Search

On January 2, 2023, the SCCM community lost one of its most senior and vital members: Dennis B. Hayes, formerly of Sandia National Laboratories, and subsequently of Lockheed Martin Nevada. Although Dennis was primarily known as a shock-wave and equation-of-state theorist, he made forays into x-rays, detonation, and other topics. He independently derived the Statistical Hot Spot (SHS) model in 1981, and was the first to apply it to reaction in shocked explosives. Dennis realized that, given a modeled estimate for burn fraction, λ, and the number density of sufficiently supercritical hot-spots, η, one may use SHS to infer the elusive speed, V̄, of hot-spot-initiated burn waves. This he did for experiments on shock-initiated porous HNS explosive. He estimated η based on simple arguments about granularity, and hence (via SHS) V̄, which he predicted to be 3.6 to 50 m/s depending on conditions. These estimates are generally consistent with more recent measurements and simulations. Here we refine his method using modern instruments and models—and use it to explore the η-V̄ relationship for PBXs 9501 and 9502. [ABSTRACT FROM AUTHOR]

A thermodynamically complete equation of state (EOS) and reactive flow model of nitromethane is developed. Empirical Davis reactant and products EOSs are based on experimental data as well as higher-fidelity models from molecular dynamics simulations and thermochemical codes. Although the Arrhenius-Wescott-Stewart-Davis (AWSD) reactive flow model was originally devised for heterogeneous plastic bonded explosives, it can capture the salient features of homogeneous shock initiation, including superdetonation prior to turnover, observed experimentally in shock-to-detonation transition experiments. This is due to the model rate form having Arrhenius sensitivity to local temperature with a suitable choice of parameters. A complete set of AWSD rate parameters are calibrated to embedded electromagnetic gauge experiments. The resulting shock-to-detonation characteristics, caveats about utilizing one-dimensional simulations are presented and effects of embedded gauges are discussed. [ABSTRACT FROM AUTHOR]

We report comparisons of the thermodynamic derivatives (isochoric heat capacity, Grüneisen parameter and sound speed) of pentaerythritol tetranitrate (PETN) products for two different theoretical methodologies: Our previously published reactive Monte Carlo density function theory (DFT-RxMC) calculations, and thermochemical calculations. In previous work we compared the pressures, energies and Chapman-Jouguet (CJ) quantities for PETN products. Here, we expand this comparison to thermodynamic derivative quantities. We find the agreement encouraging given the vast methodological differences between the two techniques. [ABSTRACT FROM AUTHOR]

Two approaches are considered for modeling the speed of detonation in a finite diameter rate stick. One approach is a simulation using a shock-fit solution to the reactive Euler equations. The second approach uses reactive flow models to solve for a set of detonation speeds at fixed curvatures and uses Detonation Shock Dynamics (DSD) to solve for the propagation speed in the rate stick. The DSD approach is much faster than the shock-fit approach but fails to make good predictions for small diameter rate sticks. This paper describes both methods and identifies a dimensionless parameter where the accuracy of the DSD method decreases compared to the shock-fit method. This shows the possibility of a hybrid method, using both techniques, to provide more computationally efficient predictions of rate stick speeds for reactive burn model calibration and uncertainty quantification studies. [ABSTRACT FROM AUTHOR]

Various shock and detonation experiments and applications are affected by lateral release waves; however, we're unaware that any simple method has been offered by which shock erosion can be quickly and easily quantified. We present for this purpose the geometric equation derived by Dennis Hayes in the late 1970s, which he never published. We wish to honor Dennis by doing so in his name, at this, the first SCCM meeting following his death in January 2023. The Hayes equation gives the angle, θ, that the release-wave leading-edge traces as it moves along the initially undisturbed shock toward the charge center. To evaluate θ, salient equation of state information must also be specified. For this purpose we derive an equation for the isentropic bulk modulus, Ks, in which we make the common assumption that the shock speed, U, and shock-induced particle velocity, u, are linearly related via the Hugoniot equation U = c0 + su. One must further specify the functional dependence of the Grüneisen parameter, Γ; for this we make the common assumption that Γ ρ=constant, and employ the Dugdale-MacDonald result for Γ0. Our final result expresses θ in terms of shock Mach number, M, and the Hugoniot slope, s. Under the same assumption, the shock pressure, P, can likewise be simply expressed in terms of M and s, plus parameters c0 and ρ0 (the initial density). Thus may θ [P] be plotted parametrically in terms of M. Besides its mathematical tractability, the beauty of the present analysis is that ρ0, c0, and s have been measured for most important inert and energetic materials. [ABSTRACT FROM AUTHOR]

