusted based on these properties. Of particular interest are materials that are graded in density, sometimes due to pressing or other assembly operations. The sensitivity of explosives to both density and temperature has been well demonstrated in the literature, but to-date the material parameters for use in a simulation were fit to a single condition and applied to the entire material, or the material had to be inserted in sections and each section assigned a condition. The reactive flow model xHVRB has been extended to shift explosive sensitivity with initial density, so that sensitivity is also graded in the material. This capability is demonstrated for use in two examples. The first models the initiation of a graded density pellet of HNS with a mild detonating fuse, and the second is a shaped charge with density gradients in the explosive. |
Monday, July 11, 2022 10:15AM - 10:30AM |
B01.00004: Effect of Non-Ideal Interfaces on Detonation Propagation Robert Knepper, Michael Sakano, David Kittell, Michael Marquez, Alexander S Tappan Non-ideal interfaces between an energetic material (EM) and adjacent materials are often present, but their potential impact on detonation performance is typically ignored. At small scales, when the EM geometry approaches failure conditions, the impact of such interfaces can be significant. In this work, we investigate the effects of non-ideal interfaces, using vapor-deposited films of the explosives hexanitrostilbene and pentaerythritol tetranitrate on substrates with varying surface roughness. Results indicate that increasing interfacial roughness can significantly reduce detonation velocity and increase detonation failure thickness. However, as EM film thickness increases, interfacial effects on performance appear to wane, and detonation velocities trend toward values consistent with samples having more ideal interfaces. Two and three-dimensional simulations with explicit surface roughness were performed in the hydrocode CTH to provide insight into the shock interactions occurring at these interfaces. Simulated detonation velocities and shock front profiles are presented for ideal, nominal, and exaggerated roughness, and two- and three-dimensional calculations are compared. |
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