The Extended History Variable Reactive Burn model (XHVRB), as proposed by Starkenburg, uses shock capturing rather than current pressure for calculating the pseudo-entropy that is used to model the reaction rate of detonating explosives. In addition to its extended capabilities for modeling explosive desensitization in multi-shock environments, XHVRB's shock capturing offers potential improvement for single shock modeling over the historically used workhorse model HVRB in CTH, an Eulerian shock physics code developed at Sandia National Labs. The detailed transition to detonation of PBX9501, as revealed by embedded gauge data, is compared to models with both HVRB and XHVRB. Improvements to the comparison of model to test data are shown with XHVRB, though not all of the details of the transition are captured by these single-rate models.
Explosive shock desensitization phenomena have been recognized for some time. It has been demonstrated that pressure-based reactive flow models do not adequately capture the basic nature of the explosive behavior. Historically, replacing the local pressure with a shock captured pressure has dramatically improved the numerical modeling approaches. A pseudo-entropy based formulation using the History Variable Reactive Burn model, as proposed by Starkenberg, was implemented into the Eulerian shock physics code CTH. Improvements in the shock capturing algorithm in the model were made that allow reproduction of single shock behavior consistent with published Pop-plot data. It is also demonstrated to capture a desensitization effect based on available literature data, and to qualitatively capture multi-dimensional desensitization behavior. This model shows promise for use in modeling and simulation problems that are relevant to the desensitization phenomena. Issues are identified with the current implementation and future work is proposed for improving and expanding model capabilities.
The use of S2 glass/SC15 epoxy woven fabric composite materials for blast and ballistic protection has been an area of on-going research over the past decade. In order to accurately model this material system within potential applications under extreme loading conditions, a well characterized and understood anisotropic equation of state (EOS) is needed. This work details both an experimental program and associated analytical modelling efforts which aim to provide better physical understanding of the anisotropic EOS behavior of this material. Experimental testing focused on planar shock impact tests loading the composite to peak pressures of 15 GPa in both the transverse and longitudinal orientations. Test results highlighted the anisotropic response of the material and provided a basis by which the associated numeric micromechanical investigation was compared. Results of the combined experimental and numerical modeling investigation provided insights into not only the constituent material influence on the composite response but also the importance of the plain weave microstructure geometry and the significance of the microstructural configuration.
With the increasing use of hydrocodes in modeling and system design, experimental benchmarking of software has never been more important. While this has been a large area of focus since the inception of computational design, comparisons with temperature data are sparse due to experimental limitations. A novel temperature measurement technique, magnetic diffusion analysis, has enabled the acquisition of in-flight temperature measurements of hyper velocity projectiles. Using this, an AC-14 bare shaped charge and an LX-14 EFP, both with copper linings, were simulated using CTH to benchmark temperature against experimental results. Particular attention was given to the slug temperature profiles after separation, and the effect of varying equation-of-state and strength models. Simulation fidelity to experiment was shown to greatly depend on strength model, ranging from better than 2% error to a worst case of 22%. This varied notably depending on the strength model used. Similar observations were made simulating the EFP case, with a minimum 4% deviation. Jet structures compare well with radiographic images and are consistent with ALEGRA simulations previously conducted. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. SAND2017-10009C.
Following previous experimental evidence of growth and arrest of Richtmyer-Meshkov instabilities in copper, we have used the CTH shock physics code to study and calibrate the effects of material strength at high strain rates. Highly resolved one and two-dimensional simulations were performed using the Johnson-Cook (JC), Mechanical Threshold Stress (MTS), and Preston-Tonks-Wallace (PTW) strength models. The one-dimensional simulations utilized a prescribed homogeneous deformation strain path covering strain rates observed in previous hydrodynamic instability experiments. Spall was modeled using a nominal threshold pressure model (PFRAC) and we use the Mie-Gruneisen equation of state to estimate the volumetric response of the experiments. Our results show good qualitative and quantitative agreement between numerical estimates and prior experiments in the strain rate regimes of interest.
With the increasing use of hydrocodes in modelling and system design, benchmarking of software against experiments has become even more vital. While substantial work has been done in this regard, comparisons with temperature data within dynamic experiments are sparse due to experimental limitations. However, novel developments in measurement techniques has enabled the in-flight acquisition of hypervelocity projectile temperature, providing a new source for validation. This is achieved by tracking the decay of an induced magnetic field which is related to conductivity and further correlated to material temperature. As such, an AC-14 bare shaped charge with a copper lining is simulated using CTH, and benchmarked against experimental temperature results observed by Uhlig and Hummer. Particular attention was given to the slug temperature profiles after separation, and the effect of varying equation-of-state and strength models. Simulations are in agreement with experimental results, with a best case of under 2% error between the observed and simulated temperatures for this shaped charge setup. This varied notably (around 20% variance) depending on strength model. Jet structures compare well with radiographic images and are consistent with ALEGRA simulations previously conducted. SAND2017-3686C.
Code validation against experimental data is vital in building confidence for the use of simulation software in modeling and system design. Temperature data is of particular interest in the study of hypervelocity impact, however the experimental measurement of temperature in such a regime is difficult. Novel developments in measurement techniques have enabled the measurement of in-flight hypervelocity projectile temperature. This is done by saturating the projectile with a magnetic field, in flight, and tracking its decay, which is related to material conductivity and therefore temperature. This study seeks to use CTH to computationally model experiments conducted by Uhlig and Hummer in which in-flight temperature of an explosively formed projectile (EFP) was measured. Comparing CTH results to physical observations serves as a benchmark for the accuracy of internal temperature calculations. Transient temperature results were shown to vary greatly with chosen strength model, with highest accuracy (3.4%) being attained with the Johnson Cook model. These results were on the same order as previously done ALEGRA simulations, though with differing variations between strength models, and EFP structure matches well with experimental x-ray. SAND2017-3687C.