The disparity between the reaction and the engineering length scales in high-explosive (HE) systems motivates the use of programmed burn methods where the detonation wave is replaced with a surface and an evolution equation. When the normal detonation velocity differs from the nominal Chapman–Jouguet value (non-zero curvature), the local expansion isentrope of the HE detonation products must be mathematically consistent with the post-flow state to yield the correct detonation energy. The hydrodynamic step associated with the HE energy release is typically treated using a velocity-adjusted equation of state or a pseudo-reaction zone model. This paper describes a model where the bulk of the chemical energy is released instantaneously at the shock and the remainder is released at the finite rate dictated by a base reactive burn model. The implementation steps rely on existing code infrastructure and use the same parameter calibration as the base burn model. Two one-dimensional test cases are presented for a spherically diverging and a spherically converging detonation. The results show that the proposed methodology is able to capture the main flow features at coarse resolutions while retaining a strong hydrodynamic coupling. [ABSTRACT FROM AUTHOR]

Understanding the path through thermodynamic space that a high explosive experiences during shock to detonation transition (SDT), detonation propagation and failure are important for understanding the roles of these experiments for reactive flow model calibration. SDT, steady detonation propagation, corner turning (ECOT), multi-shock, isothermal and isentropic compression, shock release and re-shock, GapStick and other experiments may "overlap" with respect to the thermodynamic states attained. The focus of this study is to explore a methodology to examine where the reactants equation of state are taken by experiments. To that end, clearly a complete reactive flow model is needed to faithfully ascertain the dynamics of each experiment. For this exploration, an Arrhenius-Wescott-Stewart-Davis (AWSD) model is utilized for dynamic simulations of the tri-amino-tri-nitro-benzene (TATB) based plastic bonded explosive PBX 9502. Here, only an example of SDT will be given, as it serves as a validation of the more general methodology. [ABSTRACT FROM AUTHOR]

Capturing the entirety of possible high explosive performance outcomes given limited calibration data necessitates a full uncertainty quantification study. This is in contrast to the historical approach of fitting or calibrating a single deterministic physics model–which can be very loosely interpreted as the most likely outcome. As a step in the direction for providing high explosive equations of state with rigorous uncertainty modeling, we demonstrate an uncertainty quantification framework in the context of the high explosive Composition B. Our focus in this study is on the combined reactant and product equation of state. [ABSTRACT FROM AUTHOR]

PMMA (poly methyl methacrylate) is an important material to characterize, both as a model glassy polymer and as a window for interferometry techniques. Recently, PMMA reshock experimental results have been reported which implied a large thermal pressure component for PMMA reshocked from about 45 GPa. This work calls into question the high pressure, primary Hugoniot data the original conclusions were based on and presents an alternative explanation, namely, that the average Grüneisen coefficient, as indicated by the Mie-Grüneisen EOS, is too small to be inferred by the experimental data. [ABSTRACT FROM AUTHOR]

Detonation Shock Dynamics (DSD) has proven to be a fast and accurate alternative to direct numerical simulation of propagating detonations. Here, the requisite differential equations, experimental data and calibration procedure will be outlined for the plastic bonded explosive PBX 9501. It will be shown that the DSD model can fit the existing PBX 9501 data to within the experimental uncertainty. [ABSTRACT FROM AUTHOR]

The last decade has been witness to a thousand fold gain in computational power, in addition to comparable gains from improved computational algorithms such as adaptive mesh algorithms (AMR). But, even with these gains, there are many detonation phenomena which are beyond the current and foreseeable capabilities of direct simulation of resolved reaction zones. There are many other issues that arise in the simulation of detonation which lead to ill-posed computations. Many of these issues, as well as an overview of accomplishments in the field, current state of the art, and future work on detonation simulation will be discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]